Mac OSX系统无法启动JEM.jar，如何运行Jython Music？

Hey there, let's get your JEM.jar up and running for Jython Music—this error is super common on macOS, and we can work through it step by step.

1. Verify your Java installation first #

JAR files rely on the Java Runtime Environment (JRE) to run. First, check if you have Java installed and if it's the right version:

• Open Terminal (found in Applications > Utilities)
• Run this command: java -version
  • If you see an error like "command not found", you need to install the JRE. Jython Music often works best with Java 8 (especially for older versions of JEM.jar), so grab the appropriate installer for your macOS version.
  • If you have Java installed but the version doesn't match what Jython Music requires, you can switch to the correct version temporarily. For example, if you need Java 8, run /usr/libexec/java_home -v 1.8 to get the path, then launch the jar with that specific Java instance:

    /Library/Java/JavaVirtualMachines/jdk1.8.0_XXX.jdk/Contents/Home/bin/java -jar JEM.jar
    

    (Replace jdk1.8.0_XXX with the actual folder name from the java_home output)

2. Launch the Jar via Terminal to see detailed errors #

Double-clicking a JAR on macOS often hides the real error message. Using Terminal will show you exactly what's going wrong:

• Navigate to the folder where JEM.jar is saved. For example, if it's in your Downloads folder:

  cd ~/Downloads
  

• Run the jar directly:

  java -jar JEM.jar
  

Pay attention to any error output here—it might tell you if there's a missing dependency, corrupted file, or permission issue that double-clicking didn't reveal.

3. Fix file permissions #

macOS's security settings might block the JAR from running, or the file might lack execution permissions:

• Check system security prompts: Right-click JEM.jar > Get Info. Scroll to the bottom—if you see a message saying "This file was blocked from opening because it is not from an identified developer", click Allow Anyway (you might need to enter your admin password).
• Add execution permissions via Terminal: Run this command in the folder with JEM.jar:

  chmod +x JEM.jar
  

Then try launching the jar again, either via double-click or Terminal.

4. Make sure the JAR file isn't corrupted #

Sometimes downloads get interrupted, leaving a broken JAR file. Try re-downloading JEM.jar from the official Jython Music source, wait for the download to complete fully, then attempt to launch it again.

5. Adjust macOS security settings (for unsigned JARs) #

If you're still seeing blocks, macOS might be restricting unsigned applications:

• Open System Settings > Privacy & Security.
• Scroll down to the "Security" section. If you see a message about JEM.jar being blocked, click Allow.
• If you don't see that option, you can temporarily allow apps from any source (note: this reduces security, so revert it after getting JEM.jar working):
  1. Run this in Terminal:

     sudo spctl --master-disable
     

  2. Enter your admin password (you won't see characters as you type).
  3. Go back to Privacy & Security—you should now see "Allow apps downloaded from: Any source". Select this, then launch JEM.jar.
  4. Once it's working, re-enable the security setting with:

     sudo spctl --master-enable
     

Start with step 2 first—seeing the actual error message will save you time troubleshooting. Most of the time, this is either a missing Java installation or a permission issue.

内容的提问来源于stack exchange，提问作者David James