Class ConstructorUtils


  • public class ConstructorUtils
    extends java.lang.Object

    Utility reflection methods focused on constructors, modeled after MethodUtils.

    Known Limitations

    Accessing Public Constructors In A Default Access Superclass

    There is an issue when invoking public constructors contained in a default access superclass. Reflection correctly locates these constructors and assigns them as public. However, an IllegalAccessException is thrown if the constructor is invoked.

    ConstructorUtils contains a workaround for this situation: it will attempt to call AccessibleObject.setAccessible(boolean) on this constructor. If this call succeeds, then the method can be invoked as normal. This call will only succeed when the application has sufficient security privileges. If this call fails then a warning will be logged and the method may fail.

    Since:
    2.5
    • Constructor Summary

      Constructors 
      Constructor Description
      ConstructorUtils()
      ConstructorUtils instances should NOT be constructed in standard programming.
    • Method Summary

      All Methods Static Methods Concrete Methods 
      Modifier and Type Method Description
      static <T> java.lang.reflect.Constructor<T> getAccessibleConstructor​(java.lang.Class<T> cls, java.lang.Class<?>... parameterTypes)
      Finds a constructor given a class and signature, checking accessibility.
      static <T> java.lang.reflect.Constructor<T> getAccessibleConstructor​(java.lang.reflect.Constructor<T> ctor)
      Checks if the specified constructor is accessible.
      static <T> java.lang.reflect.Constructor<T> getMatchingAccessibleConstructor​(java.lang.Class<T> cls, java.lang.Class<?>... parameterTypes)
      Finds an accessible constructor with compatible parameters.
      static <T> T invokeConstructor​(java.lang.Class<T> cls, java.lang.Object... args)
      Returns a new instance of the specified class inferring the right constructor from the types of the arguments.
      static <T> T invokeConstructor​(java.lang.Class<T> cls, java.lang.Object[] args, java.lang.Class<?>[] parameterTypes)
      Returns a new instance of the specified class choosing the right constructor from the list of parameter types.
      static <T> T invokeExactConstructor​(java.lang.Class<T> cls, java.lang.Object... args)
      Returns a new instance of the specified class inferring the right constructor from the types of the arguments.
      static <T> T invokeExactConstructor​(java.lang.Class<T> cls, java.lang.Object[] args, java.lang.Class<?>[] parameterTypes)
      Returns a new instance of the specified class choosing the right constructor from the list of parameter types.
      • Methods inherited from class java.lang.Object

        equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    • Constructor Detail

      • ConstructorUtils

        public ConstructorUtils()

        ConstructorUtils instances should NOT be constructed in standard programming. Instead, the class should be used as ConstructorUtils.invokeConstructor(cls, args).

        This constructor is public to permit tools that require a JavaBean instance to operate.

    • Method Detail

      • invokeConstructor

        public static <T> T invokeConstructor​(java.lang.Class<T> cls,
                                              java.lang.Object... args)
                                       throws java.lang.NoSuchMethodException,
                                              java.lang.IllegalAccessException,
                                              java.lang.reflect.InvocationTargetException,
                                              java.lang.InstantiationException

        Returns a new instance of the specified class inferring the right constructor from the types of the arguments.

        This locates and calls a constructor. The constructor signature must match the argument types by assignment compatibility.

        Type Parameters:
        T - the type to be constructed
        Parameters:
        cls - the class to be constructed, not null
        args - the array of arguments, null treated as empty
        Returns:
        new instance of cls, not null
        Throws:
        java.lang.NullPointerException - if cls is null
        java.lang.NoSuchMethodException - if a matching constructor cannot be found
        java.lang.IllegalAccessException - if invocation is not permitted by security
        java.lang.reflect.InvocationTargetException - if an error occurs on invocation
        java.lang.InstantiationException - if an error occurs on instantiation
        See Also:
        invokeConstructor(java.lang.Class, java.lang.Object[], java.lang.Class[])
      • invokeConstructor

        public static <T> T invokeConstructor​(java.lang.Class<T> cls,
                                              java.lang.Object[] args,
                                              java.lang.Class<?>[] parameterTypes)
                                       throws java.lang.NoSuchMethodException,
                                              java.lang.IllegalAccessException,
                                              java.lang.reflect.InvocationTargetException,
                                              java.lang.InstantiationException

        Returns a new instance of the specified class choosing the right constructor from the list of parameter types.

        This locates and calls a constructor. The constructor signature must match the parameter types by assignment compatibility.

