由于运行了一堆 Java 微服务，导致开发环境越来越慢，在扩展了一次内存之后，问题依然没有解决。free -h 和 vmstate -s 可以用来查看操作系统内存使用情况，但对于 Java 程序，jps、jmap、jinfo、jstat 等工具能让你进行更细粒度的分析。

jps

该命令用于显示运行的 JVM 的入口函数：

[root@dev-appserver ~]# jps -l
5799 com.star.epg.EpgApplication
7880 com.star.strategy.DvbStrategyApplication
6540 com.star.op.OperationsApplication
2893 com.star.smssender.SMSServiceApplication
9773 com.star.payment.PaymentApplication
10190 sun.tools.jps.Jps
7727 com.star.cms.start.Start
9615 com.star.pup.PupApplication
6672 com.star.bms.BmsServiceApplication
9201 com.star.mobilewallet.MobileWalletApplication
9012 com.star.order.OrderApplication
10132 com.star.channel.ChannelApplication
2710 com.star.css.CssApplication
9496 com.star.boss.proxy.Main
2462 org.apache.catalina.startup.Bootstrap

jmap

该命令用于显示共享对象内存映射或堆(heap)详细信息:

[root@dev-appserver ~]# jmap -heap 5799
Attaching to process ID 5799, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.131-b11

using thread-local object allocation.
Parallel GC with 4 thread(s)

Heap Configuration:
   MinHeapFreeRatio         = 0
   MaxHeapFreeRatio         = 100
   MaxHeapSize              = 2051014656 (1956.0MB)
   NewSize                  = 42991616 (41.0MB)
   MaxNewSize               = 683671552 (652.0MB)
   OldSize                  = 87031808 (83.0MB)
   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 = 634388480 (605.0MB)
   used     = 129431144 (123.4351577758789MB)
   free     = 504957336 (481.5648422241211MB)
   20.402505417500645% used
From Space:
   capacity = 25165824 (24.0MB)
   used     = 11320032 (10.795623779296875MB)
   free     = 13845792 (13.204376220703125MB)
   44.98176574707031% used
To Space:
   capacity = 24117248 (23.0MB)
   used     = 0 (0.0MB)
   free     = 24117248 (23.0MB)
   0.0% used
PS Old Generation
   capacity = 87031808 (83.0MB)
   used     = 38775616 (36.97930908203125MB)
   free     = 48256192 (46.02069091796875MB)
   44.55338443618223% used

30769 interned Strings occupying 3598960 bytes.

[root@dev-appserver ~]# jmap -histo 5799
 num     #instances         #bytes  class name
----------------------------------------------
   1:        387415       55601848  [C
   2:         51496       31275592  [I
   3:        117228       23027728  [B
   4:        186882        7475280  java.util.HashMap$KeyIterator
   5:        291963        7007112  java.lang.String
   6:        165687        5301984  java.util.HashMap$Node
   7:         75385        4221560  java.util.concurrent.ConcurrentHashMap$KeyIterator
   8:         35510        3124880  java.lang.reflect.Method
   9:         49229        3112688  [Ljava.util.HashMap$Node;
  10:        119850        2934864  [Z
  11:         64694        2869648  [Ljava.lang.Object;
  12:        118929        2854296  java.text.ParsePosition
  13:        108477        2603448  java.lang.Long
  14:         44959        2158032  java.util.HashMap
  15:         33602        1612896  java.nio.HeapByteBuffer
  16:         38012        1520480  java.util.LinkedHashMap$Entry
  17:         37508        1500320  java.util.TreeMap$Entry
  18:         13291        1479224  java.lang.Class
  19:         42219        1351008  java.util.concurrent.ConcurrentHashMap$Node
  20:         46482        1115568  java.util.concurrent.ConcurrentHashMap$MapEntry
  21:         30908         989056  java.util.concurrent.locks.AbstractQueuedSynchronizer$Node
  22:         46273         944512  [Ljava.lang.Class;
  23:         15408         862848  java.util.concurrent.ConcurrentHashMap$EntryIterator
  24:         15108         846048  java.util.LinkedHashMap
  25:         32349         776376  java.util.ArrayList
  26:         15579         747792  java.nio.HeapCharBuffer
  27:         18389         735560  java.util.HashMap$EntryIterator
  28:         22068         710928  [Ljava.lang.String;
  29:         20307         649824  java.lang.ref.WeakReference
  30:         15543         621720  java.util.HashMap$ValueIterator

jinfo

该命令用于 JVM 运行参数：

[root@dev-appserver ~]# jinfo -flags 6540
Attaching to process ID 6540, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.131-b11
Non-default VM flags: -XX:CICompilerCount=3 -XX:InitialHeapSize=268435456 -XX:MaxHeapSize=1073741824 -XX:MaxNewSize=357564416 -XX:MinHeapDeltaBytes=524288 -XX:NewSize=89128960 -XX:OldSize=179306496 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseFastUnorderedTimeStamps -XX:+UseParallelGC
Command line:  -Xms256m -Xmx1024m

jstat

该命令用于监控 JVM 统计信息：

[root@dev-appserver ~]# jstat -gcutil 6540 1000
  S0     S1     E      O      M     CCS    YGC     YGCT    FGC    FGCT     GCT
 46.49   0.00  52.64  46.14  95.90  93.65    120   64.400     3    0.281   64.681
 46.49   0.00  52.64  46.14  95.90  93.65    120   64.400     3    0.281   64.681
 46.49   0.00  52.64  46.14  95.90  93.65    120   64.400     3    0.281   64.681

未完待补充