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BeanUtils provides an easy-to-use but flexible wrapper around reflection and introspection.
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.beanutils;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Modifier;
/**
* Utility reflection methods focussed on constructors, modelled after {@link 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.
*
* @author Craig R. McClanahan
* @author Ralph Schaer
* @author Chris Audley
* @author Rey Francois
* @author Gregor Rayman
* @author Jan Sorensen
* @author Robert Burrell Donkin
* @author Rodney Waldhoff
* @version $Revision: 555824 $ $Date: 2007-07-12 20:27:15 -0400 (Thu, 12 Jul 2007) $
*/
public class ConstructorUtils {
// --------------------------------------------------------- Private Members
/** An empty class array */
private static final Class[] EMPTY_CLASS_PARAMETERS = new Class[0];
/** An empty object array */
private static final Object[] EMPTY_OBJECT_ARRAY = new Object[0];
// --------------------------------------------------------- Public Methods
/**
* 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 {@link #invokeExactConstructor(Class, Object[], Class[])} for more details.
*
* The signatures should be assignment compatible.
*
* @param klass the class to be constructed.
* @param arg the actual argument
* @return new instance of klazz
*
* @throws NoSuchMethodException If the constructor cannot be found
* @throws IllegalAccessException If an error occurs accessing the constructor
* @throws InvocationTargetException If an error occurs invoking the constructor
* @throws InstantiationException If an error occurs instantiating the class
*
* @see #invokeConstructor(java.lang.Class, java.lang.Object[], java.lang.Class[])
*/
public static Object invokeConstructor(Class klass, Object arg)
throws
NoSuchMethodException,
IllegalAccessException,
InvocationTargetException,
InstantiationException {
Object[] args = { arg };
return invokeConstructor(klass, args);
}
/**
* Returns new instance of klazz created using the actual arguments args.
* The formal parameter types are inferred from the actual values of args.
* See {@link #invokeExactConstructor(Class, Object[], Class[])} for more details.
*
* The signatures should be assignment compatible.
*
* @param klass the class to be constructed.
* @param args actual argument array
* @return new instance of klazz
*
* @throws NoSuchMethodException If the constructor cannot be found
* @throws IllegalAccessException If an error occurs accessing the constructor
* @throws InvocationTargetException If an error occurs invoking the constructor
* @throws InstantiationException If an error occurs instantiating the class
*
* @see #invokeConstructor(java.lang.Class, java.lang.Object[], java.lang.Class[])
*/
public static Object invokeConstructor(Class klass, Object[] args)
throws
NoSuchMethodException,
IllegalAccessException,
InvocationTargetException,
InstantiationException {
if (null == args) {
args = EMPTY_OBJECT_ARRAY;
}
int arguments = args.length;
Class parameterTypes[] = new Class[arguments];
for (int i = 0; i < arguments; i++) {
parameterTypes[i] = args[i].getClass();
}
return invokeConstructor(klass, args, parameterTypes);
}
/**
* Returns new instance of klazz created using constructor
* with signature parameterTypes and actual arguments args.
*
* The signatures should be assignment compatible.
*
* @param klass the class to be constructed.
* @param args actual argument array
* @param parameterTypes parameter types array
* @return new instance of klazz
*
* @throws NoSuchMethodException if matching constructor cannot be found
* @throws IllegalAccessException thrown on the constructor's invocation
* @throws InvocationTargetException thrown on the constructor's invocation
* @throws InstantiationException thrown on the constructor's invocation
* @see Constructor#newInstance
*/
public static Object invokeConstructor(
Class klass,
Object[] args,
Class[] parameterTypes)
throws
NoSuchMethodException,
IllegalAccessException,
InvocationTargetException,
InstantiationException {
if (parameterTypes == null) {
parameterTypes = EMPTY_CLASS_PARAMETERS;
}
if (args == null) {
args = EMPTY_OBJECT_ARRAY;
}
Constructor ctor =
getMatchingAccessibleConstructor(klass, parameterTypes);
if (null == ctor) {
throw new NoSuchMethodException(
"No such accessible constructor on object: " + klass.getName());
}
return ctor.newInstance(args);
}
/**
* 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 {@link #invokeExactConstructor(Class, Object[], Class[])} for more details.
*
* The signatures should match exactly.
*
* @param klass the class to be constructed.
* @param arg the actual argument
* @return new instance of klazz
*
* @throws NoSuchMethodException If the constructor cannot be found
* @throws IllegalAccessException If an error occurs accessing the constructor
* @throws InvocationTargetException If an error occurs invoking the constructor
* @throws InstantiationException If an error occurs instantiating the class
*
* @see #invokeExactConstructor(java.lang.Class, java.lang.Object[], java.lang.Class[])
*/
public static Object invokeExactConstructor(Class klass, Object arg)
throws
NoSuchMethodException,
IllegalAccessException,
InvocationTargetException,
InstantiationException {
Object[] args = { arg };
return invokeExactConstructor(klass, args);
}
/**
* Returns new instance of klazz created using the actual arguments args.
* The formal parameter types are inferred from the actual values of args.
* See {@link #invokeExactConstructor(Class, Object[], Class[])} for more details.
*
* The signatures should match exactly.
*
* @param klass the class to be constructed.
