虚拟机工具

jps

java process status

C:\Users\auas>jps
14548                  //本地虚拟机唯一ID
8840 Jps

C:\Users\auas>jps -m   //运行时传入主类的参数
C:\Users\auas>jps -V   //虚拟机参数
C:\Users\auas>jps -L   //运行的主类全名或jar包名

jstat

监控 类装载，内存，垃圾收集，jit编译的信息

C:\Users\auas>jps
14548
13288 Main
15224 Launcher
16888 Jps

C:\Users\auas>jstat -gcutil 13288
  S0     S1     E      O      M     CCS    YGC     YGCT    FGC    FGCT    CGC    CGCT     GCT
  0.00   0.00  16.67   0.00      -      -      0    0.000     0    0.000     0    0.000    0.000

C:\Users\auas>jstat -gcutil 13288 1000 10   //每个1秒输出一个，总共10个
  S0     S1     E      O      M     CCS    YGC     YGCT    FGC    FGCT    CGC    CGCT     GCT
  0.00   0.00  16.67   0.00      -      -      0    0.000     0    0.000     0    0.000    0.000
  0.00   0.00  16.67   0.00      -      -      0    0.000     0    0.000     0    0.000    0.000
  0.00   0.00  16.67   0.00      -      -      0    0.000     0    0.000     0    0.000    0.000
  0.00   0.00  16.67   0.00      -      -      0    0.000     0    0.000     0    0.000    0.000
  0.00   0.00  16.67   0.00      -      -      0    0.000     0    0.000     0    0.000    0.000
  0.00   0.00  16.67   0.00      -      -      0    0.000     0    0.000     0    0.000    0.000
  0.00   0.00  16.67   0.00      -      -      0    0.000     0    0.000     0    0.000    0.000
  0.00   0.00  16.67   0.00      -      -      0    0.000     0    0.000     0    0.000    0.000
  0.00   0.00  16.67   0.00      -      -      0    0.000     0    0.000     0    0.000    0.000
  0.00   0.00  16.67   0.00      -      -      0    0.000     0    0.000     0    0.000    0.000

jinfo

实时查看和调整虚拟机的各项参数

C:\Users\auas>jinfo -flag UseSerialGC 15224
-XX:-UseSerialGC                      // + 启用 ；- 禁用

C:\Users\auas>jinfo
Usage:
    jinfo <option> <pid>
       (to connect to a running process)

where <option> is one of:
    -flag <name>         to print the value of the named VM flag
    -flag [+|-]<name>    to enable or disable the named VM flag
    -flag <name>=<value> to set the named VM flag to the given value
    -flags               to print VM flags
    -sysprops            to print Java system properties
    <no option>          to print both VM flags and system properties
    -? | -h | --help | -help to print this help message

jmap

jmap（Memory Map for Java）命令用于生成堆转储快照。

如果不使用jmap命令，要想获取Java堆转储，可以使用“-XX:+HeapDumpOnOutOfMemoryError”参数，可以让虚拟机在OOM异常出现之后自动生成dump文件，Linux命令下可以通过kill -3发送进程退出信号也能拿到dump文件。

C:\Users\auas>jmap -dump:format=b,file=d:\a.bin 14548   //获取14548 存储到d:\a.bin中
Heap dump file created

C:\Users\auas>jmap -histo 15224     //查看信息

jhat

C:\Users\auas>jhat d:\a.bin    //查看 d:\a.bin 文件

jhat在分析完成后，使用HTTP服务器展示其分析结果。访问地址为http://<IP>:7000，可以看到类似如下的内容：

#报错！

jstack

C:\Windows\system32>jstack 15224

类似

package MyDemo.work.test10;

import java.util.Map;

public class Main {
    public static void main(String[] args) {

        Map<Thread, StackTraceElement[]> m = Thread.getAllStackTraces();
        for (Map.Entry<Thread, StackTraceElement[]> en : m.entrySet()) {
            Thread t = en.getKey();
            StackTraceElement[] v = en.getValue();

            System.out.println("Thread name is" +t.getName());
            for (StackTraceElement s : v) {
                System.out.println("\t" + s.toString());
            }

        }
    }
}

jconsole

内存监控

运行该代码

package MyDemo.work.test2;

import java.util.ArrayList;
import java.util.List;

public class JConsoleTest {
    public byte[] b1 = new byte[128 * 1024];

//    public  JConsoleTest() {
//        byte[] b1 = new byte[128 * 1024];
//    }

    public static void main(String[] args) {

        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("start...");
        fill(1000);
    }

    private static void fill(int n) {
        List<JConsoleTest> jlist = new ArrayList<>();

        for (int i = 0; i < n; i++) {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            jlist.add(new JConsoleTest());
        }
    }
}

C:\Windows\system32>jconsole

线程监控

package MyDemo.work.testc;

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {

        //阻塞
        Scanner sc = new Scanner(System.in);
        sc.next();

        new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {

                }
            }
        }, "while true").start();
        sc.next();
        testWait(new Object());
    }

    private static void testWait(Object obj) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                synchronized (obj) {
                    try {
                        wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }, "wait").start();
    }

}

在第10行，等待输入

输入：111

死锁

代码

package MyDemo.work.testd;

public class DeadLock implements Runnable{
    private Object obj1;
    private Object obj2;

    public DeadLock(Object obj1, Object obj2) {
        this.obj1 = obj1;
        this.obj2 = obj2;
    }

    @Override
    public void run() {
        synchronized (obj1){     // ti obj1   ;  t2 obj2
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            synchronized (obj2){
                System.out.println("hello");
            }
        }

    }

}

package MyDemo.work.testd;

public class Main {

    public static void main(String[] args) {

        Object obj1 = new Object();
        Object obj2 = new Object();

        new Thread(new DeadLock(obj1,obj2)).start();
        new Thread(new DeadLock(obj2,obj1)).start();

    }
}

本文地址：https://blog.csdn.net/cl66666666/article/details/112056361