Java example source code file (GenStubs.java)

This example Java source code file (GenStubs.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

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Java - Java tags/keywords

arraylist, compilationunittree, fault, file, illegalargumentexception, ioexception, javafileobject, jccompilationunit, jcfieldaccess, list, listbuffer, override, string, throwable, util

The GenStubs.java Java example source code

/*
 * Copyright (c) 2009, 2013, 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 genstubs;

import java.io.*;
import java.util.*;
import javax.tools.JavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.StandardLocation;

import com.sun.source.tree.CompilationUnitTree;
import com.sun.source.util.JavacTask;
import com.sun.tools.javac.api.JavacTool;
import com.sun.tools.javac.code.Flags;
import com.sun.tools.javac.code.TypeTag;
import com.sun.tools.javac.tree.JCTree;
import com.sun.tools.javac.tree.JCTree.JCClassDecl;
import com.sun.tools.javac.tree.JCTree.JCCompilationUnit;
import com.sun.tools.javac.tree.JCTree.JCFieldAccess;
import com.sun.tools.javac.tree.JCTree.JCIdent;
import com.sun.tools.javac.tree.JCTree.JCImport;
import com.sun.tools.javac.tree.JCTree.JCLiteral;
import com.sun.tools.javac.tree.JCTree.JCMethodDecl;
import com.sun.tools.javac.tree.JCTree.JCModifiers;
import com.sun.tools.javac.tree.JCTree.JCVariableDecl;
import com.sun.tools.javac.tree.Pretty;
import com.sun.tools.javac.tree.TreeMaker;
import com.sun.tools.javac.tree.TreeScanner;
import com.sun.tools.javac.tree.TreeTranslator;
import com.sun.tools.javac.util.Context;
import com.sun.tools.javac.util.ListBuffer;
import com.sun.tools.javac.util.Name;
import javax.tools.JavaFileManager;

/**
 * Generate stub source files by removing implementation details from input files.
 *
 * This is a special purpose stub generator, specific to the needs of generating
 * stub files for JDK 7 API that are needed to compile langtools files that depend
 * on that API. The stub generator works by removing as much of the API source code
 * as possible without affecting the public signature, in order to reduce the
 * transitive closure of the API being referenced. The resulting stubs can be
 * put on the langtools sourcepath with -implicit:none to compile the langtools
 * files that depend on the JDK 7 API.
 *
 * Usage:
 *  genstubs -s <outdir> -sourcepath  
 *
 * The specified class names are looked up on the sourcepath, and corresponding
 * stubs are written to the source output directory.
 *
 * Classes are parsed into javac ASTs, then processed with a javac TreeTranslator
 * to remove implementation details, and written out in the source output directory.
 * Documentation comments and annotations are removed. Method bodies are removed
 * and methods are marked native. Private and package-private field definitions
 * have their initializers replace with 0, 0.0, false, null as appropriate.
 */

public class GenStubs {
    static class Fault extends Exception {
        private static final long serialVersionUID = 0;
        Fault(String message) {
            super(message);
        }
        Fault(String message, Throwable cause) {
            super(message);
            initCause(cause);
        }
    }

    public static void main(String[] args) {
        boolean ok = new GenStubs().run(args);
        if (!ok)
            System.exit(1);
    }

    public boolean run(String... args) {
        File outdir = null;
        String sourcepath = null;
        List<String> classes = new ArrayList();
        for (ListIterator<String> iter = Arrays.asList(args).listIterator(); iter.hasNext(); ) {
            String arg = iter.next();
            if (arg.equals("-s") && iter.hasNext())
                outdir = new File(iter.next());
            else if (arg.equals("-sourcepath") && iter.hasNext())
                sourcepath = iter.next();
            else if (arg.startsWith("-"))
                throw new IllegalArgumentException(arg);
            else {
                classes.add(arg);
                while (iter.hasNext())
                    classes.add(iter.next());
            }
        }

        return run(sourcepath, outdir, classes);
    }

    public boolean run(String sourcepath, File outdir, List<String> classes) {
        //System.err.println("run: sourcepath:" + sourcepath + " outdir:" + outdir + " classes:" + classes);
        if (sourcepath == null)
            throw new IllegalArgumentException("sourcepath not set");
        if (outdir == null)
            throw new IllegalArgumentException("source output dir not set");

        JavacTool tool = JavacTool.create();
        StandardJavaFileManager fm = tool.getStandardFileManager(null, null, null);

        try {
            fm.setLocation(StandardLocation.SOURCE_OUTPUT, Collections.singleton(outdir));
            fm.setLocation(StandardLocation.SOURCE_PATH, splitPath(sourcepath));
            List<JavaFileObject> files = new ArrayList();
            for (String c: classes) {
                JavaFileObject fo = fm.getJavaFileForInput(
                        StandardLocation.SOURCE_PATH, c, JavaFileObject.Kind.SOURCE);
                if (fo == null)
                    error("class not found: " + c);
                else
                    files.add(fo);
            }

            JavacTask t = tool.getTask(null, fm, null, null, null, files);
            Iterable<? extends CompilationUnitTree> trees = t.parse();
            for (CompilationUnitTree tree: trees) {
                makeStub(fm, tree);
            }
        } catch (IOException e) {
            error("IO error " + e, e);
        }

        return (errors == 0);
    }

    void makeStub(StandardJavaFileManager fm, CompilationUnitTree tree) throws IOException {
        CompilationUnitTree tree2 = new StubMaker().translate(tree);
        CompilationUnitTree tree3 = new ImportCleaner(fm).removeRedundantImports(tree2);

