Java--Stream，NIO ByteBuffer，NIO MappedByteBuffer性能對比，mappedbytebuffer

Java--Stream，NIO ByteBuffer，NIO MappedByteBuffer性能對比，mappedbytebuffer

目前Java中最IO有多種文件讀取的方法，本文章對比Stream，NIO ByteBuffer，NIO MappedByteBuffer的性能，讓我們知道到底怎麼能寫出性能高的文件讀取代碼。

package com.seeyon.nio;

import org.junit.Test;

import java.io.*;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

/**
 * Created by yangyu on 16/12/28.
 */

/**
 * 比較Stream流，NIO ByteBuffer，NIO MappedByteBuffer性能對比
 * 其中Stream最慢，NIO MappedByteBuffer最快
 * Stream：1000ms
 * NIO ByteBuffer:220ms
 * NIO MappedByteBuffer:112ms
 */
public class Compare {

    /**
     * 使用stream作為IO流讀取和寫入文件
     * 速度：1000ms左右
     *
     * @throws IOException
     */
    @Test
    public void useStream() throws IOException {

        long startTime = System.currentTimeMillis();
        /**
         * 4000000個整數長度的文件
         */
        int num = 2000 * 2000;

        /**
         * 帶緩沖的輸出流，寫文件
         */
        DataOutputStream dataOutputStream = new DataOutputStream(new BufferedOutputStream(new FileOutputStream("/Users/yangyu/Downloads/compare.tmp")));
        for (int i = 0; i < num; i++) {
            dataOutputStream.writeInt(i);
        }
        dataOutputStream.close();

        int data = 0;
        /**
         * 帶緩沖的輸入流，讀文件
         */
        DataInputStream in = new DataInputStream(new BufferedInputStream(new FileInputStream("/Users/yangyu/Downloads/compare.tmp")));
        try {
            while (true) {
                data = in.readInt();
            }
        } catch (EOFException e) {
            System.out.println("讀取完成"+data);
        }
        in.close();
        long endTime = System.currentTimeMillis();
        System.out.println("ms:" + (endTime - startTime));
    }

    /**
     * 使用NIO ByteBuffer
     * 時間：220ms
     * @throws IOException
     */
    @Test
    public void useNioByteBuffer() throws IOException {
        long startTime = System.currentTimeMillis();
        int num = 2000*2000;
        /**
         * 文件輸出流
         */
        FileOutputStream fileOutputStream = new FileOutputStream("/Users/yangyu/Downloads/compare.tmp");
        /**
         * NIO Channel 通道
         */
        FileChannel fileChannel = fileOutputStream.getChannel();
        /**
         * ByteBuffer緩沖區
         */
        ByteBuffer buffer = ByteBuffer.allocate(num*5);
        for (int i = 0; i < num; i++) {
            buffer.putInt(i);
        }
        /**
         * 為寫做准備
         */
        buffer.flip();
        /**
         * 寫操作
         */
        fileChannel.write(buffer);
        fileChannel.close();

        /**
         * 緩沖區
         */
        ByteBuffer buffer1 = ByteBuffer.allocate(num*5);
        /**
         * 文件輸入流
         */
        FileInputStream in = new FileInputStream("/Users/yangyu/Downloads/compare.tmp");
        /**
         * 輸入通道
         */
        FileChannel fin = in.getChannel();
        /**
         * 為讀取做准備
         */
        buffer1.clear();
        System.out.println(buffer1.limit());
        /**
         * 讀取
         */
        fin.read(buffer1);
        fin.close();

        long endTime = System.currentTimeMillis();
        System.out.println("ms:" + (endTime - startTime));
        buffer1.flip();
        System.out.println(buffer1.limit());
    }

    /**
     * 使用MappedByteBuffer，通過FileChannel將文件映射到內存
     * 時間：112ms
     * @throws IOException
     */
    @Test
    public void useRandomAccess() throws IOException {
        long startTime = System.currentTimeMillis();
        int num = 2000*2000;

        /**
         * 使用可隨機訪問位置的RandomAccessFile
         */
        RandomAccessFile file = new RandomAccessFile("/Users/yangyu/Downloads/compare.tmp","rw");
        /**
         * 獲取通道Channel
         */
        FileChannel fileChannel = file.getChannel();
        /**
         * 將文件映射到緩沖區MappedByteBuffer
         */
        MappedByteBuffer mappedByteBuffer = fileChannel.map(FileChannel.MapMode.READ_WRITE,0,num*4);
        /**
         * 寫文件
         */
        for (int i = 0; i < num; i++) {
            mappedByteBuffer.putInt(i);
        }
        fileChannel.close();

        int data=0;
        RandomAccessFile file1 = new RandomAccessFile("/Users/yangyu/Downloads/compare.tmp","rw");
        FileChannel fc = file1.getChannel();
        MappedByteBuffer mappedByteBuffer1 = fc.map(FileChannel.MapMode.READ_WRITE,0,file1.length());
        /**
         * 讀文件
         */
        while (mappedByteBuffer1.hasRemaining()){
            data = mappedByteBuffer1.getInt();
        }
        fc.close();
        long endTime = System.currentTimeMillis();
        System.out.println("ms:" + (endTime - startTime));
        System.out.println(data);
    }
}

結論非常明顯啦，以後再使用IO讀寫文件的時候，多使用NIO MappedByteBuffer吧，畢竟NIO比老IO性能好太多啦。