java agent介绍
java agent是jvm插件或者叫做代理，她是运行在main方法之前，她内定的方法名称叫premain。
java agent 概述
https://ws1.sinaimg.cn/large/afc434bdly1fplw4dc0lzj20j70ch74u.jpg
接下来我们进行开发
-
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
-
打包
这里我们使用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> <version>3.8.1</version> <configuration> <source>${maven.compiler.source}</source> <target>${maven.compiler.target}</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> <addDefaultImplementationEntries>true</addDefaultImplementationEntries> <addDefaultSpecificationEntries>true</addDefaultSpecificationEntries> </manifest> <manifestEntries> <Premain-Class>org.xxz.AgentMain</Premain-Class> <Can-Redefine-Classes>true</Can-Redefine-Classes> <Can-Retransform-Classes>true</Can-Retransform-Classes> </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> -
使用java agent
新建一个maven工程，打包然后运行
java -jar demo.jar -javaagent:/apps/java-agent.jar执行上面的运行命令后，在我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，我们来看一个小例子。。。。。。。
新建maven工程
java-agent
--src
--main
--java
--org.xxz
--AgentMain.java
--TimeInterceptor.java
--TraceTime.java
--resource
--test
--pom.xml
首先看看我们的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>
这里我们使用了bytebuddy，不懂得看官可以上官方网站瞧瞧http://bytebuddy.net/
再来看看我们得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"))// 指定需要拦截的类
.transform(transformer)
.with(listener)
.installOn(inst);
}
}
这里我们看看我们得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,
@This Object target,
@Origin Method method,
@AllArguments Object[] args,
@Super Object delegate,
@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");
}
}
}
最后就是我们得注解了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 {
}
到这里我们得java-agent就开发完成了。。。。。是不是很简单啊。。。。
接下来，我们看看使用方式咯。。。。。
java-agent-test
--src
--main
--java
--org.xxz
--test
--AgentMainTest.java
--Demo.java
--TraceTime.java
--resource
--test
--pom.xml
依旧先看我们得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。
看看我们的测试类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");
}
}
看看我们的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。。。。注意包的结构要一样哦。。。。。
上面介绍了如何命令行使用java-agent.jar，这里我们介绍如何再IDE中使用，要上图了哦。。。。。
image
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。。。。
image
