[TOC]

jdk命令行工具

0.概览

名称	作用
jps	JVM Process Status Tool，显示系统中所有的Hotspot虚拟机进程
jstat	JVM Statistics Monitoring Tool，用于收集HotSpot虚拟机各方面的运行数据
jinfo	Configuration info for java，显示虚拟机配置信息
jmap	Memory Map for java，生成虚拟机的内存转储快照(heapdump文件)
jhat	JVM Heapdump Browser，用于分析heapdump文件，会建立一个HTTP/HTML服务器，用户可以在浏览器上查看分析结果
jstack	Stack Trace for java，显示虚拟机的线程快照

1.jps：虚拟机进程查看工具

JVM Process Status Tool,显示指定系统内所有的HotSpot虚拟机进程，类似于Linux中的ps命令。

命令格式

jps [option] [hostid]

选项及示例

[~]$ jps -help
usage: jps [-help]
       jps [-q] [-mlvV] [<hostid>]

Definitions:
    <hostid>:      <hostname>[:<port>]

[~]$ jps
30784 Bootstrap
26949 Jps
[~]$ jps -q  //仅输出虚拟机进程id，省略主类
30784
26966
[~]$ jps -m  //输出虚拟机进程启用的时候传递给主类main()函数的参数
30784 Bootstrap
26981 Jps -m
[~]$ jps -l //输出主类的全类名，如果进程执行的是jar包，输出Jar路径
30784 com.sankuai.mms.boot.Bootstrap
26998 sun.tools.jps.Jps
[~]$ jps -v //输出虚拟机进程启动时JVM参数
30784 Bootstrap -Dfile.encoding=UTF-8 -Dsun.jnu.encoding=UTF-8 -Djava.io.tmpdir=/tmp -Djava.net.preferIPv6Addresses=false -Xmx4g -Xms4g -Xmn1g -XX:SurvivorRatio=8 -XX:MetaspaceSize=256m -XX:MaxMetaspaceSize=256m -XX:+HeapDumpOnOutOfMemoryError -XX:ReservedCodeCacheSize=128m -XX:InitialCodeCacheSize=128m -XX:+DisableExplicitGC -XX:+PrintGCDetails -XX:+PrintHeapAtGC -XX:+PrintTenuringDistribution -XX:+UseConcMarkSweepGC -XX:+PrintGCTimeStamps -XX:+PrintGCDateStamps -XX:CMSFullGCsBeforeCompaction=0 -XX:+UseCMSCompactAtFullCollection -XX:CMSInitiatingOccupancyFraction=80 -Xloggc:/opt/logs/etcp-code-service/.gc.log -XX:ErrorFile=/opt/logs/etcp-code-service/.vmerr.log -XX:HeapDumpPath=/opt/logs/etcp-code-service/.heaperr.log -Djetty.appkey= -Djetty.context=/ -Djetty.logs=/opt/logs/etcp-code-service -Djetty.webroot=/opt/meituan/apps/etcp-code-service/webroot
27012 Jps -Dapplication.home=/usr/local/jdk1.7.0_76 -Xms8m

常用命令

jps -lmv

2.jstat：虚拟机统计信息监控工具

jstat(JVM Statistics Monitoring Tool)

用来监视虚拟机各种运行状态信息。可以显示类装载、内存、垃圾收集、JTI编译等运行数据

命令格式

jstat [option] [vmid] [interval] [count]

jstat -<option> [-t] [-h<lines>] <vmid> [<interval> [<count>]]
     //option                   //vmid  //查询间隔    //查询次数 
 
 -t参数可以在输出信息前加一个timestamp列，显示程序的运行时间
 -h参数可以在周期性数据输出时，输出多少行数据后，跟着输出一个表头信息。
 
 -interval参数用于指定统计数据的输出周期，单位是毫秒
 -count参数用于指定输出的次数

举例：

jstat -gcutil 1234 1000 5
1234:vmid
1000:每隔1000ms打印一次
5:一共打印5次

选项及示例

[~]$ 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.

