org.apache.commons.beanutils

## Class ConstructorUtils

- java.lang.Object
- - org.apache.commons.beanutils.ConstructorUtils

-     public class ConstructorUtils
      extends Object

  Utility reflection methods focussed on constructors, modelled 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 locates these constructors fine and correctly assigns them as public. However, an `IllegalAccessException` is thrown if the constructors is invoked.

  `ConstructorUtils` contains a workaround for this situation. It will attempt to call `setAccessible` 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 privilages. If this call fails then a warning will be logged and the method may fail.

  Version:
    $Id: ConstructorUtils.java 1540518 2013-11-10 19:04:04Z oheger $

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `ConstructorUtils()`

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `static <T> Constructor<T>` | `getAccessibleConstructor(Class<T> klass, Class<?> parameterType)` Returns a constructor with single argument.
    `static <T> Constructor<T>` | `getAccessibleConstructor(Class<T> klass, Class<?>[] parameterTypes)` Returns a constructor given a class and signature.
    `static <T> Constructor<T>` | `getAccessibleConstructor(Constructor<T> ctor)` Returns accessible version of the given constructor.
    `static <T> T` | `invokeConstructor(Class<T> klass, Object arg)` Convenience method returning new instance of `klazz` using a single argument constructor.
    `static <T> T` | `invokeConstructor(Class<T> klass, Object[] args)` Returns new instance of `klazz` created using the actual arguments `args`.
    `static <T> T` | `invokeConstructor(Class<T> klass, Object[] args, Class<?>[] parameterTypes)` Returns new instance of `klazz` created using constructor with signature `parameterTypes` and actual arguments `args`.
    `static <T> T` | `invokeExactConstructor(Class<T> klass, Object arg)` Convenience method returning new instance of `klazz` using a single argument constructor.
    `static <T> T` | `invokeExactConstructor(Class<T> klass, Object[] args)` Returns new instance of `klazz` created using the actual arguments `args`.
    `static <T> T` | `invokeExactConstructor(Class<T> klass, Object[] args, Class<?>[] parameterTypes)` Returns new instance of `klazz` created using constructor with signature `parameterTypes` and actual arguments `args`.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Constructor Detail

    - #### ConstructorUtils

          public ConstructorUtils()

  - ### Method Detail

    - #### invokeConstructor

          public static <T> T invokeConstructor(Class<T> klass,
                                Object arg)
                                     throws NoSuchMethodException,
                                            IllegalAccessException,
                                            InvocationTargetException,
                                            InstantiationException

      Convenience method returning new instance of `klazz` using a single argument constructor. The formal parameter type is inferred from the actual values of `arg`. See `invokeExactConstructor(Class, Object[], Class[])` for more details.

      The signatures should be assignment compatible.

      Type Parameters:
        `T` - the type of the object to be constructed
      Parameters:
        `klass` - the class to be constructed.
        `arg` - the actual argument. May be null (this will result in calling the default constructor).
      Returns:
        new instance of `klazz`
      Throws:
        `NoSuchMethodException` - If the constructor cannot be found
        `IllegalAccessException` - If an error occurs accessing the constructor
        `InvocationTargetException` - If an error occurs invoking the constructor
        `InstantiationException` - If an error occurs instantiating the class
      See Also:
        `invokeConstructor(java.lang.Class, java.lang.Object[], java.lang.Class[])`

    - #### invokeConstructor

          public static <T> T invokeConstructor(Class<T> klass,
                                Object[] args)
                                     throws NoSuchMethodException,
                                            IllegalAccessException,
                                            InvocationTargetException,
                                            InstantiationException

      Returns new instance of `klazz` created using the actual arguments `args`. The formal parameter types are inferred from the actual values of `args`. See `invokeExactConstructor(Class, Object[], Class[])` for more details.

      The signatures should be assignment compatible.

      Type Parameters:
        `T` - the type of the object to be constructed
      Parameters:
        `klass` - the class to be constructed.
        `args` - actual argument array. May be null (this will result in calling the default constructor).
      Returns:
        new instance of `klazz`
      Throws:
        `NoSuchMethodException` - If the constructor cannot be found
        `IllegalAccessException` - If an error occurs accessing the constructor
        `InvocationTargetException` - If an error occurs invoking the constructor
        `InstantiationException` - If an error occurs instantiating the class
      See Also:
        `invokeConstructor(java.lang.Class, java.lang.Object[], java.lang.Class[])`

    - #### invokeConstructor

          public static <T> T invokeConstructor(Class<T> klass,
                                Object[] args,
                                Class<?>[] parameterTypes)
                                     throws NoSuchMethodException,
                                            IllegalAccessException,
                                            InvocationTargetException,
                                            InstantiationException

      Returns new instance of `klazz` created using constructor with signature `parameterTypes` and actual arguments `args`.

      The signatures should be assignment compatible.

