org.apache.commons.lang3.reflect.ConstructorUtils Maven / Gradle / Ivy
/*
* 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.lang3.reflect;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Modifier;
import org.apache.commons.lang3.ArrayUtils;
import org.apache.commons.lang3.ClassUtils;
/**
* Utility reflection methods focused on constructors, modeled 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 privileges. If this call
* fails then a warning will be logged and the method may fail.
*
* @since 2.5
* @version $Id: ConstructorUtils.java 1144010 2011-07-07 20:02:10Z joehni $
*/
public class ConstructorUtils {
/**
* ConstructorUtils instances should NOT be constructed in standard
* programming. Instead, the class should be used as
* ConstructorUtils.invokeConstructor(cls, args).
*
* This constructor is public to permit tools that require a JavaBean
* instance to operate.
*/
public ConstructorUtils() {
super();
}
/**
* Returns a new instance of the specified class inferring the right constructor
* from the types of the arguments.
*
* This locates and calls a constructor.
* The constructor signature must match the argument types by assignment compatibility.
*
* @param the type to be constructed
* @param cls the class to be constructed, not null
* @param args the array of arguments, null treated as empty
* @return new instance of cls, not null
*
* @throws NoSuchMethodException if a matching constructor cannot be found
* @throws IllegalAccessException if invocation is not permitted by security
* @throws InvocationTargetException if an error occurs on invocation
* @throws InstantiationException if an error occurs on instantiation
* @see #invokeConstructor(java.lang.Class, java.lang.Object[], java.lang.Class[])
*/
public static T invokeConstructor(Class cls, Object... args)
throws NoSuchMethodException, IllegalAccessException, InvocationTargetException,
InstantiationException {
if (args == null) {
args = ArrayUtils.EMPTY_OBJECT_ARRAY;
}
Class parameterTypes[] = new Class[args.length];
for (int i = 0; i < args.length; i++) {
parameterTypes[i] = args[i].getClass();
}
return invokeConstructor(cls, args, parameterTypes);
}
/**
* Returns a new instance of the specified class choosing the right constructor
* from the list of parameter types.
*
* This locates and calls a constructor.
* The constructor signature must match the parameter types by assignment compatibility.
*
* @param the type to be constructed
* @param cls the class to be constructed, not null
* @param args the array of arguments, null treated as empty
* @param parameterTypes the array of parameter types, null treated as empty
* @return new instance of cls, not null
*
* @throws NoSuchMethodException if a matching constructor cannot be found
* @throws IllegalAccessException if invocation is not permitted by security
* @throws InvocationTargetException if an error occurs on invocation
* @throws InstantiationException if an error occurs on instantiation
* @see Constructor#newInstance
*/
public static T invokeConstructor(Class cls, Object[] args, Class[] parameterTypes)
throws NoSuchMethodException, IllegalAccessException, InvocationTargetException,
InstantiationException {
if (parameterTypes == null) {
parameterTypes = ArrayUtils.EMPTY_CLASS_ARRAY;
}
if (args == null) {
args = ArrayUtils.EMPTY_OBJECT_ARRAY;
}
Constructor ctor = getMatchingAccessibleConstructor(cls, parameterTypes);
if (ctor == null) {
throw new NoSuchMethodException(
"No such accessible constructor on object: " + cls.getName());
}
return ctor.newInstance(args);
}
/**
* Returns a new instance of the specified class inferring the right constructor
* from the types of the arguments.
*
* This locates and calls a constructor.
* The constructor signature must match the argument types exactly.
*
* @param the type to be constructed
* @param cls the class to be constructed, not null
* @param args the array of arguments, null treated as empty
* @return new instance of cls, not null
*
* @throws NoSuchMethodException if a matching constructor cannot be found
* @throws IllegalAccessException if invocation is not permitted by security
* @throws InvocationTargetException if an error occurs on invocation
* @throws InstantiationException if an error occurs on instantiation
* @see #invokeExactConstructor(java.lang.Class, java.lang.Object[], java.lang.Class[])
*/
public static T invokeExactConstructor(Class cls, Object... args)
throws NoSuchMethodException, IllegalAccessException, InvocationTargetException,
InstantiationException {
if (args == null) {
args = ArrayUtils.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(cls, args, parameterTypes);
}
/**
* Returns a new instance of the specified class choosing the right constructor
* from the list of parameter types.