选项主要分为3类

类装载、垃圾收集、运行期编译状况

-class             //监视类装载、卸载数量、总空间以及类装载所耗费的时间  
  
-gc                //监视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时间合计等信息  
-gccapacity        //监视内容与-gc基本相同，但输出主要关注java堆各个区域使用到的最大、最小空间
-gcutil            //监视内容与-gc基本相同，但输出主要关注已使用空间占总空间的百分比
-gccause           //与-gcutil功能一样，但是会额外输出导致上一次GC产生的原因

-gcnew             //监视新生代的GC状况
-gcnewcapacity     //监视内容与-gcnew基本相同，输出主要关注使用到的最大、最小空间
  
-gcold             //监视老年代的GC状况
-gcoldcapacity     //监视内容与-gcold基本相同，输出主要关注使用到的最大、最小空间

-gcpermcapacity  //输出永久代使用到的最大、最小空间

-compiler          //输出JIT编译器编译过的方法、耗时等信息
-printcompilation  //输出已经被JIT编译的方法

-class

[~]$ jstat -class 192610 500ms 5
Loaded  Bytes  Unloaded  Bytes     Time   
 13021 26691.8        0     0.0      29.06
 13021 26691.8        0     0.0      29.06
 13021 26691.8        0     0.0      29.06
 13021 26691.8        0     0.0      29.06
 13021 26691.8        0     0.0      29.06
  
Loaded：载入类的数量
Bytes：载入类的合计大小
Unloaded：卸载类的数量
Bytes：卸载类的合计大小
Time：加载类和卸载类上花费的时间

-gc

[~]$ jstat -gc 192610 1000ms 5
Warning: Unresolved Symbol: sun.gc.generation.2.space.0.capacity substituted NaN
Warning: Unresolved Symbol: sun.gc.generation.2.space.0.used substituted NaN
 S0C    S1C    S0U    S1U      EC       EU        OC         OU       PC     PU    YGC     YGCT    FGC    FGCT     GCT   
104832.0 104832.0 2687.7  0.0   838912.0 708187.2 3145728.0   321489.3    �      �       100    6.148   0      0.000    6.148
104832.0 104832.0 2687.7  0.0   838912.0 708191.6 3145728.0   321489.3    �      �       100    6.148   0      0.000    6.148
104832.0 104832.0 2687.7  0.0   838912.0 708191.6 3145728.0   321489.3    �      �       100    6.148   0      0.000    6.148
104832.0 104832.0 2687.7  0.0   838912.0 708201.2 3145728.0   321489.3    �      �       100    6.148   0      0.000    6.148
104832.0 104832.0 2687.7  0.0   838912.0 708254.4 3145728.0   321489.3    �      �       100    6.148   0      0.000    6.148

S0C：年轻代中第一个survivor(幸存区)的容量 (KB) 
S1C：年轻代中第二个survivor(幸存区)的容量 (KB) 
S0U：年轻代中第一个survivor(幸存区)目前已使用空间 (KB) 
S1U：年轻代中第二个survivor(幸存区)目前已使用空间 (KB) 
EC：年轻代中Eden(伊甸园)的容量 (KB) 
EU：年轻代中Eden(伊甸园)目前已使用空间 (KB) 
OC：Old代的容量 (KB) 
OU：Old代目前已使用空间 (KB) 
PC：Perm(持久代)的容量 (KB)   //java8中已经移除持久代
PU：Perm(持久代)目前已使用空间 (KB) //java8中已经移除持久代
YGC：从应用程序启动到采样时年轻代中gc次数 
YGCT：从应用程序启动到采样时年轻代中gc所用时间(s) 
FGC：从应用程序启动到采样时old代(全gc)gc次数 
FGCT：从应用程序启动到采样时old代(全gc)gc所用时间(s) 
GCT：从应用程序启动到采样时gc用的总时间(s)

