Java字节码删除或者添加一个类成员

以下代码需要asm-5.0.2.jar和asm-commons-5.0.2.jar两个包。

package com.shihuan.field;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.prefs.NodeChangeEvent;
import java.util.spi.LocaleNameProvider;
import java.util.spi.TimeZoneNameProvider;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;
import java.util.logging.ConsoleHandler;
import java.util.logging.Formatter;

public class AccountField {

	int mynum;
	static java.util.Date mydate;
	Long mu370;
	static Float mfhj;
	byte[] mybb;
	java.sql.Timestamp[][] parameterTt;
	static final int ABCDEF = 0;
	boolean bingop;
	java.io.InputStream[] islk;
	private int myinnn;
	protected boolean isServer;
	public static final String BUIO = "1999999999999999999999999999999999999";
	String sql = "select * from tables";
	
	public AccountField() {
		
	}

	public AccountField(boolean bingop) {
		this.bingop = bingop;
	}

	public void operation() {
        System.out.println("shihuan operation...");
    }
	
	int executeInternal() {
		
		System.out.println("shihuan executeInternal...");
		
		if (true) {
			return 2;
		}
		
		return 1;
	}
	
}

package com.shihuan.field;

public class TestAccountField {

	public static void main(String[] args) {
		AccountField t = new AccountField();
		t.operation();
		t.executeInternal();
	}

}

运行AsmDeleteField.java会删除掉AccountField.java文件中的mynum属性:

package com.shihuan.field;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;

import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.FieldVisitor;
import org.objectweb.asm.Opcodes;

public class AsmDeleteField {

	public static void main(String[] args) throws IOException {
		ClassReader cr = new ClassReader("com.shihuan.field.AccountField");
		ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS);
		ClassVisitor cv = new ClassVisitor(Opcodes.ASM5, cw) {
			
			public FieldVisitor visitField(int access, String name, String desc, String signature, Object value) {
				
		        if("mynum".equals(name)) { //值域变量名称为mynum的时候
		            return null;          //为null表示去掉
		        }
		        
		        return super.visitField(access, name, desc, signature, value); //不为null,保留   
		    }
			
			
		};
		cr.accept(cv, ClassReader.SKIP_DEBUG);

		byte[] code = cw.toByteArray();
		OutputStream fos = new FileOutputStream("D:/myworkspace/JavaAsm/bin/com/shihuan/field/AccountField.class");
		fos.write(code);
		fos.close();
	}

}

运行AsmDeleteField.java会在AccountField.java文件中添加一个公有int类型的mynum属性:

package com.shihuan.field;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;

import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.Type;

public class AsmAddField {

	public static void main(String[] args) throws IOException {
		ClassReader cr = new ClassReader("com.shihuan.field.AccountField");
		ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS);
		ClassVisitor cv = new ClassVisitor(Opcodes.ASM5, cw) {
			public void visitEnd() {
				visitField(Opcodes.ACC_PUBLIC, "mynum", Type.getDescriptor(int.class), null, null);  //添加一个名字为mynum的int类型的公有属性
				super.visitEnd();
			}
		};
		cr.accept(cv, ClassReader.SKIP_DEBUG);

		byte[] code = cw.toByteArray();
		OutputStream fos = new FileOutputStream("D:/myworkspace/JavaAsm/bin/com/shihuan/field/AccountField.class");
		fos.write(code);
		fos.close();
	}

}