How to know the main class of a jar file?

Easy. Here is an implementation from Hadoop.

java 代码

/**
 * A micro-application that prints the main class name out of a jar file.
 * @author Owen O'Malley
 */
public class PrintJarMainClass {

  /**
   * @param args
   */
  public static void main(String[] args) {
    try {
      JarFile jar_file = new JarFile(args[0]);
      if (jar_file != null) {
        Manifest manifest = jar_file.getManifest();
        if (manifest != null) {
          String value = manifest.getMainAttributes().getValue("Main-Class");
          if (value != null) {
            System.out.println(value.replaceAll("/", "."));
            return;
          }
        }
      }
    } catch (Throwable e) {
      // ignore it
    }
    System.out.println("UNKNOWN");
    System.exit(1);
  }

}

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