-gccapacity

[~]$ jstat -gccapacity 192610 100ms 5
Warning: Unresolved Symbol: sun.gc.generation.2.minCapacity substituted NaN
Warning: Unresolved Symbol: sun.gc.generation.2.maxCapacity substituted NaN
Warning: Unresolved Symbol: sun.gc.generation.2.capacity substituted NaN
Warning: Unresolved Symbol: sun.gc.generation.2.space.0.capacity substituted NaN
 NGCMN    NGCMX     NGC     S0C   S1C       EC      OGCMN      OGCMX       OGC         OC      PGCMN    PGCMX     PGC       PC     YGC    FGC 
1048576.0 1048576.0 1048576.0 104832.0 104832.0 838912.0  3145728.0  3145728.0  3145728.0  3145728.0        �        �        �        �    103     0
1048576.0 1048576.0 1048576.0 104832.0 104832.0 838912.0  3145728.0  3145728.0  3145728.0  3145728.0        �        �        �        �    103     0
1048576.0 1048576.0 1048576.0 104832.0 104832.0 838912.0  3145728.0  3145728.0  3145728.0  3145728.0        �        �        �        �    103     0
1048576.0 1048576.0 1048576.0 104832.0 104832.0 838912.0  3145728.0  3145728.0  3145728.0  3145728.0        �        �        �        �    103     0
1048576.0 1048576.0 1048576.0 104832.0 104832.0 838912.0  3145728.0  3145728.0  3145728.0  3145728.0        �        �        �        �    103     0

NGCMN：年轻代(young)中初始化(最小)的大小 (KB) 【New Generation Capacity Min】
NGCMX：年轻代(young)的最大容量 (KB) 
NGC：年轻代(young)中当前的容量 (KB) 

OGCMN：old代中初始化(最小)的大小 (KB) 
OGCMX：old代的最大容量 (KB) 
PGCMN：perm代中初始化(最小)的大小 (KB) 
PGCMX：perm代的最大容量 (KB)

-gcutil

[~]$ jstat -gcutil 192610 100ms 5
Warning: Unresolved Symbol: sun.gc.generation.2.space.0.capacity substituted NaN
Warning: Unresolved Symbol: sun.gc.generation.2.space.0.used substituted NaN
Warning: Unresolved Symbol: sun.gc.generation.2.space.0.capacity substituted NaN
  S0     S1     E      O      P     YGC     YGCT    FGC    FGCT     GCT   
  0.00   4.08  26.22  10.22      �    103    6.240     0    0.000    6.240
  0.00   4.08  26.23  10.22      �    103    6.240     0    0.000    6.240
  0.00   4.08  26.23  10.22      �    103    6.240     0    0.000    6.240
  0.00   4.08  26.23  10.22      �    103    6.240     0    0.000    6.240
  0.00   4.08  26.23  10.22      �    103    6.240     0    0.000    6.240

S0：年轻代中第一个survivor(幸存区)已使用的占当前容量百分比 
S1：年轻代中第二个survivor(幸存区)已使用的占当前容量百分比 
E：年轻代中Eden(伊甸园)已使用的占当前容量百分比 
O：old代已使用的占当前容量百分比
P：perm代已使用的占当前容量百分比 
YGC:年轻代经过的GC次数
YGCT：年轻代GC时间
FGC：老年代经过的GC次数
FGCT：老年代GC时间
GCT：所有GC总时间

-gccause

[~]$ jstat -gccause 192610 100ms 5
Warning: Unresolved Symbol: sun.gc.generation.2.space.0.capacity substituted NaN
Warning: Unresolved Symbol: sun.gc.generation.2.space.0.used substituted NaN
Warning: Unresolved Symbol: sun.gc.generation.2.space.0.capacity substituted NaN
  S0     S1     E      O      P     YGC     YGCT    FGC    FGCT     GCT    LGCC                 GCC                 
  0.00   4.08  56.14  10.22      �    103    6.240     0    0.000    6.240 Allocation Failure   No GC               
  0.00   4.08  56.14  10.22      �    103    6.240     0    0.000    6.240 Allocation Failure   No GC               
  0.00   4.08  56.14  10.22      �    103    6.240     0    0.000    6.240 Allocation Failure   No GC               
  0.00   4.08  56.14  10.22      �    103    6.240     0    0.000    6.240 Allocation Failure   No GC               
  0.00   4.08  56.14  10.22      �    103    6.240     0    0.000    6.240 Allocation Failure   No GC 

