【一】java 虚拟机 监控示例 Eclipse Memory Analyser

1.堆内存溢出示例代码

import java.util.ArrayList;
import java.util.List;
public class TestHeap {
 public static void main(String[] args) {
  List<User> list = new ArrayList<>();
  while(true) {
   list.add(new User());

  }
 }
}

Exception in thread "main" java.lang.OutOfMemoryError: GC overhead limit exceeded
at com.chaoyijuechen.easypoi.TestHeap.main(TestHeap.java:10)

问：这是个小程序，可以快速定位内存溢出的位置，若是大应用中呢？代码上百万行，很难通过代码定位。这时该如何定位呢？

答：通过分析工具定位！

问：如何通过分析工具定位？

答：首先，将内存转储成一个快照，然后通过快照对当前环境进行分析。

问：如何生存快照？ 

 答：通过Java虚拟机的参数设置！

　　　　-XX:+HeapDumpOnOutOfMemoryError　　　　　　将Java堆内存溢出的堆存储快照dump

　　　　

　　-vmargs  //虚拟机设置

     -Xms40m //初始内存

     -Xmx256m //最大内存

     -Xmn16m //最小内存

     -XX:PermSize=128M //非堆内存

     -XX:MaxPermSize=256M

最终会生成文件在项目根目录下：java_pid1124.hprof，内容如下： ( java version 1.8.0_181)

4a41 5641 2050 524f 4649 4c45 2031 2e30
2e31 0000 0000 0800 0001 6951 3126 0801
0000 0000 0000 0012 0000 7fe8 4b05 81d0
4352 4c5f 5245 4153 4f4e 0100 0000 0000
0000 2500 007f e84c 04c2 d073 756e 2f73
6563 7572 6974 792f 706b 6373 2f43 6f6e
7465 6e74 496e 666f 0100 0000 0000 0000
3100 0000 0103 45aa 4028 4c6a 6176 612f
7574 696c 2f53 6574 3c54 453b 3e3b 4c6a
6176 612f 6c61 6e67 2f4f 626a 6563 743b
2956 0100 0000 0000 0000 1300 0000 0103
4343 406c 696e 6b4d 6574 686f 6420 0100
0000 0000 0000 1f00 007f e84a 41ec 106e
616d 6541 6e64 5479 7065 4370 496e 666f
4f66 6673 6574 0100 0000 0000 0000 1a00
007f e84b 84ab 5074 7970 6520 6361 6e27
7420 6265 206e 756c 6c01 0000 0000 0000
001c 0000 0001 0346 8fa0 6973 416c 7068
614e 756d 6572 6963 5374 7269 6e67 0100
0000 0000 0000 3300 0000 0103 437a 0028
4c6a 6176 612f 6c61 6e67 2f43 6c61 7373
3c2a 3e3b 4c6a 6176 612f 6c61 6e67 2f43
6c61 7373 3c2a 3e3b 295a 0100 0000 0000
0000 5000 0000 0103 45b0 e028 4c6a 6176
612f 6c61 6e67 2f53 7472 696e 673b 5b4c
6a61 7661 2f6c 616e 672f 5374 7269 6e67
3b4c 6a61 7661 2f69 6f2f 4669 6c65 3b29
..........

 不同版本的jdk生存的快照文件可能不一样。 ( java version 1.8.0_144)

 然后下载Eclipse Memory Analyer分析工具进行分析

【Mac版 Eclipse Memory Analyzer报错问题】MemoryAnalyzer-1.8.1.20180910-macosx.cocoa.x86_64.zip

 

下载后双击解压：在文件夹窗口的显示名称是mat，命令行中看名称是mat.App。鼠标双击mat，报如下错误错

查看此log文件

!SESSION 2019-03-07 08:40:43.357 -----------------------------------------------
eclipse.buildId=unknown
java.version=1.8.0_181
java.vendor=Oracle Corporation
BootLoader constants: OS=macosx, ARCH=x86_64, WS=cocoa, NL=zh_CN
Framework arguments:  -keyring /Users/guchunchao/.eclipse_keyring
Command-line arguments:  -os macosx -ws cocoa -arch x86_64 -keyring /Users/guchunchao/.eclipse_keyring

