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 line.separator, 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