命令基于Sun JDK，用于监控和诊断HotSpot的java 虚拟机
1. jps 虚拟机进程状况工具
格式：jps [-q] [-mlvV] [<hostid>]
解释：
-l 输出主类全名。如果进程执行的是jar包，则输出包名。
-q 只输出LVMID，同进程pid
-m 输出JVM启动时传给主类main()的参数。
-v 输出JVM启动时JVM参数。
-V 输出通过标记的文件传递给JVM的参数(.hotspotrc文件,或者是通过参数-XX:Flags=指定的文件)
示例
bogon:~ hzjdemac$ jps
4081 org.eclipse.equinox.launcher_1.5.100.v20180827-1352.jar
14356 Launcher
14357 OutOfMemoryTest
14391 Jps
1290
12619 SSHMain
3453 RemoteMavenServer
bogon:~ hzjdemac$ jps -l
4081 /Users/hzjdemac/.vscode/extensions/redhat.java-0.30.0/server/plugins/org.eclipse.equinox.launcher_1.5.100.v20180827-1352.jar
14356 org.jetbrains.jps.cmdline.Launcher
14357 chapter2.OutOfMemoryTest
1290
14394 sun.tools.jps.Jps
12619 org.jetbrains.git4idea.ssh.SSHMain
3453 org.jetbrains.idea.maven.server.RemoteMavenServer
bogon:~ hzjdemac$ jps -v
4081 org.eclipse.equinox.launcher_1.5.100.v20180827-1352.jar -Declipse.application=org.eclipse.jdt.ls.core.id1 -Dosgi.bundles.defaultStartLevel=4 -Declipse.product=org.eclipse.jdt.ls.core.product -Xverify:none -Xmx1G -XX:+UseG1GC -XX:+UseStringDeduplication
14356 Launcher -Xmx700m -Djava.awt.headless=true -Djava.endorsed.dirs="" -Djdt.compiler.useSingleThread=true -Dpreload.project.path=/Users/hzjdemac/IdeaProjects/java-learning -Dpreload.config.path=/Users/hzjdemac/Library/Preferences/IntelliJIdea2017.3/options -Dcompile.parallel=false -Drebuild.on.dependency.change=true -Djava.net.preferIPv4Stack=true -Dio.netty.initialSeedUniquifier=-8492196048993142940 -Dfile.encoding=UTF-8 -Duser.language=zh -Duser.country=CN -Didea.paths.selector=IntelliJIdea2017.3 -Didea.home.path=/Applications/IntelliJ IDEA.app/Contents -Didea.config.path=/Users/hzjdemac/Library/Preferences/IntelliJIdea2017.3 -Didea.plugins.path=/Users/hzjdemac/Library/Application Support/IntelliJIdea2017.3 -Djps.log.dir=/Users/hzjdemac/Library/Logs/IntelliJIdea2017.3/build-log -Djps.fallback.jdk.home=/Applications/IntelliJ IDEA.app/Contents/jdk/Contents/Home/jre -Djps.fallback.jdk.version=1.8.0_152-release -Dio.netty.noUnsafe=true -Djava.io.tmpdir=/Users/hzjdemac/Library/Caches/IntelliJIdea2017.3/compile-server/java-l
1290 -Xms1024m -Xmx2048m -XX:ReservedCodeCacheSize=240m -XX:+UseCompressedOops -Dfile.encoding=UTF-8 -XX:+UseConcMarkSweepGC -XX:SoftRefLRUPolicyMSPerMB=50 -ea -Dsun.io.useCanonCaches=false -Djava.net.preferIPv4Stack=true -XX:+HeapDumpOnOutOfMemoryError -XX:-OmitStackTraceInFastThrow -Xverify:none -XX:ErrorFile=/Users/hzjdemac/java_error_in_idea_%p.log -XX:HeapDumpPath=/Users/hzjdemac/java_error_in_idea.hprof -Xbootclasspath/a:../lib/boot.jar -Djb.vmOptionsFile=/Applications/IntelliJ IDEA.app/Contents/bin/idea.vmoptions -Xbootclasspath/a:/Applications/IntelliJ IDEA.app/Contents/lib/boot.jar -Didea.java.redist=jdk-bundled -Didea.home.path=/Applications/IntelliJ IDEA.app/Contents -Didea.executable=idea -Didea.paths.selector=IntelliJIdea2017.3
12619 SSHMain
14397 Jps -Dapplication.home=/Library/Java/JavaVirtualMachines/jdk1.8.0_101.jdk/Contents/Home -Xms8m
3453 RemoteMavenServer -Djava.awt.headless=true -Didea.version==2017.3.1 -Xmx768m -Didea.maven.embedder.version=3.3.9 -Dfile.encoding=UTF-8
2. jinfo 实时地查看和调整虚拟机各项参数
格式：
bogon:~ hzjdemac$ jinfo -help
Usage:
jinfo [option] <pid>
(to connect to running process)
jinfo [option] <executable <core>
(to connect to a core file)
jinfo [option] [server_id@]<remote server IP or hostname>
(to connect to remote debug server)
where <option> is one of:
-flag <name> to print the value of the named VM flag// 打印给定name对应的命令行参数值。
-flag [+|-]<name> to enable or disable the named VM flag //更改boolean类型的命令行参数值
-flag <name>=<value> to set the named VM flag to the given value //更改name对应的命令行参数值为value。
-flags to print VM flags //打印传给JVM的命令参数值
-sysprops to print Java system properties //打印系统属性值
<no option> to print both of the above
-h | -help to print this help message
示例
bogon:~ hzjdemac$ jinfo -flags 15612
Attaching to process ID 15612, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.101-b13
Non-default VM flags: -XX:CICompilerCount=4 -XX:+HeapDumpOnOutOfMemoryError -XX:InitialHeapSize=83886080 -XX:MaxHeapSize=83886080 -XX:MaxNewSize=27787264 -XX:MinHeapDeltaBytes=524288 -XX:NewSize=27787264 -XX:OldSize=56098816 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseFastUnorderedTimeStamps -XX:+UseParallelGC
Command line: -Xms80m -Xmx80m -XX:+HeapDumpOnOutOfMemoryError -Dfile.encoding=UTF-8
3. jstat 虚拟机统计信息监视工具
bogon:~ hzjdemac$ 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.
