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1. JDK常用的工具--JDK8
| 工具名称 | 用途 |
|---|---|
| jps | 列出已装载的JVM --- 常用 |
| jstack | 打印线程堆栈信息 -- 常用 |
| jstat | JVM监控统计信息 -- 常用 |
| jmap | 打印JVM堆内对象情况 -- 常用 |
| jinfo | 输出JVM配置信息-- 常用 |
| jconsole | GUI监控工具 |
| jvisualvm | GUI监控工具 |
| jhat | 堆离线分析工具 |
| jdb | java进程调试工具 |
| jstatd | 远程JVM监控统计信息 |
2. jps命令
下面是我在自己Linux服务器上运行的(服务器上面跑了一个Tomcat)
[root@iZwz9jcjzd6wfh44nnnsv4Z ~]# jps
25057 Bootstrap
25116 Jps
3. jstack命令
[root@iZwz9jcjzd6wfh44nnnsv4Z ~]# jstack --help
Usage:
jstack [-l] <pid>
(to connect to running process)
jstack -F [-m] [-l] <pid>
(to connect to a hung process)
jstack [-m] [-l] <executable> <core>
(to connect to a core file)
jstack [-m] [-l] [server_id@]<remote server IP or hostname>
(to connect to a remote debug server)
Options:
-F to force a thread dump. Use when jstack <pid> does not respond (process is hung)
-m to print both java and native frames (mixed mode)
-l long listing. Prints additional information about locks
-h or -help to print this help message
上面是使用的说明，下面来看一下实际的使用的打印情况
[root@iZwz9jcjzd6wfh44nnnsv4Z ~]# jstack -l 25057
2019-03-17 10:25:00
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.131-b11 mixed mode):
"Attach Listener" #44 daemon prio=9 os_prio=0 tid=0x00007f3738001800 nid=0x6253 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
Locked ownable synchronizers:
- None
"ajp-nio-8009-Acceptor-0" #42 daemon prio=5 os_prio=0 tid=0x00007f376c6ff800 nid=0x620e runnable [0x00007f373c4bf000]
java.lang.Thread.State: RUNNABLE
at sun.nio.ch.ServerSocketChannelImpl.accept0(Native Method)
at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:422)
at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:250)
- locked <0x00000000c5a99fc8> (a java.lang.Object)
at org.apache.tomcat.util.net.NioEndpoint.serverSocketAccept(NioEndpoint.java:448)
at org.apache.tomcat.util.net.NioEndpoint.serverSocketAccept(NioEndpoint.java:70)
at org.apache.tomcat.util.net.Acceptor.run(Acceptor.java:95)
at java.lang.Thread.run(Thread.java:748)
Locked ownable synchronizers:
- None
"ajp-nio-8009-ClientPoller-1" #41 daemon prio=5 os_prio=0 tid=0x00007f376c6fd800 nid=0x620d runnable [0x00007f373c5c0000]
java.lang.Thread.State: RUNNABLE
at sun.nio.ch.EPollArrayWrapper.epollWait(Native Method)
at sun.nio.ch.EPollArrayWrapper.poll(EPollArrayWrapper.java:269)
at sun.nio.ch.EPollSelectorImpl.doSelect(EPollSelectorImpl.java:93)
at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
- locked <0x00000000f4475350> (a sun.nio.ch.Util$3)
- locked <0x00000000f4475340> (a java.util.Collections$UnmodifiableSet)
- locked <0x00000000f4475208> (a sun.nio.ch.EPollSelectorImpl)
at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
at org.apache.tomcat.util.net.NioEndpoint$Poller.run(NioEndpoint.java:743)
at java.lang.Thread.run(Thread.java:748)
Locked ownable synchronizers:
- None
jstack 可以用来定位死锁、死循环、线程阻塞等问题
4. jstat命令
[root@iZwz9jcjzd6wfh44nnnsv4Z ~]# jstat -help
Usage: jstat -help|-options
jstat -<option> [-t] [-h<lines>] <vmid> [<interval> [<count>]]
Definitions:
<option> An option reported by the -options option
<vmid> Virtual Machine Identifier. A vmid takes the following form:
<lvmid>[@<hostname>[:<port>]]
Where <lvmid> is the local vm identifier for the target
Java virtual machine, typically a process id; <hostname> is
the name of the host running the target Java virtual machine;
and <port> is the port number for the rmiregistry on the
target host. See the jvmstat documentation for a more complete
description of the Virtual Machine Identifier.
