main 方法的书写（1）

1、打印消息并且退出

/**
     * <p>
     * Prints out the given exception or message, and then exit.
     * </p>
     *
     * @param printUsage
     *            the flag indicates whether printing out the usage is needed.
     * @param exitCode
     *            the exit status.
     * @param exception
     *            the exception to print.
     * @param message
     *            the message to print.
     */
    private static void printAndExit(boolean printUsage, int exitCode, Throwable exception, String message) {
        if (message != null) {
            // Print out the error message
            System.out.println(message);
        }
        if (exception != null) {
            // Print out the exception
            exception.printStackTrace(System.out);
        }

 

        if (printUsage) {
            // Print out the usage to the screen
            System.out.println(USAGE_MESSAGE);
        }

        // Exit
        System.exit(exitCode);
    }

     注意上面参数中的exitCode，如果程序正常结束则为0，如果遇到错误，则根据错误码的含义以对应的错误码结束。

2、帮助信息的打印

/**
     * <p>
     * Represents the usage message.
     * </p>
     */
    private static final String USAGE_MESSAGE = "Usage: java -jar converter.jar"
        + " [-config=<configFile>] [-countryCode=<CODE1 CODE2 ... CODEN>] [-h|-help]" + LINE_SEP
        + "               <configFile> Optional. The file path of the configuration file."
        + " Default is 'config.properties'. If given, it must be the first parameter." + LINE_SEP
        + "    <CODE1 CODE2 ... CODEN> Optional. One or more country codes separated by white spaces"
        + " for which price files are to be converted." + LINE_SEP
        + "                   -h|-help Optional. Prints out this usage message.";