关于JAVA中流的flush问题

目前在学习Socket，因为和IO关系紧密，于是顺便也学了下IO

发现有这样一句话：

The flush method is valid on any output stream,but has no effect unless the stream is buffered

这句话意思是所有的输出流都有flush方法，但是仅对缓冲流有效

看到这里，笔者想到了自己写的serversocket类，部分代码如下，没有用buffered流也调用了flush方法啊？于是进行了一番探讨

private OutputStream ous;
ous = socket.getOutputStream();
public void sendMsg(String msg){
		PrintWriter out = new PrintWriter(ous);
		out.println("消息:"+msg);
		out.flush();
}

看到这里用PrintWriter包装了OutputStream流，OutputStream肯定为非缓冲流，所以问题一定出在PrintWriter上

让我们来看一下PrintWriter的底层代码，部分相关代码如下

public class PrintWriter extends Writer {
    protected Writer out;
    private final boolean autoFlush;

     /**
     * Creates a new PrintWriter, without automatic line flushing.
     *
     * @param  out        A character-output stream
     */
    public PrintWriter (Writer out) {
        this(out, false);
    }
     /**
     * Creates a new PrintWriter.
     *
     * @param  out        A character-output stream
     * @param  autoFlush  A boolean; if true, the <tt>println</tt>,
     *                    <tt>printf</tt>, or <tt>format</tt> methods will
     *                    flush the output buffer
     */
    public PrintWriter(Writer out,
                       boolean autoFlush) {
        super(out);
        this.out = out;
        this.autoFlush = autoFlush;
        lineSeparator = java.security.AccessController.doPrivileged(
            new sun.security.action.GetPropertyAction("line.separator"));
    }
    public PrintWriter(OutputStream out) {
        this(out, false);
    }
}

如上所示，这样我们就很清楚了，当调用包装OutputStream的构造方法时，autoFlush参数是falus