Java example source code file (Gen.java)

This example Java source code file (Gen.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.

Learn more about this Java project at its project page.

Java - Java tags/keywords

bytearrayoutputstream, character, charsequence, fileobject, gen, ioexception, list, mangle, printwriter, stack, string, stringbuilder, typeelement, util, variableelement

The Gen.java Java example source code

/*
 * Copyright (c) 2002, 2012, 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 com.sun.tools.javah;

import java.io.UnsupportedEncodingException;
import java.io.ByteArrayOutputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Set;
import java.util.Stack;

import javax.annotation.processing.ProcessingEnvironment;

import javax.lang.model.element.ExecutableElement;
import javax.lang.model.element.Modifier;
import javax.lang.model.element.TypeElement;
import javax.lang.model.element.VariableElement;
import javax.lang.model.util.ElementFilter;
import javax.lang.model.util.Elements;
import javax.lang.model.util.Types;

import javax.tools.FileObject;
import javax.tools.JavaFileManager;
import javax.tools.JavaFileObject;
import javax.tools.StandardLocation;

/**
 * An abstraction for generating support files required by native methods.
 * Subclasses are for specific native interfaces. At the time of its
 * original writing, this interface is rich enough to support JNI and the
 * old 1.0-style native method interface.
 *
 * <p>This is NOT part of any supported API.
 * If you write code that depends on this, you do so at your own
 * risk.  This code and its internal interfaces are subject to change
 * or deletion without notice.</b>

 *
 * @author  Sucheta Dambalkar(Revised)
 */
public abstract class Gen {
    protected String lineSep = System.getProperty("line.separator");

    protected ProcessingEnvironment processingEnvironment;
    protected Types types;
    protected Elements elems;
    protected Mangle mangler;
    protected Util util;

    protected Gen(Util util) {
        this.util = util;
    }

    /*
     * List of classes for which we must generate output.
     */
    protected Set<TypeElement> classes;
    static private final boolean isWindows =
        System.getProperty("os.name").startsWith("Windows");


    /**
     * Override this abstract method, generating content for the named
     * class into the outputstream.
     */
    protected abstract void write(OutputStream o, TypeElement clazz) throws Util.Exit;

    /**
     * Override this method to provide a list of #include statements
     * required by the native interface.
     */
    protected abstract String getIncludes();

    /*
     * Output location.
     */
    protected JavaFileManager fileManager;
    protected JavaFileObject outFile;

    public void setFileManager(JavaFileManager fm) {
        fileManager = fm;
    }

    public void setOutFile(JavaFileObject outFile) {
        this.outFile = outFile;
    }


    public void setClasses(Set<TypeElement> classes) {
        this.classes = classes;
    }

    void setProcessingEnvironment(ProcessingEnvironment pEnv) {
        processingEnvironment = pEnv;
        elems = pEnv.getElementUtils();
        types = pEnv.getTypeUtils();
        mangler = new Mangle(elems, types);
    }

    /*
     * Smartness with generated files.
     */
    protected boolean force = false;

    public void setForce(boolean state) {
        force = state;
    }

    /**
     * We explicitly need to write ASCII files because that is what C
     * compilers understand.
     */
    protected PrintWriter wrapWriter(OutputStream o) throws Util.Exit {
        try {
            return new PrintWriter(new OutputStreamWriter(o, "ISO8859_1"), true);
        } catch (UnsupportedEncodingException use) {
            util.bug("encoding.iso8859_1.not.found");
            return null; /* dead code */
        }
    }

    /**
     * After initializing state of an instance, use this method to start
     * processing.
     *
     * Buffer size chosen as an approximation from a single sampling of:
     *         expr `du -sk` / `ls *.h | wc -l`
     */
    public void run() throws IOException, ClassNotFoundException, Util.Exit {
        int i = 0;
        if (outFile != null) {
            /* Everything goes to one big file... */
            ByteArrayOutputStream bout = new ByteArrayOutputStream(8192);
            writeFileTop(bout); /* only once */

            for (TypeElement t: classes) {
                write(bout, t);
            }

            writeIfChanged(bout.toByteArray(), outFile);
        } else {
            /* Each class goes to its own file... */
            for (TypeElement t: classes) {
                ByteArrayOutputStream bout = new ByteArrayOutputStream(8192);
                writeFileTop(bout);
                write(bout, t);
                writeIfChanged(bout.toByteArray(), getFileObject(t.getQualifiedName()));
            }
        }
    }

    /*
     * Write the contents of byte[] b to a file named file.  Writing
     * is done if either the file doesn't exist or if the contents are
     * different.
     */
    private void writeIfChanged(byte[] b, FileObject file) throws IOException {
        boolean mustWrite = false;
        String event = "[No need to update file ";

        if (force) {
            mustWrite = true;
            event = "[Forcefully writing file ";
        } else {
            InputStream in;
            byte[] a;
            try {
                // regrettably, there's no API to get the length in bytes
                // for a FileObject, so we can't short-circuit reading the
                // file here
                in = file.openInputStream();
                a = readBytes(in);
                if (!Arrays.equals(a, b)) {
                    mustWrite = true;
                    event = "[Overwriting file ";

