# dump
dump online tutorialopen in new window
TIP
Dump the bytecode for the particular classes to the specified directory.
The dump command is used to dump the bytecode of classes actually running in the JVM to a specified directory. It is suitable for bulk downloading the bytecode of classes in a specific package directory. If you need to decompile a single class or view class information in real-time, you can refer to jad.
# Options
| Name | Specification |
|---|---|
| class-pattern | class name pattern |
[c:] | hashcode of the class loader that loaded the target class |
[classLoaderClass:] | The class name of the ClassLoader that executes the expression. |
[d:] | set the destination directory for class files |
[E] | turn on regex match, the default behavior is wild card match |
# Usage
$ dump java.lang.String
HASHCODE CLASSLOADER LOCATION
null /Users/admin/logs/arthas/classdump/java/lang/String.class
Affect(row-cnt:1) cost in 119 ms.
$ dump demo.*
HASHCODE CLASSLOADER LOCATION
3d4eac69 +-sun.misc.Launcher$AppClassLoader@3d4eac69 /Users/admin/logs/arthas/classdump/sun.misc.Launcher$AppClassLoader-3d4eac69/demo/MathGame.class
+-sun.misc.Launcher$ExtClassLoader@66350f69
Affect(row-cnt:1) cost in 39 ms.
$ dump -d /tmp/output java.lang.String
HASHCODE CLASSLOADER LOCATION
null /tmp/output/java/lang/String.class
Affect(row-cnt:1) cost in 138 ms.
- Specify classLoader
Note that the hashcode changes, you need to check the current ClassLoader information first, and extract the hashcode corresponding to the ClassLoader.
if you use-c, you have to manually type hashcode by -c <hashcode>.
$ dump -c 3d4eac69 demo.*
For classloader with only one instance, it can be specified by --classLoaderClass using class name, which is more convenient to use.
$ dump --classLoaderClass sun.misc.Launcher$AppClassLoader demo.*
HASHCODE CLASSLOADER LOCATION
3d4eac69 +-sun.misc.Launcher$AppClassLoader@3d4eac69 /Users/admin/logs/arthas/classdump/sun.misc.Launcher$AppClassLoader-3d4eac69/demo/MathGame.class
+-sun.misc.Launcher$ExtClassLoader@66350f69
Affect(row-cnt:1) cost in 39 ms.
- PS: Here the classLoaderClass in java 8 is sun.misc.Launcher$AppClassLoader, while in java 11 it's jdk.internal.loader.ClassLoaders$AppClassLoader. Currently killercoda using java 11.
The value of --classloaderclass is the class name of classloader. It can only work when it matches a unique classloader instance. The purpose is to facilitate the input of general commands. However, -c <hashcode> is dynamic.