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Apache Commons Lang, a package of Java utility classes for the
classes that are in java.lang's hierarchy, or are considered to be so
standard as to justify existence in java.lang.
/*
* 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.util.Objects;
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 {@code public} constructors
* contained in a default access superclass. Reflection correctly locates these
* constructors and assigns them as {@code public}. However, an
* {@link IllegalAccessException} is thrown if the constructor is
* invoked.
*
* {@link ConstructorUtils} contains a workaround for this situation: it
* will attempt to call {@link java.lang.reflect.AccessibleObject#setAccessible(boolean)} 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
*/
public class ConstructorUtils {
/**
* ConstructorUtils instances should NOT be constructed in standard
* programming. Instead, the class should be used as
* {@code ConstructorUtils.invokeConstructor(cls, args)}.
*
* This constructor is {@code public} to permit tools that require a JavaBean
* instance to operate.
*/
public ConstructorUtils() {
}
/**
* 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 {@code null}
* @param args the array of arguments, {@code null} treated as empty
* @return new instance of {@code cls}, not {@code null}
*
* @throws NullPointerException if {@code cls} is {@code 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(Class, Object[], Class[])
*/
public static T invokeConstructor(final Class cls, Object... args)
throws NoSuchMethodException, IllegalAccessException, InvocationTargetException,
InstantiationException {
args = ArrayUtils.nullToEmpty(args);
return invokeConstructor(cls, args, ClassUtils.toClass(args));
}
/**
* 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 {@code null}
* @param args the array of arguments, {@code null} treated as empty
* @param parameterTypes the array of parameter types, {@code null} treated as empty
* @return new instance of {@code cls}, not {@code null}
*
* @throws NullPointerException if {@code cls} is {@code 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(final Class cls, Object[] args, Class[] parameterTypes)
throws NoSuchMethodException, IllegalAccessException, InvocationTargetException,
InstantiationException {
args = ArrayUtils.nullToEmpty(args);
parameterTypes = ArrayUtils.nullToEmpty(parameterTypes);
final Constructor ctor = getMatchingAccessibleConstructor(cls, parameterTypes);
if (ctor == null) {
throw new NoSuchMethodException(
"No such accessible constructor on object: " + cls.getName());
}
if (ctor.isVarArgs()) {
final Class[] methodParameterTypes = ctor.getParameterTypes();
args = MethodUtils.getVarArgs(args, methodParameterTypes);
}
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 {@code null}
* @param args the array of arguments, {@code null} treated as empty
* @return new instance of {@code cls}, not {@code null}
*
* @throws NullPointerException if {@code cls} is {@code 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(Class, Object[], Class[])
*/
public static T invokeExactConstructor(final Class cls, Object... args)
throws NoSuchMethodException, IllegalAccessException, InvocationTargetException,
InstantiationException {
args = ArrayUtils.nullToEmpty(args);
return invokeExactConstructor(cls, args, ClassUtils.toClass(args));
}
/**
* 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 {@code null}
* @param args the array of arguments, {@code null} treated as empty
* @param parameterTypes the array of parameter types, {@code null} treated as empty
* @return new instance of {@code cls}, not {@code null}
*
* @throws NullPointerException if {@code cls} is {@code 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(final Class cls, Object[] args,
Class[] parameterTypes) throws NoSuchMethodException, IllegalAccessException,
InvocationTargetException, InstantiationException {
args = ArrayUtils.nullToEmpty(args);
parameterTypes = ArrayUtils.nullToEmpty(parameterTypes);
final 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 {@code null}
* @param parameterTypes the array of parameter types, {@code null} treated as empty
* @return the constructor, {@code null} if no matching accessible constructor found
* @see Class#getConstructor
* @see #getAccessibleConstructor(java.lang.reflect.Constructor)
* @throws NullPointerException if {@code cls} is {@code null}
*/
public static Constructor getAccessibleConstructor(final Class cls,
final Class... parameterTypes) {
Objects.requireNonNull(cls, "cls");
try {
return getAccessibleConstructor(cls.getConstructor(parameterTypes));
} catch (final 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 {@code null}
* @return the constructor, {@code null} if no matching accessible constructor found
* @see SecurityManager
* @throws NullPointerException if {@code ctor} is {@code null}
*/
public static Constructor getAccessibleConstructor(final Constructor ctor) {
Objects.requireNonNull(ctor, "ctor");
return MemberUtils.isAccessible(ctor)
&& isAccessible(ctor.getDeclaringClass()) ? 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 {@code null}
* @param parameterTypes find method with compatible parameters
* @return the constructor, null if no matching accessible constructor found
* @throws NullPointerException if {@code cls} is {@code null}
*/
public static Constructor getMatchingAccessibleConstructor(final Class cls,
final Class... parameterTypes) {
Objects.requireNonNull(cls, "cls");
// see if we can find the constructor directly
// most of the time this works and it's much faster
try {
return MemberUtils.setAccessibleWorkaround(cls.getConstructor(parameterTypes));
} catch (final NoSuchMethodException ignored) {
// ignore
}
Constructor result = null;
/*
* (1) Class.getConstructors() is documented to return Constructor so as
* long as the array is not subsequently modified, everything's fine.
*/
final Constructor[] ctors = cls.getConstructors();
// return best match:
for (Constructor ctor : ctors) {
// compare parameters
if (MemberUtils.isMatchingConstructor(ctor, parameterTypes)) {
// get accessible version of constructor
ctor = getAccessibleConstructor(ctor);
if (ctor != null) {
MemberUtils.setAccessibleWorkaround(ctor);
if (result == null || MemberUtils.compareConstructorFit(ctor, result, parameterTypes) < 0) {
// temporary variable for annotation, see comment above (1)
@SuppressWarnings("unchecked")
final Constructor constructor = (Constructor) ctor;
result = constructor;
}
}
}
}
return result;
}
/**
* Tests whether the specified class is generally accessible, i.e. is
* declared in an entirely {@code public} manner.
* @param type to check
* @return {@code true} if {@code type} and any enclosing classes are
* {@code public}.
*/
private static boolean isAccessible(final Class type) {
Class cls = type;
while (cls != null) {
if (!ClassUtils.isPublic(cls)) {
return false;
}
cls = cls.getEnclosingClass();
}
return true;
}
}