Package com.fasterxml.jackson.core

Class JsonParser

  • All Implemented Interfaces:
    Versioned, java.io.Closeable, java.lang.AutoCloseable
    Direct Known Subclasses:
    JsonParserDelegate, ParserMinimalBase
    public abstract class JsonParser
extends java.lang.Object
implements java.io.Closeable, Versioned
    Base class that defines public API for reading JSON content. Instances are created using factory methods of a JsonFactory instance.

    • Method Detail

      • getCodec

        public abstract ObjectCodec getCodec()
        Accessor for ObjectCodec associated with this parser, if any. Codec is used by readValueAs(Class) method (and its variants).
        Returns:
        Codec assigned to this parser, if any; null if none

      • setCodec

        public abstract void setCodec​(ObjectCodec oc)
        Setter that allows defining ObjectCodec associated with this parser, if any. Codec is used by readValueAs(Class) method (and its variants).
        Parameters:
        oc - Codec to assign, if any; null if none

      • getInputSource

        public java.lang.Object getInputSource()
        Method that can be used to get access to object that is used to access input being parsed; this is usually either InputStream or Reader, depending on what parser was constructed with. Note that returned value may be null in some cases; including case where parser implementation does not want to exposed raw source to caller. In cases where input has been decorated, object returned here is the decorated version; this allows some level of interaction between users of parser and decorator object.

        In general use of this accessor should be considered as "last effort", i.e. only used if no other mechanism is applicable.

        Returns:
        Input source this parser was configured with

      • setRequestPayloadOnError

        public void setRequestPayloadOnError​(RequestPayload payload)
        Sets the payload to be passed if JsonParseException is thrown.
        Parameters:
        payload - Payload to pass
        Since:
        2.8

      • setRequestPayloadOnError

        public void setRequestPayloadOnError​(byte[] payload,
                                     java.lang.String charset)
        Sets the byte[] request payload and the charset
        Parameters:
        payload - Payload to pass
        charset - Character encoding for (lazily) decoding payload
        Since:
        2.8

      • setRequestPayloadOnError

        public void setRequestPayloadOnError​(java.lang.String payload)
        Sets the String request payload
        Parameters:
        payload - Payload to pass
        Since:
        2.8

      • setSchema

        public void setSchema​(FormatSchema schema)
        Method to call to make this parser use specified schema. Method must be called before trying to parse any content, right after parser instance has been created. Note that not all parsers support schemas; and those that do usually only accept specific types of schemas: ones defined for data format parser can read.

        If parser does not support specified schema, UnsupportedOperationException is thrown.

        Parameters:
        schema - Schema to use
        Throws:
        java.lang.UnsupportedOperationException - if parser does not support schema

      • getSchema

        public FormatSchema getSchema()
        Method for accessing Schema that this parser uses, if any. Default implementation returns null.
        Returns:
        Schema in use by this parser, if any; null if none
        Since:
        2.1

      • canUseSchema

        public boolean canUseSchema​(FormatSchema schema)
        Method that can be used to verify that given schema can be used with this parser (using setSchema(com.fasterxml.jackson.core.FormatSchema)).
        Parameters:
        schema - Schema to check
        Returns:
        True if this parser can use given schema; false if not

      • requiresCustomCodec

        public boolean requiresCustomCodec()
        Method that can be called to determine if a custom ObjectCodec is needed for binding data parsed using JsonParser constructed by this factory (which typically also implies the same for serialization with JsonGenerator).
        Returns:
        True if format-specific codec is needed with this parser; false if a general ObjectCodec is enough
        Since:
        2.1

      • canParseAsync

        public boolean canParseAsync()
        Method that can be called to determine if this parser instance uses non-blocking ("asynchronous") input access for decoding or not. Access mode is determined by earlier calls via JsonFactory; it may not be changed after construction.

        If non-blocking decoding is (@code true}, it is possible to call getNonBlockingInputFeeder() to obtain object to use for feeding input; otherwise (false returned) input is read by blocking

        Returns:
        True if this is a non-blocking ("asynchronous") parser
        Since:
        2.9

      • getNonBlockingInputFeeder

        public NonBlockingInputFeeder getNonBlockingInputFeeder()
        Method that will either return a feeder instance (if parser uses non-blocking, aka asynchronous access); or null for parsers that use blocking I/O.
        Returns:
        Input feeder to use with non-blocking (async) parsing
        Since:
        2.9

      • getReadCapabilities

        public JacksonFeatureSet<StreamReadCapability> getReadCapabilities()
        Accessor for getting metadata on capabilities of this parser, based on underlying data format being read (directly or indirectly).
        Returns:
        Set of read capabilities for content to read via this parser
        Since:
        2.12

      • version

        public abstract Version version()
        Accessor for getting version of the core package, given a parser instance. Left for sub-classes to implement.
        Specified by:
        version in interface Versioned
        Returns:
        Version of this generator (derived from version declared for jackson-core jar that contains the class

      • close

        public abstract void close()
                    throws java.io.IOException
        Closes the parser so that no further iteration or data access can be made; will also close the underlying input source if parser either owns the input source, or feature JsonParser.Feature.AUTO_CLOSE_SOURCE is enabled. Whether parser owns the input source depends on factory method that was used to construct instance (so check JsonFactory for details, but the general idea is that if caller passes in closable resource (such as InputStream or Reader) parser does NOT own the source; but if it passes a reference (such as File or URL and creates stream or reader it does own them.
        Specified by:
        close in interface java.lang.AutoCloseable
        Specified by:
        close in interface java.io.Closeable
        Throws:
        java.io.IOException - if there is either an underlying I/O problem

      • isClosed

        public abstract boolean isClosed()
        Method that can be called to determine whether this parser is closed or not. If it is closed, no new tokens can be retrieved by calling nextToken() (and the underlying stream may be closed). Closing may be due to an explicit call to close() or because parser has encountered end of input.
        Returns:
        True if this parser instance has been closed

      • getParsingContext

        public abstract JsonStreamContext getParsingContext()
        Method that can be used to access current parsing context reader is in. There are 3 different types: root, array and object contexts, with slightly different available information. Contexts are hierarchically nested, and can be used for example for figuring out part of the input document that correspond to specific array or object (for highlighting purposes, or error reporting). Contexts can also be used for simple xpath-like matching of input, if so desired.
        Returns:
        Stream input context (JsonStreamContext) associated with this parser

      • currentLocation

        public JsonLocation currentLocation()
        Method that returns location of the last processed input unit (character or byte) from the input; usually for error reporting purposes.