* @param args actual argument array
* @return new instance of klazz
*
* @throws NoSuchMethodException If the constructor cannot be found
* @throws IllegalAccessException If an error occurs accessing the constructor
* @throws InvocationTargetException If an error occurs invoking the constructor
* @throws InstantiationException If an error occurs instantiating the class
*
* @see #invokeExactConstructor(java.lang.Class, java.lang.Object[], java.lang.Class[])
*/
public static Object invokeExactConstructor(Class klass, Object[] args)
throws
NoSuchMethodException,
IllegalAccessException,
InvocationTargetException,
InstantiationException {
if (null == args) {
args = EMPTY_OBJECT_ARRAY;
}
int arguments = args.length;
Class parameterTypes[] = new Class[arguments];
for (int i = 0; i < arguments; i++) {
parameterTypes[i] = args[i].getClass();
}
return invokeExactConstructor(klass, args, parameterTypes);
}
/**
* Returns new instance of klazz created using constructor
* with signature parameterTypes and actual arguments
* args.
*
* The signatures should match exactly.
*
* @param klass the class to be constructed.
* @param args actual argument array
* @param parameterTypes parameter types array
* @return new instance of klazz
*
* @throws NoSuchMethodException if matching constructor cannot be found
* @throws IllegalAccessException thrown on the constructor's invocation
* @throws InvocationTargetException thrown on the constructor's invocation
* @throws InstantiationException thrown on the constructor's invocation
* @see Constructor#newInstance
*/
public static Object invokeExactConstructor(
Class klass,
Object[] args,
Class[] parameterTypes)
throws
NoSuchMethodException,
IllegalAccessException,
InvocationTargetException,
InstantiationException {
if (args == null) {
args = EMPTY_OBJECT_ARRAY;
}
if (parameterTypes == null) {
parameterTypes = EMPTY_CLASS_PARAMETERS;
}
Constructor ctor = getAccessibleConstructor(klass, parameterTypes);
if (null == ctor) {
throw new NoSuchMethodException(
"No such accessible constructor on object: " + klass.getName());
}
return ctor.newInstance(args);
}
/**
* Returns a constructor with single argument.
* @param klass the class to be constructed
* @param parameterType The constructor parameter type
* @return null if matching accessible constructor can not be found.
* @see Class#getConstructor
* @see #getAccessibleConstructor(java.lang.reflect.Constructor)
*/
public static Constructor getAccessibleConstructor(
Class klass,
Class parameterType) {
Class[] parameterTypes = { parameterType };
return getAccessibleConstructor(klass, parameterTypes);
}
/**
* Returns a constructor given a class and signature.
* @param klass the class to be constructed
* @param parameterTypes the parameter array
* @return null if matching accessible constructor can not be found
* @see Class#getConstructor
* @see #getAccessibleConstructor(java.lang.reflect.Constructor)
*/
public static Constructor getAccessibleConstructor(
Class klass,
Class[] parameterTypes) {
try {
return getAccessibleConstructor(
klass.getConstructor(parameterTypes));
} catch (NoSuchMethodException e) {
return (null);
}
}
/**
* Returns accessible version of the given constructor.
* @param ctor prototype constructor object.
* @return null if accessible constructor can not be found.
* @see java.lang.SecurityManager
*/
public static Constructor getAccessibleConstructor(Constructor ctor) {
// Make sure we have a method to check
if (ctor == null) {
return (null);
}
// If the requested method is not public we cannot call it
if (!Modifier.isPublic(ctor.getModifiers())) {
return (null);
}
// If the declaring class is public, we are done
Class clazz = ctor.getDeclaringClass();
if (Modifier.isPublic(clazz.getModifiers())) {
return (ctor);
}
// what else can we do?
return null;
}
// -------------------------------------------------------- Private Methods
/**
* 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.
*
* @param clazz find constructor for this class
* @param parameterTypes find method with compatible parameters
* @return a valid Constructor object. If there's no matching constructor, returns null.
*/
private static Constructor getMatchingAccessibleConstructor(
Class clazz,
Class[] parameterTypes) {
// see if we can find the method directly
// most of the time this works and it's much faster
try {
Constructor ctor = clazz.getConstructor(parameterTypes);
try {
//
// XXX Default access superclass workaround
//
// When a public class has a default access superclass
// with public methods, these methods are accessible.
// Calling them from compiled code works fine.
//
// Unfortunately, using reflection to invoke these methods
// seems to (wrongly) to prevent access even when the method
// modifer is public.
//
// The following workaround solves the problem but will only
// work from sufficiently privilages code.
//
// Better workarounds would be greatfully accepted.
//
ctor.setAccessible(true);
} catch (SecurityException se) {
/* SWALLOW, if workaround fails don't fret. */
}
return ctor;
} catch (NoSuchMethodException e) { /* SWALLOW */
}
// search through all methods
int paramSize = parameterTypes.length;
Constructor[] ctors = clazz.getConstructors();
for (int i = 0, size = ctors.length; i < size; i++) {
// compare parameters
Class[] ctorParams = ctors[i].getParameterTypes();
int ctorParamSize = ctorParams.length;
if (ctorParamSize == paramSize) {
boolean match = true;
for (int n = 0; n < ctorParamSize; n++) {
if (!MethodUtils
.isAssignmentCompatible(
ctorParams[n],
parameterTypes[n])) {
match = false;
break;
}
}
if (match) {
// get accessible version of method
Constructor ctor = getAccessibleConstructor(ctors[i]);
if (ctor != null) {
try {
ctor.setAccessible(true);
} catch (SecurityException se) {
/* Swallow SecurityException
* TODO: Why?
*/
}
return ctor;
}
}
}
}
return null;
}
}
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