Java讀寫Properties檔案及JavaIO中位元組流和字元的轉換

讀寫properties檔案

Java讀寫Properties檔案是一個比較常見的需求，一般的做法是將properties檔案讀到Properties類對象中，通過Properteis對象來操作。下面是一段執行個體代碼：

    /**     * Read Properties file with ASCII codes only     */ public static Properties getProperties(String fileName, String path){    Properties props = new Properties();        InputStream in = null;try {in = new FileInputStream(path + fileName);} catch (FileNotFoundException e1) {System.out.println("Can't find c3p0.properties");}    try {props.load(in);in.close();} catch (IOException e) {System.out.println("Can't load c3p0.properties");}       return props;    }

上面的代碼是用於讀取僅包含ASCII碼的properties檔案，特點是只用了FileInputStream，而沒有像往常一樣在外面套個FileReader。下面的代碼用於寫ASCII編碼的properties檔案：

    /**     *      */    private void setPassword(String passWord){    Properties props = DBUtil.getC3P0Properties();    FileOutputStream out;try {String path = DBUtil.getFullPath(this.getClass());out = new FileOutputStream(path + "/c3p0.properties" );            props.setProperty("c3p0.password", passWord);            props.store(out, "Prevent connect for failed connection");            out.close();} catch (FileNotFoundException e) {// TODO Auto-generated catch blocke.printStackTrace();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}    }

位元組流到字元的轉換

關於Java I/O的更全面資訊，可以參考Developerworks上的這篇文章：http://www.ibm.com/developerworks/cn/java/j-lo-javaio/

這裡貼一下StreamDecoder中的核心方法，看看StreamDecoder是怎樣將Stream轉為Character的吧：

  private int read0() throws IOException {        synchronized (lock) {            // Return the leftover char, if there is one            if (haveLeftoverChar) {                haveLeftoverChar = false;                return leftoverChar;            }            // Convert more bytes            char cb[] = new char[2];            int n = read(cb, 0, 2);            switch (n) {            case -1:                return -1;            case 2:                leftoverChar = cb[1];                haveLeftoverChar = true;                // FALL THROUGH            case 1:                return cb[0];            default:                assert false : n;                return -1;            }        }    }

從上面的代碼可以看出，StreamDecoder每次讀入兩個byte，然後逐個位元組進行解析。