jstack的主要作用是生成JVM当前时刻线程的快照（threaddump，即当前进程中所有线程的信息）。可以帮助定位程序中出现的问题，如长时间停顿，CPU占有率过高等问题，也可以看出哪些程序是守护线程，哪些程序是用户线程。
在命令行输出jstack即可看出相关帮助信息：
jstack的基本语法是：jstack [option] <pid>
- 如果jstack后面加了-l参数，那么就会打印一些关于锁的信息；
- pid就是进程的id；
这里运行下面这段代码查看线程快照：
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34package dgb.test.concurrent; import java.lang.management.ManagementFactory; /** * @author Dongguabai * @date 2018/9/2 19:35 */ public class SuspendTest { public static void main(String[] args) throws InterruptedException { ChangeObjectThread c1 = new ChangeObjectThread("thread-1"); ChangeObjectThread c2 = new ChangeObjectThread("thread-2"); c1.start(); c2.start(); // Thread.sleep(1000); c1.resume(); c2.resume(); } public static class ChangeObjectThread extends Thread { public ChangeObjectThread(String name) { super(name); } @Override public void run() { System.out.println("线程【" + getName() + "】正在执行"); Thread.currentThread().suspend(); } } }
查看当前进程的PID（通过Java代码查看pid的方法可以参看：Java程序中获取当前进程的pid，也可以使用 jps 命令）后执行命令：jstack -l <PID>：
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134C:UsersDongguabai>jstack -l 3572 //当前线程快照生成的时间 2018-09-02 20:11:42 //运行的时候的JRE的版本信息，这里是服务器端版本 Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.65-b01 mixed mode): "DestroyJavaVM" #13 prio=5 os_prio=0 tid=0x0000000002a49000 nid=0x4828 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE Locked ownable synchronizers: - None //这是是刚刚我们创建的线程,pri=5是线程的优先级（默认为5，数字越大优先级越高）； //线程类型：线程分为守护线程 (daemon) 和非守护线程 (non-daemon) 两种，通常都是守护线程； //如果使用 java.lang.Thread 类生成一个线程的时候，线程名称为 Thread-(数字) 的形式； //tid是JVM线程的id：JVM内部线程的唯一标识，通过 java.lang.Thread.getId()获取，通常用自增的方式实现； //nid=0x395c系统线程id：对应的系统线程id（Native Thread ID)，可以通过 top 命令进行查看，id是十六进制的形式；结合top H可以快速查看CPU占用过高的线程； "thread-2" #12 prio=5 os_prio=0 tid=0x0000000019543800 nid=0x395c runnable //0x000000001a1af000起始栈地址：线程堆栈调用的其实内存地址； [0x000000001a1af000] //RUNNABLE实线程的状态； java.lang.Thread.State: RUNNABLE //线程的RUNNABLE状态是由这个导致的； at java.lang.Thread.suspend0(Native Method) at java.lang.Thread.suspend(Thread.java:1029) at dgb.test.concurrent.SuspendTest$ChangeObjectThread.run(SuspendTest.java:32) //由于加了-l参数，所以会出现下面的消息；当前线程是否处于同步块内； Locked ownable synchronizers: - None "thread-1" #11 prio=5 os_prio=0 tid=0x0000000019542800 nid=0xcf0 runnable [0x000000001a0af000] java.lang.Thread.State: RUNNABLE at java.lang.Thread.suspend0(Native Method) at java.lang.Thread.suspend(Thread.java:1029) at dgb.test.concurrent.SuspendTest$ChangeObjectThread.run(SuspendTest.java:32) Locked ownable synchronizers: - None "Service Thread" #10 daemon prio=9 os_prio=0 tid=0x00000000194e6800 nid=0x471c runnable [0x0000000000000000] java.lang.Thread.State: RUNNABLE Locked ownable synchronizers: - None "C1 CompilerThread2" #9 daemon prio=9 os_prio=2 tid=0x00000000194cb800 nid=0x4b70 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE Locked ownable synchronizers: - None "C2 CompilerThread1" #8 daemon prio=9 os_prio=2 tid=0x000000001946d000 nid=0x4508 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE Locked ownable synchronizers: - None "C2 CompilerThread0" #7 daemon prio=9 os_prio=2 tid=0x0000000019469000 nid=0x1438 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE Locked ownable synchronizers: - None "Monitor Ctrl-Break" #6 daemon prio=5 os_prio=0 tid=0x00000000193b2000 nid=0x4274 runnable [0x0000000019aae000] java.lang.Thread.State: RUNNABLE at java.net.SocketInputStream.socketRead0(Native Method) at java.net.SocketInputStream.socketRead(SocketInputStream.java:116) at java.net.SocketInputStream.read(SocketInputStream.java:170) at java.net.SocketInputStream.read(SocketInputStream.java:141) at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284) at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326) at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178) - locked <0x00000000d650dfa0> (a java.io.InputStreamReader) at java.io.InputStreamReader.read(InputStreamReader.java:184) at java.io.BufferedReader.fill(BufferedReader.java:161) at java.io.BufferedReader.readLine(BufferedReader.java:324) - locked <0x00000000d650dfa0> (a java.io.InputStreamReader) at java.io.BufferedReader.readLine(BufferedReader.java:389) at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:64) Locked ownable synchronizers: - None "Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x0000000018bf3800 nid=0xe64 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE Locked ownable synchronizers: - None "Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x0000000017850000 nid=0x4a00 runnable [0x0000000000000000] java.lang.Thread.State: RUNNABLE Locked ownable synchronizers: - None "Finalizer" #3 daemon prio=8 os_prio=1 tid=0x0000000002b39800 nid=0xb94 in Object.wait() [0x0000000018bae000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00000000d5f870b8> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143) - locked <0x00000000d5f870b8> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:164) at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:209) Locked ownable synchronizers: - None "Reference Handler" #2 daemon prio=10 os_prio=2 tid=0x0000000017819000 nid=0x3734 in Object.wait() [0x0000000018aaf000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00000000d5f86af8> (a java.lang.ref.Reference$Lock) at java.lang.Object.wait(Object.java:502) at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:157) - locked <0x00000000d5f86af8> (a java.lang.ref.Reference$Lock) Locked ownable synchronizers: - None "VM Thread" os_prio=2 tid=0x0000000017817800 nid=0x4c8 runnable "GC task thread#0 (ParallelGC)" os_prio=0 tid=0x0000000002a5e800 nid=0x3860 runnable "GC task thread#1 (ParallelGC)" os_prio=0 tid=0x0000000002a60000 nid=0x4548 runnable "GC task thread#2 (ParallelGC)" os_prio=0 tid=0x0000000002a62000 nid=0x45d0 runnable "GC task thread#3 (ParallelGC)" os_prio=0 tid=0x0000000002a63800 nid=0x2d1c runnable "VM Periodic Task Thread" os_prio=2 tid=0x000000001959e800 nid=0xaec waiting on condition JNI global references: 19
也可以使用：
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1jstack -l 1111 >1.txt
导出到 1.txt 文件。
最后
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