*
* This locates and calls a constructor.
* The constructor signature must match the parameter types exactly.
*
* @param the type to be constructed
* @param cls the class to be constructed, not null
* @param args the array of arguments, null treated as empty
* @param parameterTypes the array of parameter types, null treated as empty
* @return new instance of cls, not null
*
* @throws NoSuchMethodException if a matching constructor cannot be found
* @throws IllegalAccessException if invocation is not permitted by security
* @throws InvocationTargetException if an error occurs on invocation
* @throws InstantiationException if an error occurs on instantiation
* @see Constructor#newInstance
*/
public static T invokeExactConstructor(Class cls, Object[] args,
Class[] parameterTypes) throws NoSuchMethodException, IllegalAccessException,
InvocationTargetException, InstantiationException {
if (args == null) {
args = ArrayUtils.EMPTY_OBJECT_ARRAY;
}
if (parameterTypes == null) {
parameterTypes = ArrayUtils.EMPTY_CLASS_ARRAY;
}
Constructor ctor = getAccessibleConstructor(cls, parameterTypes);
if (ctor == null) {
throw new NoSuchMethodException(
"No such accessible constructor on object: "+ cls.getName());
}
return ctor.newInstance(args);
}
//-----------------------------------------------------------------------
/**
* Finds a constructor given a class and signature, checking accessibility.
*
* This finds the constructor and ensures that it is accessible.
* The constructor signature must match the parameter types exactly.
*
* @param the constructor type
* @param cls the class to find a constructor for, not null
* @param parameterTypes the array of parameter types, null treated as empty
* @return the constructor, null if no matching accessible constructor found
* @see Class#getConstructor
* @see #getAccessibleConstructor(java.lang.reflect.Constructor)
*/
public static Constructor getAccessibleConstructor(Class cls,
Class... parameterTypes) {
try {
return getAccessibleConstructor(cls.getConstructor(parameterTypes));
} catch (NoSuchMethodException e) {
return null;
}
}
/**
* Checks if the specified constructor is accessible.
*
* This simply ensures that the constructor is accessible.
*
* @param the constructor type
* @param ctor the prototype constructor object, not null
* @return the constructor, null if no matching accessible constructor found
* @see java.lang.SecurityManager
*/
public static Constructor getAccessibleConstructor(Constructor ctor) {
return MemberUtils.isAccessible(ctor)
&& Modifier.isPublic(ctor.getDeclaringClass().getModifiers()) ? ctor : null;
}
/**
* Finds an accessible constructor with compatible parameters.
*
* This checks all the constructor and finds one with compatible parameters
* This requires that every parameter is assignable from the given parameter types.
* This is a more flexible search than the normal exact matching algorithm.
*
* First it checks if there is a constructor matching the exact signature.
* If not then all the constructors of the class are checked to see if their
* signatures are assignment compatible with the parameter types.
* The first assignment compatible matching constructor is returned.
*
* @param the constructor type
* @param cls the class to find a constructor for, not null
* @param parameterTypes find method with compatible parameters
* @return the constructor, null if no matching accessible constructor found
*/
public static Constructor getMatchingAccessibleConstructor(Class cls,
Class... parameterTypes) {
// see if we can find the constructor directly
// most of the time this works and it's much faster
try {
Constructor ctor = cls.getConstructor(parameterTypes);
MemberUtils.setAccessibleWorkaround(ctor);
return ctor;
} catch (NoSuchMethodException e) { // NOPMD - Swallow
}
Constructor result = null;
/*
* (1) Class.getConstructors() is documented to return Constructor so as
* long as the array is not subsequently modified, everything's fine.
*/
Constructor[] ctors = cls.getConstructors();
// return best match:
for (Constructor ctor : ctors) {
// compare parameters
if (ClassUtils.isAssignable(parameterTypes, ctor.getParameterTypes(), true)) {
// get accessible version of constructor
ctor = getAccessibleConstructor(ctor);
if (ctor != null) {
MemberUtils.setAccessibleWorkaround(ctor);
if (result == null
|| MemberUtils.compareParameterTypes(ctor.getParameterTypes(), result
.getParameterTypes(), parameterTypes) < 0) {
// temporary variable for annotation, see comment above (1)
@SuppressWarnings("unchecked")
Constructor constructor = (Constructor)ctor;
result = constructor;
}
}
}
}
return result;
}
}