读取文件有多种方式,基于传统的输入流方式或基于nio的Buffer缓冲对象和管道读取方式甚至非常快速的内存映射读取文件。
java中四种读取文件方式:(推荐:java视频教程)
1、RandomAccessFile:随机读取,比较慢优点就是该类可读可写可操作文件指针
2、FileInputStream:io普通输入流方式,速度效率一般
3、Buffer缓冲读取:基于nio Buffer和FileChannel读取,速度较快
4、内存映射读取:基于MappedByteBuffer,速度最快
RandomAccessFile读取
//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读取
//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缓冲对象读取
// 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(); }
内存映射读取
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
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