abstractstructurewithattributes.java

Java Bytecode Editor 是一个 JAVA 的字节码反汇编和修改器。它可以很方便的修改已经编译成 Class 文件的 JAVA 文件。

/*
    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public
    License as published by the Free Software Foundation; either
    version 2 of the license, or (at your option) any later version.
*/

package org.gjt.jclasslib.structures;

import java.io.*;

/**
    Base class for all structures with attributes.
 
    @author <a href="mailto:[e-mail]">Ingo Kegel</a>
    @version $Revision: 1.1 $ $Date: 2005/11/01 13:18:24 $
*/
public abstract class AbstractStructureWithAttributes extends AbstractStructure {

    /** Attributes of this structure. */
    protected AttributeInfo[] attributes;

    /**
        Get the attributes of this structure.
        @return the attributes
     */
    public AttributeInfo[] getAttributes() {
        return attributes;
    }
    
    /**
        Set the attributes of this structure.
        @param attributes the new attributes
     */
    public void setAttributes(AttributeInfo[] attributes) {
        this.attributes = attributes;
    }
    
    /**
        Find an attribute of a certain class.
        @param attributeClass the class of the attribute
        @return the found attribute, <tt>null</tt> if not found
     */
    public AttributeInfo findAttribute(Class attributeClass) {
        AttributeInfo foundAttribute = null;
        for (int i = 0; i < attributes.length; i++) {
            if (attributes[i].getClass() == attributeClass) {
                foundAttribute = attributes[i];
                break;
            }
        }
        return foundAttribute;
    }

    /**
        Read the attributes of this structure from the given <tt>DataInput</tt>. <p>
     
        Excpects <tt>DataInput</tt> to be in JVM class file format and just
        before an attribute length field.
        @param in the <tt>DataInput</tt> from which to read
        @throws InvalidByteCodeException if the byte code is invalid
        @throws IOException if an exception occurs with the <tt>DataInput</tt>
     */
    protected void readAttributes(DataInput in)
        throws InvalidByteCodeException, IOException {
            
        int attributesCount = in.readUnsignedShort();
        attributes = new AttributeInfo[attributesCount];
        
        for (int i = 0; i < attributesCount; i++) {
            attributes[i] = AttributeInfo.createOrSkip(in, classFile);
        }
    }

    /**
        Write the attributes of this structure to the given <tt>DataOutput</tt>. <p>
     
        The written bytes are in JVM class file format.
        @param out the <tt>DataOutput</tt> to which to write
        @throws InvalidByteCodeException if the structure is internally inconsistent
        @throws IOException if an exception occurs with the <tt>DataOutput</tt>
     */
    protected void writeAttributes(DataOutput out)
        throws InvalidByteCodeException, IOException {
            
        int attributesCount = getLength(attributes);

        out.writeShort(attributesCount);

        for (int i = 0; i < attributesCount; i++) {
            if (attributes[i] == null) {
                throw new InvalidByteCodeException("attribute " + i + " is null");
            }
            attributes[i].write(out);
        }
    }
    
    /**
        Get the length of all attributes as a number of bytes.
        @return the length
     */
    protected int getTotalAttributesLength() {
        int totalLength = 0;
        int attributesCount = getLength(attributes);
        for (int i = 0; i < attributesCount; i++) {
            if (attributes[i] != null) {
                totalLength += attributes[i].getAttributeLength();
            }
        }
        return totalLength;
    }
}