讀取檔案有多種方式，基於傳統(tǒng)的輸入流方式或基於nio的Buffer緩衝物件和管道讀取方式甚至非常快速的記憶體映射讀取檔案。

java中四種讀取檔案方式：（建議：java影片教學(xué)）

#1、RandomAccessFile：隨機讀取，比較慢優(yōu)點就是該類別可讀可寫入可操作檔案指標

2、FileInputStream：io普通輸入流方式，速度效率一般

3、Buffer緩衝讀?。夯秐io Buffer和FileChannel讀取，速度較快

4、記憶體映射讀取：基於MappedByteBuffer,速度最快

#RandomAccessFile讀取

//RandomAccessFile類的核心在于其既能讀又能寫

public?void?useRandomAccessFileTest()?throws?Exception?{

????RandomAccessFile?randomAccessFile?=?new?RandomAccessFile(new?File("e:/nio/test.txt"),?"r");

????byte[]?bytes?=?new?byte[1024];
????int?len?=?0;
????while?((len?=?randomAccessFile.read(bytes))?!=?-1)?{
????????System.out.println(new?String(bytes,?0,?len,?"gbk"));
????}

????randomAccessFile.close();
}

##FielInputStream讀取

//使用FileInputStream文件輸入流,比較中規(guī)中矩的一種方式,傳統(tǒng)阻塞IO操作。

public?void?testFielInputStreamTest()?throws?Exception?{

????FileInputStream?inputStream?=?new?FileInputStream(new?File("e:/nio/test.txt"));

????//?使用輸入流讀取文件,以下代碼塊幾乎就是模板代碼
????byte[]?bytes?=?new?byte[1024];
????int?len?=?0;
????while?((len?=?inputStream.read(bytes))?!=?-1)?{//?如果有數(shù)據(jù)就一直讀寫,否則就退出循環(huán)體,關(guān)閉流資源。
????????System.out.println(new?String(bytes,?0,?len,?"gbk"));
????}
????inputStream.close();
}

Buffer緩衝物件讀取

//?nio?讀取

public?void?testBufferChannel()?throws?Exception?{

????FileInputStream?inputStream?=?new?FileInputStream(new?File("e:/nio/test.txt"));

????FileChannel?fileChannel?=?inputStream.getChannel();
????ByteBuffer?buffer?=?ByteBuffer.allocate(1024);

????//?以下代碼也幾乎是Buffer和Channle的標準讀寫操作。
????while?(true)?{
????????buffer.clear();
????????int?result?=?fileChannel.read(buffer);
????????buffer.flip();
????????if?(result?==?-1)?{
????????????break;
????????}
????????System.out.println(new?String(buffer.array(),?0,?result,?"gbk"));
????}
????inputStream.close();
}

記憶體映射讀取

public?void?testmappedByteBuffer()?throws?Exception?{

????FileInputStream?inputStream?=?new?FileInputStream(new?File("e:/nio/test.txt"));
????FileOutputStream?outputStream?=?new?FileOutputStream(new?File("e:/nio/testcopy.txt"),true);

????FileChannel?inChannel?=?inputStream.getChannel();
????FileChannel?outChannel?=?outputStream.getChannel();

????System.out.println(inChannel.size());
????MappedByteBuffer?mappedByteBuffer?=?inChannel.map(MapMode.READ_ONLY,?0,?inChannel.size());

????System.out.println(mappedByteBuffer.limit());
????System.out.println(mappedByteBuffer.position());

????mappedByteBuffer.flip();
????outChannel.write(mappedByteBuffer);

????outChannel.close();
????inChannel.close();
????outputStream.close();
????inputStream.close();

}

//基于內(nèi)存映射這種方式，這么寫好像有問題。


MappedByteBuffer和RandomAcessFile這兩個類要單獨重點研究一下。

//TODO?大文件讀取

java基礎(chǔ)教程專欄。

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