com.google.common.reflect.Reflection.java Source code

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/*
 * Copyright (C) 2005 The Guava 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 com.google.common.reflect;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;

/**
 * Static utilities relating to Java reflection.
 *
 * @since 12.0
 */
@Beta
public final class Reflection {

    /**
     * Returns the package name of {@code clazz} according to the Java Language Specification (section
     * 6.7). Unlike {@link Class#getPackage}, this method only parses the class name, without
     * attempting to define the {@link Package} and hence load files.
     */
    public static String getPackageName(Class<?> clazz) {
        return getPackageName(clazz.getName());
    }

    /**
     * Returns the package name of {@code classFullName} according to the Java Language Specification
     * (section 6.7). Unlike {@link Class#getPackage}, this method only parses the class name, without
     * attempting to define the {@link Package} and hence load files.
     */
    public static String getPackageName(String classFullName) {
        int lastDot = classFullName.lastIndexOf('.');
        return (lastDot < 0) ? "" : classFullName.substring(0, lastDot);
    }

    /**
     * Ensures that the given classes are initialized, as described in
     * <a href="http://java.sun.com/docs/books/jls/third_edition/html/execution.html#12.4.2">
     * JLS Section 12.4.2</a>.
     *
     * <p>WARNING: Normally it's a smell if a class needs to be explicitly initialized, because static
     * state hurts system maintainability and testability. In cases when you have no choice while
     * inter-operating with a legacy framework, this method helps to keep the code less ugly.
     *
     * @throws ExceptionInInitializerError if an exception is thrown during
     *   initialization of a class
     */
    public static void initialize(Class<?>... classes) {
        for (Class<?> clazz : classes) {
            try {
                Class.forName(clazz.getName(), true, clazz.getClassLoader());
            } catch (ClassNotFoundException e) {
                throw new AssertionError(e);
            }
        }
    }

    /**
     * Returns a proxy instance that implements {@code interfaceType} by
     * dispatching method invocations to {@code handler}. The class loader of
     * {@code interfaceType} will be used to define the proxy class. To implement
     * multiple interfaces or specify a class loader, use
     * {@link Proxy#newProxyInstance}.
     *
     * @throws IllegalArgumentException if {@code interfaceType} does not specify
     *     the type of a Java interface
     */
    public static <T> T newProxy(Class<T> interfaceType, InvocationHandler handler) {
        checkNotNull(handler);
        checkArgument(interfaceType.isInterface(), "%s is not an interface", interfaceType);
        Object object = Proxy.newProxyInstance(interfaceType.getClassLoader(), new Class<?>[] { interfaceType },
                handler);
        return interfaceType.cast(object);
    }

    private Reflection() {
    }
}