        Type Parameters:
        T - the type to be constructed
        Parameters:
        cls - the class to be constructed, not null
        args - the array of arguments, null treated as empty
        parameterTypes - the array of parameter types, null treated as empty
        Returns:
        new instance of cls, not null
        Throws:
        java.lang.NullPointerException - if cls is null
        java.lang.NoSuchMethodException - if a matching constructor cannot be found
        java.lang.IllegalAccessException - if invocation is not permitted by security
        java.lang.reflect.InvocationTargetException - if an error occurs on invocation
        java.lang.InstantiationException - if an error occurs on instantiation
        See Also:
        Constructor.newInstance(java.lang.Object...)
      • invokeExactConstructor

        public static <T> T invokeExactConstructor​(java.lang.Class<T> cls,
                                                   java.lang.Object... args)
                                            throws java.lang.NoSuchMethodException,
                                                   java.lang.IllegalAccessException,
                                                   java.lang.reflect.InvocationTargetException,
                                                   java.lang.InstantiationException

        Returns a new instance of the specified class inferring the right constructor from the types of the arguments.

        This locates and calls a constructor. The constructor signature must match the argument types exactly.

        Type Parameters:
        T - the type to be constructed
        Parameters:
        cls - the class to be constructed, not null
        args - the array of arguments, null treated as empty
        Returns:
        new instance of cls, not null
        Throws:
        java.lang.NullPointerException - if cls is null
        java.lang.NoSuchMethodException - if a matching constructor cannot be found
        java.lang.IllegalAccessException - if invocation is not permitted by security
        java.lang.reflect.InvocationTargetException - if an error occurs on invocation
        java.lang.InstantiationException - if an error occurs on instantiation
        See Also:
        invokeExactConstructor(java.lang.Class, java.lang.Object[], java.lang.Class[])
      • invokeExactConstructor

        public static <T> T invokeExactConstructor​(java.lang.Class<T> cls,
                                                   java.lang.Object[] args,
                                                   java.lang.Class<?>[] parameterTypes)
                                            throws java.lang.NoSuchMethodException,
                                                   java.lang.IllegalAccessException,
                                                   java.lang.reflect.InvocationTargetException,
                                                   java.lang.InstantiationException

        Returns a new instance of the specified class choosing the right constructor from the list of parameter types.

        This locates and calls a constructor. The constructor signature must match the parameter types exactly.

        Type Parameters:
        T - the type to be constructed
        Parameters:
        cls - the class to be constructed, not null
        args - the array of arguments, null treated as empty
        parameterTypes - the array of parameter types, null treated as empty
        Returns:
        new instance of cls, not null
        Throws:
        java.lang.NullPointerException - if cls is null
        java.lang.NoSuchMethodException - if a matching constructor cannot be found
        java.lang.IllegalAccessException - if invocation is not permitted by security
        java.lang.reflect.InvocationTargetException - if an error occurs on invocation
        java.lang.InstantiationException - if an error occurs on instantiation
        See Also:
        Constructor.newInstance(java.lang.Object...)
      • getAccessibleConstructor

        public static <T> java.lang.reflect.Constructor<T> getAccessibleConstructor​(java.lang.Class<T> cls,
                                                                                    java.lang.Class<?>... parameterTypes)

        Finds a constructor given a class and signature, checking accessibility.

        This finds the constructor and ensures that it is accessible. The constructor signature must match the parameter types exactly.

        Type Parameters:
        T - the constructor type
        Parameters:
        cls - the class to find a constructor for, not null
        parameterTypes - the array of parameter types, null treated as empty
        Returns:
        the constructor, null if no matching accessible constructor found
        Throws:
        java.lang.NullPointerException - if cls is null
        See Also:
        Class.getConstructor(java.lang.Class<?>...), getAccessibleConstructor(java.lang.reflect.Constructor)
      • getAccessibleConstructor

        public static <T> java.lang.reflect.Constructor<T> getAccessibleConstructor​(java.lang.reflect.Constructor<T> ctor)

        Checks if the specified constructor is accessible.

        This simply ensures that the constructor is accessible.

        Type Parameters:
        T - the constructor type
        Parameters:
        ctor - the prototype constructor object, not null
        Returns:
        the constructor, null if no matching accessible constructor found
        Throws:
        java.lang.NullPointerException - if ctor is null
        See Also:
        SecurityManager
      • getMatchingAccessibleConstructor

        public static <T> java.lang.reflect.Constructor<T> getMatchingAccessibleConstructor​(java.lang.Class<T> cls,
                                                                                            java.lang.Class<?>... parameterTypes)

        Finds an accessible constructor with compatible parameters.

        This checks all the constructor and finds one with compatible parameters This requires that every parameter is assignable from the given parameter types. This is a more flexible search than the normal exact matching algorithm.

        First it checks if there is a constructor matching the exact signature. If not then all the constructors of the class are checked to see if their signatures are assignment-compatible with the parameter types. The first assignment-compatible matching constructor is returned.

        Type Parameters:
        T - the constructor type
        Parameters:
        cls - the class to find a constructor for, not null
        parameterTypes - find method with compatible parameters
        Returns:
        the constructor, null if no matching accessible constructor found
        Throws:
        java.lang.NullPointerException - if cls is null