Java读写Properties文件及JavaIO中字节流和字符的转换

读写properties文件

Java读写Properties文件是一个比较常见的需求，一般的做法是将properties文件读到Properties类对象中，通过Properteis对象来操作。下面是一段实例代码：

    /**
     * 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;
    }

上面的代码是用于读取仅包含ASCII码的properties文件，特点是只用了FileInputStream，而没有像往常一样在外面套个FileReader。下面的代码用于写ASCII编码的properties文件：

    /**
     * 
     */
    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 block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
    }

字节流到字符的转换

关于Java I/O的更全面信息，可以参考Developerworks上的这篇文章：http://www.ibm.com/developerworks/cn/java/j-lo-javaio/

这里贴一下StreamDecoder中的核心方法，看看StreamDecoder是怎样将Stream转为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;
            }
        }
    }

从上面的代码可以看出，StreamDecoder每次读入两个byte，然后逐个字节进行解析。