java agent开发

java agent介绍

java agent是jvm插件或者叫作代理，她是运行在main方法以前，她内定的方法名称叫premain。

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java agent 概述

接下来咱们进行开发

1. 实现premain方法

   package org.xxz;
   
   public class AgentMain {
     public static void premain(String args, Instrumentation inst) {
       System.out.println('hello java agent');
     }
   }

   上面的这段代码就完成了java agent的第一步了

2. 打包

   这里咱们使用maven的方式进行打包，请看下面的配置文件

   <build>
             <finalName>java-agent</finalName>
           <plugins>
               <plugin>
                   <groupId>org.apache.maven.plugins</groupId>
                   <artifactId>maven-compiler-plugin</artifactId>
                   <configuration>
                       <source>1.8</source>
                       <target>1.8</target>
                       <encoding>utf-8</encoding>
                   </configuration>
               </plugin>
               <plugin>
                   <groupId>org.apache.maven.plugins</groupId>
                   <artifactId>maven-assembly-plugin</artifactId>
                   <version>3.0.0</version>
                   <configuration>
                       <archive>
                           <manifest>
                               <addClasspath>true</addClasspath>
                           </manifest>
                           <manifestEntries>
                               <Premain-Class>org.xxz.AgentMain</Premain-Class>
                           </manifestEntries>
                       </archive>
                       <descriptorRefs>
                           <descriptorRef>jar-with-dependencies</descriptorRef>
                       </descriptorRefs>
                   </configuration>
                   <executions>
                       <execution>
                           <id>make-assembly</id>
                           <phase>package</phase>
                           <goals>
                               <goal>single</goal>
                           </goals>
                       </execution>
                   </executions>
               </plugin>
           </plugins>
       </build>

3. 使用java agent

   新建一个maven工程，打包而后运行

   java -jar demo.jar -javaagent:/apps/java-agent.jar

   执行上面的运行命令后，在咱们控制台输出时就会看到hello java agent的字样哦！！！

看到这里就结束了吗？没有哦，咱们来看一个小例子。。。。。。。

新建maven工程

java-agent
--src
    --main
        --java
            --org.xxz
                --AgentMain.java
                --TimeInterceptor.java
                --TraceTime.java
        --resource
    --test
--pom.xml

首先看看咱们的pom.xml是如何配置的

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.xxz</groupId>
    <artifactId>java-agent</artifactId>
    <version>1.0</version>

    <properties>
        <bytebuddy.version>1.8.0</bytebuddy.version>
        <slf4j.version>1.7.25</slf4j.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>net.bytebuddy</groupId>
            <artifactId>byte-buddy</artifactId>
            <version>${bytebuddy.version}</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>${slf4j.version}</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <encoding>utf-8</encoding>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-assembly-plugin</artifactId>
                <version>3.0.0</version>
                <configuration>
                    <archive>
                        <manifest>
                            <addClasspath>true</addClasspath>
                        </manifest>
                        <manifestEntries>
                            <Premain-Class>org.xxz.AgentMain</Premain-Class>
                        </manifestEntries>
                    </archive>
                    <descriptorRefs>
                        <descriptorRef>jar-with-dependencies</descriptorRef>
                    </descriptorRefs>
                </configuration>
                <executions>
                    <execution>
                        <id>make-assembly</id>
                        <phase>package</phase>
                        <goals>
                            <goal>single</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

这里咱们使用了bytebuddy，不懂得看官能够上官方网站瞧瞧http://bytebuddy.net/

再来看看咱们得AgentMain.java

package org.xxz;

import net.bytebuddy.agent.builder.AgentBuilder;
import net.bytebuddy.description.method.MethodDescription;
import net.bytebuddy.description.type.TypeDescription;
import net.bytebuddy.dynamic.DynamicType;
import net.bytebuddy.implementation.MethodDelegation;
import net.bytebuddy.matcher.ElementMatchers;
import net.bytebuddy.utility.JavaModule;

import java.lang.instrument.Instrumentation;