LGCC：上次GC的原因【Last GC Cause】
GCC：当前GC的原因

-gcnew

[~]$ jstat -gcnew 192610 100ms 5
 S0C    S1C    S0U    S1U   TT MTT  DSS      EC       EU     YGC     YGCT  
104832.0 104832.0    0.0 4276.9 15  15 52416.0 838912.0 541449.0    103    6.240
104832.0 104832.0    0.0 4276.9 15  15 52416.0 838912.0 541466.0    103    6.240
104832.0 104832.0    0.0 4276.9 15  15 52416.0 838912.0 541468.2    103    6.240
104832.0 104832.0    0.0 4276.9 15  15 52416.0 838912.0 541468.2    103    6.240
104832.0 104832.0    0.0 4276.9 15  15 52416.0 838912.0 541468.2    103    6.240


TT：新生代对象晋升到老年代的年龄。Tenuring threshold(提升阈值)
MTT：新生代对象晋升到老年代的年龄的最大值。最大的tenuring threshold
DSS：所需的Survivor大小。survivor区域大小 (KB)

-gcnewcapacity

[~]$ jstat -gcnewcapacity 192610 100ms 5
  NGCMN      NGCMX       NGC      S0CMX     S0C     S1CMX     S1C       ECMX        EC      YGC   FGC 
 1048576.0  1048576.0  1048576.0 104832.0 104832.0 104832.0 104832.0   838912.0   838912.0   103     0
 1048576.0  1048576.0  1048576.0 104832.0 104832.0 104832.0 104832.0   838912.0   838912.0   103     0
 1048576.0  1048576.0  1048576.0 104832.0 104832.0 104832.0 104832.0   838912.0   838912.0   103     0
 1048576.0  1048576.0  1048576.0 104832.0 104832.0 104832.0 104832.0   838912.0   838912.0   103     0
 1048576.0  1048576.0  1048576.0 104832.0 104832.0 104832.0 104832.0   838912.0   838912.0   103     0
 
S0CMX:最大的S0空间 (KB) 
S1CMX:最大的S1空间(KB)
ECMX:最大eden空间 (KB)

-compiler

[~]$ jstat -compiler 192610 100ms 5
Compiled Failed Invalid   Time   FailedType FailedMethod
   60656     17       0   283.55          1 com/alibaba/fastjson/parser/deserializer/JavaBeanDeserializer deserialze
   60656     17       0   283.55          1 com/alibaba/fastjson/parser/deserializer/JavaBeanDeserializer deserialze
   60656     17       0   283.55          1 com/alibaba/fastjson/parser/deserializer/JavaBeanDeserializer deserialze
   60656     17       0   283.55          1 com/alibaba/fastjson/parser/deserializer/JavaBeanDeserializer deserialze
   60656     17       0   283.55          1 com/alibaba/fastjson/parser/deserializer/JavaBeanDeserializer deserialze

Compiled：编译任务执行的次数
Failed：编译失败的次数
Invalid：编译不可用的次数
FailedType：最后一次编译失败的类型
FailedMethod：最后一次编译失败的类名和方法名

-printcompilation

[~]$ jstat -printcompilation 192610 100ms 5
Compiled  Size  Type Method
   60663      5    1 java/lang/ThreadLocal access$400
   60663      5    1 java/lang/ThreadLocal access$400
   60663      5    1 java/lang/ThreadLocal access$400
   60663      5    1 java/lang/ThreadLocal access$400
   60663      5    1 java/lang/ThreadLocal access$400
   
Compiled：编译任务执行的次数
Size：方法字节码的字节数
Type：编译类型
Method：编译方法的类名和方法名。类名使用”/” 代替 “.” 作为空间分隔符. 方法名是给出类的方法名. 格式是同HotSpot - XX:+PrintComplation选项一致

3.jinfo：java配置信息查看工具

jinfo(JVM Configuration info)这个命令作用是实时查看和调整虚拟机运行参数，甚至支持在运行时修改部分参数。

jps -v命令只能查看到显示指定的参数，如果想要查看未被显示指定的参数的值就要使用jinfo口令

命令格式

[~]$ 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
    -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 of the above
    -h | -help           to print this help message

jinfo [option] [args] LVMID

选项及示例

-flag <name>：打印JVM指定参数值
-flag [+|-]<name>：设置指定JVM参数的布尔值
-flag <name>=<value>：设置指定JVM参数的值

