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

一、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);}

二、效果比较

写1M数据效果如下

写10M数据效果如下

写100M效果如下

三、总结

通过比较能看到在高频写数据到磁盘时，mmap的性能非常显著，有类似的场景时可以优先考虑mmap。当然最好是自己做下基准测试