<lines> Number of samples between header lines.
<interval> Sampling interval. The following forms are allowed:
<n>["ms"|"s"]
Where <n> is an integer and the suffix specifies the units as
milliseconds("ms") or seconds("s"). The default units are "ms".
<count> Number of samples to take before terminating.
-J<flag> Pass <flag> directly to the runtime system.
[root@iZwz9jcjzd6wfh44nnnsv4Z ~]# jstat -options
-class
-compiler
-gc
-gccapacity
-gccause
-gcmetacapacity
-gcnew
-gcnewcapacity
-gcold
-gcoldcapacity
-gcutil
-printcompilation
使用例子：
[root@iZwz9jcjzd6wfh44nnnsv4Z ~]# jstat -gc 25057
S0C S1C S0U S1U EC EU OC OU MC MU CCSC CCSU YGC YGCT FGC FGCT GCT
9216.0 9216.0 1248.1 0.0 121856.0 79308.8 40960.0 15612.7 18560.0 18067.8 2176.0 1998.5 8 0.089 0 0.000 0.089
5. jmap命令
[root@iZwz9jcjzd6wfh44nnnsv4Z ~]# jmap
Usage:
jmap [option] <pid>
(to connect to running process)
jmap [option] <executable <core>
(to connect to a core file)
jmap [option] [server_id@]<remote server IP or hostname>
(to connect to remote debug server)
where <option> is one of:
<none> to print same info as Solaris pmap
-heap to print java heap summary
-histo[:live] to print histogram of java object heap; if the "live"
suboption is specified, only count live objects
-clstats to print class loader statistics
-finalizerinfo to print information on objects awaiting finalization
-dump:<dump-options> to dump java heap in hprof binary format
dump-options:
live dump only live objects; if not specified,
all objects in the heap are dumped.
format=b binary format
file=<file> dump heap to <file>
Example: jmap -dump:live,format=b,file=heap.bin <pid>
-F force. Use with -dump:<dump-options> <pid> or -histo
to force a heap dump or histogram when <pid> does not
respond. The "live" suboption is not supported
in this mode.
-h | -help to print this help message
-J<flag> to pass <flag> directly to the runtime system
看一下使用
[root@iZwz9jcjzd6wfh44nnnsv4Z ~]# jmap -heap 25057
Attaching to process ID 25057, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.131-b11
using thread-local object allocation.
Parallel GC with 2 thread(s)
Heap Configuration:
MinHeapFreeRatio = 0
MaxHeapFreeRatio = 100
MaxHeapSize = 994050048 (948.0MB)
NewSize = 20971520 (20.0MB)
MaxNewSize = 331350016 (316.0MB)
OldSize = 41943040 (40.0MB)
NewRatio = 2
SurvivorRatio = 8
MetaspaceSize = 21807104 (20.796875MB)
CompressedClassSpaceSize = 1073741824 (1024.0MB)
MaxMetaspaceSize = 17592186044415 MB
G1HeapRegionSize = 0 (0.0MB)
Heap Usage:
PS Young Generation
Eden Space:
capacity = 124780544 (119.0MB)
used = 84413336 (80.5028305053711MB)
free = 40367208 (38.497169494628906MB)
67.64943739947151% used
From Space:
capacity = 9437184 (9.0MB)
used = 1278016 (1.21881103515625MB)
free = 8159168 (7.78118896484375MB)
13.542344835069445% used
To Space:
capacity = 9437184 (9.0MB)
used = 0 (0.0MB)
free = 9437184 (9.0MB)
0.0% used
PS Old Generation
capacity = 41943040 (40.0MB)
used = 15987400 (15.246772766113281MB)
free = 25955640 (24.75322723388672MB)
38.1169319152832% used
12505 interned Strings occupying 1754736 bytes.
6 总结
上面是一些常用的命令用来查看JVM在运行过程中的一些状态和查询问题。除了使用Java自带的命令还可以借助一些工具，例如：
以上工具都能提供更好的分析，命令可以在简单问题排查提供便利不需要进行下载其他的工具。
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