/**
 * @author tt
 */
public class AgentMain {

    public static void premain(String args, Instrumentation inst) {

        AgentBuilder.Transformer transformer = new AgentBuilder.Transformer() {
            @Override
            public DynamicType.Builder<?> transform(DynamicType.Builder<?> builder,
                                                    TypeDescription typeDescription,
                                                    ClassLoader classLoader,
                                                    JavaModule javaModule) {
                return builder
                        .method(ElementMatchers.any()) // 拦截任意方法
                        .intercept(MethodDelegation.to(TimeInterceptor.class)); // 委托
            }
        };

        AgentBuilder.Listener listener = new AgentBuilder.Listener() {
            @Override
            public void onDiscovery(String s, ClassLoader classLoader, JavaModule javaModule, boolean b) {

            }

            @Override
            public void onTransformation(TypeDescription typeDescription, ClassLoader classLoader, JavaModule javaModule, boolean b, DynamicType dynamicType) {

            }

            @Override
            public void onIgnored(TypeDescription typeDescription, ClassLoader classLoader, JavaModule javaModule, boolean b) {

            }

            @Override
            public void onError(String s, ClassLoader classLoader, JavaModule javaModule, boolean b, Throwable throwable) {

            }

            @Override
            public void onComplete(String s, ClassLoader classLoader, JavaModule javaModule, boolean b) {

            }
        };

        new AgentBuilder
                .Default()
                .type(ElementMatchers.nameStartsWith("org.xxz"))// 指定须要拦截的类
                .transform(transformer)
                .with(listener)
                .installOn(inst);

    }

}

这里咱们看看咱们得TimeInterceptor.java

package org.xxz;

import net.bytebuddy.implementation.bind.annotation.Origin;
import net.bytebuddy.implementation.bind.annotation.RuntimeType;
import net.bytebuddy.implementation.bind.annotation.SuperCall;

import java.lang.reflect.Method;
import java.util.concurrent.Callable;

/**
 * @author tt
 */
public class TimeInterceptor {

    @RuntimeType
    public static Object interceptor(@Origin Class clazz,
                                   @Origin Method method,
                                   @SuperCall Callable<?> callable) throws Exception {

        TraceTime traceTime = method.getAnnotation(TraceTime.class);

        if (traceTime == null) {
            return callable.call();
        }

        long start = System.currentTimeMillis();
        try {
            // 原有函数执行
            return callable.call();
        } finally {
            System.out.println(clazz.getSimpleName() + "#" + method.getName() + " cost " + (System.currentTimeMillis() - start) + "ms");
        }
    }

}

最后就是咱们得注解了TraceTime.java

package org.xxz;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * @author tt
 */
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface TraceTime {
}

到这里咱们得java-agent就开发完成了。。。。。是否是很简单啊。。。。

接下来，咱们看看使用方式咯。。。。。

java-agent-test
--src
    --main
        --java
            --org.xxz
                --test
                    --AgentMainTest.java
                    --Demo.java
                --TraceTime.java
        --resource
    --test
--pom.xml

依旧先看咱们得pom文件

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.xxz</groupId>
    <artifactId>java-agent-test</artifactId>
    <version>1.0</version>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <encoding>utf-8</encoding>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

这里的pom文件上面的简单多了。

看看咱们的测试类AgentMainTest.java

package org.xxz.test;
/**
 * @author tt
 */
public class AgentMainTest {

    public static void main(String[] args) throws Exception {
        Demo demo = new Demo();
        demo.print("agent");
    }
}

看看咱们的Demo.java

package org.xxz.test;

import org.xxz.TraceTime;

/**
 * @author tt
 */
public class Demo {

    @TraceTime
    public void print(String string) throws InterruptedException {
        Thread.sleep(100L);
        System.out.println("hello " + string);
    }
}

这里还少了一个TraceTime.java，把上面的拷贝过来哦。。。。注意包的结构要同样哦。。。。。

上面介绍了如何命令行使用java-agent.jar，这里咱们介绍如何再IDE中使用，要上图了哦。。。。。

好了，今天的文章到这里就结束了。。。

最后还来一张运行结果吧。。。。

原文地址：https://blog.uyiplus.com/2018/java-agent-01/