        Note that the location is not guaranteed to be accurate (although most implementation will try their best): some implementations may only report specific boundary locations (start or end locations of tokens) and others only return JsonLocation.NA due to not having access to input location information (when delegating actual decoding work to other library)

        Returns:
        Location of the last processed input unit (byte or character)
        Since:
        2.13

      • currentTokenLocation

        public JsonLocation currentTokenLocation()
        Method that return the starting location of the current (most recently returned) token; that is, the position of the first input unit (character or byte) from input that starts the current token.

        Note that the location is not guaranteed to be accurate (although most implementation will try their best): some implementations may only return JsonLocation.NA due to not having access to input location information (when delegating actual decoding work to other library)

        Returns:
        Starting location of the token parser currently points to
        Since:
        2.13 (will eventually replace getTokenLocation())

      • getCurrentLocation

        public abstract JsonLocation getCurrentLocation()
        Alias for currentLocation(), to be deprecated in later Jackson 2.x versions (and removed from Jackson 3.0).
        Returns:
        Location of the last processed input unit (byte or character)

      • getTokenLocation

        public abstract JsonLocation getTokenLocation()
        Alias for currentTokenLocation(), to be deprecated in later Jackson 2.x versions (and removed from Jackson 3.0).
        Returns:
        Starting location of the token parser currently points to

      • currentValue

        public java.lang.Object currentValue()
        Helper method, usually equivalent to: getParsingContext().getCurrentValue();

        Note that "current value" is NOT populated (or used) by Streaming parser; it is only used by higher-level data-binding functionality. The reason it is included here is that it can be stored and accessed hierarchically, and gets passed through data-binding.

        Returns:
        "Current value" associated with the current input context (state) of this parser
        Since:
        2.13 (added as replacement for older getCurrentValue()

      • assignCurrentValue

        public void assignCurrentValue​(java.lang.Object v)
        Helper method, usually equivalent to: getParsingContext().setCurrentValue(v);
        Parameters:
        v - Current value to assign for the current input context of this parser
        Since:
        2.13 (added as replacement for older setCurrentValue(java.lang.Object)

      • getCurrentValue

        public java.lang.Object getCurrentValue()
        Alias for currentValue(), to be deprecated in later Jackson 2.x versions (and removed from Jackson 3.0).
        Returns:
        Location of the last processed input unit (byte or character)

      • setCurrentValue

        public void setCurrentValue​(java.lang.Object v)
        Alias for assignCurrentValue(java.lang.Object), to be deprecated in later Jackson 2.x versions (and removed from Jackson 3.0).
        Parameters:
        v - Current value to assign for the current input context of this parser

      • releaseBuffered

        public int releaseBuffered​(java.io.OutputStream out)
                    throws java.io.IOException
        Method that can be called to push back any content that has been read but not consumed by the parser. This is usually done after reading all content of interest using parser. Content is released by writing it to given stream if possible; if underlying input is byte-based it can released, if not (char-based) it can not.
        Parameters:
        out - OutputStream to which buffered, undecoded content is written to
        Returns:
        -1 if the underlying content source is not byte based (that is, input can not be sent to OutputStream; otherwise number of bytes released (0 if there was nothing to release)
        Throws:
        java.io.IOException - if write to stream threw exception

      • releaseBuffered

        public int releaseBuffered​(java.io.Writer w)
                    throws java.io.IOException
        Method that can be called to push back any content that has been read but not consumed by the parser. This is usually done after reading all content of interest using parser. Content is released by writing it to given writer if possible; if underlying input is char-based it can released, if not (byte-based) it can not.
        Parameters:
        w - Writer to which buffered but unprocessed content is written to
        Returns:
        -1 if the underlying content source is not char-based (that is, input can not be sent to Writer; otherwise number of chars released (0 if there was nothing to release)
        Throws:
        java.io.IOException - if write using Writer threw exception

      • enable

        public JsonParser enable​(JsonParser.Feature f)
        Method for enabling specified parser feature (check JsonParser.Feature for list of features)
        Parameters:
        f - Feature to enable
        Returns:
        This parser, to allow call chaining

      • disable

        public JsonParser disable​(JsonParser.Feature f)
        Method for disabling specified feature (check JsonParser.Feature for list of features)
        Parameters:
        f - Feature to disable
        Returns:
        This parser, to allow call chaining

      • configure

        public JsonParser configure​(JsonParser.Feature f,
                            boolean state)
        Method for enabling or disabling specified feature (check JsonParser.Feature for list of features)
        Parameters:
        f - Feature to enable or disable
        state - Whether to enable feature (true) or disable (false)
        Returns:
        This parser, to allow call chaining

      • isEnabled

        public boolean isEnabled​(JsonParser.Feature f)
        Method for checking whether specified JsonParser.Feature is enabled.
        Parameters:
        f - Feature to check
        Returns:
        True if feature is enabled; false otherwise

      • isEnabled

        public boolean isEnabled​(StreamReadFeature f)
        Method for checking whether specified JsonParser.Feature is enabled.
        Parameters:
        f - Feature to check
        Returns:
        True if feature is enabled; false otherwise
        Since:
        2.10

      • getFeatureMask

        public int getFeatureMask()
        Bulk access method for getting state of all standard JsonParser.Features.
        Returns:
        Bit mask that defines current states of all standard JsonParser.Features.
        Since:
        2.3

