java中如何读取文件？
内容摘要
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、RandomAcce
文章正文
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
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | //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
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | //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
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | // 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
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 | 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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