!ENTRY org.eclipse.osgi 4 0 2019-03-07 08:40:48.803
!MESSAGE Application error
!STACK 1
java.lang.IllegalStateException: The platform metadata area could not be written: /private/var/folders/37/y__4k3h10q77946z33vk7hqm0000gn/T/AppTranslocation/65F1F51A-AE28-408E-BD87-E0A4EAA7E11E/d/mat.app/Contents/MacOS/workspace/.metadata.  By default the platform writes its content
under the current working directory when the platform is launched.  Use the -data parameter to
specify a different content area for the platform.
    at org.eclipse.core.internal.runtime.DataArea.assertLocationInitialized(DataArea.java:70)
    at org.eclipse.core.internal.runtime.DataArea.getStateLocation(DataArea.java:138)
    at org.eclipse.core.internal.preferences.InstancePreferences.getBaseLocation(InstancePreferences.java:44)
    at org.eclipse.core.internal.preferences.InstancePreferences.initializeChildren(InstancePreferences.java:209)
    at org.eclipse.core.internal.preferences.InstancePreferences.<init>(InstancePreferences.java:59)
    at org.eclipse.core.internal.preferences.InstancePreferences.internalCreate(InstancePreferences.java:220)
    at org.eclipse.core.internal.preferences.EclipsePreferences.create(EclipsePreferences.java:349)
    at org.eclipse.core.internal.preferences.EclipsePreferences.create(EclipsePreferences.java:337)
    at org.eclipse.core.internal.preferences.PreferencesService.createNode(PreferencesService.java:393)
    at org.eclipse.core.internal.preferences.RootPreferences.getChild(RootPreferences.java:60)
    at org.eclipse.core.internal.preferences.RootPreferences.getNode(RootPreferences.java:95)
    at org.eclipse.core.internal.preferences.RootPreferences.node(RootPreferences.java:84)
    at org.eclipse.core.internal.preferences.AbstractScope.getNode(AbstractScope.java:38)
    at org.eclipse.core.runtime.preferences.InstanceScope.getNode(InstanceScope.java:77)
    at org.eclipse.ui.preferences.ScopedPreferenceStore.getStorePreferences(ScopedPreferenceStore.java:225)
    at org.eclipse.ui.preferences.ScopedPreferenceStore.<init>(ScopedPreferenceStore.java:132)
    at org.eclipse.ui.plugin.AbstractUIPlugin.getPreferenceStore(AbstractUIPlugin.java:287)
    at org.eclipse.ui.internal.Workbench.lambda$3(Workbench.java:609)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:336)
    at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:597)
    at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:148)
    at org.eclipse.mat.ui.rcp.Application.start(Application.java:26)
    at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:388)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:243)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:656)
    at org.eclipse.equinox.launcher.Main.basicRun(Main.java:592)
    at org.eclipse.equinox.launcher.Main.run(Main.java:1498)

原因：/private/var/folders/37/y__4k3h10q77946z33vk7hqm0000gn/T/AppTranslocation/65F1F51A-AE28-408E-BD87-E0A4EAA7E11E/d/mat.app/Contents/MacOS/workspace/.metadata文件是只读的。

   解决方案：

   1、新建/Users/guchunchao/eclipse-analyser-log 目录

  2、重新定义log文件所在位置：打开mat.app/Contents/Eclipse/MemoryAnalyzer.ini,填入如下2行数据，位置一定要放在 --launcher.library之前

-startup
../Eclipse/plugins/org.eclipse.equinox.launcher_1.5.0.v20180512-1130.jar
-data
/Users/guchunchao/eclipse-analyser-log
--launcher.library
../Eclipse/plugins/org.eclipse.equinox.launcher.cocoa.macosx.x86_64_1.1.700.v20180518-1200
-vmargs
-Xmx1024m
-Dorg.eclipse.swt.internal.carbon.smallFonts
-XstartOnFirstThread

将mat复制到【应用程序】中，这样就可以通过【启动台】点击打开了

 

 图1

图2