      • setFeatureMask

        @Deprecated
public JsonParser setFeatureMask​(int mask)
        Deprecated.
        Since 2.7, use overrideStdFeatures(int, int) instead
        Bulk set method for (re)setting states of all standard JsonParser.Features
        Parameters:
        mask - Bit mask that defines set of features to enable
        Returns:
        This parser, to allow call chaining
        Since:
        2.3

      • overrideStdFeatures

        public JsonParser overrideStdFeatures​(int values,
                                      int mask)
        Bulk set method for (re)setting states of features specified by mask. Functionally equivalent to int oldState = getFeatureMask(); int newState = (oldState & ~mask) | (values & mask); setFeatureMask(newState); but preferred as this lets caller more efficiently specify actual changes made.
        Parameters:
        values - Bit mask of set/clear state for features to change
        mask - Bit mask of features to change
        Returns:
        This parser, to allow call chaining
        Since:
        2.6

      • getFormatFeatures

        public int getFormatFeatures()
        Bulk access method for getting state of all FormatFeatures, format-specific on/off configuration settings.
        Returns:
        Bit mask that defines current states of all standard FormatFeatures.
        Since:
        2.6

      • overrideFormatFeatures

        public JsonParser overrideFormatFeatures​(int values,
                                         int mask)
        Bulk set method for (re)setting states of FormatFeatures, by specifying values (set / clear) along with a mask, to determine which features to change, if any.

        Default implementation will simply throw an exception to indicate that the parser implementation does not support any FormatFeatures.

        Parameters:
        values - Bit mask of set/clear state for features to change
        mask - Bit mask of features to change
        Returns:
        This parser, to allow call chaining
        Since:
        2.6

      • nextToken

        public abstract JsonToken nextToken()
                             throws java.io.IOException
        Main iteration method, which will advance stream enough to determine type of the next token, if any. If none remaining (stream has no content other than possible white space before ending), null will be returned.
        Returns:
        Next token from the stream, if any found, or null to indicate end-of-input
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • nextValue

        public abstract JsonToken nextValue()
                             throws java.io.IOException
        Iteration method that will advance stream enough to determine type of the next token that is a value type (including JSON Array and Object start/end markers). Or put another way, nextToken() will be called once, and if JsonToken.FIELD_NAME is returned, another time to get the value for the field. Method is most useful for iterating over value entries of JSON objects; field name will still be available by calling getCurrentName() when parser points to the value.
        Returns:
        Next non-field-name token from the stream, if any found, or null to indicate end-of-input (or, for non-blocking parsers, JsonToken.NOT_AVAILABLE if no tokens were available yet)
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • nextFieldName

        public boolean nextFieldName​(SerializableString str)
                      throws java.io.IOException
        Method that fetches next token (as if calling nextToken()) and verifies whether it is JsonToken.FIELD_NAME with specified name and returns result of that comparison. It is functionally equivalent to: 
          return (nextToken() == JsonToken.FIELD_NAME) && str.getValue().equals(getCurrentName());
        but may be faster for parser to verify, and can therefore be used if caller expects to get such a property name from input next.
        Parameters:
        str - Property name to compare next token to (if next token is JsonToken.FIELD_NAME)
        Returns:
        True if parser advanced to JsonToken.FIELD_NAME with specified name; false otherwise (different token or non-matching name)
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • nextFieldName

        public java.lang.String nextFieldName()
                               throws java.io.IOException
        Method that fetches next token (as if calling nextToken()) and verifies whether it is JsonToken.FIELD_NAME; if it is, returns same as getCurrentName(), otherwise null.
        Returns:
        Name of the the JsonToken.FIELD_NAME parser advanced to, if any; null if next token is of some other type
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems
        Since:
        2.5

      • nextTextValue

        public java.lang.String nextTextValue()
                               throws java.io.IOException
        Method that fetches next token (as if calling nextToken()) and if it is JsonToken.VALUE_STRING returns contained String value; otherwise returns null. It is functionally equivalent to: 
          return (nextToken() == JsonToken.VALUE_STRING) ? getText() : null;
        but may be faster for parser to process, and can therefore be used if caller expects to get a String value next from input.
        Returns:
        Text value of the JsonToken.VALUE_STRING token parser advanced to; or null if next token is of some other type
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • nextIntValue

        public int nextIntValue​(int defaultValue)
                 throws java.io.IOException
        Method that fetches next token (as if calling nextToken()) and if it is JsonToken.VALUE_NUMBER_INT returns 32-bit int value; otherwise returns specified default value It is functionally equivalent to: 
          return (nextToken() == JsonToken.VALUE_NUMBER_INT) ? getIntValue() : defaultValue;
        but may be faster for parser to process, and can therefore be used if caller expects to get an int value next from input.

        NOTE: value checks are performed similar to getIntValue()

        Parameters:
        defaultValue - Value to return if next token is NOT of type JsonToken.VALUE_NUMBER_INT
        Returns:
        Integer (int) value of the JsonToken.VALUE_NUMBER_INT token parser advanced to; or defaultValue if next token is of some other type
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems
        InputCoercionException - if integer number does not fit in Java int

      • nextLongValue

        public long nextLongValue​(long defaultValue)
                   throws java.io.IOException
        Method that fetches next token (as if calling nextToken()) and if it is JsonToken.VALUE_NUMBER_INT returns 64-bit long value; otherwise returns specified default value It is functionally equivalent to: 
          return (nextToken() == JsonToken.VALUE_NUMBER_INT) ? getLongValue() : defaultValue;
        but may be faster for parser to process, and can therefore be used if caller expects to get a long value next from input.

