Decompile Java Class File May 2026

All you have is a .jar file (or a lone .class file). Is the code lost forever?

#!/bin/bash # decompile.sh JAR_FILE=$1 OUTPUT_DIR="./decompiled_src" unzip $JAR_FILE -d ./temp_classes Decompile all .class files find ./temp_classes -name "*.class" -type f | while read class; do java -jar cfr.jar "$class" --outputdir "$OUTPUT_DIR" done Clean up rm -rf ./temp_classes decompile java class file

Have a war story about decompiling a nasty legacy system? Share it in the comments below. All you have is a

public class UserService private String apiKey = "secret"; public String greetUser(String name) name.isBlank()) return "Hello, Guest!"; return "Hello, " + name.trim() + "!"; Share it in the comments below

// Original public void process(int userId, String userName) ... // Decompiled (without debug symbols) public void process(int n, String s) ... Here’s a practical script to decompile a whole JAR using CFR: