reflectionutils.java

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/*
 * Copyright 2002-2007 the original author or authors.
 *
 * Licensed 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.springframework.util;

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Arrays;

/**
 * Simple utility class for handling reflection exceptions.
 * Only intended for internal use.
 *
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @since 1.2.2
 */
public abstract class ReflectionUtils {

	/**
	 * Handle the given reflection exception. Should only be called if
	 * no checked exception is expected to be thrown by the target method.
	 * <p>Throws the underlying RuntimeException or Error in case of an
	 * InvocationTargetException with such a root cause. Throws an
	 * IllegalStateException with an appropriate message else.
	 * @param ex the reflection exception to handle
	 */
	public static void handleReflectionException(Exception ex) {
		if (ex instanceof NoSuchMethodException) {
			throw new IllegalStateException("Method not found: " + ex.getMessage());
		}
		if (ex instanceof IllegalAccessException) {
			throw new IllegalStateException("Could not access method: " + ex.getMessage());
		}
		if (ex instanceof InvocationTargetException) {
			handleInvocationTargetException((InvocationTargetException) ex);
		}
		throw new IllegalStateException(
				"Unexpected reflection exception - " + ex.getClass().getName() + ": " + ex.getMessage());
	}

	/**
	 * Handle the given invocation target exception. Should only be called if
	 * no checked exception is expected to be thrown by the target method.
	 * <p>Throws the underlying RuntimeException or Error in case
	 * of such a root cause. Throws an IllegalStateException else.
	 * @param ex the invocation target exception to handle
	 */
	public static void handleInvocationTargetException(InvocationTargetException ex) {
		if (ex.getTargetException() instanceof RuntimeException) {
			throw (RuntimeException) ex.getTargetException();
		}
		if (ex.getTargetException() instanceof Error) {
			throw (Error) ex.getTargetException();
		}
		throw new IllegalStateException(
				"Unexpected exception thrown by method - " + ex.getTargetException().getClass().getName() +
				": " + ex.getTargetException().getMessage());
	}

	/**
	 * Attempt to find a {@link Method} on the supplied type with the supplied name
	 * and parameter types. Searches all superclasses up to <code>Object</code>.
	 * Returns <code>null</code> if no {@link Method} can be found.
	 */
	public static Method findMethod(Class type, String name, Class[] paramTypes) {
		Assert.notNull(type, "'type' cannot be null.");
		Assert.notNull(name, "'name' cannot be null.");
		Class searchType = type;
		while(!Object.class.equals(searchType) && searchType != null) {
			Method[] methods = (searchType.isInterface() ? searchType.getMethods() : searchType.getDeclaredMethods());
			for (int i = 0; i < methods.length; i++) {
				Method method = methods[i];
				if(name.equals(method.getName()) && Arrays.equals(paramTypes, method.getParameterTypes())) {
					return method;
				}
			}
			searchType = searchType.getSuperclass();
		}
		return null;
	}

	/**
	 * Invoke the specified {@link Method} against the supplied target object
	 * with no arguments. The target object can be <code>null</code> when
	 * invoking a static {@link Method}.
	 * <p>Thrown exceptions are handled via a call to {@link #handleReflectionException}.
	 * @see #invokeMethod(java.lang.reflect.Method, Object, Object[])
	 */
	public static Object invokeMethod(Method method, Object target) {
		return invokeMethod(method, target, null);
	}

	/**
	 * Invoke the specified {@link Method} against the supplied target object
	 * with the supplied arguments. The target object can be <code>null</code>
	 * when invoking a static {@link Method}.
	 * <p>Thrown exceptions are handled via a call to {@link #handleReflectionException}.
	 * @see #invokeMethod(java.lang.reflect.Method, Object, Object[])
	 */
	public static Object invokeMethod(Method method, Object target, Object[] args) {
		try {
			return method.invoke(target, args);
		}
		catch (IllegalAccessException ex) {
			handleReflectionException(ex);
			throw new IllegalStateException(
					"Unexpected reflection exception - " + ex.getClass().getName() + ": " + ex.getMessage());
		}
		catch (InvocationTargetException ex) {
			handleReflectionException(ex);
			throw new IllegalStateException(
					"Unexpected reflection exception - " + ex.getClass().getName() + ": " + ex.getMessage());
		}
	}

	/**
	 * Determine whether the given field is a "public static final" constant.
	 * @param field the field to check
	 */
	public static boolean isPublicStaticFinal(Field field) {
		int modifiers = field.getModifiers();
		return (Modifier.isPublic(modifiers) && Modifier.isStatic(modifiers) && Modifier.isFinal(modifiers));
	}

	/**
	 * Make the given field accessible, explicitly setting it accessible if necessary.
	 * The <code>setAccessible(true)</code> method is only called when actually necessary,
	 * to avoid unnecessary conflicts with a JVM SecurityManager (if active).
	 * @param field the field to make accessible
	 * @see java.lang.reflect.Field#setAccessible
	 */
	public static void makeAccessible(Field field) {
		if (!Modifier.isPublic(field.getModifiers()) ||
				!Modifier.isPublic(field.getDeclaringClass().getModifiers())) {
			field.setAccessible(true);
		}
	}

}