java輸出換行的標准姿勢"line.separator"

java中寫.txt文件，實現換行的幾種方法：
1.使用java中的轉義符"\r\n": 
windows下的文本文件換行符:\r\n
linux/unix下的文本文件換行符:\r
Mac下的文本文件換行符:\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，在寫client與server進行測試的通訊程序時，用pw.println(str)可以把數據發送給客戶端，而pw.write(str)卻不行！
查看源碼發現:
pw.println(str)方法是由write方法與println()方法組成，而println()方法中執行了newLine()方法。
    而 newLine()實現中有一條out.write(lineSeparator);
    即println(str)方法比write方法中多輸出了一個lineSeparator字符;  
    其中lineSeparator實現為：
    lineSeparator = (String) java.security.AccessController.doPrivileged(new sun.security.action.GetPropertyAction("line.separator"));
   而line.separator屬性跟據每個系統又是不一樣的。
   println()方法的注釋說明中提到:
  /**
   * 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>).
   */
    在我機器上（windows）測試，默認的lineSeparator輸出的十六進制為13 10即\r\n
    這樣write方法修改為:write(str+"\r\n")即達到了與println(str)一樣的效果了。

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