ConstructorUtils.java
/*
* 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
*
* https://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}.
*
* <h2>Known Limitations</h2>
* <h3>Accessing Public Constructors In A Default Access Superclass</h3>
* <p>
* 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.
* </p>
*
* <p>
* {@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.
* </p>
*
* @since 2.5
*/
public class ConstructorUtils {
/**
* Finds a constructor given a class and signature, checking accessibility.
*
* <p>
* This finds the constructor and ensures that it is accessible. The constructor signature must match the parameter types exactly.
* </p>
*
* @param <T> 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.
* @throws NullPointerException if {@code cls} is {@code null}
* @throws SecurityException Thrown if a security manager is present and the caller's class loader is not the same as or an ancestor of the class loader
* for the class and invocation of {@link SecurityManager#checkPackageAccess(String)} denies access to the package of the
* class.
* @see Class#getConstructor
* @see #getAccessibleConstructor(java.lang.reflect.Constructor)
*/
public static <T> Constructor<T> getAccessibleConstructor(final Class<T> 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.
*
* <p>
* This simply ensures that the constructor is accessible.
* </p>
*
* @param <T> 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}
* @throws SecurityException Thrown if a security manager is present and a caller's class loader is not the same as or an ancestor of the class loader
* for a class and invocation of {@link SecurityManager#checkPackageAccess(String)} denies access to the package of the class.
*/
public static <T> Constructor<T> getAccessibleConstructor(final Constructor<T> ctor) {
Objects.requireNonNull(ctor, "ctor");
return MemberUtils.isAccessible(ctor) && isAccessible(ctor.getDeclaringClass()) ? ctor : null;
}
/**
* Finds an accessible constructor with compatible parameters.
*
* <p>
* 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.
* </p>
* <p>
* 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.
* </p>
*
* @param <T> 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 Thrown if {@code cls} is {@code null}
* @throws SecurityException Thrown if a security manager is present and the caller's class loader is not the same as or an ancestor of the class loader for the
* class and invocation of {@link SecurityManager#checkPackageAccess(String)} denies access to the package of the class.
* @see SecurityManager#checkPackageAccess(String)
*/
public static <T> Constructor<T> getMatchingAccessibleConstructor(final Class<T> 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<T> result = null;
/*
* (1) Class.getConstructors() is documented to return Constructor<T> 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<T> constructor = (Constructor<T>) ctor;
result = constructor;
}
}
}
}
return result;
}
/**
* Returns a new instance of the specified class inferring the right constructor from the types of the arguments.
*
* <p>
* This locates and calls a constructor. The constructor signature must match the argument types by assignment compatibility.
* </p>
*
* @param <T> 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 Thrown if {@code cls} is {@code null}.
* @throws NoSuchMethodException Thrown if a matching constructor cannot be found.
* @throws IllegalAccessException Thrown if the found {@code Constructor} is enforcing Java language access control and the underlying constructor is
* inaccessible.
* @throws IllegalArgumentException Thrown if:
* <ul>
* <li>the number of actual and formal parameters differ; or</li>
* <li>an unwrapping conversion for primitive arguments fails; or</li>
* <li>after possible unwrapping, a parameter value cannot be converted to the corresponding formal parameter type by a
* method invocation conversion; if this constructor pertains to an enum type.
* </ul>
* @throws InstantiationException Thrown if the class that declares the underlying constructor represents an abstract class.
* @throws InvocationTargetException Thrown if the underlying constructor throws an exception.
* @throws ExceptionInInitializerError Thrown if the initialization provoked by this method fails.
* @throws SecurityException Thrown if a security manager is present and the caller's class loader is not the same as or an ancestor of the class
* loader for the class and invocation of {@link SecurityManager#checkPackageAccess(String)} denies access to the
* package of the class.
* @see #invokeConstructor(Class, Object[], Class[])
*/
public static <T> T invokeConstructor(final Class<T> cls, final Object... args)
throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
final Object[] actuals = ArrayUtils.nullToEmpty(args);
return invokeConstructor(cls, actuals, ClassUtils.toClass(actuals));
}
/**
* Returns a new instance of the specified class choosing the right constructor from the list of parameter types.
*
* <p>
* This locates and calls a constructor. The constructor signature must match the parameter types by assignment compatibility.
* </p>
*
* @param <T> 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 Thrown if {@code cls} is {@code null}.
* @throws NoSuchMethodException Thrown if a matching constructor cannot be found.
* @throws IllegalAccessException Thrown if the found {@code Constructor} is enforcing Java language access control and the underlying constructor is
* inaccessible.
* @throws IllegalArgumentException Thrown if:
* <ul>
* <li>the number of actual and formal parameters differ; or</li>
* <li>an unwrapping conversion for primitive arguments fails; or</li>
* <li>after possible unwrapping, a parameter value cannot be converted to the corresponding formal parameter type by a
* method invocation conversion; if this constructor pertains to an enum type.
* </ul>
* @throws InstantiationException Thrown if the class that declares the underlying constructor represents an abstract class.
* @throws InvocationTargetException Thrown if the underlying constructor throws an exception.
* @throws ExceptionInInitializerError Thrown if the initialization provoked by this method fails.
