关于JAVA中流的flush问题

来源：互联网发布：linux setid 编辑：程序博客网时间：2024/04/29 20:51

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

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