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] [
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]
(to connect to running process)
jinfo [option]
(to connect to a core file)
jinfo [option] [server_id@]
(to connect to remote debug server)
where 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 -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]
(to connect to running process)
jmap [option]
(to connect to a core file)
jmap [option] [server_id@]
(to connect to remote debug server)
where 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=: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]
(to connect to running process)
jstack -F [-m] [-l]
(to connect to a hung process)
jstack [-m] [-l]
(to connect to a core file)
jstack [-m] [-l] [server_id@]
(to connect to a remote debug server)
Options:
-F to force a thread dump. Use when jstack 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