* @throws SecurityException Thrown if a security manager is present and the caller's class loader is not the same as or an ancestor of the class
* loader for the class and invocation of {@link SecurityManager#checkPackageAccess(String)} denies access to the
* package of the class.
* @see Constructor#newInstance(Object...)
* @see Constructor#newInstance
*/
public static <T> T invokeConstructor(final Class<T> cls, final Object[] args, final Class<?>[] parameterTypes)
throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
final Object[] actuals = ArrayUtils.nullToEmpty(args);
final Constructor<T> ctor = getMatchingAccessibleConstructor(cls, ArrayUtils.nullToEmpty(parameterTypes));
if (ctor == null) {
throw new NoSuchMethodException("No such accessible constructor on object: " + cls.getName());
}
return ctor.newInstance(MethodUtils.toVarArgs(ctor, actuals));
}
/**
* Returns a new instance of the specified class inferring the right constructor from the types of the arguments.
*
* <p>
* This locates and calls a constructor. The constructor signature must match the argument types exactly.
* </p>
*
* @param <T> 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 Thrown if {@code cls} is {@code null}.
* @throws NoSuchMethodException Thrown if a matching constructor cannot be found.
* @throws IllegalAccessException Thrown if the found {@code Constructor} is enforcing Java language access control and the underlying constructor is
* inaccessible.
* @throws IllegalArgumentException Thrown if:
* <ul>
* <li>the number of actual and formal parameters differ; or</li>
* <li>an unwrapping conversion for primitive arguments fails; or</li>
* <li>after possible unwrapping, a parameter value cannot be converted to the corresponding formal parameter type by a
* method invocation conversion; if this constructor pertains to an enum type.
* </ul>
* @throws InstantiationException Thrown if the class that declares the underlying constructor represents an abstract class.
* @throws InvocationTargetException Thrown if the underlying constructor throws an exception.
* @throws ExceptionInInitializerError Thrown if the initialization provoked by this method fails.
* @throws SecurityException Thrown if a security manager is present and the caller's class loader is not the same as or an ancestor of the class
* loader for the class and invocation of {@link SecurityManager#checkPackageAccess(String)} denies access to the
* package of the class.
* @see Constructor#newInstance(Object...)
* @see #invokeExactConstructor(Class, Object[], Class[])
*/
public static <T> T invokeExactConstructor(final Class<T> cls, final Object... args)
throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
final Object[] actuals = ArrayUtils.nullToEmpty(args);
return invokeExactConstructor(cls, actuals, ClassUtils.toClass(actuals));
}
/**
* Returns a new instance of the specified class choosing the right constructor from the list of parameter types.
*
* <p>
* This locates and calls a constructor. The constructor signature must match the parameter types exactly.
* </p>
*
* @param <T> the type to construct.
* @param cls the class to construct, 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 Thrown if {@code cls} is {@code null}.
* @throws NoSuchMethodException Thrown if a matching constructor cannot be found.
* @throws IllegalAccessException Thrown if the found {@code Constructor} is enforcing Java language access control and the underlying constructor is
* inaccessible.
* @throws IllegalArgumentException Thrown if:
* <ul>
* <li>the number of actual and formal parameters differ; or</li>
* <li>an unwrapping conversion for primitive arguments fails; or</li>
* <li>after possible unwrapping, a parameter value cannot be converted to the corresponding formal parameter type by a
* method invocation conversion; if this constructor pertains to an enum type.
* </ul>
* @throws InstantiationException Thrown if the class that declares the underlying constructor represents an abstract class.
* @throws InvocationTargetException Thrown if the underlying constructor throws an exception.
* @throws ExceptionInInitializerError Thrown if the initialization provoked by this method fails.
* @throws SecurityException Thrown if a security manager is present and the caller's class loader is not the same as or an ancestor of the class
* loader for the class and invocation of {@link SecurityManager#checkPackageAccess(String)} denies access to the
* package of the class.
* @see Constructor#newInstance(Object...)
*/
public static <T> T invokeExactConstructor(final Class<T> cls, final Object[] args, final Class<?>[] parameterTypes)
throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
final Constructor<T> ctor = getAccessibleConstructor(cls, ArrayUtils.nullToEmpty(parameterTypes));
if (ctor == null) {
throw new NoSuchMethodException("No such accessible constructor on object: " + cls.getName());
}
return ctor.newInstance(ArrayUtils.nullToEmpty(args));
}
/**
* 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}.
* @throws SecurityException Thrown if a security manager is present and a caller's class loader is not the same as or an ancestor of the class loader for a
* class and invocation of {@link SecurityManager#checkPackageAccess(String)} denies access to the package of the class.
*/
private static boolean isAccessible(final Class<?> type) {
Class<?> cls = type;
while (cls != null) {
if (!ClassUtils.isPublic(cls)) {
return false;
}
cls = cls.getEnclosingClass();
}
return true;
}
/**
* ConstructorUtils instances should NOT be constructed in standard programming. Instead, the class should be used as
* {@code ConstructorUtils.invokeConstructor(cls, args)}.
*
* <p>
* This constructor is {@code public} to permit tools that require a JavaBean instance to operate.
* </p>
*
* @deprecated TODO Make private in 4.0.
*/
@Deprecated
public ConstructorUtils() {
// empty
}
}