How to Modify Class Files Inside a JAR Using JD-GUI and Eclipse

First, install JD‑GUI with brew cask install jd-gui . Open the target JAR (e.g., sdklibs.jar ) in JD‑GUI, locate the class you want to change (such as CodeConfig.class ), and save it as a Java source file.

Create a new Java project in Eclipse (or any IDE) and import the saved Java file, ensuring the package structure matches the original decompiled file; otherwise compilation errors will occur.

Modify the desired fields in the Java source (for example, change the CLOUD_SERVER_URL constant), then compile the project to generate a new .class file.

Verify the compiled class by opening it with JD‑GUI to confirm the changes took effect.

Extract the original JAR with tar -zxvf sdklibs.jar . Inside the extracted directory, navigate to the com folder, delete the old class file, and copy the newly compiled .class file into the same location.

Re‑package the JAR, preserving the original directory layout, using the command: jar cfm Holmes.jar META-INF/MANIFEST.MF ./

The resulting Holmes.jar is the updated JAR containing the modified class.