classloader

查看classloader的继承树，urls，类加载信息

classloader 命令将 JVM 中所有的classloader的信息统计出来，并可以展示继承树，urls等。

可以让指定的classloader去getResources，打印出所有查找到的resources的url。对于ResourceNotFoundException比较有用。

参数说明

参数名称 参数说明
[l] 按类加载实例进行统计
[t] 打印所有ClassLoader的继承树
[a] 列出所有ClassLoader加载的类，请谨慎使用
[c:] ClassLoader的hashcode
[c: r:] 用ClassLoader去查找resource
[c: load:] 用ClassLoader去加载指定的类

使用参考

按类加载类型查看统计信息

  1. $ classloader
  2.  name                                       numberOfInstances  loadedCountTotal
  3.  com.taobao.arthas.agent.ArthasClassloader  1                  2115
  4.  BootstrapClassLoader                       1                  1861
  5.  sun.reflect.DelegatingClassLoader          5                  5
  6.  sun.misc.Launcher$AppClassLoader           1                  4
  7.  sun.misc.Launcher$ExtClassLoader           1                  1
  8. Affect(row-cnt:5) cost in 3 ms.

按类加载实例查看统计信息

  1. $ classloader -l
  2.  name                                                loadedCount  hash      parent
  3.  BootstrapClassLoader                                1861         null      null
  4.  com.taobao.arthas.agent.ArthasClassloader@68b31f0a  2115         68b31f0a  sun.misc.Launcher$ExtClassLoader@66350f69
  5.  sun.misc.Launcher$AppClassLoader@3d4eac69           4            3d4eac69  sun.misc.Launcher$ExtClassLoader@66350f69
  6.  sun.misc.Launcher$ExtClassLoader@66350f69           1            66350f69  null
  7. Affect(row-cnt:4) cost in 2 ms.

查看ClassLoader的继承树

  1. $ classloader -t
  2. +-BootstrapClassLoader
  3. +-sun.misc.Launcher$ExtClassLoader@66350f69
  4.   +-com.taobao.arthas.agent.ArthasClassloader@68b31f0a
  5.   +-sun.misc.Launcher$AppClassLoader@3d4eac69
  6. Affect(row-cnt:4) cost in 3 ms.

查看URLClassLoader实际的urls

  1. $ classloader -c 3d4eac69
  2. file:/private/tmp/arthas-demo.jar
  3. file:/Users/hengyunabc/.arthas/lib/3.0.5/arthas/arthas-agent.jar
  5. Affect(row-cnt:9) cost in 3 ms.

使用ClassLoader去查找resource

  1. $ classloader -c 3d4eac69  -r META-INF/MANIFEST.MF
  2.  jar:file:/System/Library/Java/Extensions/MRJToolkit.jar!/META-INF/MANIFEST.MF
  3.  jar:file:/private/tmp/arthas-demo.jar!/META-INF/MANIFEST.MF
  4.  jar:file:/Users/hengyunabc/.arthas/lib/3.0.5/arthas/arthas-agent.jar!/META-INF/MANIFEST.MF

也可以尝试查找类的class文件：

  1. $ classloader -c 1b6d3586 -r java/lang/String.class
  2.  jar:file:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/rt.jar!/java/lang/String.class

使用ClassLoader去加载类

  1. $ classloader -c 3d4eac69 --load demo.MathGame
  2. load class success.
  3.  class-info        demo.MathGame
  4.  code-source       /private/tmp/arthas-demo.jar
  5.  name              demo.MathGame
  6.  isInterface       false
  7.  isAnnotation      false
  8.  isEnum            false
  9.  isAnonymousClass  false
  10.  isArray           false
  11.  isLocalClass      false
  12.  isMemberClass     false
  13.  isPrimitive       false
  14.  isSynthetic       false
  15.  simple-name       MathGame
  16.  modifier          public
  17.  annotation
  18.  interfaces
  19.  super-class       +-java.lang.Object
  20.  class-loader      +-sun.misc.Launcher$AppClassLoader@3d4eac69
  21.                      +-sun.misc.Launcher$ExtClassLoader@66350f69
  22.  classLoaderHash   3d4eac69