        NOTE: value checks are performed similar to getLongValue()

        Parameters:
        defaultValue - Value to return if next token is NOT of type JsonToken.VALUE_NUMBER_INT
        Returns:
        long value of the JsonToken.VALUE_NUMBER_INT token parser advanced to; or defaultValue if next token is of some other type
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems
        InputCoercionException - if integer number does not fit in Java long

      • nextBooleanValue

        public java.lang.Boolean nextBooleanValue()
                                   throws java.io.IOException
        Method that fetches next token (as if calling nextToken()) and if it is JsonToken.VALUE_TRUE or JsonToken.VALUE_FALSE returns matching Boolean value; otherwise return null. It is functionally equivalent to: 
          JsonToken t = nextToken();
  if (t == JsonToken.VALUE_TRUE) return Boolean.TRUE;
  if (t == JsonToken.VALUE_FALSE) return Boolean.FALSE;
  return null;
        but may be faster for parser to process, and can therefore be used if caller expects to get a Boolean value next from input.
        Returns:
        Boolean value of the JsonToken.VALUE_TRUE or JsonToken.VALUE_FALSE token parser advanced to; or null if next token is of some other type
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • skipChildren

        public abstract JsonParser skipChildren()
                                 throws java.io.IOException
        Method that will skip all child tokens of an array or object token that the parser currently points to, iff stream points to JsonToken.START_OBJECT or JsonToken.START_ARRAY. If not, it will do nothing. After skipping, stream will point to matching JsonToken.END_OBJECT or JsonToken.END_ARRAY (possibly skipping nested pairs of START/END OBJECT/ARRAY tokens as well as value tokens). The idea is that after calling this method, application will call nextToken() to point to the next available token, if any.
        Returns:
        This parser, to allow call chaining
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • finishToken

        public void finishToken()
                 throws java.io.IOException
        Method that may be used to force full handling of the current token so that even if lazy processing is enabled, the whole contents are read for possible retrieval. This is usually used to ensure that the token end location is available, as well as token contents (similar to what calling, say getTextCharacters(), would achieve).

        Note that for many dataformat implementations this method will not do anything; this is the default implementation unless overridden by sub-classes.

        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems
        Since:
        2.8

      • currentToken

        public JsonToken currentToken()
        Accessor to find which token parser currently points to, if any; null will be returned if none. If return value is non-null, data associated with the token is available via other accessor methods.
        Returns:
        Type of the token this parser currently points to, if any: null before any tokens have been read, and after end-of-input has been encountered, as well as if the current token has been explicitly cleared.
        Since:
        2.8

      • currentTokenId

        public int currentTokenId()
        Method similar to getCurrentToken() but that returns an int instead of JsonToken (enum value).

        Use of int directly is typically more efficient on switch statements, so this method may be useful when building low-overhead codecs. Note, however, that effect may not be big enough to matter: make sure to profile performance before deciding to use this method.

        Returns:
        int matching one of constants from JsonTokenId.
        Since:
        2.8

      • getCurrentToken

        public abstract JsonToken getCurrentToken()
        Alias for currentToken(), may be deprecated sometime after Jackson 2.13 (will be removed from 3.0).
        Returns:
        Type of the token this parser currently points to, if any: null before any tokens have been read, and

      • getCurrentTokenId

        @Deprecated
public abstract int getCurrentTokenId()
        Deprecated.
        Since 2.12 use currentTokenId() instead
        Deprecated alias for currentTokenId().
        Returns:
        int matching one of constants from JsonTokenId.

      • hasCurrentToken

        public abstract boolean hasCurrentToken()
        Method for checking whether parser currently points to a token (and data for that token is available). Equivalent to check for parser.getCurrentToken() != null.
        Returns:
        True if the parser just returned a valid token via nextToken(); false otherwise (parser was just constructed, encountered end-of-input and returned null from nextToken(), or the token has been consumed)

      • hasTokenId

        public abstract boolean hasTokenId​(int id)
        Method that is functionally equivalent to: return currentTokenId() == id but may be more efficiently implemented.

        Note that no traversal or conversion is performed; so in some cases calling method like isExpectedStartArrayToken() is necessary instead.

        Parameters:
        id - Token id to match (from (@link JsonTokenId})
        Returns:
        True if the parser current points to specified token
        Since:
        2.5

      • hasToken

        public abstract boolean hasToken​(JsonToken t)
        Method that is functionally equivalent to: return currentToken() == t but may be more efficiently implemented.

        Note that no traversal or conversion is performed; so in some cases calling method like isExpectedStartArrayToken() is necessary instead.

        Parameters:
        t - Token to match
        Returns:
        True if the parser current points to specified token
        Since:
        2.6

      • isExpectedStartArrayToken

        public boolean isExpectedStartArrayToken()
        Specialized accessor that can be used to verify that the current token indicates start array (usually meaning that current token is JsonToken.START_ARRAY) when start array is expected. For some specialized parsers this can return true for other cases as well; this is usually done to emulate arrays in cases underlying format is ambiguous (XML, for example, has no format-level difference between Objects and Arrays; it just has elements).

        Default implementation is equivalent to: 

           currentToken() == JsonToken.START_ARRAY
        but may be overridden by custom parser implementations.
        Returns:
        True if the current token can be considered as a start-array marker (such JsonToken.START_ARRAY); false if not

      • isExpectedNumberIntToken

        public boolean isExpectedNumberIntToken()
        Similar to isExpectedStartArrayToken(), but checks whether stream currently points to JsonToken.VALUE_NUMBER_INT.

        The initial use case is for XML backend to efficiently (attempt to) coerce textual content into numbers.

        Returns:
        True if the current token can be considered as a start-array marker (such JsonToken.VALUE_NUMBER_INT); false if not
        Since:
        2.12

      • isNaN

        public boolean isNaN()
              throws java.io.IOException
        Access for checking whether current token is a numeric value token, but one that is of "not-a-number" (NaN) variety (including both "NaN" AND positive/negative infinity!): not supported by all formats, but often supported for JsonToken.VALUE_NUMBER_FLOAT. NOTE: roughly equivalent to calling !Double.isFinite() on value you would get from calling getDoubleValue().
        Returns:
        True if the current token is of type JsonToken.VALUE_NUMBER_FLOAT but represents a "Not a Number"; false for other tokens and regular floating-point numbers
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems
        Since:
        2.9

      • clearCurrentToken

        public abstract void clearCurrentToken()
        Method called to "consume" the current token by effectively removing it so that hasCurrentToken() returns false, and getCurrentToken() null). Cleared token value can still be accessed by calling getLastClearedToken() (if absolutely needed), but usually isn't.

