如何使用java agent修改字节码并在springboot启动时自动生效_Java

在java开发的过程中，我们经常遇到一些需要对某个方法做切面的需求，通常做法是使用spring提供的aop功能，对方法做切面，例如方法出入参打印，接口mock等等。但很多时候，需要切面的方法是非spring容器管理的类，例如需要对okhttp、apachehttpclient请求做mock，判断http请求的参数、url为某个值时，返回测试结果，例如请求参数中包含username=tester，返回code=200。这种使用可以使用java agent，通过java agent修改类的字节码，实现对非spring容器管理对象的aop处理。但是使用javaagent后，启动时需要添加参数-javaagent:xxx.jar，使用方还需要下载对象的jar到本地，使用起来略显麻烦。proxy-sdk就是为了解决这个问题，通过maven、gradle依赖工具直接引入jar依赖即可，然后添加你的切面逻辑，springboot服务启动即可生效。

github - yingxinguo95/proxy-agent: java agent with springboot

按照github上的readme的指引我们引入jar包，从maven的中央仓库下载依赖。

<dependency>
  <groupid>io.github.yingxinguo95</groupid>
  <artifactid>proxy-sdk</artifactid>
  <version>0.0.1</version>
  <!-- 0.0.1拉取不到可以试试0.0.1-release -->
  <!--<version>0.0.1-release</version>-->
</dependency>

配置需要代理方法配置和定义我们自己的需要重写逻辑，例如我们需要apache httpclient的请求方法，实现接口mock，判断当请求某个地址时返回测试数据，而不是真的请求对方。

例如以下代码，前置重写httpclient的execute方法，当请求baidu.com时就返回测试的json数据{\"code\":\"200\", \"msg\":\"mock data\"}

import io.github.proxy.annotation.proxyrecodecfg;
import io.github.proxy.annotation.recodetype;
import io.github.proxy.service.proxyrecode;
import lombok.sneakythrows;
import org.apache.http.*;
import org.apache.http.client.methods.closeablehttpresponse;
import org.apache.http.client.methods.httpentityenclosingrequestbase;
import org.apache.http.client.methods.httpurirequest;
import org.apache.http.entity.basichttpentity;
import org.apache.http.message.basichttpresponse;
import org.apache.http.message.basicstatusline;
import org.apache.http.protocol.httpcontext;
import org.apache.http.util.entityutils;
import org.springframework.stereotype.component;
import java.io.bytearrayinputstream;
import java.io.ioexception;
import java.io.inputstream;
import java.nio.charset.standardcharsets;
import java.util.locale;
/**
 * 重写apachehttp请求处理逻辑，实现mock功能
 */
@component
public class mockapachehttprecoder implements proxyrecode {
    @sneakythrows
    @proxyrecodecfg(proxyclassname="org.apache.http.impl.client.closeablehttpclient", method="execute", type = recodetype.before)
    public static closeablehttpresponse executeproxy1(httpurirequest request, httpcontext context) {
        string path = request.geturi().tostring();
        if (request instanceof httpentityenclosingrequestbase) {
            //post请求读取body
            httpentity entity = ((httpentityenclosingrequestbase)request).getentity();
            if (entity == null) {
                return null;
            }
            string reqbody = entityutils.tostring(entity, standardcharsets.utf_8);
        }
        if (path.startswith("http://baidu.com")) {
            return buildmockresponse("{\"code\":\"200\", \"msg\":\"mock data\"}", null);
        }
        return null;
    }
    @sneakythrows
    @proxyrecodecfg(proxyclassname="org.apache.http.impl.client.closeablehttpclient", method="execute", type = recodetype.before)
    public static closeablehttpresponse executeproxy2(httphost target, httprequest request, httpcontext context) {
        string path = request.getrequestline().geturi();
        if (request instanceof httpentityenclosingrequestbase) {
            //post请求读取body
            httpentity entity = ((httpentityenclosingrequestbase)request).getentity();
            if (entity == null) {
                return null;
            }
            string reqbody = entityutils.tostring(entity, standardcharsets.utf_8);
        }
        if (path.startswith("http://baidu.com")) {
            return buildmockresponse("{\"code\":\"200\", \"msg\":\"mock返回\"}", null);
        }
        return null;
    }
    public static closeablehttpresponse buildmockresponse(string mockvalue, header[] headers) {
        protocolversion protocolversion = new protocolversion("http", 1, 1);
        string reasonphrase = "ok";
        statusline statusline = new basicstatusline(protocolversion, httpstatus.sc_ok, reasonphrase);
        mockcloseablehttpresponse mockresponse = new mockcloseablehttpresponse(statusline);
        basichttpentity entity = new basichttpentity();
        inputstream inputstream = new bytearrayinputstream(mockvalue.getbytes());
        entity.setcontent(inputstream);
        entity.setcontentlength(mockvalue.length());
        entity.setchunked(false);
        mockresponse.setentity(entity);
        if (headers != null) {
            mockresponse.setheaders(headers);
        }
        return mockresponse;
    }
    public static class mockcloseablehttpresponse extends basichttpresponse implements closeablehttpresponse {
        public mockcloseablehttpresponse(statusline statusline, reasonphrasecatalog catalog, locale locale) {
            super(statusline, catalog, locale);
        }
        public mockcloseablehttpresponse(statusline statusline) {
            super(statusline);
        }
        public mockcloseablehttpresponse(protocolversion ver, int code, string reason) {
            super(ver, code, reason);
        }
        @override
        public void close() throws ioexception {
        }
    }
}

我们在springboot启动后请求试试

@springbootapplication
public class appmain {
    @sneakythrows
    public static void main(string[] args) {
        springapplication.run(appmain.class, args);
        //创建httpclient对象
        closeablehttpclient httpclient = httpclients.createdefault();
        //创建请求对象
        httpget httpget = new httpget("http://baidu.com");
        //发送请求，请求响应结果
        closeablehttpresponse response = httpclient.execute(httpget);
        //获取服务器返回的状态码
        int statuscode = response.getstatusline().getstatuscode();
        system.out.println(">>>>>>>>>服务端返回成功的状态码为："+statuscode);
        httpentity entity = response.getentity();
        string body = entityutils.tostring(entity);
        system.out.println(">>>>>>>>>服务端返回的数据为："+body);
        //关闭资源
        response.close();
        httpclient.close();
    }
}

启动服务，在控制台可以看到打印了对org.apache.http.impl.client.closeablehttpclient类做字节码重写

[attach listener] info i.g.p.transformer.recodertransformer -[proxy-agent] rewrite class:[org.apache.http.impl.client.closeablehttpclient]
[attach listener] info io.github.proxy.agentmain -[proxy-agent] redefine loaded class complete, cost:171ms

springboot启动后请求baidu.com，得到结果，顺利得到了我们需要的测试数据