使用java agent修改字节码，并在springboot启动时自动生效

        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agent jar到本地设置启动参数，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>0.0.2</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

我们调整下代码，new HttpGet("http://zhihu.com")，换一个请求地址，然后发起请求

执行了httpClient的原始逻辑，请求zhihu.com拿到了响应。

简单试验就到这里了，其他用法可以按照github上readme指引试验一下。觉的这个小工具不错小伙伴可以点个star~