Class ConstructorUtils
Utility reflection methods focussed on constructors, modelled after MethodUtils
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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:
- $Id$
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Field Summary
Fields -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionstatic <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.private static <T> Constructor
<T> getMatchingAccessibleConstructor
(Class<T> clazz, Class<?>[] parameterTypes) Find an accessible constructor with compatible parameters.static <T> T
invokeConstructor
(Class<T> klass, Object arg) Convenience method returning new instance ofklazz
using a single argument constructor.static <T> T
invokeConstructor
(Class<T> klass, Object[] args) Returns new instance ofklazz
created using the actual argumentsargs
.static <T> T
invokeConstructor
(Class<T> klass, Object[] args, Class<?>[] parameterTypes) Returns new instance ofklazz
created using constructor with signatureparameterTypes
and actual argumentsargs
.static <T> T
invokeExactConstructor
(Class<T> klass, Object arg) Convenience method returning new instance ofklazz
using a single argument constructor.static <T> T
invokeExactConstructor
(Class<T> klass, Object[] args) Returns new instance ofklazz
created using the actual argumentsargs
.static <T> T
invokeExactConstructor
(Class<T> klass, Object[] args, Class<?>[] parameterTypes) Returns new instance ofklazz
created using constructor with signatureparameterTypes
and actual argumentsargs
.private static Object[]
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Field Details
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EMPTY_CLASS_PARAMETERS
An empty class array -
EMPTY_OBJECT_ARRAY
An empty object array
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Constructor Details
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ConstructorUtils
public ConstructorUtils()
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Method Details
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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 ofarg
. SeeinvokeExactConstructor(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 foundIllegalAccessException
- If an error occurs accessing the constructorInvocationTargetException
- If an error occurs invoking the constructorInstantiationException
- If an error occurs instantiating the class- See Also:
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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 argumentsargs
. The formal parameter types are inferred from the actual values ofargs
. SeeinvokeExactConstructor(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 foundIllegalAccessException
- If an error occurs accessing the constructorInvocationTargetException
- If an error occurs invoking the constructorInstantiationException
- If an error occurs instantiating the class- See Also:
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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 signatureparameterTypes
and actual argumentsargs
.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 foundIllegalAccessException
- thrown on the constructor's invocationInvocationTargetException
- thrown on the constructor's invocationInstantiationException
- thrown on the constructor's invocation- See Also:
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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 ofarg
. SeeinvokeExactConstructor(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 foundIllegalAccessException
- If an error occurs accessing the constructorInvocationTargetException
- If an error occurs invoking the constructorInstantiationException
- If an error occurs instantiating the class- See Also:
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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 argumentsargs
. The formal parameter types are inferred from the actual values ofargs
. SeeinvokeExactConstructor(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 foundIllegalAccessException
- If an error occurs accessing the constructorInvocationTargetException
- If an error occurs invoking the constructorInstantiationException
- If an error occurs instantiating the class- See Also:
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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 signatureparameterTypes
and actual argumentsargs
.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 foundIllegalAccessException
- thrown on the constructor's invocationInvocationTargetException
- thrown on the constructor's invocationInstantiationException
- thrown on the constructor's invocation- See Also:
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getAccessibleConstructor
Returns a constructor with single argument.- Type Parameters:
T
- the type of the constructor- Parameters:
klass
- the class to be constructedparameterType
- The constructor parameter type- Returns:
- null if matching accessible constructor can not be found.
- See Also:
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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 constructedparameterTypes
- the parameter array- Returns:
- null if matching accessible constructor can not be found
- See Also:
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getAccessibleConstructor
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:
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toArray
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getMatchingAccessibleConstructor
private static <T> Constructor<T> getMatchingAccessibleConstructor(Class<T> clazz, Class<?>[] parameterTypes) Find an accessible constructor with compatible parameters. Compatible parameters mean that every method parameter is assignable from the given parameters. In other words, it finds constructor that will take the parameters given.
First it checks if there is constructor matching the exact signature. If no such, all the constructors of the class are tested if their signatures are assignment compatible with the parameter types. The first matching constructor is returned.
- Type Parameters:
T
- the type of the class to be inspected- Parameters:
clazz
- find constructor for this classparameterTypes
- find method with compatible parameters- Returns:
- a valid Constructor object. If there's no matching constructor, returns
null
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