bogon:~ hzjdemac$ jstat -options
-class //监视类装载、卸载数量、总空间以及类装载所耗费的时间.
-compiler //显示编译器编译过的方法、耗时等信息.
-gc //显示Java堆状况、包括Eden区、两个survivor区、老年代、永久代等的容量、已用空间、GC次数以及时间等信息.
-gccapacity //显示VM内存中三代(young,old,perm）对象的使用和占用大小
-gcutil //gc统计信息, 输出主要关注已使用空间占总弓箭的百分比
-gccause //与-gcutil基本相同, 会额外输出导致上一次GC产生的原因
-gcnew //显示新生代GC状况
-gcnewcapacity //显示内容与-gcnew相同,输出主要关注使用到的最大最小空间
-gcold // 显示老年代GC状况
-gcoldcapacity //显示内容与-gcold相同,输出主要关注使用到的最大最小空间
-printcompilation //当前vm执行的信息
示例
bogon:~ hzjdemac$ jstat -gc 16229 2000 5 //每2s执行一次查询统计,执行5次gc统计输出
S0C S1C S0U S1U EC EU OC OU MC MU CCSC CCSU YGC YGCT FGC FGCT GCT
10752.0 10752.0 0.0 0.0 65536.0 3932.6 175104.0 0.0 4480.0 774.0 384.0 75.8 0 0.000 0 0.000 0.000
10752.0 10752.0 0.0 0.0 65536.0 3932.6 175104.0 0.0 4480.0 774.0 384.0 75.8 0 0.000 0 0.000 0.000
10752.0 10752.0 0.0 0.0 65536.0 3932.6 175104.0 0.0 4480.0 774.0 384.0 75.8 0 0.000 0 0.000 0.000
10752.0 10752.0 0.0 0.0 65536.0 3932.6 175104.0 0.0 4480.0 774.0 384.0 75.8 0 0.000 0 0.000 0.000
10752.0 10752.0 0.0 0.0 65536.0 3932.6 175104.0 0.0 4480.0 774.0 384.0 75.8 0 0.000 0 0.000 0.000
bogon:~ hzjdemac$ jstat -class 16229
Loaded Bytes Unloaded Bytes Time
421 868.0 0 0.0 0.05
S0C: 新生代中Survivor space 0区总空间
S1C: 新生代中Survivor space 1区总空间
S0U:新生代中Survivor space 0区已使用空间
S1U:新生代中Survivor space 1区已使用空间
EC: 新生代中总空间
EU:新生代已使用空间
OC: 老年代总空间
OU:老年代中已使用空间
MC：方法区大小
MU：方法区使用大小
CCSC:压缩类空间大小
CCSU:压缩类空间使用大小
YGC: 从应用程序启动到当前，发生Yang GC 的次数
YGCT: 从应用程序启动到当前，Yang GC所用的时间【单位秒】
FGC: 从应用程序启动到当前，发生Full GC的次数
FGCT: 从应用程序启动到当前，Full GC所用的时间
GCT: 从应用程序启动到当前，用于垃圾回收的总时间【单位秒】
4. jmap 打印指定Java进程(或核心文件、远程调试服务器)的共享对象内存映射或堆内存细节
bogon:~ hzjdemac$ jmap -help
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 //打印jvm heap的情况，例如GC收集器，参数配置，JVM内存分区情况
-histo[:live] to print histogram of java object heap; if the "live"
suboption is specified, only count live objects //打印jvm heap的直方图。其输出信息包括类名，对象数量，对象占用大小
-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
示例
bogon:~ hzjdemac$ jmap -heap 16229
Attaching to process ID 16229, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.101-b13
using thread-local object allocation.
