Java-J2SE-IO-drain()和flush()

Javadoc中關於這兩個方法的描述如下

drain(): Drain any buffered data in ObjectOutputStream. Similar to flush but does not propagate the flush to the underlying stream. 將當前流中的所有緩衝數據寫入底層流，但不會對底層流執行flush.

flush(): Flushes this stream by writing any buffered output to the underlying stream.flush()方法強制將當前輸出流緩衝區中所有數據寫入底層流，若當前流已是最底層則將流中所有數據寫入預期目標中（如文件）.

 

這裏選取ObjectOutputStream中的兩個有具體實現的drain()和flush()方法進行對比

drain()

/**
 * Writes all buffered data from this stream to the underlying stream,
 * but does not flush underlying stream.
 * 將當前流中的所有緩衝數據寫入底層流（這裏底層流一般是FileOutputStream），但不會對底層流執行flush。
 */
 void drain() throws IOException {
     if (pos == 0) {
         return;
     }
     if (blkmode) {
         writeBlockHeader(pos);
     }
     //buf: 用於寫入常規/塊數據的緩衝區,是整個ObjectOutputStream的緩衝區
     out.write(buf, 0, pos);
     pos = 0;
 }

flush()

/**
 * Flushes the stream. This will write any buffered output bytes and flush
 * through to the underlying stream.
 * flush()方法強制將當前輸出流緩衝區中所有數據寫入底層流（這裏底層流一般是FileOutputStream）
 * 若當前流已是最底層（如當前流是FileOutputStream）則將流中所有數據寫入預期目標中（如文件）
 */
 public void flush() throws IOException {
     bout.flush();
 }