【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   524f  4c45  2e30
2e31
     7fe8 4b05 81d0
 4c5f   4f4e
  007f e84c 04c2 d073 756e 2f73
   792f 706b  2f43 6f6e
 6e74 496e 666f
   45aa  4c6a  612f
 696c 2f53  3c54 453b 3e3b 4c6a
 612f 6c61 6e67 2f4f 626a  743b

 406c 696e 6b4d  686f
   1f00 007f e84a 41ec 106e
616d  6e64    496e 666f
4f66       1a00
007f e84b 84ab     6e27
  206e 756c 6c01
001c    8fa0  416c
614e 756d     6e67
      437a
4c6a  612f 6c61 6e67 2f43 6c61
3c2a 3e3b 4c6a  612f 6c61 6e67 2f43
6c61  3c2a 3e3b 295a
    45b0 e028 4c6a
612f 6c61 6e67 2f53  696e 673b 5b4c
6a61  2f6c 616e 672f   6e67
3b4c 6a61  2f69 6f2f  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 -- ::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   -- ::48.803
!MESSAGE Application error
!STACK
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:)
    at org.eclipse.core.internal.runtime.DataArea.getStateLocation(DataArea.java:)
    at org.eclipse.core.internal.preferences.InstancePreferences.getBaseLocation(InstancePreferences.java:)
    at org.eclipse.core.internal.preferences.InstancePreferences.initializeChildren(InstancePreferences.java:)
    at org.eclipse.core.internal.preferences.InstancePreferences.<init>(InstancePreferences.java:)
    at org.eclipse.core.internal.preferences.InstancePreferences.internalCreate(InstancePreferences.java:)
    at org.eclipse.core.internal.preferences.EclipsePreferences.create(EclipsePreferences.java:)
    at org.eclipse.core.internal.preferences.EclipsePreferences.create(EclipsePreferences.java:)
    at org.eclipse.core.internal.preferences.PreferencesService.createNode(PreferencesService.java:)
    at org.eclipse.core.internal.preferences.RootPreferences.getChild(RootPreferences.java:)
    at org.eclipse.core.internal.preferences.RootPreferences.getNode(RootPreferences.java:)
    at org.eclipse.core.internal.preferences.RootPreferences.node(RootPreferences.java:)
    at org.eclipse.core.internal.preferences.AbstractScope.getNode(AbstractScope.java:)
    at org.eclipse.core.runtime.preferences.InstanceScope.getNode(InstanceScope.java:)
    at org.eclipse.ui.preferences.ScopedPreferenceStore.getStorePreferences(ScopedPreferenceStore.java:)
    at org.eclipse.ui.preferences.ScopedPreferenceStore.<init>(ScopedPreferenceStore.java:)
    at org.eclipse.ui.plugin.AbstractUIPlugin.getPreferenceStore(AbstractUIPlugin.java:)
    at org.eclipse.ui.internal.Workbench.lambda$(Workbench.java:)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:)
    at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:)
    at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:)
    at org.eclipse.mat.ui.rcp.Application.start(Application.java:)
    at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:)
    at java.lang.reflect.Method.invoke(Method.java:)
    at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:)
    at org.eclipse.equinox.launcher.Main.basicRun(Main.java:)
    at org.eclipse.equinox.launcher.Main.run(Main.java:)

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-.jar
-data
/Users/guchunchao/eclipse-analyser-log
--launcher.library
../Eclipse/plugins/org.eclipse.equinox.launcher.cocoa.macosx.x86_64_1.1.700.v20180518-
-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