Parallel GC with 8 thread(s)
Heap Configuration: //#堆内存初始化配置
MinHeapFreeRatio = 0 //-XX:MinHeapFreeRatio设置JVM堆最小空闲比率
MaxHeapFreeRatio = 100 //-XX:MaxHeapFreeRatio设置JVM堆最大空闲比率
MaxHeapSize = 4294967296 (4096.0MB) //-XX:MaxHeapSize=设置JVM堆的最大大小
NewSize = 89128960 (85.0MB) //-XX:NewSize=设置JVM堆新生代的默认大小
MaxNewSize = 1431306240 (1365.0MB) //-XX:MaxNewSize=设置JVM堆的‘新生代’的最大大小
OldSize = 179306496 (171.0MB) //-XX:OldSize=设置JVM堆的‘老生代’的大小
NewRatio = 2 //#-XX:NewRatio=:‘新生代’和‘老生代’的大小比率
SurvivorRatio = 8 //-XX:SurvivorRatio=设置年轻代中Eden区与Survivor区的大小比值
MetaspaceSize = 21807104 (20.796875MB) //-XX:PermSize=<value>:设置JVM堆的‘持久代’的初始大小
CompressedClassSpaceSize = 1073741824 (1024.0MB)
MaxMetaspaceSize = 17592186044415 MB
G1HeapRegionSize = 0 (0.0MB)
Heap Usage:
PS Young Generation
Eden Space:
capacity = 67108864 (64.0MB)
used = 4026944 (3.84039306640625MB)
free = 63081920 (60.15960693359375MB)
6.000614166259766% used
From Space:
capacity = 11010048 (10.5MB)
used = 0 (0.0MB)
free = 11010048 (10.5MB)
0.0% used
To Space:
capacity = 11010048 (10.5MB)
used = 0 (0.0MB)
free = 11010048 (10.5MB)
0.0% used
PS Old Generation
capacity = 179306496 (171.0MB)
used = 0 (0.0MB)
free = 179306496 (171.0MB)
0.0% used
758 interned Strings occupying 50832 bytes.
bogon:~ hzjdemac$ jmap -histo 16229
num #instances #bytes class name
----------------------------------------------
1: 439 4642832 [I
2: 2553 347560 [C
3: 731 145760 [B
4: 487 55504 java.lang.Class
5: 1699 40776 java.lang.String
6: 584 30504 [Ljava.lang.Object;
7: 115 8280 java.lang.reflect.Field
8: 199 6368 java.io.File
9: 238 5712 java.lang.StringBuilder
10: 89 5696 java.net.URL
11: 11 4136 java.lang.Thread
12: 258 4128 java.lang.Integer
13: 98 3920 java.lang.ref.SoftReference
14: 122 3904 java.util.Hashtable$Entry
...
bogon:~ hzjdemac$ jmap -dump:format=b,file=a.log 16229 //保存快照
Dumping heap to /Users/hzjdemac/a.log ...
Heap dump file created
配置JVM启动参数，让JVM在遇到OutOfMemoryError时自动生成Dump文件
-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/path
5. jstack 堆栈跟踪工具
bogon:~ hzjdemac$ 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
示例
bogon:~ hzjdemac$ jstack 16229
2019-03-18 18:27:04
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.101-b13 mixed mode):
"Attach Listener" #13 daemon prio=9 os_prio=31 tid=0x00007fa6c5001000 nid=0xc07 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"DestroyJavaVM" #12 prio=5 os_prio=31 tid=0x00007fa6c589f000 nid=0x1803 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Thread-1" #11 prio=5 os_prio=31 tid=0x00007fa6c589e000 nid=0x5603 waiting for monitor entry [0x000070000c031000]
java.lang.Thread.State: BLOCKED (on object monitor)
at chapter1.DeadLockDemo$2.run(DeadLockDemo.java:38)
- waiting to lock <0x000000076abaccd8> (a java.lang.String)
- locked <0x000000076abacd08> (a java.lang.String)
at java.lang.Thread.run(Thread.java:745)
"Thread-0" #10 prio=5 os_prio=31 tid=0x00007fa6c589d800 nid=0xa903 waiting for monitor entry [0x000070000bf2e000]
java.lang.Thread.State: BLOCKED (on object monitor)
at chapter1.DeadLockDemo$1.run(DeadLockDemo.java:28)
- waiting to lock <0x000000076abacd08> (a java.lang.String)
- locked <0x000000076abaccd8> (a java.lang.String)
at java.lang.Thread.run(Thread.java:745)
...
参考：
[1].https://www.cnblogs.com/dennisit/p/9119535.html
[2]. 深入理解Java虚拟机
