Java使用BIO和NIO进行文件操作比较

package com.zhi.test;

import java.io.FileInputStream;
import java.io.FileReader;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;

/**
 * 文件读取，缓冲区大小对NIO的性能影响特别大，对BIO无影响<br>
 * 1024缓冲区大小下：2K的文件，BIO耗时1毫秒，NIO耗时5毫秒；5M的文件，BIO耗时46毫秒，NIO耗时37毫秒<br>
 * 
 * @author 张远志
 * @since 2020年5月9日19:20:49
 *
 */
public class FileRead {
    /**
     * 缓冲区大小
     */
    private static final int BF_SIZE = 1024;

    /**
     * 使用BIO读取文件
     * 
     * @param fileName 待读文件名
     * @return
     * @throws IOException
     */
    public static String bioRead(String fileName) throws IOException {
        long startTime = System.currentTimeMillis();
        try {
            FileReader reader = new FileReader(fileName);

            StringBuffer buf = new StringBuffer();
            char[] cbuf = new char[BF_SIZE];
            while (reader.read(cbuf) != -1) {
                buf.append(cbuf);
            }
            reader.close();
            return buf.toString();
        } finally {
            System.out.println("使用BIO读取文件耗时：" + (System.currentTimeMillis() - startTime) + "毫秒");
        }
    }

    /**
     * 使用NIO读取文件
     * 
     * @param fileName 待读文件名
     * @return
     * @throws IOException
     */
    public static String nioRead(String fileName) throws IOException {
        long startTime = System.currentTimeMillis();
        try {
            FileInputStream input = new FileInputStream(fileName);
            FileChannel channel = input.getChannel();

            CharsetDecoder decoder = Charset.defaultCharset().newDecoder();
            StringBuffer buf = new StringBuffer();
            CharBuffer cBuf = CharBuffer.allocate(BF_SIZE);
            ByteBuffer bBuf = ByteBuffer.allocate(BF_SIZE);
            while (channel.read(bBuf) != -1) {
                bBuf.flip();
                decoder.decode(bBuf, cBuf, false); // 解码，byte转char，最后一个参数非常关键
                bBuf.clear();
                buf.append(cBuf.array(), 0, cBuf.position());
                cBuf.compact(); // 压缩
            }
            input.close();
            return buf.toString();
        } finally {
            System.out.println("使用NIO读取文件耗时：" + (System.currentTimeMillis() - startTime) + "毫秒");
        }
    }

    public static void main(String[] args) throws IOException {
        String fileName = "E:/source.txt";
        FileRead.bioRead(fileName);
        FileRead.nioRead(fileName);
    }
}

package com.zhi.test;

import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

/**
 * 文件写<br>
 * 10M的数据，BIO耗时61毫秒，NIO耗时33毫秒
 * 
 * @author 张远志
 * @since 2020年5月9日21:04:40
 *
 */
public class FileWrite {
    /**
     * 使用BIO进行文件写
     * 
     * @param fileName 文件名称
     * @param content  待写内存
     * @throws IOException
     */
    public static void bioWrite(String fileName, String content) throws IOException {
        long startTime = System.currentTimeMillis();
        try {
            FileWriter writer = new FileWriter(fileName);
            writer.write(content);
            writer.close();
        } finally {
            System.out.println("使用BIO写文件耗时：" + (System.currentTimeMillis() - startTime) + "毫秒");
        }
    }

    /**
     * 使用NIO进行文件写
     * 
     * @param fileName 文件名称
     * @param content  待写内存
     * @throws IOException
     */
    public static void nioWrite(String fileName, String content) throws IOException {
        long startTime = System.currentTimeMillis();
        try {
            FileOutputStream out = new FileOutputStream(fileName);
            FileChannel channel = out.getChannel();
            ByteBuffer buf = ByteBuffer.wrap(content.getBytes());
            channel.write(buf);
            out.close();
        } finally {
            System.out.println("使用NIO写文件耗时：" + (System.currentTimeMillis() - startTime) + "毫秒");
        }
    }

    public static void main(String[] args) throws IOException {
        String content = FileRead.nioRead("E:/source.txt");
        FileWrite.bioWrite("E:/target1.txt", content);
        FileWrite.nioWrite("E:/target2.txt", content);
    }
}

package com.zhi.test;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.channels.FileChannel;

/**
 * 文件复制<br>
 * 5M的文件，bio耗时29毫秒，nio耗时9毫秒
 * 
 * @author 张远志
 * @since 2020年5月9日17:18:01
 *
 */
public class FileCopy {
    /**
     * 使用BIO复制一个文件
     * 
     * @param target 源文件
     * @param source 目标文件
     * 
     * @throws IOException
     */
    public static void bioCopy(String source, String target) throws IOException {
        long startTime = System.currentTimeMillis();
        FileInputStream fin = new FileInputStream(source);
        FileOutputStream fout = new FileOutputStream(target);

        byte[] byt = new byte[1024];
        while (fin.read(byt) > -1) {
            fout.write(byt);
        }

        fin.close();
        fout.close();
        System.out.println("使用BIO复制文件耗时：" + (System.currentTimeMillis() - startTime) + "毫秒");
    }

    /**
     * 使用NIO复制一个文件
     * 
     * @param target 源文件
     * @param source 目标文件
     * 
     * @throws IOException
     */
    public static void nioCopy(String source, String target) throws IOException {
        long startTime = System.currentTimeMillis();

        FileInputStream fin = new FileInputStream(source);
        FileChannel inChannel = fin.getChannel();
        FileOutputStream fout = new FileOutputStream(target);
        FileChannel outChannel = fout.getChannel();

        inChannel.transferTo(0, inChannel.size(), outChannel);

        fin.close();
        fout.close();
        System.out.println("使用NIO复制文件耗时：" + (System.currentTimeMillis() - startTime) + "毫秒");
    }

    public static void main(String[] args) throws IOException {
        String source = "E:/source.txt", target1 = "E:/target1.txt", target2 = "E:/target2.txt";
        FileCopy.bioCopy(source, target1);
        FileCopy.nioCopy(source, target2);
    }
}