Java Agent探针技术详解示例

package com.hiwei;
import java.lang.instrument.Instrumentation;
public class DemoAgent {
    /**
     * 该方法在main方法之前运行
     */
    public static void premain(String arg, Instrumentation instrumentation) {
        System.out.println("执行premain方法");
    }
}

      <plugins>
        <plugin>
          <artifactId>maven-shade-plugin</artifactId>
          <executions>
            <execution>
              <phase>package</phase>
              <goals>
                <goal>shade</goal>
              </goals>
              <configuration>
                <shadedArtifactAttached>false</shadedArtifactAttached>
                <createDependencyReducedPom>true</createDependencyReducedPom>
                <createSourcesJar>true</createSourcesJar>
                <shadeSourcesContent>true</shadeSourcesContent>
                <transformers>
                  <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                    <manifestEntries>
                      <!-- 包含premain方法的类 -->
                      <Premain-Class>${premain.class}</Premain-Class>
                      <!-- 对目标类字节码操作权限 -->
                      <Can-Redefine-Classes>${can.redefine.classes}</Can-Redefine-Classes>
                      <!-- 对目标类字节码操作权限 -->
                      <Can-Retransform-Classes>${can.retransform.classes}</Can-Retransform-Classes>
                    </manifestEntries>
                  </transformer>
                </transformers>
              </configuration>
            </execution>
          </executions>
        </plugin>
      </plugins>

package com.hiwe.demo.cache;
public class TestCache {
    public static void main(String[] args) {
        System.out.println("测试类");
    }
}

package com.hiwei.test.agent;
import com.hiwei.test.agent.utils.StringUtils;
import java.io.*;
import java.lang.instrument.Instrumentation;
import java.nio.charset.StandardCharsets;
public class DemoAgent {
    /**
     * 该方法在main方法之前运行
     * @param arg 文件路径
     * @param instrumentation
     */
    public static void premain(String arg, Instrumentation instrumentation) {
        //读取mock文件
        try {
            FileInputStream file = new FileInputStream(arg);
            BufferedReader rd = new BufferedReader(new InputStreamReader(file, StandardCharsets.UTF_8));
            String configStr = readToString(rd);
            if(StringUtils.isNotEmpty(configStr)){
                MockConfig.parseConfig(configStr);
                instrumentation.addTransformer(new DemoTransformer());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    private static String readToString(Reader rd) throws IOException {
        StringBuilder sb = new StringBuilder();
        int i;
        while ((i = rd.read()) != -1) {
            sb.append((char) i);
        }
        return sb.toString();
    }
}

package com.hiwei.test.agent;
import com.alibaba.fastjson.JSONObject;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
public class MockConfig {
    private static Map<String, Map<String, Object>> mockData = new HashMap<>();
    public static void parseConfig(String configStr) {
        JSONObject config = JSONObject.parseObject(configStr);
        Set<String> classNameSet = config.keySet();
        classNameSet.forEach(className -> {
            Map<String, Object> methodMock = new HashMap<>();
            JSONObject methods = config.getJSONObject(className);
            Set<String> mSet = methods.keySet();
            mSet.forEach(m -> {
                methodMock.put(m, methods.get(m));
            });
            mockData.put(className, methodMock);
        });
    }
    public static boolean isMock(String className) {
        return !(mockData.get(className) == null);
    }
    public static Object getMockData(String className, String methodName) {
        Map<String, Object> stringJSONObjectMap = mockData.get(className);
        if (stringJSONObjectMap != null) {
            return stringJSONObjectMap.get(methodName);
        }
        return null;
    }
}

package com.hiwei.test.agent;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;
import java.lang.instrument.ClassFileTransformer;
import java.security.ProtectionDomain;
public class DemoTransformer implements ClassFileTransformer {
    @Override
    public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) {
        ClassPool classPool = ClassPool.getDefault();
        String realClassName = className.replaceAll("/", ".");
        //获取类
        if(MockConfig.isMock(realClassName)){
            try {
                CtClass ctClass = classPool.get(realClassName);
                CtMethod[] declaredMethods = ctClass.getDeclaredMethods();
                for (CtMethod m : declaredMethods) {
                    String mName = m.getName();
                    Object mockData = MockConfig.getMockData(realClassName, mName);
                    if(mockData!=null){
                        String mock = String.format("if(true){%s}", mockData);
                        m.insertBefore(mock);
                    }
                }
                return ctClass.toBytecode();
            } catch (Throwable e) {
                e.printStackTrace();
            }
        }
        return classfileBuffer;
    }
}