static void fileRead() throws IOException { long time = System.currentTimeMillis(); int bufSize = 10 * 1024 * 1024; byte[] bs = new byte[bufSize]; ByteBuffer byteBuf = ByteBuffer.allocate(bufSize); FileChannel channel = new RandomAccessFile(input_path, "r").getChannel(); FileWriter fw = null; for (int i = 0; channel.read(byteBuf) != -1; i++) { byteBuf.rewind(); int size = byteBuf.limit(); byteBuf.get(bs); fw = new FileWriter(String.format(output_path_format1, i)); String line = new String(bs, 0, size); fw.append(line + System.getProperty("line.separator")); fw.flush(); byteBuf.clear(); } fw.close(); time = System.currentTimeMillis() - time; System.out.println("file read time = " + time); } private static void bufferRead() throws IOException { long time = System.currentTimeMillis(); BufferedInputStream bis = new BufferedInputStream(new FileInputStream(new File(input_path))); int bufferSize = 10 * 1024 * 1024; BufferedReader in = new BufferedReader(new InputStreamReader(bis, "utf-8"), bufferSize); FileWriter fw = new FileWriter(String.format(output_path_format2, 0)); for (int i = 0; in.ready(); i++) { if (i % 100 == 0) { fw = new FileWriter(String.format(output_path_format2, i / 100)); } String line = in.readLine(); fw.append(line + System.getProperty("line.separator")); if (i % 100 == 0) { fw.flush(); } } in.close(); fw.close(); time = System.currentTimeMillis() - time; System.out.println("buffer read time = " + time); }

 

这是生成大文件的代码，修改for循环次数控制文件大小，下面生成的文件大小是2G左右

    private static String input_path = System.getProperty("user.dir") + File.separator + "data" + File.separator + "bigdata.txt";
    private static String output_path_format1 = System.getProperty("user.dir") + File.separator + "data" + File.separator + "part_1_%s.txt";
    private static String output_path_format2 = System.getProperty("user.dir") + File.separator + "data" + File.separator + "part_2_%s.txt";
    private static  int bufSize = 10 * 1024 * 1024;

     private static void makeBigData() throws IOException {
        FileWriter fw = new FileWriter(input_path);
        String line = "start ";
        for (int i = 0; i < 20000; i++) {
            line += i;
            fw.append(line + System.getProperty("line.separator"));
        }
        fw.flush();
        fw.close();
        System.out.println("end");
    }

 

三

因为是自己琢磨的，总感觉写的有点丑，特别是生成大文件那里，希望各位指正一番。

源码地址 https://github.com/247292980/spring-boot 。fork的比star还多什么道理啊。

 

java 读写操作大文件 BufferedReader和RandomAccessFile

标签：and   make   stream   read   for循环次数控制   大小   put   cep   out