Glassfish example source code file (ClassFile.java)

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

Java - Glassfish tags/keywords

acc_final, acc_native, acc_static, acc_synchronized, acc_threadsafe, acc_transient, bytebuffer, bytebuffer, classfile, classfile, constantpoolinfo, constantpoolinfo, io, ioexception, ioexception, nio

The Glassfish ClassFile.java source code

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright (c) 1997-2010 Oracle and/or its affiliates. All rights reserved.
 *
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License.  You can
 * obtain a copy of the License at
 * https://glassfish.dev.java.net/public/CDDL+GPL_1_1.html
 * or packager/legal/LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 *
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at packager/legal/LICENSE.txt.
 *
 * GPL Classpath Exception:
 * Oracle designates this particular file as subject to the "Classpath"
 * exception as provided by Oracle in the GPL Version 2 section of the License
 * file that accompanied this code.
 *
 * Modifications:
 * If applicable, add the following below the License Header, with the fields
 * enclosed by brackets [] replaced by your own identifying information:
 * "Portions Copyright [year] [name of copyright owner]"
 *
 * Contributor(s):
 * If you wish your version of this file to be governed by only the CDDL or
 * only the GPL Version 2, indicate your decision by adding "[Contributor]
 * elects to include this software in this distribution under the [CDDL or GPL
 * Version 2] license."  If you don't indicate a single choice of license, a
 * recipient has the option to distribute your version of this file under
 * either the CDDL, the GPL Version 2 or to extend the choice of license to
 * its licensees as provided above.  However, if you add GPL Version 2 code
 * and therefore, elected the GPL Version 2 license, then the option applies
 * only if the new code is made subject to such option by the copyright
 * holder.
 */

package com.sun.enterprise.deployment.annotation.introspection;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.ReadableByteChannel;

/**
 * This class is encapsulating binary .class file information as 
 * defined at 
 * http://java.sun.com/docs/books/vmspec/2nd-edition/html/ClassFile.doc.html
 *
 * This is used by the annotation frameworks to quickly scan .class files 
 * for the presence of annotations. This avoid the annotation framework having
 * to load each .class file in the class loader.
 *
 * The bytecode to be scanned could come from either a File (which lends itself
 * easily to a channel) or from a JAR (which works better with a byte array).  So
 * we provide two variants of the containsAnnotation method, one for each.
 *
 * @author Jerome Dochez
 */
public class ClassFile {
    
    ByteBuffer header;
    ConstantPoolInfo constantPoolInfo;

    /** Creates a new instance of ClassFile */
    public ClassFile(ConstantPoolInfo poolInfo) {
        header = ByteBuffer.allocate(12000);
        constantPoolInfo = poolInfo;
    }

    /**
     * Read the input channel and initialize instance data
     * structure.
     */public boolean containsAnnotation(ReadableByteChannel in, long size) throws IOException {
        header.clear();
        if (size!=-1 && size>header.capacity()) {
            // time to expand...
            header = ByteBuffer.allocate((int) size);
        }
        long read = (long) in.read(header);
        if (size!=-1 && read!=size) {
            return false;
        }
        header.rewind();
        return containsAnnotation(header);
    }

    /**
     * Read the input channel and initialize instance data
     * structure.
     */
    public boolean containsAnnotation(final byte[] bytecode) throws IOException {
        final ByteBuffer wrappedHeader = ByteBuffer.wrap(bytecode);
        return containsAnnotation(wrappedHeader);
    }

    private boolean containsAnnotation(final ByteBuffer headerBuffer) throws IOException {


        /**
         * this is the .class file layout
         *
        ClassFile {
            u4 magic;
            u2 minor_version;
            u2 major_version;
            u2 constant_pool_count;
            cp_info constant_pool[constant_pool_count-1];
            u2 access_flags;
            u2 this_class;
            u2 super_class;
            u2 interfaces_count;
            u2 interfaces[interfaces_count];
            u2 fields_count;
            field_info fields[fields_count];
            u2 methods_count;
            method_info methods[methods_count];
            u2 attributes_count;
            attribute_info attributes[attributes_count];
        }        
         **/
                
        if (headerBuffer.getInt()!=magic) {
            return false;
        }
        
        majorVersion = headerBuffer.getShort();
        minorVersion = headerBuffer.getShort();
        int constantPoolSize = headerBuffer.getShort();

        return constantPoolInfo.containsAnnotation(constantPoolSize, headerBuffer);
        
    }
    
    public short	       	majorVersion;
    public short       		minorVersion;
    public ConstantPoolInfo	constantPool[];
    public short	        accessFlags;
    public ConstantPoolInfo	thisClass;
    public ConstantPoolInfo	superClass;
    public ConstantPoolInfo	interfaces[];
    /**
     * bunch of stuff I really don't care too much for now.
     *
    FieldInfo		    fields[];
    MethodInfo		    methods[];
    AttributeInfo	    attributes[];
     */
    boolean		        isValidClass = false;

    private static final int magic = 0xCAFEBABE;
    
    public static final int ACC_PUBLIC 		= 0x1;
    public static final int ACC_PRIVATE 	= 0x2;
    public static final int ACC_PROTECTED 	= 0x4;
    public static final int ACC_STATIC 		= 0x8;
    public static final int ACC_FINAL 		= 0x10;
    public static final int ACC_SYNCHRONIZED 	= 0x20;
    public static final int ACC_THREADSAFE 	= 0x40;
    public static final int ACC_TRANSIENT 	= 0x80;
    public static final int ACC_NATIVE 		= 0x100;
    public static final int ACC_INTERFACE 	= 0x200;
    public static final int ACC_ABSTRACT 	= 0x400;
    
}