Web application failed to launch Spark job using SparkLauncher

Question

I want to launch a Spark job from a Javaee Web application, but SparkLauncher started without exception and there is no job started on Spark cluster. Anybody can help?

public static void runJob(String userId) throws Exception {
    long previous = System.currentTimeMillis();
    logger.info("initialize spark context...");
    init("spark-cluster-test.properties"); 
    Process spark = new SparkLauncher()
            .setSparkHome(spark_home)
            .setMaster(spark_master)
            .setAppName(app_name+timestamp)
            .setAppResource(jar_file)
            .setMainClass(main_class)
            .setConf(SparkLauncher.DRIVER_MEMORY, spark_driver_memory)
            .setConf("spark.network.timeout",spark_network_timeout)
            .setConf(SparkLauncher.DRIVER_EXTRA_CLASSPATH, class_path)
            .setConf(SparkLauncher.EXECUTOR_EXTRA_CLASSPATH, class_path)
            .setDeployMode(spark_deploy_mode)
            .addAppArgs(userId)
            .launch();
    spark.waitFor();
    logger.info("spark job is returned after " + (System.currentTimeMillis() - previous) + " miliseconds.");
}

Web server's log:

2016-01-20 10:27:17 -67129627 [http-bio-8088-exec-127] INFO    - SparkJobLauncher is started with userId=102
2016-01-20 10:27:17 -67129628 [http-bio-8088-exec-127] INFO    - initialize spark context...
2016-01-20 10:27:19 -67130838 [http-bio-8088-exec-127] INFO    - spark job is returned after 1 seconds.
2016-01-20 10:27:19 -67130839 [http-bio-8088-exec-127] DEBUG   - Creating a new SqlSession

But no job is started on Spark cluster. And the spark.waitFor() method returned right after the invoke, which is supposed to run for several seconds.