        Method was added to be used by the optional data binder, since it has to be able to consume last token used for binding (so that it will not be used again).

      • getLastClearedToken

        public abstract JsonToken getLastClearedToken()
        Method that can be called to get the last token that was cleared using clearCurrentToken(). This is not necessarily the latest token read. Will return null if no tokens have been cleared, or if parser has been closed.
        Returns:
        Last cleared token, if any; null otherwise

      • overrideCurrentName

        public abstract void overrideCurrentName​(java.lang.String name)
        Method that can be used to change what is considered to be the current (field) name. May be needed to support non-JSON data formats or unusual binding conventions; not needed for typical processing.

        Note that use of this method should only be done as sort of last resort, as it is a work-around for regular operation.

        Parameters:
        name - Name to use as the current name; may be null.

      • getCurrentName

        public abstract java.lang.String getCurrentName()
                                         throws java.io.IOException
        Alias of currentName().
        Returns:
        Name of the current field in the parsing context
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • currentName

        public java.lang.String currentName()
                             throws java.io.IOException
        Method that can be called to get the name associated with the current token: for JsonToken.FIELD_NAMEs it will be the same as what getText() returns; for field values it will be preceding field name; and for others (array values, root-level values) null.
        Returns:
        Name of the current field in the parsing context
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems
        Since:
        2.10

      • getText

        public abstract java.lang.String getText()
                                  throws java.io.IOException
        Method for accessing textual representation of the current token; if no current token (before first call to nextToken(), or after encountering end-of-input), returns null. Method can be called for any token type.
        Returns:
        Textual value associated with the current token (one returned by nextToken() or other iteration methods)
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getText

        public int getText​(java.io.Writer writer)
            throws java.io.IOException,
                   java.lang.UnsupportedOperationException
        Method to read the textual representation of the current token in chunks and pass it to the given Writer. Conceptually same as calling: 
          writer.write(parser.getText());
        but should typically be more efficient as longer content does need to be combined into a single String to return, and write can occur directly from intermediate buffers Jackson uses.
        Parameters:
        writer - Writer to write textual content to
        Returns:
        The number of characters written to the Writer
        Throws:
        java.io.IOException - for low-level read issues or writes using passed writer, or JsonParseException for decoding problems
        java.lang.UnsupportedOperationException
        Since:
        2.8

      • getTextCharacters

        public abstract char[] getTextCharacters()
                                  throws java.io.IOException
        Method similar to getText(), but that will return underlying (unmodifiable) character array that contains textual value, instead of constructing a String object to contain this information. Note, however, that:
        • Textual contents are not guaranteed to start at index 0 (rather, call getTextOffset()) to know the actual offset
        • Length of textual contents may be less than the length of returned buffer: call getTextLength() for actual length of returned content.

        Note that caller MUST NOT modify the returned character array in any way -- doing so may corrupt current parser state and render parser instance useless.

        The only reason to call this method (over getText()) is to avoid construction of a String object (which will make a copy of contents).

        Returns:
        Buffer that contains the current textual value (but not necessarily at offset 0, and not necessarily until the end of buffer)
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getTextLength

        public abstract int getTextLength()
                           throws java.io.IOException
        Accessor used with getTextCharacters(), to know length of String stored in returned buffer.
        Returns:
        Number of characters within buffer returned by getTextCharacters() that are part of textual content of the current token.
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getTextOffset

        public abstract int getTextOffset()
                           throws java.io.IOException
        Accessor used with getTextCharacters(), to know offset of the first text content character within buffer.
        Returns:
        Offset of the first character within buffer returned by getTextCharacters() that is part of textual content of the current token.
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • hasTextCharacters

        public abstract boolean hasTextCharacters()
        Method that can be used to determine whether calling of getTextCharacters() would be the most efficient way to access textual content for the event parser currently points to.

        Default implementation simply returns false since only actual implementation class has knowledge of its internal buffering state. Implementations are strongly encouraged to properly override this method, to allow efficient copying of content by other code.

        Returns:
        True if parser currently has character array that can be efficiently returned via getTextCharacters(); false means that it may or may not exist

      • getNumberValue

        public abstract java.lang.Number getNumberValue()
                                         throws java.io.IOException
        Generic number value accessor method that will work for all kinds of numeric values. It will return the optimal (simplest/smallest possible) wrapper object that can express the numeric value just parsed.
        Returns:
        Numeric value of the current token in its most optimal representation
        Throws:
        java.io.IOException - Problem with access: JsonParseException if the current token is not numeric, or if decoding of the value fails (invalid format for numbers); plain IOException if underlying content read fails (possible if values are extracted lazily)

      • getNumberValueExact

        public java.lang.Number getNumberValueExact()
                                     throws java.io.IOException
        Method similar to getNumberValue() with the difference that for floating-point numbers value returned may be BigDecimal if the underlying format does not store floating-point numbers using native representation: for example, textual formats represent numbers as Strings (which are 10-based), and conversion to Double is potentially lossy operation.

        Default implementation simply returns getNumberValue()

        Returns:
        Numeric value of the current token using most accurate representation
        Throws:
        java.io.IOException - Problem with access: JsonParseException if the current token is not numeric, or if decoding of the value fails (invalid format for numbers); plain IOException if underlying content read fails (possible if values are extracted lazily)
        Since:
        2.12

      • getByteValue

        public byte getByteValue()
                  throws java.io.IOException
        Numeric accessor that can be called when the current token is of type JsonToken.VALUE_NUMBER_INT and it can be expressed as a value of Java byte primitive type. Note that in addition to "natural" input range of [-128, 127], this also allows "unsigned 8-bit byte" values [128, 255]: but for this range value will be translated by truncation, leading to sign change.

