java四种文件读写方式及性能比较

测试代码

package com.boot.demo.test.io;

import java.io.*;
import java.lang.reflect.Method;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.security.AccessController;
import java.security.PrivilegedAction;

/**
 * @author braska
 * @date 2020/3/19
 **/
public class FileTest {

    public static void fileStream(String sourceFile, String targetFile) {
        File file = new File(targetFile);
        try (FileInputStream fis = new FileInputStream(sourceFile);
             FileOutputStream fos = new FileOutputStream(file)) {
            byte[] bytes = new byte[1024 * 1024];
            int len;
            while ((len = fis.read(bytes)) > 0) {
                fos.write(bytes, 0, len);
            }
        } catch (Exception e) {

        }
    }

    public static void bufferStream(String sourceFile, String targetFile) {
        try (BufferedInputStream bis = new BufferedInputStream(Files.newInputStream(Paths.get(sourceFile)));
             BufferedOutputStream bos =
                     new BufferedOutputStream(Files.newOutputStream(Paths.get(targetFile),
                             StandardOpenOption.CREATE,
                             StandardOpenOption.TRUNCATE_EXISTING,
                             StandardOpenOption.WRITE))) {
            byte[] bytes = new byte[1024 * 1024];
            int len;
            while ((len = bis.read(bytes)) > 0) {
                bos.write(bytes, 0, len);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void randomFile(String sourceFile, String targetFile) {
        try (RandomAccessFile read = new RandomAccessFile(sourceFile, "r");
             RandomAccessFile write = new RandomAccessFile(targetFile, "rw")) {
            byte[] bytes = new byte[1024 * 1024];
            int len;
            while ((len = read.read(bytes)) > 0) {
                write.write(bytes, 0, len);
            }
        } catch (Exception e) {

        }
    }


    public static void memoryMap(String sourceFile, String targetFile) {
        try (FileChannel rc = FileChannel.open(Paths.get(sourceFile));
             FileChannel wc = FileChannel.open(Paths.get(targetFile),
                     StandardOpenOption.CREATE,
                     StandardOpenOption.READ,
                     StandardOpenOption.TRUNCATE_EXISTING,
                     StandardOpenOption.WRITE)) {
            long copy = 1L << 30;
            long cur = 0;
            long fileLength = rc.size();
            while (cur < fileLength) {
                copy = cur + copy > fileLength ? (fileLength - cur) : copy;
                MappedByteBuffer rMap = rc.map(FileChannel.MapMode.READ_ONLY, cur, copy);
                MappedByteBuffer wMap = wc.map(FileChannel.MapMode.READ_WRITE, cur, copy);
                for (int i = 0; i < copy; i++) {
                    byte b = rMap.get(i);			//从源文件读取字节
                    wMap.put(i, b);					//把字节写到目标文件中
                }
                System.gc();				//手动调用 GC		<必须的，否则出现异常>
                System.runFinalization();
                cur += copy;
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private static String buildFilePath(String path, String fileName, String extension) {
        return String.format("%s%s.%s", path, fileName, extension);
    }

    public static void main(String[] args) {
/*        String path = "F:\workspace\demo\";
        String extension = "hprof";
        // 30M文件
        String sourceFile = buildFilePath(path, "01", extension);*/

/*        String path = "E:\software\";
        String extension = "exe";
        // 460M文件
        String sourceFile = buildFilePath(path, "Anaconda3-2019.10-Windows-x86_64", extension);*/

        String path = "E:\software\";
        String extension = "zip";
        // 1.47G文件
        String sourceFile = buildFilePath(path, "software", extension);
        String targetFile;
        long start;

/*        targetFile = buildFilePath(path, "target_file_stream", extension);
        start = System.currentTimeMillis();
        FileTest.fileStream(sourceFile, targetFile);
        System.out.println("file stream used time:" + (System.currentTimeMillis() - start));*/

/*        targetFile = buildFilePath(path, "target_buffer_stream", extension);
        start = System.currentTimeMillis();
        FileTest.bufferStream(sourceFile, targetFile);
        System.out.println("buffer stream used time:" + (System.currentTimeMillis() - start));*/

