Package org.apache.commons.beanutils2

Class ConstructorUtils

java.lang.Object

org.apache.commons.beanutils2.ConstructorUtils

public class ConstructorUtils
extends 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 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 privileges. If this call fails then a warning will be logged and the method may fail.

Constructor Summary

Constructors

Constructor	Description
ConstructorUtils()

Method Summary

Modifier and Type	Method	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</code> created using the actual arguments <code>args.
static <T> T	invokeConstructor(Class<T> klass, Object[] args, Class<?>[] parameterTypes)	Returns new instance of klazz created using constructor with signature parameterTypes</code> and actual arguments <code>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</code> created using the actual arguments <code>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.
static <T> T[]	newArray(Class<T> componentType, int length)	Delegates to Array.newInstance(Class, int).

Methods inherited from class java.lang.Object

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

Constructor Details

ConstructorUtils

public ConstructorUtils()

Method Details

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 cannot 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 cannot 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 cannot be found.

See Also:

• SecurityManager

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(Class, Object[], Class[])

invokeConstructor

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

Returns new instance of klazz</code> created using the actual arguments <code>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(Class, Object[], 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</code> and actual arguments <code>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(Class, Object[], Class[])

invokeExactConstructor

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

Returns new instance of klazz</code> created using the actual arguments <code>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(Class, Object[], 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...)

newArray

public static <T> T[] newArray(Class<T> componentType,
 int length)

Delegates to Array.newInstance(Class, int).

Type Parameters:

T - Component type.

Parameters:

componentType - See Array.newInstance(Class, int).

length - See Array.newInstance(Class, int).

Returns:

See Array.newInstance(Class, int).