Decompile Java — Class File High Quality

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

#!/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 public class UserService private String apiKey = "secret";

All you have is a .jar file (or a lone .class file). Is the code lost forever? It’s decent for Java 11 but falls behind

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.