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# 基于JavaAgent的全链路监控四《JVM内存与GC信息》

作者：小傅哥
博客：https://bugstack.cn (opens new window)

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# 案例简述

除了监控java方法的执行耗时，我们还需要获取应用实例的jvm内存与gc信息，以实时把控我们的服务器性能是否在安全范围。监控jvm内存与gc信息是非常重要的，尤其是在大促以及微博火热爆点的时候，我们需要根据监控信息进行扩容，以保证系统稳定。

# 环境准备

  1. IntelliJ IDEA Community Edition
  2. jdk1.8.0_45 64位

# 配置信息（路径相关修改为自己的）

  1. 配置位置：Run/Debug Configurations -> VM options
  2. 配置内容：-javaagent:E:\itstack\GIT\itstack.org\itstack-demo-agent\itstack-demo-agent-04\target\itstack-demo-agent-04-1.0.0-SNAPSHOT.jar=testargs

# 代码示例

itstack-demo-agent-04
├── pom.xml
└── src
    ├── main
    │   ├── java
    │   │   └── org.itstack.demo.agent
    │   │       ├── JvmStack.java
    │   │	    └── MyAgent.java
    │	└── resources
    │       └── META-INF
    │           └── MANIFEST.MF 	
    └── test
         └── java
             └── org.itstack.demo.test
                 └── ApiTest.java
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JvmStack.java

/**
 * 博客：http://itstack.org
 * 论坛：http://bugstack.cn
 * 公众号：bugstack虫洞栈  ｛获取学习源码｝
 * create by fuzhengwei on 2019
 */
class JvmStack {

    private static final long MB = 1048576L;

    static void printMemoryInfo() {
        MemoryMXBean memory = ManagementFactory.getMemoryMXBean();
        MemoryUsage headMemory = memory.getHeapMemoryUsage();

        String info = String.format("\ninit: %s\t max: %s\t used: %s\t committed: %s\t use rate: %s\n",
                headMemory.getInit() / MB + "MB",
                headMemory.getMax() / MB + "MB", headMemory.getUsed() / MB + "MB",
                headMemory.getCommitted() / MB + "MB",
                headMemory.getUsed() * 100 / headMemory.getCommitted() + "%"

        );

        System.out.print(info);

        MemoryUsage nonheadMemory = memory.getNonHeapMemoryUsage();

        info = String.format("init: %s\t max: %s\t used: %s\t committed: %s\t use rate: %s\n",
                nonheadMemory.getInit() / MB + "MB",
                nonheadMemory.getMax() / MB + "MB", nonheadMemory.getUsed() / MB + "MB",
                nonheadMemory.getCommitted() / MB + "MB",
                nonheadMemory.getUsed() * 100 / nonheadMemory.getCommitted() + "%"

        );
        System.out.println(info);

    }

    static void printGCInfo() {
        List<GarbageCollectorMXBean> garbages = ManagementFactory.getGarbageCollectorMXBeans();
        for (GarbageCollectorMXBean garbage : garbages) {
            String info = String.format("name: %s\t count:%s\t took:%s\t pool name:%s",
                    garbage.getName(),
                    garbage.getCollectionCount(),
                    garbage.getCollectionTime(),
                    Arrays.deepToString(garbage.getMemoryPoolNames()));
            System.out.println(info);
        }
    }

}
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MyAgent.java

/**
 * 博客：http://itstack.org
 * 论坛：http://bugstack.cn
 * 公众号：bugstack虫洞栈  ｛获取学习源码｝
 * create by fuzhengwei on 2019
 */
public class MyAgent {

    public static void premain(String agentArgs, Instrumentation inst) {
        System.out.println("this is my agent：" + agentArgs);

        Executors.newScheduledThreadPool(1).scheduleAtFixedRate(new Runnable() {
            public void run() {
                JvmStack.printMemoryInfo();
                JvmStack.printGCInfo();
                System.out.println("===================================================================================================");
            }
        }, 0, 5000, TimeUnit.MILLISECONDS);
    }

}
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MANIFEST.MF

Manifest-Version: 1.0
Premain-Class: org.itstack.demo.agent.MyAgent
Can-Redefine-Classes: true
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ApiTest.java

/**
 * 博客：http://itstack.org
 * 论坛：http://bugstack.cn
 * 公众号：bugstack虫洞栈  ｛获取学习源码｝
 * create by fuzhengwei on 2019
 * -javaagent:E:\itstack\GIT\itstack.org\itstack-demo-agent\itstack-demo-agent-04\target\itstack-demo-agent-04-1.0.0-SNAPSHOT.jar=testargs
 */
public class ApiTest {

    public static void main(String[] args) {
        while (true) {
            List<Object> list = new LinkedList<>();
            list.add("嗨！JavaAgent");
            list.add("嗨！JavaAgent");
            list.add("嗨！JavaAgent");
        }
    }

}
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# 测试结果

this is my agent：testargs

init: 192MB	 max: 2708MB	 used: 5MB	 committed: 184MB	 use rate: 3%
init: 2MB	 max: 0MB	 used: 5MB	 committed: 7MB	 use rate: 75%

name: PS Scavenge	 count:1	 took:2	 pool name:[PS Eden Space, PS Survivor Space]
name: PS MarkSweep	 count:0	 took:0	 pool name:[PS Eden Space, PS Survivor Space, PS Old Gen]
===================================================================================================

init: 192MB	 max: 2708MB	 used: 249MB	 committed: 624MB	 use rate: 39%
init: 2MB	 max: 0MB	 used: 6MB	 committed: 7MB	 use rate: 78%

name: PS Scavenge	 count:32	 took:98	 pool name:[PS Eden Space, PS Survivor Space]
name: PS MarkSweep	 count:0	 took:0	 pool name:[PS Eden Space, PS Survivor Space, PS Old Gen]
===================================================================================================

Process finished with exit code -1
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