先上源碼：

/*** Flushes this output stream and forces any buffered output bytes* to be written out. The general contract of <code>flush</code> is* that calling it is an indication that, if any bytes previously* written have been buffered by the implementation of the output* stream, such bytes should immediately be written to their* intended destination.* <p>* If the intended destination of this stream is an abstraction provided by* the underlying operating system, for example a file, then flushing the* stream guarantees only that bytes previously written to the stream are* passed to the operating system for writing; it does not guarantee that* they are actually written to a physical device such as a disk drive.* <p>* The <code>flush</code> method of <code>OutputStream</code> does nothing.** @exception IOException if an I/O error occurs.*/public void flush() throws IOException {}

總結(jié)有以下幾點(diǎn)：

1. flush()下達(dá)一條命令給緩沖區(qū)，讓它將所儲(chǔ)存的數(shù)據(jù)全部清空，即發(fā)送給下一級(jí)。

2. flush()刷空輸出流，并輸出所有被緩存的字節(jié)。由于某些流支持緩存功能，該方法將把緩存中所有內(nèi)容強(qiáng)制輸出到流中。

3.?OutputStream.flush()方法將所有寫(xiě)入到OutputStream的數(shù)據(jù)沖刷到相應(yīng)的目標(biāo)媒介中。比如，如果輸出流是FileOutputStream，那么寫(xiě)入到其中的數(shù)據(jù)可能并沒(méi)有真正寫(xiě)入到磁盤(pán)中。即使所有數(shù)據(jù)都寫(xiě)入到了FileOutputStream，這些數(shù)據(jù)還是有可能保留在內(nèi)存的緩沖區(qū)中。通過(guò)調(diào)用flush()方法，可以把緩沖區(qū)內(nèi)的數(shù)據(jù)刷新到磁盤(pán)(或者網(wǎng)絡(luò)，以及其他任何形式的目標(biāo)媒介)中。

例子：

// 模擬瀏覽器，給tomcat服務(wù)端發(fā)送符合http協(xié)議的請(qǐng)求消息 public static void main(String[] args) throws IOException {Socket s = new Socket("127.0.0.1", 80);PrintWriter out = new PrintWriter(s.getOutputStream());out.println("GET /myweb/test.jsp HTTP/1.1");out.println("Accept: */*");out.println("Accept-Language: zh-CN");out.println("Accept-Encoding: gzip, deflate");out.println();out.flush(); // 清空緩存并輸出流InputStream in = s.getInputStream();byte b[] = new byte[1024];int leng = 0;while((leng = in .read(b)) != -1){String str = new String(b, 0, leng);System.out.println(str);}s.close(); }

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總結(jié)

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