Java常用读写类的速度比较

本文读写的内容为简单的字符串，主要比较了BufferedWriter（BufferedReader）、BufferedOutputStream（BufferedInputStream）、ByteBuffer(write&read)和MappedByteBuffer（write&read）的读写速度差异。测试时都是先写入文件5000000个字符串“Java is one of the best computer languages!\n”，然后再将所有数据读取到内存中。程序分别记录了上述四种方法的读写速度。

测试程序为：

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"));
			
			//要慢一点605ms，但是使用比较方便
//			String inputline = br.readLine();
//			while(inputline != null) {
//				inputline = br.readLine();
//			}
			//要快一点
			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();
			}
		}
	}
}

测试结果为：

可以看出来，BufferedWriter的写速度是最快的，MappedByteBuffer的读速度是最快的，但是一般BufferedReader操作方便，并且其速度也不是特别慢。所以一般情况下建议字符串读写用BufferedWriter&BufferedReader；对于全文读速度要求高的话可以用MappedByteBuffer。