BSKJ/java-decompiler-plugin/skills/decompile-classes/SKILL.md

name	description	version
decompile-classes	Decompile Java .class files back to source code. Use when user wants to restore compiled Java projects, reverse engineer class files, or convert bytecode to readable Java source.	1.0.0

Java Class Decompilation Guide

This skill guides the decompilation of Java .class files back to readable source code.

When to Use

• User has compiled .class files without source code
• User wants to restore a Java project from compiled artifacts
• User needs to understand legacy compiled code
• User wants to reverse engineer a Java application

Decompilation Process

Step 1: Assess the Project

Before decompiling, gather information:

# Count class files
find <classes_dir> -name "*.class" | wc -l

# List package structure
find <classes_dir> -name "*.class" | sed 's|/[^/]*\.class$||' | sort -u

# Check for inner classes
find <classes_dir> -name "*\$*.class" | wc -l

Step 2: Download CFR Decompiler

CFR is the recommended decompiler for modern Java:

# Download to plugin scripts directory
curl -L -o scripts/cfr.jar https://github.com/leibnitz27/cfr/releases/download/0.152/cfr-0.152.jar

Step 3: Run Batch Decompilation

Use the decompile script:

bash C:/Users/K/.claude/plugins/cache/claude-plugins-official/plugin-dev/9eae436aa296/scripts/decompile.sh <input_dir> <output_dir>

Or decompile individual files:

java -jar cfr.jar MyClass.class --outputdir ./src

Step 4: Handle Decompilation Issues

Common issues and solutions:

Issue	Solution
Enum classes	CFR handles these well by default
Lambda expressions	Use --decodelambdas true
Inner classes	CFR outputs them as separate files
Obfuscated code	Use --renamedupmembers true
Missing dependencies	Add classpath with --extraclasspath

Step 5: Verify Decompiled Code

After decompilation:

1. Check file count matches original
2. Look for decompilation errors in output
3. Verify package structure is preserved
4. Spot-check complex classes for correctness

CFR Command Options

java -jar cfr.jar <input> [options]

Options:
  --outputdir <dir>     Output directory
  --silent              Suppress progress output
  --decodelambdas       Decode lambda expressions
  --decodestringswitch  Decode string switches
  --decodeswitch        Decode switch statements
  --renamedupmembers    Rename duplicate members
  --removeboilerplate   Remove boilerplate code
  --removeinnerclasses  Remove inner class references
  --showinferredlambdaithrows  Show inferred lambda throws
  --extraclasspath <path>  Additional classpath for dependencies

Post-Decompilation

After successful decompilation:

1. Run analyze-structure to understand the project
2. Run generate-project to create Maven/Gradle structure
3. Run analyze-dependencies to map dependencies
4. Review and fix any decompilation artifacts

Tips

• Large projects: Process in batches to manage memory
• Error recovery: CFR is resilient, but check output for errors
• Naming conflicts: Inner classes may cause naming issues
• Encoding: Ensure UTF-8 for Chinese/Unicode content
• Dependencies: Some classes may reference external JARs