参数使用示例

1.查看参数值

[~]$ jinfo -flag SurvivorRatio 192610
-XX:SurvivorRatio=8

2.修改参数值

[~]$ jinfo -flag +PrintGCDetails 192610

4.jmap：Java内存映射工具

jmap(Memory Map for Java)命令用于生成堆转储快照heapdump。

如果不使用这个命令，还可以使用-XX:+HeapDumpOnOutOfMemoryError参数来让虚拟机出现OOM的时候生成。

[sankuai@set-xr-cx-etcp-code-test02 ~]$ 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
    -permstat            to print permanent generation 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

命令格式

jmap [option] <pid>

选项及示例

参数包括

dump : 生成堆转储快照
finalizerinfo : 显示在F-Queue队列等待Finalizer线程执行finalizer方法的对象
heap : 显示Java堆详细信息
histo : 显示堆中对象的统计信息
permstat : to print permanent generation statistics
F : 当-dump没有响应时，强制生成dump快照

-dump：生成dump文件

jmap -dump:live,format=b,file=<filename> pid
//dump堆到文件,format=b指定输出格式为二进制知识，live指明是活着的对象,file指定文件名

[~]$ jmap -dump:live,format=b,file=dump.hprof 25052
Dumping heap to /home/sankuai/dump.hprof ...
Heap dump file created

-heap：输出堆的概要信息

jmap -heap pid

[~]$ ./jmap -heap 192610
Attaching to process ID 192610, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.45-b02

using parallel threads in the new generation.
using thread-local object allocation.
Concurrent Mark-Sweep GC

Heap Configuration:
   MinHeapFreeRatio         = 40
   MaxHeapFreeRatio         = 70
   MaxHeapSize              = 4294967296 (4096.0MB)
   NewSize                  = 1073741824 (1024.0MB)
   MaxNewSize               = 1073741824 (1024.0MB)
   OldSize                  = 3221225472 (3072.0MB)
   NewRatio                 = 2
   SurvivorRatio            = 8
   MetaspaceSize            = 268435456 (256.0MB)
   CompressedClassSpaceSize = 1073741824 (1024.0MB)
   MaxMetaspaceSize         = 268435456 (256.0MB)
   G1HeapRegionSize         = 0 (0.0MB)

Heap Usage:
New Generation (Eden + 1 Survivor Space):	
   capacity = 966393856 (921.625MB)
   used     = 641636608 (611.912353515625MB)
   free     = 324757248 (309.712646484375MB)
   66.39493866980877% used
Eden Space:
   capacity = 859045888 (819.25MB)
   used     = 637358448 (607.8323822021484MB)
   free     = 221687440 (211.41761779785156MB)
   74.19376041527597% used
From Space:
   capacity = 107347968 (102.375MB)
   used     = 4278160 (4.0799713134765625MB)
   free     = 103069808 (98.29502868652344MB)
   3.9853199643238706% used
To Space:
   capacity = 107347968 (102.375MB)
   used     = 0 (0.0MB)
   free     = 107347968 (102.375MB)
   0.0% used
concurrent mark-sweep generation:
   capacity = 3221225472 (3072.0MB)
   used     = 230203712 (219.53936767578125MB)
   free     = 2991021760 (2852.4606323242188MB)
   7.146463791529338% used

40359 interned Strings occupying 4225896 bytes.

-histo:(histogram 直方图)

打印堆的对象统计，包括对象数、内存大小等等 (因为在dump:live前会进行full gc，如果带上live则只统计活对象，因此不加live的堆大小要大于加live堆的大小 )

