Ant example source code file (ClassFile.java)

This example Ant 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 - Ant tags/keywords

class_magic, class_magic, classcpinfo, classcpinfo, classformaterror, code, constantpool, constantpool, datainputstream, io, java, no, string, util, vector, vector

The ClassFile.java source code

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You 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 org.apache.tools.ant.taskdefs.optional.depend;

import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Vector;
import org.apache.tools.ant.taskdefs.optional.depend.constantpool.ClassCPInfo;
import org.apache.tools.ant.taskdefs.optional.depend.constantpool.ConstantPool;
import org.apache.tools.ant.taskdefs.optional.depend.constantpool.ConstantPoolEntry;

/**
 * A ClassFile object stores information about a Java class. The class may
 * be read from a DataInputStream.and written to a DataOutputStream. These
 * are usually streams from a Java class file or a class file component of a
 * Jar file.
 *
 */
public class ClassFile {

    /** The Magic Value that marks the start of a Java class file  */
    private static final int CLASS_MAGIC = 0xCAFEBABE;

    /** This class' constant pool.  */
    private ConstantPool constantPool;

    /** The class name for this class.  */
    private String className;

    /**
     * Read the class from a data stream. This method takes an InputStream
     * as input and parses the class from the stream. <p>
     *
     *
     *
     * @param stream an InputStream from which the class will be read
     * @exception IOException if there is a problem reading from the given
     *      stream.
     * @exception ClassFormatError if the class cannot be parsed correctly
     */
    public void read(InputStream stream) throws IOException, ClassFormatError {
        DataInputStream classStream = new DataInputStream(stream);

        if (classStream.readInt() != CLASS_MAGIC) {
            throw new ClassFormatError("No Magic Code Found "
                + "- probably not a Java class file.");
        }

        // right we have a good looking class file.
        /* int minorVersion = */ classStream.readUnsignedShort();
        /* int majorVersion = */ classStream.readUnsignedShort();

        // read the constant pool in and resolve it
        constantPool = new ConstantPool();

        constantPool.read(classStream);
        constantPool.resolve();

        /* int accessFlags = */ classStream.readUnsignedShort();
        int thisClassIndex = classStream.readUnsignedShort();
        /* int superClassIndex = */ classStream.readUnsignedShort();
        ClassCPInfo classInfo
            = (ClassCPInfo) constantPool.getEntry(thisClassIndex);
        className  = classInfo.getClassName();
    }


    /**
     * Get the classes which this class references.
     *
     * @return a vector of class names which this class references
     */
    public Vector getClassRefs() {

        Vector classRefs = new Vector();

        for (int i = 0; i < constantPool.size(); ++i) {
            ConstantPoolEntry entry = constantPool.getEntry(i);

            if (entry != null
                && entry.getTag() == ConstantPoolEntry.CONSTANT_CLASS) {
                ClassCPInfo classEntry = (ClassCPInfo) entry;

                if (!classEntry.getClassName().equals(className)) {
                    classRefs.addElement(
                        ClassFileUtils.convertSlashName(classEntry.getClassName()));
                }
            }
        }

        return classRefs;
    }

    /**
     * Get the class' fully qualified name in dot format.
     *
     * @return the class name in dot format (eg. java.lang.Object)
     */
    public String getFullClassName() {
        return ClassFileUtils.convertSlashName(className);
    }
}