Java常用讀寫類的速度比較

一、本文讀寫的內容爲簡單的字符串，主要比較了BufferedWriter（BufferedReader）、BufferedOutputStream（BufferedInputStream）、ByteBuffer(write&read)和MappedByteBuffer（write&read）的讀寫速度差異。測試時都是先寫入文件5000000個字符串“Java is one of the best computer languages!\n”，然後再將所有數據讀取到內存中。程序分別記錄了上述四種方法的讀寫速度。

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測試程序爲：

import java.io.BufferedInputStream;  
import java.io.BufferedOutputStream;  
import java.io.BufferedReader;  
import java.io.BufferedWriter;  
import java.io.FileInputStream;  
import java.io.FileOutputStream;  
import java.io.IOException;  
import java.io.InputStreamReader;  
import java.io.OutputStreamWriter;  
import java.io.RandomAccessFile;  
import java.nio.ByteBuffer;  
import java.nio.channels.FileChannel;  

public class IOStudy {  

    public static void main(String[] args) {  
        test1();//BufferedWriter（BufferedReader）  
        test2();//BufferedOutputStream（BufferedInputStream）  
        test3();//ByteBuffer(write&read)  
        test4();//MappedByteBuffer（write&read）  
    }  

    public static void test1() {  
        BufferedWriter bw = null;  
        BufferedReader br = null;  
        long time;  
        try {  
            time = System.currentTimeMillis();  
            bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(".//data//test1.txt"), "utf-8"));  
            for(int i = 0; i < 5000000; i++) {  
                bw.write("Java is one of the best computer languages!\n");  
            }  
            bw.flush();  
            System.out.println("BufferedWriter: " + (System.currentTimeMillis() - time) + "ms");  

            time = System.currentTimeMillis();  
            br = new BufferedReader(new InputStreamReader(new FileInputStream(".//data//test1.txt"), "utf-8"));  

            //要慢一點605ms，但是使用比較方便  
//          String inputline = br.readLine();  
//          while(inputline != null) {  
//              inputline = br.readLine();  
//          }  
            //要快一點  
            char[] data = new char[5000000 * 44];  
            br.read(data);  
            System.out.println("BufferedReader: " + (System.currentTimeMillis() - time) + "ms");  

        } catch (IOException e) {  
            e.printStackTrace();  
        } finally {  
            try {  
                if(bw != null)  bw.close();  
                if(br != null)  br.close();  
            } catch (IOException e) {  
                e.printStackTrace();  
            }  
        }  
    }  

    public static void test2() {  
        BufferedOutputStream bos = null;  
        BufferedInputStream bis = null;  
        long time;  
        try {  
            time = System.currentTimeMillis();  
            bos = new BufferedOutputStream(new FileOutputStream(".//data//test2.txt"));  
            for(int i = 0; i < 5000000; i++) {  
                bos.write("Java is one of the best computer languages!\n".getBytes());  
            }  
            bos.flush();  
            System.out.println("BufferedOutputStream: " + (System.currentTimeMillis() - time) + "ms");  

            time = System.currentTimeMillis();  
            bis = new BufferedInputStream(new FileInputStream(".//data//test2.txt"));  
            byte[] data = new byte[5000000 * 44];  
            bis.read(data);  
            System.out.println("BufferedInputStream: " + (System.currentTimeMillis() - time) + "ms");  

        } catch (IOException e) {  
            e.printStackTrace();  
        } finally {  
            try {  
                if(bos != null) bos.close();  
                if(bis != null) bis.close();  
            } catch (IOException e) {  
                e.printStackTrace();  
            }  
        }  
    }  

    public static void test3() {  
        FileOutputStream fos = null;  
        FileChannel fc1 = null;  
        FileInputStream fis = null;  
        FileChannel fc2 = null;  
        long time;  
        try {  
            time = System.currentTimeMillis();  
            fos = new FileOutputStream(".//data//test3.txt");  
            fc1 = fos.getChannel();  
            ByteBuffer b = ByteBuffer.wrap("Java is one of the best computer languages!\n".getBytes());  
            for(int i = 0; i < 5000000; i++) {  
                fc1.write(b);  
                b.rewind();  
            }  
            System.out.println("ByteBuffer(write): " + (System.currentTimeMillis() - time) + "ms");  

            time = System.currentTimeMillis();  
            fis = new FileInputStream(".//data//test3.txt");  
            fc2 = fis.getChannel();  
            ByteBuffer data = ByteBuffer.allocate(5000000 * 44);  
            fc2.read(data);  
            System.out.println("ByteBuffer(read): " + (System.currentTimeMillis() - time) + "ms");  

        } catch (IOException e) {  
            e.printStackTrace();  
        } finally {  
            try {  
                if(fc1 != null) fc1.close();  
                if(fc2 != null) fc1.close();  
                if(fos != null) fos.close();  
                if(fis != null) fis.close();  
            } catch (IOException e) {  
                e.printStackTrace();  
            }  
        }  
    }  

    public static void test4() {  
        FileChannel fc1 = null;  
        FileChannel fc2 = null;  
        long time;  
        try {  
            time = System.currentTimeMillis();  
            fc1 = new RandomAccessFile(".//data//test4.txt", "rw").getChannel();  
            ByteBuffer b = fc1.map(FileChannel.MapMode.READ_WRITE, 0, 5000000 * 44);  
            for(int i = 0; i < 5000000; i++) {  
                b.put("Java is one of the best computer languages!\n".getBytes());  
            }  
            System.out.println("MappedByteBuffer(write): " + (System.currentTimeMillis() - time) + "ms");  

            time = System.currentTimeMillis();  
            fc2 = new FileInputStream(".//data//test4.txt").getChannel();  
            b = fc2.map(FileChannel.MapMode.READ_ONLY, 0, fc2.size());  
            byte[] data = new byte[5000000 * 44];  
            b.get(data);  
            System.out.println("MappedByteBuffer(read): " + (System.currentTimeMillis() - time) + "ms");  

        } catch (IOException e) {  
            e.printStackTrace();  
        } finally {  
            try {  
                if(fc1 != null) fc1.close();  
                if(fc2 != null) fc2.close();  
            } catch (IOException e) {  
                e.printStackTrace();  
            }  
        }  
    }  
} 

測試結果爲：

可以看出來，BufferedWriter的寫速度是最快的，MappedByteBuffer的讀速度是最快的，但是一般BufferedReader操作方便，並且其速度也不是特別慢。所以一般情況下建議字符串讀寫用BufferedWriter&BufferedReader；對於全文讀速度要求高的話可以用MappedByteBuffer。