org.apache.commons.beanutils.ConstructorUtils Maven / Gradle / Ivy
Go to download
This artifact provides a single jar that contains all classes required to use remote EJB and JMS, including
all dependencies. It is intended for use by those not using maven, maven users should just import the EJB and
JMS BOM's instead (shaded JAR's cause lots of problems with maven, as it is very easy to inadvertently end up
with different versions on classes on the class path).
/*
* 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.
*
* @version $Id$
*/
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 the type of the object to be constructed
* @param klass the class to be constructed.
* @param arg the actual argument. May be null (this will result in calling the default constructor).
* @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 T invokeConstructor(final Class klass, final Object arg)
throws
NoSuchMethodException,
IllegalAccessException,
InvocationTargetException,
InstantiationException {
final Object[] args = toArray(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 the type of the object to be constructed
* @param klass the class to be constructed.
* @param args actual argument array. May be null (this will result in calling the default constructor).
* @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 T invokeConstructor(final Class klass, Object[] args)
throws
NoSuchMethodException,
IllegalAccessException,
InvocationTargetException,
InstantiationException {
if (null == args) {
args = EMPTY_OBJECT_ARRAY;
}
final int arguments = args.length;
final 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 the type of the object to be constructed
* @param klass the class to be constructed.
* @param args actual argument array. May be null (this will result in calling the default constructor).
* @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 T invokeConstructor(
final 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;
}
final 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 the type of the object to be constructed
* @param klass the class to be constructed.
* @param arg the actual argument. May be null (this will result in calling the default constructor).
* @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 T invokeExactConstructor(final Class klass, final Object arg)
throws
NoSuchMethodException,
IllegalAccessException,
InvocationTargetException,
InstantiationException {
final Object[] args = toArray(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 the type of the object to be constructed
* @param klass the class to be constructed.
* @param args actual argument array. May be null (this will result in calling the default constructor).
* @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 T invokeExactConstructor(final Class klass, Object[] args)
throws
NoSuchMethodException,
IllegalAccessException,
InvocationTargetException,
InstantiationException {
if (null == args) {
args = EMPTY_OBJECT_ARRAY;
}
final int arguments = args.length;
final 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 the type of the object to be constructed
* @param klass the class to be constructed.
* @param args actual argument array. May be null (this will result in calling the default constructor).
* @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 T invokeExactConstructor(
final 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;
}
final 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 the type of the constructor
* @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(
final Class klass,
final Class parameterType) {
final Class[] parameterTypes = { parameterType };
return getAccessibleConstructor(klass, parameterTypes);
}
/**
* Returns a constructor given a class and signature.
* @param the type to be constructed
* @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(
final Class klass,
final Class[] parameterTypes) {
try {
return getAccessibleConstructor(
klass.getConstructor(parameterTypes));
} catch (final NoSuchMethodException e) {
return (null);
}
}
/**
* Returns accessible version of the given constructor.
* @param the type of the constructor
* @param ctor prototype constructor object.
* @return null if accessible constructor can not be found.
* @see java.lang.SecurityManager
*/
public static Constructor getAccessibleConstructor(final 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
final Class clazz = ctor.getDeclaringClass();
if (Modifier.isPublic(clazz.getModifiers())) {
return (ctor);
}
// what else can we do?
return null;
}
private static Object[] toArray(final Object arg) {
Object[] args = null;
if (arg != null) {
args = new Object[] { arg };
}
return args;
}
// -------------------------------------------------------- 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 the type of the class to be inspected
* @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(
final Class clazz,
final Class[] parameterTypes) {
// see if we can find the method directly
// most of the time this works and it's much faster
try {
final 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 (final SecurityException se) {
/* SWALLOW, if workaround fails don't fret. */
}
return ctor;
} catch (final NoSuchMethodException e) { /* SWALLOW */
}
// search through all methods
final int paramSize = parameterTypes.length;
final Constructor[] ctors = clazz.getConstructors();
for (Constructor ctor2 : ctors) {
// compare parameters
final Class[] ctorParams = ctor2.getParameterTypes();
final 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
final Constructor ctor = getAccessibleConstructor(ctor2);
if (ctor != null) {
try {
ctor.setAccessible(true);
} catch (final SecurityException se) {
/* Swallow SecurityException
* TODO: Why?
*/
}
@SuppressWarnings("unchecked")
final
// Class.getConstructors() actually returns constructors
// of type T, so it is safe to cast.
Constructor typedCtor = (Constructor) ctor;
return typedCtor;
}
}
}
}
return null;
}
}