      Type Parameters:
        `T` - the type of the object to be constructed
      Parameters:
        `klass` - the class to be constructed.
        `args` - actual argument array. May be null (this will result in calling the default constructor).
        `parameterTypes` - parameter types array
      Returns:
        new instance of `klazz`
      Throws:
        `NoSuchMethodException` - if matching constructor cannot be found
        `IllegalAccessException` - thrown on the constructor's invocation
        `InvocationTargetException` - thrown on the constructor's invocation
        `InstantiationException` - thrown on the constructor's invocation
      See Also:
        `Constructor.newInstance(java.lang.Object...)`

    - #### invokeExactConstructor

          public static <T> T invokeExactConstructor(Class<T> klass,
                                     Object arg)
                                          throws NoSuchMethodException,
                                                 IllegalAccessException,
                                                 InvocationTargetException,
                                                 InstantiationException

      Convenience method returning new instance of `klazz` using a single argument constructor. The formal parameter type is inferred from the actual values of `arg`. See `invokeExactConstructor(Class, Object[], Class[])` for more details.

      The signatures should match exactly.

      Type Parameters:
        `T` - the type of the object to be constructed
      Parameters:
        `klass` - the class to be constructed.
        `arg` - the actual argument. May be null (this will result in calling the default constructor).
      Returns:
        new instance of `klazz`
      Throws:
        `NoSuchMethodException` - If the constructor cannot be found
        `IllegalAccessException` - If an error occurs accessing the constructor
        `InvocationTargetException` - If an error occurs invoking the constructor
        `InstantiationException` - If an error occurs instantiating the class
      See Also:
        `invokeExactConstructor(java.lang.Class, java.lang.Object[], java.lang.Class[])`

    - #### invokeExactConstructor

          public static <T> T invokeExactConstructor(Class<T> klass,
                                     Object[] args)
                                          throws NoSuchMethodException,
                                                 IllegalAccessException,
                                                 InvocationTargetException,
                                                 InstantiationException

      Returns new instance of `klazz` created using the actual arguments `args`. The formal parameter types are inferred from the actual values of `args`. See `invokeExactConstructor(Class, Object[], Class[])` for more details.

      The signatures should match exactly.

      Type Parameters:
        `T` - the type of the object to be constructed
      Parameters:
        `klass` - the class to be constructed.
        `args` - actual argument array. May be null (this will result in calling the default constructor).
      Returns:
        new instance of `klazz`
      Throws:
        `NoSuchMethodException` - If the constructor cannot be found
        `IllegalAccessException` - If an error occurs accessing the constructor
        `InvocationTargetException` - If an error occurs invoking the constructor
        `InstantiationException` - If an error occurs instantiating the class
      See Also:
        `invokeExactConstructor(java.lang.Class, java.lang.Object[], java.lang.Class[])`

    - #### invokeExactConstructor

          public static <T> T invokeExactConstructor(Class<T> klass,
                                     Object[] args,
                                     Class<?>[] parameterTypes)
                                          throws NoSuchMethodException,
                                                 IllegalAccessException,
                                                 InvocationTargetException,
                                                 InstantiationException

      Returns new instance of `klazz` created using constructor with signature `parameterTypes` and actual arguments `args`.

      The signatures should match exactly.

      Type Parameters:
        `T` - the type of the object to be constructed
      Parameters:
        `klass` - the class to be constructed.
        `args` - actual argument array. May be null (this will result in calling the default constructor).
        `parameterTypes` - parameter types array
      Returns:
        new instance of `klazz`
      Throws:
        `NoSuchMethodException` - if matching constructor cannot be found
        `IllegalAccessException` - thrown on the constructor's invocation
        `InvocationTargetException` - thrown on the constructor's invocation
        `InstantiationException` - thrown on the constructor's invocation
      See Also:
        `Constructor.newInstance(java.lang.Object...)`

    - #### getAccessibleConstructor

          public static <T> Constructor<T> getAccessibleConstructor(Class<T> klass,
                                                    Class<?> parameterType)

      Returns a constructor with single argument.
      Type Parameters:
        `T` - the type of the constructor
      Parameters:
        `klass` - the class to be constructed
        `parameterType` - The constructor parameter type
      Returns:
        null if matching accessible constructor can not be found.
      See Also:
        `Class.getConstructor(java.lang.Class<?>...)`, `getAccessibleConstructor(java.lang.reflect.Constructor)`

    - #### getAccessibleConstructor

          public static <T> Constructor<T> getAccessibleConstructor(Class<T> klass,
                                                    Class<?>[] parameterTypes)

      Returns a constructor given a class and signature.
      Type Parameters:
        `T` - the type to be constructed
      Parameters:
        `klass` - the class to be constructed
        `parameterTypes` - the parameter array
      Returns:
        null if matching accessible constructor can not be found
      See Also:
        `Class.getConstructor(java.lang.Class<?>...)`, `getAccessibleConstructor(java.lang.reflect.Constructor)`

    - #### getAccessibleConstructor

          public static <T> Constructor<T> getAccessibleConstructor(Constructor<T> ctor)

      Returns accessible version of the given constructor.
      Type Parameters:
        `T` - the type of the constructor
      Parameters:
        `ctor` - prototype constructor object.
      Returns:
        `null` if accessible constructor can not be found.
      See Also:
        `SecurityManager`

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