        It can also be called for JsonToken.VALUE_NUMBER_FLOAT; if so, it is equivalent to calling getDoubleValue() and then casting; except for possible overflow/underflow exception.

        Note: if the resulting integer value falls outside range of [-128, 255], a InputCoercionException will be thrown to indicate numeric overflow/underflow.

        Returns:
        Current number value as byte (if numeric token within range of [-128, 255]); otherwise exception thrown
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getShortValue

        public short getShortValue()
                    throws java.io.IOException
        Numeric accessor that can be called when the current token is of type JsonToken.VALUE_NUMBER_INT and it can be expressed as a value of Java short primitive type. It can also be called for JsonToken.VALUE_NUMBER_FLOAT; if so, it is equivalent to calling getDoubleValue() and then casting; except for possible overflow/underflow exception.

        Note: if the resulting integer value falls outside range of Java short, a InputCoercionException will be thrown to indicate numeric overflow/underflow.

        Returns:
        Current number value as short (if numeric token within Java 16-bit signed short range); otherwise exception thrown
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getIntValue

        public abstract int getIntValue()
                         throws java.io.IOException
        Numeric accessor that can be called when the current token is of type JsonToken.VALUE_NUMBER_INT and it can be expressed as a value of Java int primitive type. It can also be called for JsonToken.VALUE_NUMBER_FLOAT; if so, it is equivalent to calling getDoubleValue() and then casting; except for possible overflow/underflow exception.

        Note: if the resulting integer value falls outside range of Java int, a InputCoercionException may be thrown to indicate numeric overflow/underflow.

        Returns:
        Current number value as int (if numeric token within Java 32-bit signed int range); otherwise exception thrown
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getLongValue

        public abstract long getLongValue()
                           throws java.io.IOException
        Numeric accessor that can be called when the current token is of type JsonToken.VALUE_NUMBER_INT and it can be expressed as a Java long primitive type. It can also be called for JsonToken.VALUE_NUMBER_FLOAT; if so, it is equivalent to calling getDoubleValue() and then casting to int; except for possible overflow/underflow exception.

        Note: if the token is an integer, but its value falls outside of range of Java long, a InputCoercionException may be thrown to indicate numeric overflow/underflow.

        Returns:
        Current number value as long (if numeric token within Java 32-bit signed long range); otherwise exception thrown
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getBigIntegerValue

        public abstract java.math.BigInteger getBigIntegerValue()
                                                 throws java.io.IOException
        Numeric accessor that can be called when the current token is of type JsonToken.VALUE_NUMBER_INT and it can not be used as a Java long primitive type due to its magnitude. It can also be called for JsonToken.VALUE_NUMBER_FLOAT; if so, it is equivalent to calling getDecimalValue() and then constructing a BigInteger from that value.
        Returns:
        Current number value as BigInteger (if numeric token); otherwise exception thrown
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getFloatValue

        public abstract float getFloatValue()
                             throws java.io.IOException
        Numeric accessor that can be called when the current token is of type JsonToken.VALUE_NUMBER_FLOAT and it can be expressed as a Java float primitive type. It can also be called for JsonToken.VALUE_NUMBER_INT; if so, it is equivalent to calling getLongValue() and then casting; except for possible overflow/underflow exception.

        Note: if the value falls outside of range of Java float, a InputCoercionException will be thrown to indicate numeric overflow/underflow.

        Returns:
        Current number value as float (if numeric token within Java float range); otherwise exception thrown
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getDoubleValue

        public abstract double getDoubleValue()
                               throws java.io.IOException
        Numeric accessor that can be called when the current token is of type JsonToken.VALUE_NUMBER_FLOAT and it can be expressed as a Java double primitive type. It can also be called for JsonToken.VALUE_NUMBER_INT; if so, it is equivalent to calling getLongValue() and then casting; except for possible overflow/underflow exception.

        Note: if the value falls outside of range of Java double, a InputCoercionException will be thrown to indicate numeric overflow/underflow.

        Returns:
        Current number value as double (if numeric token within Java double range); otherwise exception thrown
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getDecimalValue

        public abstract java.math.BigDecimal getDecimalValue()
                                              throws java.io.IOException
        Numeric accessor that can be called when the current token is of type JsonToken.VALUE_NUMBER_FLOAT or JsonToken.VALUE_NUMBER_INT. No under/overflow exceptions are ever thrown.
        Returns:
        Current number value as BigDecimal (if numeric token); otherwise exception thrown
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getBooleanValue

        public boolean getBooleanValue()
                        throws java.io.IOException
        Convenience accessor that can be called when the current token is JsonToken.VALUE_TRUE or JsonToken.VALUE_FALSE, to return matching boolean value. If the current token is of some other type, JsonParseException will be thrown
        Returns:
        True if current token is JsonToken.VALUE_TRUE, false if current token is JsonToken.VALUE_FALSE; otherwise throws JsonParseException
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getEmbeddedObject

        public java.lang.Object getEmbeddedObject()
                                   throws java.io.IOException
        Accessor that can be called if (and only if) the current token is JsonToken.VALUE_EMBEDDED_OBJECT. For other token types, null is returned.

        Note: only some specialized parser implementations support embedding of objects (usually ones that are facades on top of non-streaming sources, such as object trees). One exception is access to binary content (whether via base64 encoding or not) which typically is accessible using this method, as well as getBinaryValue().

        Returns:
        Embedded value (usually of "native" type supported by format) for the current token, if any; null otherwise
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getBinaryValue

        public abstract byte[] getBinaryValue​(Base64Variant bv)
                               throws java.io.IOException
        Method that can be used to read (and consume -- results may not be accessible using other methods after the call) base64-encoded binary data included in the current textual JSON value. It works similar to getting String value via getText() and decoding result (except for decoding part), but should be significantly more performant.

        Note that non-decoded textual contents of the current token are not guaranteed to be accessible after this method is called. Current implementation, for example, clears up textual content during decoding. Decoded binary content, however, will be retained until parser is advanced to the next event.