/*        targetFile = buildFilePath(path, "target_random_file", extension);
        start = System.currentTimeMillis();
        FileTest.randomFile(sourceFile, targetFile);
        System.out.println("random file used time:" + (System.currentTimeMillis() - start));*/


        targetFile = buildFilePath(path, "target_memory_map", extension);
        start = System.currentTimeMillis();
        FileTest.memoryMap(sourceFile, targetFile);
        System.out.println("memory map used time:" + (System.currentTimeMillis() - start));
    }
}

　　

测试结果

文件大小	读写方式	耗时
30M	普通文件流	50-60 ms
	缓存流	32-35 ms
	随机文件方式	40-50 ms
	内存映射文件	50-60 ms
461M	普通文件流	1300-2300 ms
	缓存流	1700-2000 ms
	随机文件方式	1300-3000 ms
	内存映射文件	890-1000 ms
1.47G	普通文件流	11s
	缓存流	9s
	随机文件方式	10s
	内存映射文件	3s(首次较慢)

结尾：测试1.47G大文件时，内存映射文件中copy大小做了调整，当copy为1G时(copy=1L<<30)性能最佳，整过过程1-3秒左右。调至128M、512M。大约耗时都在15秒左右。为了公平起见，把其他方法中的byte缓冲区大小也做了同样调整，耗时变化不大。有些甚至更慢。

封装MappedBuffer工具类，代码如下：

package com.boot.demo.test.io;

import java.io.Closeable;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;

/**
 * @author braska
 * @date 2020/3/20
 **/
public class MappedByteBufferReader implements Closeable {

    private static final int BUFFERED_SIZE = 1 << 27;
    private static final FileChannel.MapMode MAP_MODE = FileChannel.MapMode.READ_ONLY;

    private FileChannel fileChannel;
    private final long fileSize;
    private final int bufferedSize;

    BlockingQueue<MappedByteBuffer> queue;

    public MappedByteBufferReader(String file) throws Exception {
        this(file, BUFFERED_SIZE, MAP_MODE);
    }

    public MappedByteBufferReader(String file, int bufferedSize) throws Exception {
        this(file, bufferedSize, MAP_MODE);
    }

    public MappedByteBufferReader(String file, FileChannel.MapMode mapMode) throws Exception {
        this(file, BUFFERED_SIZE, mapMode);
    }

    public MappedByteBufferReader(String file, int bufferedSize, FileChannel.MapMode mapMode) throws Exception {
        this.fileChannel = FileChannel.open(Paths.get(file));
        this.fileSize = fileChannel.size();
        this.bufferedSize = bufferedSize;
        int capacity = (int) Math.ceil((double) fileSize / (double) bufferedSize);
        this.queue = new ArrayBlockingQueue(capacity);
        long readSize = bufferedSize;
        long cursor = 0l;
        while (cursor < fileSize) {
            readSize = cursor + readSize > fileSize ? fileSize - cursor : readSize;
            queue.add(
                    fileChannel.map(mapMode, cursor, readSize)
            );
            cursor += readSize;
        }
    }

    public byte[] read() {
        byte[] bytes;
        MappedByteBuffer byteBuffer = queue.poll();
        if (byteBuffer != null) {
            int limit = byteBuffer.limit();
            int position = byteBuffer.position();

            int realSize = this.bufferedSize;
            if (limit - position < this.bufferedSize) {
                realSize = limit - position;
            }
            bytes = new byte[realSize];
            byteBuffer.get(bytes);
            byteBuffer.clear();
            return bytes;
        }

        return null;
    }

    public long size() {
        return this.fileSize;
    }

    @Override
    public void close() throws IOException {
        if (this.fileChannel != null) {
            this.fileChannel.close();
        }
    }

    public static void main(String[] args) {
        long start = System.currentTimeMillis();
        try (MappedByteBufferReader reader = new MappedByteBufferReader("E:\software\software.zip", 1 << 30);
             FileChannel wc = FileChannel.open(Paths.get("E:\software\software_reader.zip"),
                     StandardOpenOption.CREATE,
                     StandardOpenOption.READ,
                     StandardOpenOption.TRUNCATE_EXISTING,
                     StandardOpenOption.WRITE)) {
            byte[] data;
            MappedByteBuffer writer = wc.map(FileChannel.MapMode.READ_WRITE, 0, reader.size());
            while ((data = reader.read()) != null) {
                writer.put(data);
            }
            writer.clear();
            System.out.println("used times: " + (System.currentTimeMillis() - start));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}