Java tutorial
/* * Copyright (c) 2005, 2018, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package javax.tools; import java.security.AccessController; import java.security.PrivilegedAction; import java.util.Iterator; import java.util.ServiceConfigurationError; import java.util.ServiceLoader; /** * Provides methods for locating tool providers, for example, * providers of compilers. This class complements the * functionality of {@link java.util.ServiceLoader}. * * @author Peter von der Ahé * @since 1.6 */ public class ToolProvider { private static final String systemJavaCompilerModule = "jdk.compiler"; private static final String systemJavaCompilerName = "com.sun.tools.javac.api.JavacTool"; /** * Returns the Java™ programming language compiler provided * with this platform. * <p>The file manager returned by calling * {@link JavaCompiler#getStandardFileManager getStandardFileManager} * on this compiler supports paths provided by any * {@linkplain java.nio.file.FileSystem filesystem}.</p> * @return the compiler provided with this platform or * {@code null} if no compiler is provided * @implNote This implementation returns the compiler provided * by the {@code jdk.compiler} module if that module is available, * and {@code null} otherwise. */ public static JavaCompiler getSystemJavaCompiler() { return getSystemTool(JavaCompiler.class, systemJavaCompilerModule, systemJavaCompilerName); } private static final String systemDocumentationToolModule = "jdk.javadoc"; private static final String systemDocumentationToolName = "jdk.javadoc.internal.api.JavadocTool"; /** * Returns the Java™ programming language documentation tool provided * with this platform. * <p>The file manager returned by calling * {@link DocumentationTool#getStandardFileManager getStandardFileManager} * on this tool supports paths provided by any * {@linkplain java.nio.file.FileSystem filesystem}.</p> * @return the documentation tool provided with this platform or * {@code null} if no documentation tool is provided * @implNote This implementation returns the tool provided * by the {@code jdk.javadoc} module if that module is available, * and {@code null} otherwise. */ public static DocumentationTool getSystemDocumentationTool() { return getSystemTool(DocumentationTool.class, systemDocumentationToolModule, systemDocumentationToolName); } /** * Returns a class loader that may be used to load system tools, * or {@code null} if no such special loader is provided. * @implSpec This implementation always returns {@code null}. * @deprecated This method is subject to removal in a future version of * Java SE. * Use the {@link java.util.spi.ToolProvider system tool provider} or * {@link java.util.ServiceLoader service loader} mechanisms to * locate system tools as well as user-installed tools. * @return a class loader, or {@code null} */ @Deprecated(since = "9") public static ClassLoader getSystemToolClassLoader() { return null; } /** * Get an instance of a system tool using the service loader. * @implNote By default, this returns the implementation in the specified module. * For limited backward compatibility, if this code is run on an older version * of the Java platform that does not support modules, this method will * try and create an instance of the named class. Note that implies the * class must be available on the system class path. * @param <T> the interface of the tool * @param clazz the interface of the tool * @param moduleName the name of the module containing the desired implementation * @param className the class name of the desired implementation * @return the specified implementation of the tool */ private static <T> T getSystemTool(Class<T> clazz, String moduleName, String className) { try { ServiceLoader<T> sl = ServiceLoader.load(clazz, ClassLoader.getSystemClassLoader()); for (Iterator<T> iter = sl.iterator(); iter.hasNext();) { T tool = iter.next(); if (matches(tool, moduleName)) return tool; } } catch (ServiceConfigurationError e) { throw new Error(e); } return null; } /** * Determine if this is the desired tool instance. * @param <T> the interface of the tool * @param tool the instance of the tool * @param moduleName the name of the module containing the desired implementation * @return true if and only if the tool matches the specified criteria */ private static <T> boolean matches(T tool, String moduleName) { PrivilegedAction<Boolean> pa = () -> { Module toolModule = tool.getClass().getModule(); String toolModuleName = toolModule.getName(); return toolModuleName.equals(moduleName); }; return AccessController.doPrivileged(pa); } }