哇塞，这几种Java文件读写性能差距居然这么大？

news2024/11/20 16:36:02

引言

这是一篇性能比较的文章，不分析实现原理。主要是对比Java几种常见的文件写入方式

测试代码

主要分析Stream、Stream+Buffer和mmap三种方式，对应的大致代码如下

    public static void testBasicFileIO(List<Persona> list, String path) throws Exception {
        File file = new File(path);
        if (file.exists()){
            file.delete();
        }
        FileOutputStream out = new FileOutputStream(file);

        long startTime = System.currentTimeMillis();
        for (int i = 0; i < list.size(); i++) {
            out.write(list.get(i).toString().getBytes());
        }
        long costTime = System.currentTimeMillis()-startTime;
        System.out.println("testBasicFileIO cost:"+costTime);
    }
    
    public static void testBufferedFileIO(List<Persona> list, String path) throws Exception {
        File file = new File(path);
        if (file.exists()){
            file.delete();
        }
        BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(file));


        long startTime = System.currentTimeMillis();
        for (int i = 0; i < list.size(); i++) {
            out.write(list.get(i).toString().getBytes());
        }
        long costTime = System.currentTimeMillis()-startTime;
        System.out.println("testBufferedFileIO cost:"+costTime);
    }
    
    public static void testMmapWrite(List<Persona> list, String path) throws Exception {
        File file = new File(path);
        if (file.exists()){
            file.delete();
        }
        RandomAccessFile raf = new RandomAccessFile(path, "rw");
        FileChannel rafchannel = raf.getChannel();
        //mmap 使得jvm堆和pageCache有一块映射空间
        MappedByteBuffer map = rafchannel.map(FileChannel.MapMode.READ_WRITE, 0, 4096 * 1024 * 250);  // 1000M的pageCache大小

        long startTime = System.currentTimeMillis();

        for (int i = 0; i < list.size(); i++) {
            map.put(list.get(i).toString().getBytes());
        }
        long costTime = System.currentTimeMillis()-startTime;
        System.out.println("mmap cost:"+costTime);
    }