java输出换行的标准姿势"line.separator"

java中写.txt文件，实现换行的几种方法：
1.使用java中的转义符"\r\n": 
windows下的文本文件换行符:\r\n
linux/unix下的文本文件换行符:\r
Mac下的文本文件换行符:\n

1.String str="aaa";
2.str+="\r\n";  

2.BufferedWriter的newline()方法:

FileOutputStream fos=new FileOutputStream("c;\\11.txt");
BufferedWriter bw=new BufferedWriter(fos);
bw.write("你好");
bw.newline();
bw.write("java");
bw.newline();   

    /**
     * Creates a new buffered character-output stream that uses an output
     * buffer of the given size.
     *
     * @param  out  A Writer
     * @param  sz   Output-buffer size, a positive integer
     *
     * @exception  IllegalArgumentException  If sz is <= 0
     */
    public BufferedWriter(Writer out, int sz) {
    super(out);
    if (sz <= 0)
        throw new IllegalArgumentException("Buffer size <= 0");
    this.out = out;
    cb = new char[sz];
    nChars = sz;
    nextChar = 0;
 
    lineSeparator =    (String) java.security.AccessController.doPrivileged(
               new sun.security.action.GetPropertyAction("line.separator"));
    }

BufferedWriter中newline()方法：
  /**
     * Writes a line separator.  The line separator string is defined by the
     * system property <tt>line.separator</tt>, and is not necessarily a single
     * newline ('\n') character.
     *
     * @exception  IOException  If an I/O error occurs
     */
    public void newLine() throws IOException {
    write(lineSeparator);
    }

3.使用System.getProperty()方法:

String str = "Output:"+System.getProperty("line.separator");  

http://www.cnblogs.com/todoit/archive/2012/04/27/2473232.html

PrintWriter在以下以pw代替，在写client与server进行测试的通讯程序时，用pw.println(str)可以把数据发送给客户端，而pw.write(str)却不行！
查看源码发现:
pw.println(str)方法是由write方法与println()方法组成，而println()方法中执行了newLine()方法。
    而 newLine()实现中有一条out.write(lineSeparator);
    即println(str)方法比write方法中多输出了一个lineSeparator字符;  
    其中lineSeparator实现为：
    lineSeparator = (String) java.security.AccessController.doPrivileged(new sun.security.action.GetPropertyAction("line.separator"));
   而line.separator属性跟据每个系统又是不一样的。
   println()方法的注释说明中提到:
  /**
   * Terminates the current line by writing the line separator string.  The
   * line separator string is defined by the system property
   * <code>line.separator</code>, and is not necessarily a single newline
   * character (<code>'\n'</code>).
   */
    在我机器上（windows）测试，默认的lineSeparator输出的十六进制为13 10即\r\n
    这样write方法修改为:write(str+"\r\n")即达到了与println(str)一样的效果了。

http://blog.csdn.net/vhomes/article/details/6650576