Java tutorial
// Copyright 2015 The Bazel Authors. All rights reserved. // // 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.devtools.build.java.bazel; import com.google.common.collect.ImmutableList; import java.io.File; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.io.Writer; import java.net.MalformedURLException; import java.net.URL; import java.net.URLClassLoader; import java.nio.charset.Charset; import java.util.List; import java.util.Locale; import java.util.Set; import javax.lang.model.SourceVersion; import javax.tools.DiagnosticListener; import javax.tools.JavaCompiler; import javax.tools.JavaFileManager; import javax.tools.JavaFileObject; import javax.tools.StandardJavaFileManager; import javax.tools.StandardLocation; /** * Provides a {@link JavaCompiler} that has behavior as similar as possible to the java compiler * provided by default by Bazel. Replace calls to {@link * javax.tools.ToolProvider#getSystemJavaCompiler} with calls to {@link * BazelJavaCompiler#newInstance}. * * <p>This class is typically used only from a host build tool or in tests. When using this in * production, langtools.jar and the bootclasspath jars are deployed as separate jar files within * the runfiles directory. */ public class BazelJavaCompiler { // The default blessed javac options. private static final String DEFAULT_BOOTCLASSPATH = JavacBootclasspath.asString(); private static final ImmutableList<String> DEFAULT_JAVACOPTS = ImmutableList.<String>builder() .addAll(JavaBuilderConfig.defaultJavacOpts()) // The bootclasspath must be specified both via an invocation option and // via fileManager.setLocation(PLATFORM_CLASS_PATH), to work around what // appears to be a bug in jdk[6,8] javac. .add("-bootclasspath").add(DEFAULT_BOOTCLASSPATH).build(); private static final Class<? extends JavaCompiler> JAVA_COMPILER_CLASS = getJavaCompilerClass(); private static class LangtoolsClassLoader extends URLClassLoader { public LangtoolsClassLoader() throws MalformedURLException { super(new URL[] { getLangtoolsJar().toURI().toURL() }, // We use the bootstrap classloader (null) as the parent classloader // instead of the default "system" class loader; we intentionally do // not consult the classpath. This way the class path is not // polluted, we reduce the risk of having multiple langtools on the // classpath, and langtools.jar is only opened if this method is // called. And this will reduce problems for automated java // dependency analysis, which other teams are trying to do. null); } } private static Class<? extends JavaCompiler> getJavaCompilerClass() { try { ClassLoader cl = new LangtoolsClassLoader(); return getJavaCompilerClass(cl); } catch (Exception e) { throw new RuntimeException("Cannot get java compiler", e); } } private static Class<? extends JavaCompiler> getJavaCompilerClass(ClassLoader cl) throws Exception { return Class.forName("com.sun.tools.javac.api.JavacTool", true, cl).asSubclass(JavaCompiler.class); } /** Returns the langtools jar. */ public static File getLangtoolsJar() { return JavaLangtools.file(); } /** Returns the default javacopts, including the blessed bootclasspath. */ public static List<String> getDefaultJavacopts() { return DEFAULT_JAVACOPTS; } /** * Returns a new {@link JavaCompiler} that has behavior as similar as possible to the java * compiler provided by default by the bazel build system, independent of the user-specified * {@code JAVABASE}. * * <p>More precisely, this method works analogously to {@link * javax.tools.ToolProvider#getSystemJavaCompiler}, but returns a {@code JavaCompiler} that * differs in these details: * * <ul> * <li> uses the blessed javac implementation: {@code //tools/defaults:java_langtools}, as * defined by bazel's --java_langtools flag. * <li> uses the blessed boot class path: {@code //tools/defaults:javac_bootclasspath}, as * defined by bazel's --javac_bootclasspath flag. * <li> uses the blessed default values for javac options such as {@code -source} * </ul> * * <p>This class ensures that (by default) the {@code -source}, {@code -target} and {@code * -bootclasspath} flags all agree and specify the same (blessed) JDK version, for language and * API compatibility. * * <p>This method finds the javac implementation using a custom classloader that does not consult * the user's classpath. This works well, unless the return value is cast to a * javac-implementation class like {@code JavacTask}, in which case the dreaded classloader error * "can't cast JavacTaskImpl to JavacTask" raises its ugly head, in which case you should use * {@link #newInstance(ClassLoader)} instead. */ public static JavaCompiler newInstance() { try { return newInstance(JAVA_COMPILER_CLASS.getConstructor().newInstance()); } catch (Exception e) { throw new RuntimeException("Cannot get java compiler", e); } } /** * Returns a new {@link JavaCompiler} that has behavior as similar as possible to the java * compiler provided by default by bazel, independent of the user-specified {@code JAVABASE}. * * <p>This method has effect identical to {@link #newInstance()} (and that method is generally * preferred to this one), except that the javac implementation is found via the provided * classloader instead of defining a custom classloader that knows the standard location of the * blessed javac implementation. * * <p>This method is needed when the return value is cast to a javac-implementation class like * {@code JavacTask}, to avoid the dreaded multiple classloader error "can't cast JavacTaskImpl to * JavacTask". * * <p>Typically, users should pass {@code ClassLoader.getSystemClassLoader()} as the argument to * this method. */ public static JavaCompiler newInstance(ClassLoader cl) { try { return newInstance(getJavaCompilerClass(cl).getConstructor().newInstance()); } catch (Exception e) { throw new RuntimeException("Cannot get java compiler", e); } } private static JavaCompiler newInstance(final JavaCompiler delegate) { // We forward most operations to the JavaCompiler implementation in langtools.jar. return new JavaCompiler() { @Override public CompilationTask getTask(Writer out, JavaFileManager fileManager, DiagnosticListener<? super JavaFileObject> diagnosticListener, Iterable<String> options, Iterable<String> classes, Iterable<? extends JavaFileObject> compilationUnits) { // We prepend bazel's default javacopts to user javacopts, // so that the user can override them. javac supports this // "last option wins" style of option override. ImmutableList.Builder<String> fullOptions = ImmutableList.builder(); fullOptions.addAll(getDefaultJavacopts()); if (options != null) { fullOptions.addAll(options); } return delegate.getTask(out, fileManager, diagnosticListener, fullOptions.build(), classes, compilationUnits); } @Override public StandardJavaFileManager getStandardFileManager( DiagnosticListener<? super JavaFileObject> diagnosticListener, Locale locale, Charset charset) { StandardJavaFileManager fileManager = delegate.getStandardFileManager(diagnosticListener, locale, charset); try { fileManager.setLocation(StandardLocation.PLATFORM_CLASS_PATH, // bootclasspath JavacBootclasspath.asFiles()); } catch (IOException e) { // Should never happen, according to javadocs for setLocation throw new RuntimeException(e); } return fileManager; } @Override public int run(InputStream in, OutputStream out, OutputStream err, String... arguments) { // prepend bazel's default javacopts to user arguments List<String> args = ImmutableList.<String>builder().addAll(getDefaultJavacopts()).add(arguments) .build(); return delegate.run(in, out, err, args.toArray(new String[0])); } @Override public Set<SourceVersion> getSourceVersions() { return delegate.getSourceVersions(); } @Override public int isSupportedOption(String option) { return delegate.isSupportedOption(option); } }; } }