        String className = fm.inferBinaryName(StandardLocation.SOURCE_PATH, tree.getSourceFile());
        JavaFileObject fo = fm.getJavaFileForOutput(StandardLocation.SOURCE_OUTPUT,
                className, JavaFileObject.Kind.SOURCE, null);
        // System.err.println("Writing " + className + " to " + fo.getName());
        Writer out = fo.openWriter();
        try {
            new Pretty(out, true).printExpr((JCTree) tree3);
        } finally {
            out.close();
        }
    }

    List<File> splitPath(String path) {
        List<File> list = new ArrayList();
        for (String p: path.split(File.pathSeparator)) {
            if (p.length() > 0)
                list.add(new File(p));
        }
        return list;
    }

    void error(String message) {
        System.err.println(message);
        errors++;
    }

    void error(String message, Throwable cause) {
        error(message);
    }

    int errors;

    class StubMaker extends TreeTranslator {
        CompilationUnitTree translate(CompilationUnitTree tree) {
            return super.translate((JCCompilationUnit) tree);
        }

        /**
         * compilation units: remove javadoc comments
         * -- required, in order to remove @deprecated tags, since we
         * (separately) remove all annotations, including @Deprecated
         */
        public void visitTopLevel(JCCompilationUnit tree) {
            super.visitTopLevel(tree);
            tree.docComments = null;
        }

        /**
         * methods: remove method bodies, make methods native
         */
        @Override
        public void visitClassDef(JCClassDecl tree) {
            long prevClassMods = currClassMods;
            currClassMods = tree.mods.flags;
            try {
                super.visitClassDef(tree);;
            } finally {
                currClassMods = prevClassMods;
            }
        }
        private long currClassMods = 0;

        /**
         * methods: remove method bodies, make methods native
         */
        @Override
        public void visitMethodDef(JCMethodDecl tree) {
            tree.mods = translate(tree.mods);
            tree.restype = translate(tree.restype);
            tree.typarams = translateTypeParams(tree.typarams);
            tree.params = translateVarDefs(tree.params);
            tree.thrown = translate(tree.thrown);
            if (tree.body != null) {
                if ((currClassMods & Flags.INTERFACE) != 0) {
                    tree.mods.flags &= ~(Flags.DEFAULT | Flags.STATIC);
                } else {
                    tree.mods.flags |= Flags.NATIVE;
                }
                tree.body = null;
            }
            result = tree;
        }

        /**
         * modifiers: remove annotations
         */
        @Override
        public void visitModifiers(JCModifiers tree) {
            tree.annotations = com.sun.tools.javac.util.List.nil();
            result = tree;
        }

        /**
         * field definitions: replace initializers with 0, 0.0, false etc
         * when possible -- i.e. leave public, protected initializers alone
         */
        @Override
        public void visitVarDef(JCVariableDecl tree) {
            tree.mods = translate(tree.mods);
            tree.vartype = translate(tree.vartype);
            if (tree.init != null) {
                if ((tree.mods.flags & (Flags.PUBLIC | Flags.PROTECTED)) != 0)
                    tree.init = translate(tree.init);
                else {
                    String t = tree.vartype.toString();
                    if (t.equals("boolean"))
                        tree.init = new JCLiteral(TypeTag.BOOLEAN, 0) { };
                    else if (t.equals("byte"))
                        tree.init = new JCLiteral(TypeTag.BYTE, 0) { };
                    else if (t.equals("char"))
                        tree.init = new JCLiteral(TypeTag.CHAR, 0) { };
                    else if (t.equals("double"))
                        tree.init = new JCLiteral(TypeTag.DOUBLE, 0.d) { };
                    else if (t.equals("float"))
                        tree.init = new JCLiteral(TypeTag.FLOAT, 0.f) { };
                    else if (t.equals("int"))
                        tree.init = new JCLiteral(TypeTag.INT, 0) { };
                    else if (t.equals("long"))
                        tree.init = new JCLiteral(TypeTag.LONG, 0) { };
                    else if (t.equals("short"))
                        tree.init = new JCLiteral(TypeTag.SHORT, 0) { };
                    else
                        tree.init = new JCLiteral(TypeTag.BOT, null) { };
                }
            }
            result = tree;
        }
    }

    class ImportCleaner extends TreeScanner {
        private Set<Name> names = new HashSet();
        private TreeMaker m;

        ImportCleaner(JavaFileManager fm) {
            // ImportCleaner itself doesn't require a filemanager, but instantiating
            // a TreeMaker does, indirectly (via ClassReader, sigh)
            Context c = new Context();
            c.put(JavaFileManager.class, fm);
            m = TreeMaker.instance(c);
        }

        CompilationUnitTree removeRedundantImports(CompilationUnitTree t) {
            JCCompilationUnit tree = (JCCompilationUnit) t;
            tree.accept(this);
            ListBuffer<JCTree> defs = new ListBuffer();
            for (JCTree def: tree.defs) {
                if (def.getTag() == JCTree.Tag.IMPORT) {
                    JCImport imp = (JCImport) def;
                    if (imp.qualid.getTag() == JCTree.Tag.SELECT) {
                        JCFieldAccess qualid = (JCFieldAccess) imp.qualid;
                        if (!qualid.name.toString().equals("*")
                                && !names.contains(qualid.name)) {
                            continue;
                        }
                    }
                }
                defs.add(def);
            }
            return m.TopLevel(tree.packageAnnotations, tree.pid, defs.toList());
        }

        @Override
        public void visitImport(JCImport tree) { } // ignore names found in imports

        @Override
        public void visitIdent(JCIdent tree) {
            names.add(tree.name);
        }

        @Override
        public void visitSelect(JCFieldAccess tree) {
            super.visitSelect(tree);
            names.add(tree.name);
        }
    }
}