Have a war story about decompiling a nasty legacy system? Share it in the comments below.
public class UserService private String apiKey = "secret"; public String greetUser(String name) name.isBlank()) return "Hello, Guest!"; return "Hello, " + name.trim() + "!";
java -jar procyon-decompiler.jar -o ./output MyClass.class If you use IntelliJ IDEA, you already have a decompiler. Open any .class file inside a JAR dependency. IDEA uses FernFlower under the hood. It’s decent for Java 11 but falls behind CFR for bleeding-edge syntax. Real-World Example: Decompiling a Simple Class Let's say you have this compiled UserService.class : decompile java class file
public class UserService private String apiKey = "secret"; public String greetUser(String name)
All you have is a .jar file (or a lone .class file). Is the code lost forever? Have a war story about decompiling a nasty legacy system
// 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:
We’ve all been there. You inherit a legacy project with no source code, a critical dependency throws an unexplainable error, or a vendor goes out of business taking their documentation with you. Open any
#!/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