        Parameters:
        bv - Expected variant of base64 encoded content (see Base64Variants for definitions of "standard" variants).
        Returns:
        Decoded binary data
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • readBinaryValue

        public int readBinaryValue​(java.io.OutputStream out)
                    throws java.io.IOException
        Method that can be used as an alternative to getBigIntegerValue(), especially when value can be large. The main difference (beyond method of returning content using OutputStream instead of as byte array) is that content will NOT remain accessible after method returns: any content processed will be consumed and is not buffered in any way. If caller needs buffering, it has to implement it.
        Parameters:
        out - Output stream to use for passing decoded binary data
        Returns:
        Number of bytes that were decoded and written via OutputStream
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems
        Since:
        2.1

      • readBinaryValue

        public int readBinaryValue​(Base64Variant bv,
                           java.io.OutputStream out)
                    throws java.io.IOException
        Similar to readBinaryValue(OutputStream) but allows explicitly specifying base64 variant to use.
        Parameters:
        bv - base64 variant to use
        out - Output stream to use for passing decoded binary data
        Returns:
        Number of bytes that were decoded and written via OutputStream
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems
        Since:
        2.1

      • getValueAsInt

        public int getValueAsInt()
                  throws java.io.IOException
        Method that will try to convert value of current token to a Java int value. Numbers are coerced using default Java rules; booleans convert to 0 (false) and 1 (true), and Strings are parsed using default Java language integer parsing rules.

        If representation can not be converted to an int (including structured type markers like start/end Object/Array) default value of 0 will be returned; no exceptions are thrown.

        Returns:
        int value current token is converted to, if possible; exception thrown otherwise
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getValueAsInt

        public int getValueAsInt​(int def)
                  throws java.io.IOException
        Method that will try to convert value of current token to a int. Numbers are coerced using default Java rules; booleans convert to 0 (false) and 1 (true), and Strings are parsed using default Java language integer parsing rules.

        If representation can not be converted to an int (including structured type markers like start/end Object/Array) specified def will be returned; no exceptions are thrown.

        Parameters:
        def - Default value to return if conversion to int is not possible
        Returns:
        int value current token is converted to, if possible; def otherwise
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getValueAsLong

        public long getValueAsLong()
                    throws java.io.IOException
        Method that will try to convert value of current token to a long. Numbers are coerced using default Java rules; booleans convert to 0 (false) and 1 (true), and Strings are parsed using default Java language integer parsing rules.

        If representation can not be converted to a long (including structured type markers like start/end Object/Array) default value of 0L will be returned; no exceptions are thrown.

        Returns:
        long value current token is converted to, if possible; exception thrown otherwise
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getValueAsLong

        public long getValueAsLong​(long def)
                    throws java.io.IOException
        Method that will try to convert value of current token to a long. Numbers are coerced using default Java rules; booleans convert to 0 (false) and 1 (true), and Strings are parsed using default Java language integer parsing rules.

        If representation can not be converted to a long (including structured type markers like start/end Object/Array) specified def will be returned; no exceptions are thrown.

        Parameters:
        def - Default value to return if conversion to long is not possible
        Returns:
        long value current token is converted to, if possible; def otherwise
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getValueAsDouble

        public double getValueAsDouble()
                        throws java.io.IOException
        Method that will try to convert value of current token to a Java double. Numbers are coerced using default Java rules; booleans convert to 0.0 (false) and 1.0 (true), and Strings are parsed using default Java language floating point parsing rules.

        If representation can not be converted to a double (including structured types like Objects and Arrays), default value of 0.0 will be returned; no exceptions are thrown.

        Returns:
        double value current token is converted to, if possible; exception thrown otherwise
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getValueAsDouble

        public double getValueAsDouble​(double def)
                        throws java.io.IOException
        Method that will try to convert value of current token to a Java double. Numbers are coerced using default Java rules; booleans convert to 0.0 (false) and 1.0 (true), and Strings are parsed using default Java language floating point parsing rules.

        If representation can not be converted to a double (including structured types like Objects and Arrays), specified def will be returned; no exceptions are thrown.

        Parameters:
        def - Default value to return if conversion to double is not possible
        Returns:
        double value current token is converted to, if possible; def otherwise
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getValueAsBoolean

        public boolean getValueAsBoolean()
                          throws java.io.IOException
        Method that will try to convert value of current token to a boolean. JSON booleans map naturally; integer numbers other than 0 map to true, and 0 maps to false and Strings 'true' and 'false' map to corresponding values.

        If representation can not be converted to a boolean value (including structured types like Objects and Arrays), default value of false will be returned; no exceptions are thrown.

        Returns:
        boolean value current token is converted to, if possible; exception thrown otherwise
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getValueAsBoolean

        public boolean getValueAsBoolean​(boolean def)
                          throws java.io.IOException
        Method that will try to convert value of current token to a boolean. JSON booleans map naturally; integer numbers other than 0 map to true, and 0 maps to false and Strings 'true' and 'false' map to corresponding values.

        If representation can not be converted to a boolean value (including structured types like Objects and Arrays), specified def will be returned; no exceptions are thrown.

        Parameters:
        def - Default value to return if conversion to boolean is not possible
        Returns:
        boolean value current token is converted to, if possible; def otherwise
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems

      • getValueAsString

        public java.lang.String getValueAsString()
                                  throws java.io.IOException
        Method that will try to convert value of current token to a String. JSON Strings map naturally; scalar values get converted to their textual representation. If representation can not be converted to a String value (including structured types like Objects and Arrays and null token), default value of null will be returned; no exceptions are thrown.
        Returns:
        String value current token is converted to, if possible; null otherwise
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems
        Since:
        2.1

      • getValueAsString

        public abstract java.lang.String getValueAsString​(java.lang.String def)
                                           throws java.io.IOException
        Method that will try to convert value of current token to a String. JSON Strings map naturally; scalar values get converted to their textual representation. If representation can not be converted to a String value (including structured types like Objects and Arrays and null token), specified default value will be returned; no exceptions are thrown.
        Parameters:
        def - Default value to return if conversion to String is not possible
        Returns:
        String value current token is converted to, if possible; def otherwise
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems
        Since:
        2.1

      • canReadObjectId

        public boolean canReadObjectId()
        Introspection method that may be called to see if the underlying data format supports some kind of Object Ids natively (many do not; for example, JSON doesn't).

        Default implementation returns true; overridden by data formats that do support native Object Ids. Caller is expected to either use a non-native notation (explicit property or such), or fail, in case it can not use native object ids.

        Returns:
        True if the format being read supports native Object Ids; false if not
        Since:
        2.3

      • canReadTypeId

        public boolean canReadTypeId()
        Introspection method that may be called to see if the underlying data format supports some kind of Type Ids natively (many do not; for example, JSON doesn't).

        Default implementation returns true; overridden by data formats that do support native Type Ids. Caller is expected to either use a non-native notation (explicit property or such), or fail, in case it can not use native type ids.

        Returns:
        True if the format being read supports native Type Ids; false if not
        Since:
        2.3

      • getObjectId

        public java.lang.Object getObjectId()
                             throws java.io.IOException
        Method that can be called to check whether current token (one that was just read) has an associated Object id, and if so, return it. Note that while typically caller should check with canReadObjectId() first, it is not illegal to call this method even if that method returns true; but if so, it will return null. This may be used to simplify calling code.

        Default implementation will simply return null.

        Returns:
        Native Object id associated with the current token, if any; null if none
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems
        Since:
        2.3

      • getTypeId

        public java.lang.Object getTypeId()
                           throws java.io.IOException
        Method that can be called to check whether current token (one that was just read) has an associated type id, and if so, return it. Note that while typically caller should check with canReadTypeId() first, it is not illegal to call this method even if that method returns true; but if so, it will return null. This may be used to simplify calling code.

        Default implementation will simply return null.

        Returns:
        Native Type Id associated with the current token, if any; null if none
        Throws:
        java.io.IOException - for low-level read issues, or JsonParseException for decoding problems
        Since:
        2.3

      • readValueAs

        public <T> T readValueAs​(java.lang.Class<T> valueType)
                  throws java.io.IOException
        Method to deserialize JSON content into a non-container type (it can be an array type, however): typically a bean, array or a wrapper type (like Boolean). Note: method can only be called if the parser has an object codec assigned; this is true for parsers constructed by MappingJsonFactory (from "jackson-databind" jar) but not for JsonFactory (unless its setCodec method has been explicitly called).

        This method may advance the event stream, for structured types the current token will be the closing end marker (END_ARRAY, END_OBJECT) of the bound structure. For non-structured Json types (and for JsonToken.VALUE_EMBEDDED_OBJECT) stream is not advanced.

        Note: this method should NOT be used if the result type is a container (Collection or Map. The reason is that due to type erasure, key and value types can not be introspected when using this method.

        Type Parameters:
        T - Nominal type parameter for value type
        Parameters:
        valueType - Java type to read content as (passed to ObjectCodec that deserializes content)
        Returns:
        Java value read from content
        Throws:
        java.io.IOException - if there is either an underlying I/O problem or decoding issue at format layer

      • readValueAs

        public <T> T readValueAs​(TypeReference<?> valueTypeRef)
                  throws java.io.IOException
        Method to deserialize JSON content into a Java type, reference to which is passed as argument. Type is passed using so-called "super type token" and specifically needs to be used if the root type is a parameterized (generic) container type. Note: method can only be called if the parser has an object codec assigned; this is true for parsers constructed by MappingJsonFactory (defined in 'jackson-databind' bundle) but not for JsonFactory (unless its setCodec method has been explicitly called).

        This method may advance the event stream, for structured types the current token will be the closing end marker (END_ARRAY, END_OBJECT) of the bound structure. For non-structured Json types (and for JsonToken.VALUE_EMBEDDED_OBJECT) stream is not advanced.

        Type Parameters:
        T - Nominal type parameter for value type
        Parameters:
        valueTypeRef - Java type to read content as (passed to ObjectCodec that deserializes content)
        Returns:
        Java value read from content
        Throws:
        java.io.IOException - if there is either an underlying I/O problem or decoding issue at format layer

      • readValuesAs

        public <T> java.util.Iterator<T> readValuesAs​(java.lang.Class<T> valueType)
                                       throws java.io.IOException
        Method for reading sequence of Objects from parser stream, all with same specified value type.
        Type Parameters:
        T - Nominal type parameter for value type
        Parameters:
        valueType - Java type to read content as (passed to ObjectCodec that deserializes content)
        Returns:
        Iterator for reading multiple Java values from content
        Throws:
        java.io.IOException - if there is either an underlying I/O problem or decoding issue at format layer

      • readValuesAs

        public <T> java.util.Iterator<T> readValuesAs​(TypeReference<T> valueTypeRef)
                                       throws java.io.IOException
        Method for reading sequence of Objects from parser stream, all with same specified value type.
        Type Parameters:
        T - Nominal type parameter for value type
        Parameters:
        valueTypeRef - Java type to read content as (passed to ObjectCodec that deserializes content)
        Returns:
        Iterator for reading multiple Java values from content
        Throws:
        java.io.IOException - if there is either an underlying I/O problem or decoding issue at format layer

      • readValueAsTree

        public <T extends TreeNode> T readValueAsTree()
                                       throws java.io.IOException
        Method to deserialize JSON content into equivalent "tree model", represented by root TreeNode of resulting model. For JSON Arrays it will an array node (with child nodes), for objects object node (with child nodes), and for other types matching leaf node type. Empty or whitespace documents are null.
        Type Parameters:
        T - Nominal type parameter for result node type (to reduce need for casting)
        Returns:
        root of the document, or null if empty or whitespace.
        Throws:
        java.io.IOException - if there is either an underlying I/O problem or decoding issue at format layer