Java中ByteBuddy动态字节码操作库的使用技术指南

<!-- bytebuddy -->
<dependency>
    <groupId>net.bytebuddy</groupId>
    <artifactId>byte-buddy</artifactId>
    <version>1.14.5</version>
</dependency>
<dependency>
    <groupId>net.bytebuddy</groupId>
    <artifactId>byte-buddy-agent</artifactId>
    <version>1.14.5</version>
</dependency>

import net.bytebuddy.ByteBuddy;
import net.bytebuddy.dynamic.DynamicType;
import net.bytebuddy.implementation.FixedValue;

public class ByteBuddyExample {
    public static void main(String[] args) throws IllegalAccessException, InstantiationException {
        // 使用 ByteBuddy 动态生成一个类
        Class<?> dynamicClass = new ByteBuddy()
                .subclass(Object.class) // 继承自 Object
                .name("com.example.DynamicClass") // 设置类名
                .method(named("toString")) // 覆盖 toString 方法
                .intercept(FixedValue.value("Hello, ByteBuddy!")) // 返回固定值
                .make() // 创建类定义
                .load(ByteBuddyExample.class.getClassLoader()) // 加载到当前类加载器
                .getLoaded();

        // 实例化动态类并调用 toString 方法
        Object instance = dynamicClass.newInstance();
        System.out.println(instance.toString()); // 输出：Hello, ByteBuddy!
    }
}

import net.bytebuddy.agent.ByteBuddyAgent;
import net.bytebuddy.agent.builder.AgentBuilder;
import net.bytebuddy.agent.builder.ResettableClassFileTransformer;
import net.bytebuddy.asm.Advice;
import net.bytebuddy.description.type.TypeDescription;
import net.bytebuddy.dynamic.DynamicType;
import net.bytebuddy.utility.JavaModule;

import java.lang.instrument.Instrumentation;
import java.security.ProtectionDomain;

import static net.bytebuddy.matcher.ElementMatchers.named;

public class ModifyClassExample {
    public static void main(String[] args) {
        Instrumentation install = ByteBuddyAgent.install();// 安装 ByteBuddy 的代理

        ResettableClassFileTransformer sayHello = new AgentBuilder.Default()
                .type(named("com.lm.bytebuddy.ele.ExistingClass")) // 匹配目标类
                .transform(new AgentBuilder.Transformer() {
                               @Override
                               public DynamicType.Builder<?> transform(DynamicType.Builder<?> builder, TypeDescription typeDescription, ClassLoader classLoader, JavaModule javaModule, ProtectionDomain protectionDomain) {
                                   return builder.method(named("sayHello")) // 匹配目标方法
                                           .intercept(Advice.to(SayHelloAdvice.class));
                               }
                           } // 添加切面逻辑
                ).installOnByteBuddyAgent();

        // 调用修改后的方法
        ExistingClass existingClass = new ExistingClass();
        existingClass.sayHello(); // 输出：Modified: Hello, World!
    }

    public static class SayHelloAdvice {
        @Advice.OnMethodEnter
        public static void onEnter() {
            System.out.println("Modified: Hello, World!");
        }
    }
}

class ExistingClass {
    public void sayHello() {
        System.out.println("Hello, World!");
    }
}

import net.bytebuddy.ByteBuddy;
import net.bytebuddy.implementation.InvocationHandlerAdapter;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

public class DynamicProxyExample {
    public static void main(String[] args) throws Exception {
        // 动态生成代理类
        Class<?> proxyClass = new ByteBuddy()
                .subclass(Object.class)
                .implement(Greeting.class) // 实现接口
                .method(named("greet")) // 匹配接口方法
                .intercept(InvocationHandlerAdapter.of(new GreetingHandler())) // 拦截方法调用
                .make()
                .load(DynamicProxyExample.class.getClassLoader())
                .getLoaded();

        // 实例化代理类并调用方法
        Greeting greeting = (Greeting) proxyClass.getConstructor().newInstance();
        System.out.println(greeting.greet("ByteBuddy")); // 输出：Hello, ByteBuddy!
    }
}

public interface Greeting {
    String greet(String name);
}

public class GreetingHandler implements InvocationHandler {
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        return "Hello, " + args[0] + "!";
    }
}