[sankuai@set-xr-cx-etcp-code-test02 bin]$ jmap -histo:live 192610|more

 num     #instances         #bytes  class name
----------------------------------------------
   1:         46961      131287216  [B
   2:         97908       11794768  [C
   3:         97796        3129472  java.util.HashMap$Node
   4:         96182        2308368  java.lang.String
   5:         40884        1962432  java.util.zip.Inflater
   6:         19559        1721192  java.lang.reflect.Method
   7:         41890        1675600  java.lang.ref.Finalizer
   8:         13968        1601808  java.lang.Class
   9:         40355        1291360  java.util.concurrent.ConcurrentHashMap$Node
  10:         18310        1216328  [Ljava.lang.Object;
  11:          8753        1120216  [Ljava.util.HashMap$Node;
  12:         25015        1000600  java.util.WeakHashMap$Entry
  13:         40884         981216  java.util.zip.ZStreamRef
  14:         35328         847872  io.netty.buffer.PoolThreadCache$MemoryRegionCache$Entry
  15:         16585         796080  org.aspectj.weaver.reflect.ShadowMatchImpl
  16:         15397         684208  [Z
  17:         16585         530720  org.aspectj.weaver.patterns.ExposedState
  18:           965         500552  [Ljava.util.concurrent.ConcurrentHashMap$Node;
  19:           582         469072  [Ljava.util.WeakHashMap$Entry;
  20:         10759         430360  java.util.LinkedHashMap$Entry
  21:          6367         425216  [I
  22:         11721         375072  java.lang.ref.WeakReference
  23:          6664         373184  java.util.LinkedHashMap
  24:         10486         335552  java.util.Hashtable$Entry
  25:          6118         293664  java.util.HashMap
  26:         18146         290336  java.lang.Integer
  27:          9961         239056  [Lorg.aspectj.weaver.ast.Var;
  28:          9721         233304  java.lang.Long
  29:          9096         218304  java.util.ArrayList
  30:          5303         212120  java.util.TreeMap$Entry
  31:          5158         206320  java.lang.ref.SoftReference
  32:          8806         191152  [Ljava.lang.Class;
  33:          3742         174048  [Ljava.lang.String;
  34:          5170         165440  org.jacoco.agent.rt.internal_b0d6a23.core.data.ExecutionData
  35:            80         142592  [Lio.netty.buffer.PoolThreadCache$MemoryRegionCache$Entry;
  36:          2073         132672  java.util.concurrent.ConcurrentHashMap
  37:          5514         132336  java.beans.MethodRef
  38:          1634         130720  java.lang.reflect.Constructor
  39:           411         119296  [Ljava.util.Hashtable$Entry;
  40:          6966         111456  java.lang.Object
  41:           293         110168  java.lang.Thread
  42:          1069         102624  org.springframework.beans.GenericTypeAwarePropertyDescriptor
  43:          3984          95616  java.util.concurrent.atomic.AtomicLong
  44:            62          91416  [Ljava.nio.ByteBuffer;
  45:          3712          89088  org.springframework.core.MethodClassKey
  46:          3661          87864  sun.reflect.generics.tree.SimpleClassTypeSignature
  47:          1500          84000  java.beans.MethodDescriptor
  48:          1162          83664  java.lang.reflect.Field
  49:          2447          78304  java.util.LinkedList
  50:          3132          75168  java.util.jar.Attributes$Name
  51:          2924          70176  java.util.LinkedList$Node

class name表示对象类型
B  byte
C  char
D  double
F  float
I  int
J  long
Z  boolean
[  数组，如[I表示int[]
[L+类名 其他对象

5.jhat

jhat(JVM Heap Analysis Tool)与jmap配合使用，来分析jmap生成的heapdump。

jhat内置了一个HTTP/HTML服务器，可以在浏览器中查看dump文件的分析结果。

一般不用jhat来分析dump文件，jhat功能比较简陋。

一般会download dump文件到本地，使用Eclipse Memory Analyzer(MAT)等工具进行分析。

6.jstack：Java堆栈跟踪工具

jstack用于生成java虚拟机当前时刻的线程快照。线程快照是当前java虚拟机内每一条线程正在执行的方法堆栈的集合。

生成线程快照的主要目的是定位线程出现长时间停顿的原因，如线程间死锁、死循环、请求外部资源导致的长时间等待等。

[sankuai@set-xr-cx-etcp-code-test02 bin]$ jstack
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

命令格式

jstack [option] <pid>

选项及示例

-F : 当正常输出请求不被响应时，强制输出线程堆栈
-l : 除堆栈外，显示关于锁的附加信息
-m : 如果调用到本地方法的话，可以显示C/C++的堆栈

java

java -XX:+PrintCommandLineFlags -version

打印手动设置的参数

java -XX:+PrintFlagsFinal -version | grep :

打印虚拟机所有参数

jmap -heap

参考资料

• jamp -heap https://www.cnblogs.com/dragonsuc/p/6927824.html
• java https://blog.csdn.net/earthhour/article/details/76468084

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