主要是瞭解mac下vmmap命令配合使用情況，mmap記憶體對映對應java nio的RandomAccessFile的FileChannel進行map()操作。

public class RandomMapFileReadTest {
    static int length = 0x8000000; // 128 Mb

    public static void main(String[] args) throws FileNotFoundException {
        try{
            // 為了以可讀可寫的方式開啟檔案，這裡使用RandomAccessFile來建立檔案。
 

            FileChannel fc = new RandomAccessFile("test.dat", "rw").getChannel();
            //注意，檔案通道的可讀可寫要建立在檔案流本身可讀寫的基礎之上
            MappedByteBuffer out = fc.map(FileChannel.MapMode.READ_WRITE, 0, length);
            //寫128M的內容
            byte[] readArray = new byte[1024];
            for (int i = 0
 
; i < length; i++) {
                byte byteChar = out.get();
                readArray[i%1024] = byteChar;
                if(i == length/2) {
                    Thread.sleep(20);
                    System.out.println("read half...");
                }
            }
//            System.out.println("Finished writing");
 

            //讀取檔案中間6個位元組內容


            System.out.println("Finished getting " + readArray.length);
            fc.close();
        }catch (Exception e) {
            e.printStackTrace();
        }

    }
}

一個已經存在的128M檔案，在map後，通過for迴圈不斷讀入記憶體，可以通過

vmmap -resident <pid>

命令看出，map的resident記憶體是一步一步讀入的：

yangyamin:~ yangyamin$ vmmap -resident 1486 | grep test
mapped file            0000000115a8d000-000000011da8d000 [128.0M  56.9M] rw-/rwx SM=PRV  /Users/yangyamin/data/spv/test.dat
yangyamin:~ yangyamin$ vmmap -resident 1486 | grep test
mapped file            0000000115a8d000-000000011da8d000 [128.0M  89.7M] rw-/rwx SM=PRV  /Users/yangyamin/data/spv/test.dat
yangyamin:~ yangyamin$ vmmap -resident 1486 | grep test
\mapped file            0000000115a8d000-000000011da8d000 [128.0M 107.5M] rw-/rwx SM=PRV  /Users/yangyamin/data/spv/test.dat
yangyamin:~ yangyamin$ vmmap -resident 1486 | grep test
mapped file            0000000115a8d000-000000011da8d000 [128.0M 125.9M] rw-/rwx SM=PRV  /Users/yangyamin/data/spv/test.dat
yangyamin:~ yangyamin$ vmmap -resident 1486 | grep test
mapped file            0000000115a8d000-000000011da8d000 [128.0M 128.0M] rw-/rwx SM=PRV  /Users/yangyamin/data/spv/test.dat
yangyamin:~ yangyamin$ vmmap -resident 1486 | grep test
mapped file            0000000115a8d000-000000011da8d000 [128.0M 128.0M] rw-/rwx SM=PRV  /Users/yangyamin/data/spv/test.dat