Awesome

JVM Explorer

JVM Explorer is a Java desktop application for browsing loaded class files inside locally running Java Virtual Machines.

Features

Browse local JVMs
View all classes inside each JVM
Search to find specific classes (supports regex)
View classloader hierarchy
View decompiled bytecode
View disassembled bytecode
Re-assemble bytecode
Re-compile class file
Modify method implementations (insert, replace method body with java code)
Execute code in local JVMs
Export loaded classes to a JAR file
Browse the state of all static variables in a class (and their nested fields)
Modify the state of static variables (and their nested fields)
Replace class file definitions
View system properties of running JVMs
Run JAR files with a patched ProcessBuilder to remove any -XX:+DisableAttachMechanism argument

Demos

<details> <summary>Browse Classes And Fields</summary>

Notes:

Ctrl + Click on a class name in the class file viewer to open it
Search and press enter to open a class with the specified name
Edit a field value (under Fields tab) through Right Click -> Edit - only works for primitives and Strings

Browse Classes Example

</details> <details> <summary>Execute Code In Remote JVM</summary>

Notes:

You can call methods in the remote classes - the loaded classes are used for the compiler classpath

Execute Code Example

</details> <details> <summary>Show Class Loader Hierarchy</summary>

Class Loader Hierarchy Example

</details> <details> <summary>Launch Jar With Patched ProcessBuilder</summary>

Launch Patched Jar Example

</details> <details> <summary>Export Classes In Package</summary>

Export Classes Example

</details> <details> <summary>Modify Method</summary>

Notes:

You can insert code to the beginning of a method or replace the entire method body
The compiler currently uses the loaded classes as the classpath, so if a parameter type or return type isn't loaded, it may fail (you can replace the type with Object to make it compile if you don't need that type)
To access fields in the class, add a field with the same name and type in the class to compile - the reference will automatically be replaced

Modify Method Example

</details> <details> <summary>Modify Class</summary>

Notes:

Ctrl+S to re-recompile and patch class (or Right-Click -> Save Changes)
Often, decompiled code is not valid Java code, so it may not compile in some cases - the modify method feature is the workaround for this
The compiler currently uses the loaded classes as the classpath, so if some required type isn't loaded, it may fail

Modify Class Example

</details> <details> <summary>Modify Bytecode</summary>

Notes:

Ctrl+S to re-assemble and patch class (or Right-Click -> Save Changes)
The disassembler/assembler isn't perfect - it works most of the time but struggles with some cases (it uses OpenJDK AsmTools)

Modify Bytecode Example

</details>

Getting Started

There are three ways to run the application. Execute a provided platform-specific installer, a provided JAR file, or build and run it yourself. This application is intended to run on Java 11+ and can attach to JVMs running Java 7+.

Run Installer:

The platform-specific installers currently support Windows, Linux, and Mac with Intel 64-bit arch

Download a platform-specific installer (look at file extension) from the latest release
Run the installer
Launch the installed program

Run JAR:

A platform-specific JAR is provided for each OS/arch combinations

Download a jvm-explorer.jar file for your OS/arch (look at file name) from the latest release
Run the JAR (Java 11+)

Build And Run:

This approach will work on all platforms and architectures.

Clone with Git

git clone https://github.com/Naton1/jvm-explorer.git

Change into the project directory

cd jvm-explorer

Run with Gradle (Java 11+)

./gradlew run

Troubleshooting

Two logs files application.log and agent.log are created at [User Home]/jvm-explorer/logs

Must run the application with a Java version of at least Java 11
Must attach to a JVM running a Java version of at least Java 7
Must attach to a JVM running the same architecture - a 32-bit JVM must attach to a 32-bit JVM
May have to attach to a JVM that the same user started
Must attach to a JVM that supports the Java Attach API
If you run an old version of this application and attach it to a JVM, then update to a newer version and try to re-attach, the agent will be outdated. If there are changes in the client-server protocol, the agent will fail. Restart the target JVM to fix this.

Note: this uses the Java Attach API so any limitations will apply here.

Project Principles

Maintain a simple and easy-to-use interface
Take advantage of attaching to running JVMs - this is not a traditional GUI decompiler

Possible Enhancements

Plugins/scripting
Tabs/open multiple classes
Search code/improved search mechanism
Option to load all classes
Internationalization
Observe changes in fields

License

MIT License