fieldgen.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。

package org.apache.bcel.generic;

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 * The Apache Software License, Version 1.1
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 * reserved.
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 * modification, are permitted provided that the following conditions
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 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
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 *    "Apache BCEL" must not be used to endorse or promote products
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 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

import org.apache.bcel.Constants;
import org.apache.bcel.classfile.*;
import java.util.ArrayList;
import java.util.Iterator;

/**
 * Template class for building up a field. The only extraordinary thing one can
 * do is to add a constant value attribute to a field (which must of course be
 * compatible with to the declared type).
 * 
 * @version $Id: FieldGen.java,v 1.3 2006/08/23 13:48:30 andos Exp $
 * @author <A HREF="mailto:[e-mail]">M. Dahm</A>
 * @see Field
 */
public class FieldGen extends FieldGenOrMethodGen {
	/**
	 * 
	 */
	private static final long serialVersionUID = 6827938423085341455L;
	private Object value = null;

	/**
	 * Declare a field. If it is static (isStatic() == true) and has a basic
	 * type like int or String it may have an initial value associated with it
	 * as defined by setInitValue().
	 * 
	 * @param access_flags
	 *            access qualifiers
	 * @param type
	 *            field type
	 * @param name
	 *            field name
	 * @param cp
	 *            constant pool
	 */
	public FieldGen(int access_flags, Type type, String name, ConstantPoolGen cp) {
		setAccessFlags(access_flags);
		setType(type);
		setName(name);
		setConstantPool(cp);
	}

	/**
	 * Instantiate from existing field.
	 * 
	 * @param field
	 *            Field object
	 * @param cp
	 *            constant pool (must contain the same entries as the field's
	 *            constant pool)
	 */
	public FieldGen(Field field, ConstantPoolGen cp) {
		this(field.getAccessFlags(), Type.getType(field.getSignature()), field
				.getName(), cp);

		Attribute[] attrs = field.getAttributes();

		for (int i = 0; i < attrs.length; i++) {
			if (attrs[i] instanceof ConstantValue)
				setValue(((ConstantValue) attrs[i]).getConstantValueIndex());
			else
				addAttribute(attrs[i]);
		}
	}

	public FieldGen(int accessFlags, String name, String descriptor,
			ConstantPoolGen cpg) {
		setAccessFlags(accessFlags);
		setDescriptor(descriptor);
		setName(name);
		setConstantPool(cpg);
	}

	private void setValue(int index) {
		ConstantPool cp = this.cp.getConstantPool();
		Constant c = cp.getConstant(index);
		value = ((ConstantObject) c).getConstantValue(cp);
	}

	/**
	 * Set (optional) initial value of field, otherwise it will be set to
	 * null/0/false by the JVM automatically.
	 */
	public void setInitValue(String str) {
		checkType(new ObjectType("java.lang.String"));

		if (str != null)
			value = str;
	}

	public void setInitValue(long l) {
		checkType(Type.LONG);

		if (l != 0L)
			value = new Long(l);
	}

	public void setInitValue(int i) {
		checkType(Type.INT);

		if (i != 0)
			value = new Integer(i);
	}

	public void setInitValue(short s) {
		checkType(Type.SHORT);

		if (s != 0)
			value = new Integer(s);
	}

	public void setInitValue(char c) {
		checkType(Type.CHAR);

		if (c != 0)
			value = new Integer(c);
	}

	public void setInitValue(byte b) {
		checkType(Type.BYTE);

		if (b != 0)
			value = new Integer(b);
	}

	public void setInitValue(boolean b) {
		checkType(Type.BOOLEAN);

		if (b)
			value = new Integer(1);
	}

	public void setInitValue(float f) {
		checkType(Type.FLOAT);

		if (f != 0.0)
			value = new Float(f);
	}

	public void setInitValue(double d) {
		checkType(Type.DOUBLE);

		if (d != 0.0)
			value = new Double(d);
	}

	/**
	 * Remove any initial value.
	 */
	public void cancelInitValue() {
		value = null;
	}

	private void checkType(Type atype) {
		if (type == null)
			throw new ClassGenException(
					"You haven't defined the type of the field yet");

		if (!isFinal())
			throw new ClassGenException(
					"Only final fields may have an initial value!");

		if (!type.equals(atype))
			throw new ClassGenException("Types are not compatible: " + type
					+ " vs. " + atype);
	}

	/**
	 * Get field object after having set up all necessary values.
	 */
	public Field getField() {
		String signature;
		if (descriptor == null) {
			signature = getSignature();
		}else {
			signature = descriptor;
		}
		int name_index = cp.addUtf8(name);
		int signature_index = cp.addUtf8(signature);

		if (value != null) {
			checkType(type);
			int index = addConstant();
			addAttribute(new ConstantValue(cp.addUtf8("ConstantValue"), 2,
					index, cp.getConstantPool()));
		}

		return new Field(access_flags, name_index, signature_index,
				getAttributes(), cp.getConstantPool());
	}

	private int addConstant() {
		switch (type.getType()) {
		case Constants.T_INT:
		case Constants.T_CHAR:
		case Constants.T_BYTE:
		case Constants.T_BOOLEAN:
		case Constants.T_SHORT:
			return cp.addInteger(((Integer) value).intValue());

		case Constants.T_FLOAT:
			return cp.addFloat(((Float) value).floatValue());

		case Constants.T_DOUBLE:
			return cp.addDouble(((Double) value).doubleValue());

		case Constants.T_LONG:
			return cp.addLong(((Long) value).longValue());

		case Constants.T_REFERENCE:
			return cp.addString(((String) value));

		default:
			throw new RuntimeException("Oops: Unhandled : " + type.getType());
		}
	}

	public String getSignature() {
		return type.getSignature();
	}

	private ArrayList<FieldObserver> observers;

	/**
	 * Add observer for this object.
	 */
	public void addObserver(FieldObserver o) {
		if (observers == null)
			observers = new ArrayList<FieldObserver>();

		observers.add(o);
	}

	/**
	 * Remove observer for this object.
	 */
	public void removeObserver(FieldObserver o) {
		if (observers != null)
			observers.remove(o);
	}

	/**
	 * Call notify() method on all observers. This method is not called
	 * automatically whenever the state has changed, but has to be called by the
	 * user after he has finished editing the object.
	 */
	public void update() {
		if (observers != null)
			for (Iterator e = observers.iterator(); e.hasNext();)
				((FieldObserver) e.next()).notify(this);
	}

	public String getInitValue() {
		if (value != null) {
			return value.toString();
		} else
			return null;
	}

	/**
	 * Return string representation close to declaration format, `public static
	 * final short MAX = 100', e.g..
	 * 
	 * @return String representation of field
	 */
	public final String toString() {
		String name, signature, access; // Short cuts to constant pool

		access = Utility.accessToString(access_flags);
		access = access.equals("") ? "" : (access + " ");
		signature = type.toString();
		name = getName();

		StringBuffer buf = new StringBuffer(access + signature + " " + name);
		String value = getInitValue();

		if (value != null)
			buf.append(" = " + value);

		return buf.toString();
	}

	/**
	 * @return deep copy of this field
	 */
	public FieldGen copy(ConstantPoolGen cp) {
		FieldGen fg = (FieldGen) clone();

		fg.setConstantPool(cp);
		return fg;
	}
}