main 方法的书写（2）

3、从参数列表中提取参数

    /**
     * <p>
     * Parses value from the argument.
     * </p>
     * 
     * @param arg
     *            the argument.
     * @param key
     *            the switch key.
     * 
     * @return the parsed value.
     */
    private static String parseArg(String arg, String key) {

        String value = arg.substring(key.length());

        // Value cannot be empty
        if (value.trim().length() == 0) {
            printAndExit(false, -1, null, "The value of switch '" + key
                    + "' cannot be empty.");
        }

        return value;
    }

4、常用变量的定义

/**
     * <p>
     * Represents the switch '-config='.
     * </p>
     */
    private static final String SWITCH_CONFIG = "-config=";

    /**
     * <p>
     * Represents the switch to print usage message.
     * </p>
     */
    private static final List<String> SWITCH_HELP = Arrays.asList(new String[]{
            "-help", "-h"});
   /**
     * <p>
     * Represents the line separator.
     * </p>
     */
    private static final String LINE_SEP = System.getProperty("line.separator");