                }
            } catch (FileNotFoundException e) {
                mustWrite = true;
                event = "[Creating file ";
            }
        }

        if (util.verbose)
            util.log(event + file + "]");

        if (mustWrite) {
            OutputStream out = file.openOutputStream();
            out.write(b); /* No buffering, just one big write! */
            out.close();
        }
    }

    protected byte[] readBytes(InputStream in) throws IOException {
        try {
            byte[] array = new byte[in.available() + 1];
            int offset = 0;
            int n;
            while ((n = in.read(array, offset, array.length - offset)) != -1) {
                offset += n;
                if (offset == array.length)
                    array = Arrays.copyOf(array, array.length * 2);
            }

            return Arrays.copyOf(array, offset);
        } finally {
            in.close();
        }
    }

    protected String defineForStatic(TypeElement c, VariableElement f)
            throws Util.Exit {
        CharSequence cnamedoc = c.getQualifiedName();
        CharSequence fnamedoc = f.getSimpleName();

        String cname = mangler.mangle(cnamedoc, Mangle.Type.CLASS);
        String fname = mangler.mangle(fnamedoc, Mangle.Type.FIELDSTUB);

        if (!f.getModifiers().contains(Modifier.STATIC))
            util.bug("tried.to.define.non.static");

        if (f.getModifiers().contains(Modifier.FINAL)) {
            Object value = null;

            value = f.getConstantValue();

            if (value != null) { /* so it is a ConstantExpression */
                String constString = null;
                if ((value instanceof Integer)
                    || (value instanceof Byte)
                    || (value instanceof Short)) {
                    /* covers byte, short, int */
                    constString = value.toString() + "L";
                } else if (value instanceof Boolean) {
                    constString = ((Boolean) value) ? "1L" : "0L";
                } else if (value instanceof Character) {
                    Character ch = (Character) value;
                    constString = String.valueOf(((int) ch) & 0xffff) + "L";
                } else if (value instanceof Long) {
                    // Visual C++ supports the i64 suffix, not LL.
                    if (isWindows)
                        constString = value.toString() + "i64";
                    else
                        constString = value.toString() + "LL";
                } else if (value instanceof Float) {
                    /* bug for bug */
                    float fv = ((Float)value).floatValue();
                    if (Float.isInfinite(fv))
                        constString = ((fv < 0) ? "-" : "") + "Inff";
                    else
                        constString = value.toString() + "f";
                } else if (value instanceof Double) {
                    /* bug for bug */
                    double d = ((Double)value).doubleValue();
                    if (Double.isInfinite(d))
                        constString = ((d < 0) ? "-" : "") + "InfD";
                    else
                        constString = value.toString();
                }
                if (constString != null) {
                    StringBuilder s = new StringBuilder("#undef ");
                    s.append(cname); s.append("_"); s.append(fname); s.append(lineSep);
                    s.append("#define "); s.append(cname); s.append("_");
                    s.append(fname); s.append(" "); s.append(constString);
                    return s.toString();
                }

            }
        }
        return null;
    }

    /*
     * Deal with the C pre-processor.
     */
    protected String cppGuardBegin() {
        return "#ifdef __cplusplus" + lineSep + "extern \"C\" {" + lineSep + "#endif";
    }

    protected String cppGuardEnd() {
        return "#ifdef __cplusplus" + lineSep + "}" + lineSep + "#endif";
    }

    protected String guardBegin(String cname) {
        return "/* Header for class " + cname + " */" + lineSep + lineSep +
            "#ifndef _Included_" + cname + lineSep +
            "#define _Included_" + cname;
    }

    protected String guardEnd(String cname) {
        return "#endif";
    }

    /*
     * File name and file preamble related operations.
     */
    protected void writeFileTop(OutputStream o) throws Util.Exit {
        PrintWriter pw = wrapWriter(o);
        pw.println("/* DO NOT EDIT THIS FILE - it is machine generated */" + lineSep +
                   getIncludes());
    }

    protected String baseFileName(CharSequence className) {
        return mangler.mangle(className, Mangle.Type.CLASS);
    }

    protected FileObject getFileObject(CharSequence className) throws IOException {
        String name = baseFileName(className) + getFileSuffix();
        return fileManager.getFileForOutput(StandardLocation.SOURCE_OUTPUT, "", name, null);
    }

    protected String getFileSuffix() {
        return ".h";
    }

    /**
     * Including super classes' fields.
     */

    List<VariableElement> getAllFields(TypeElement subclazz) {
        List<VariableElement> fields = new ArrayList();
        TypeElement cd = null;
        Stack<TypeElement> s = new Stack();

        cd = subclazz;
        while (true) {
            s.push(cd);
            TypeElement c = (TypeElement) (types.asElement(cd.getSuperclass()));
            if (c == null)
                break;
            cd = c;
        }

        while (!s.empty()) {
            cd = s.pop();
            fields.addAll(ElementFilter.fieldsIn(cd.getEnclosedElements()));
        }

        return fields;
    }

    // c.f. MethodDoc.signature
    String signature(ExecutableElement e) {
        StringBuilder sb = new StringBuilder("(");
        String sep = "";
        for (VariableElement p: e.getParameters()) {
            sb.append(sep);
            sb.append(types.erasure(p.asType()).toString());
            sep = ",";
        }
        sb.append(")");
        return sb.toString();
    }
}