Java--Stream，NIO ByteBuffer，NIO MappedByteBuffer效能對比

標籤：記憶體   unit   rtt   load   sys   檔案   created   buffer   隨機   

目前Java中最IO有多種檔案讀取的方法，本文章對比Stream，NIO ByteBuffer，NIO MappedByteBuffer的效能，讓我們知道到底怎麼能寫出效能高的檔案讀取代碼。

 

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效能對比 * 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流讀取和寫入檔案     * 速度：1000ms左右     *     * @throws IOException     */    @Test    public void useStream() throws IOException {        long startTime = System.currentTimeMillis();        /**         * 4000000個整數長度的檔案         */        int num = 2000 * 2000;        /**         * 帶緩衝的輸出資料流，寫檔案         */        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;        /**         * 帶緩衝的輸入資料流，讀檔案         */        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;        /**         * 檔案輸出資料流         */        FileOutputStream fileOutputStream = new FileOutputStream("/Users/yangyu/Downloads/compare.tmp");        /**         * NIO Channel 通道         */        FileChannel fileChannel = fileOutputStream.getChannel();        /**         * ByteBuffer緩衝區         */        ByteBuffer buffer = ByteBuffer.allocate(num*5);        for (int i = 0; i < num; i++) {            buffer.putInt(i);        }        /**         * 為寫做準備         */        buffer.flip();        /**         * 寫操作         */        fileChannel.write(buffer);        fileChannel.close();        /**         * 緩衝區         */        ByteBuffer buffer1 = ByteBuffer.allocate(num*5);        /**         * 檔案輸入資料流         */        FileInputStream in = new FileInputStream("/Users/yangyu/Downloads/compare.tmp");        /**         * 輸入通道         */        FileChannel fin = in.getChannel();        /**         * 為讀取做準備         */        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將檔案對應到記憶體     * 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");        /**         * 擷取通道Channel         */        FileChannel fileChannel = file.getChannel();        /**         * 將檔案對應到緩衝區MappedByteBuffer         */        MappedByteBuffer mappedByteBuffer = fileChannel.map(FileChannel.MapMode.READ_WRITE,0,num*4);        /**         * 寫檔案         */        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());        /**         * 讀檔案         */        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讀寫檔案的時候，多使用NIO MappedByteBuffer吧，畢竟NIO比老IO效能好太多啦。

Java--Stream，NIO ByteBuffer，NIO MappedByteBuffer效能對比