讀取檔案有多種方式，基於傳統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）
#1、RandomAccessFile：隨機讀取，比較慢優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緩衝讀取：基於nio 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类的核心在于其既能读又能写
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文件输入流,比较中规中矩的一种方式,传统阻塞IO操作。
public void testFielInputStreamTest() throws Exception {
FileInputStream inputStream = new FileInputStream(new File("e:/nio/test.txt"));
// 使用输入流读取文件,以下代码块几乎就是模板代码
byte[] bytes = new byte[1024];
int len = 0;
while ((len = inputStream.read(bytes)) != -1) {// 如果有数据就一直读写,否则就退出循环体,关闭流资源。
System.out.println(new String(bytes, 0, len, "gbk"));
}
inputStream.close();
}Buffer緩衝物件讀取
// nio 读取
public void testBufferChannel() throws Exception {
FileInputStream inputStream = new FileInputStream(new File("e:/nio/test.txt"));
FileChannel fileChannel = inputStream.getChannel();
ByteBuffer buffer = ByteBuffer.allocate(1024);
// 以下代码也几乎是Buffer和Channle的标准读写操作。
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();
}
//基于内存映射这种方式，这么写好像有问题。
MappedByteBuffer和RandomAcessFile这两个类要单独重点研究一下。
//TODO 大文件读取java基礎教程專欄。
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