使用ASM生成Java字节码（可以通过代码动态生成java字节码）

使用ASM生成Java字节码，下面通过java程序模拟实现spring aop 动态织入

 

Account.java

package com.market.search.test;

/**
 * Created by xiaotian on 2018/5/8.
 */
public class Account {
    public void operation() {
        //通过字节码生成技术 动态添加check功能  模拟aop 动态织入
        System.out.println("operation....");
    }

}

SecurityChecker.java

package com.market.search.test;

/**
 * Created by xiaotian on 2018/5/8.
 * 将checkSecurity 通过ASE方式动态 增强Account.operation 中
 */
public class SecurityChecker {

    public static boolean checkSecurity() {
        System.out.println("SecurityChecker.checkSecurity ...");
        return true;
    }

}

AddSecurityCheckClassAdapter.java  类适配

package com.market.search.test;

import jdk.internal.org.objectweb.asm.ClassVisitor;
import jdk.internal.org.objectweb.asm.MethodVisitor;
import jdk.internal.org.objectweb.asm.Opcodes;

/**
 * Created by xiaotian on 2018/5/8.
 */
public class AddSecurityCheckClassAdapter extends ClassVisitor {
    public AddSecurityCheckClassAdapter( ClassVisitor cv) {
        super(Opcodes.ASM5, cv);
    }
    // 重写 visitMethod，访问到 "operation" 方法时，
    // 给出自定义 MethodVisitor，实际改写方法内容
    public MethodVisitor visitMethod(final int access, final String name,
                                     final String desc, final String signature, final String[] exceptions) {
        MethodVisitor mv = cv.visitMethod(access, name, desc, signature,exceptions);
        MethodVisitor wrappedMv = mv;
        if (mv != null) {
            // 对于 "operation" 方法
            if (name.equals("operation")) {
                // 使用自定义 MethodVisitor，实际改写方法内容
                wrappedMv = new AddSecurityCheckMethodAdapter(mv);
            }
        }
        return wrappedMv;
    }

}

AddSecurityCheckMethodAdapter.java 方法适配

package com.market.search.test;

import jdk.internal.org.objectweb.asm.MethodVisitor;
import jdk.internal.org.objectweb.asm.Opcodes;

/**
 * Created by xiaotian on 2018/5/8.
 */
public class AddSecurityCheckMethodAdapter extends MethodVisitor {
    public AddSecurityCheckMethodAdapter(MethodVisitor mv) {
        super(Opcodes.ASM5,mv);
    }
    public void visitCode() {
        visitMethodInsn(Opcodes.INVOKESTATIC, "com/market/search/test/SecurityChecker",
                "checkSecurity", "()Z");
        super.visitCode();
    }

}

Generator.java  测试生成字节码

package com.market.search.test;

import jdk.internal.org.objectweb.asm.ClassReader;
import jdk.internal.org.objectweb.asm.ClassWriter;

import java.io.File;
import java.io.FileOutputStream;
import java.net.URL;
import java.net.URLClassLoader;

/**
 * Created by xiaotian on 2018/5/8.
 */
public class Generator {
    private static AccountGeneratorClassLoader classLoader = new AccountGeneratorClassLoader();
    public static void main(String args[]) throws Exception {
        ClassReader cr = new ClassReader("com.market.search.test.Account");
        ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS|ClassWriter.COMPUTE_FRAMES);
        AddSecurityCheckClassAdapter classAdapter = new AddSecurityCheckClassAdapter(cw);
        cr.accept(classAdapter, ClassReader.SKIP_DEBUG);

        byte[] data = cw.toByteArray();
        //File file = new File("C:\\Users\\xiaotian\\Desktop\\jvm原理\\Account.class");
        File file = new File("D:\\devlop\\workspace.market.new\\market-search-main-BL\\search-service_1.0.2_BR\\target\\classes\\com\\market\\search\\test\\Account.class");
        FileOutputStream fout = new FileOutputStream(file);
        fout.write(data);
        fout.close();

//        Class account = classLoader.defineClassFromClassFile("com.market.search.test.Account", data);
//        Account acc =(Account) account.newInstance();
//        acc.operation();
        Account account = new Account();
        account.operation();


    }
    private static class AccountGeneratorClassLoader extends ClassLoader {
        public Class defineClassFromClassFile(String className, byte[] classFile) throws ClassFormatError {
            return defineClass(className, classFile, 0,classFile.length);
        }
    }
}