Java-NIO 之 Buffer 与 Channel

import org.junit.Test;

import java.nio.ByteBuffer;

public class TestBuffer {
    @Test
    public void markAndReset() {
        String str = "abcde14693090";
        // 分配直接缓冲区
        ByteBuffer buf = ByteBuffer.allocateDirect(1024);

        // 存入数据
        buf.put(str.getBytes());
        // 切换到读取模式
        buf.flip();

        byte[] dst = new byte[buf.limit()];
        buf.get(dst, 0, 2);
        System.out.println(new String(dst, 0, 2));
        System.out.println(buf.position());

        // mark() : 标记
        buf.mark();

        buf.get(dst, 2, 2);
        System.out.println(new String(dst, 2, 2));
        System.out.println(buf.position());

        // reset() : 恢复到 mark 的位置
        buf.reset();
        System.out.println(buf.position());

        // 判断缓冲区中是否还有剩余数据
        if (buf.hasRemaining()) {
            // 获取缓冲区中可以操作的数量
            System.out.println(buf.remaining());
        }
    }

    @Test
    public void getAndPut() {
        String str = "abcde";

        //1. 分配一个指定大小的缓冲区
        ByteBuffer buf = ByteBuffer.allocate(1024);

        System.out.println("allocate()：" + buf.position() + "\t" + buf.limit() + "\t" + buf.capacity());

        //2. 利用 put() 存入数据到缓冲区中
        buf.put(str.getBytes());

        System.out.println("put()：" + buf.position() + "\t" + buf.limit() + "\t" + buf.capacity());

        //3. 切换读取数据模式
        buf.flip();

        System.out.println("flip()：" + buf.position() + "\t" + buf.limit() + "\t" + buf.capacity());

        //4. 利用 get() 读取缓冲区中的数据
        byte[] dst = new byte[buf.limit()];
        buf.get(dst);
        System.out.println(new String(dst, 0, dst.length));

        System.out.println("get()：" + buf.position() + "\t" + buf.limit() + "\t" + buf.capacity());

        //5. rewind() : 可重复读
        buf.rewind();

        System.out.println("rewind()：" + buf.position() + "\t" + buf.limit() + "\t" + buf.capacity());

        //6. clear() : 清空缓冲区. 但是缓冲区中的数据依然存在，只是处于“被遗忘”状态
        buf.clear();

        System.out.println("clear()：" + buf.position() + "\t" + buf.limit() + "\t" + buf.capacity());

        // 获取单个字符
        System.out.println((char) buf.get());
    }
}

// 通道之间的数据传输(直接缓冲区)
@Test
public void channelCopy() throws IOException {
    FileChannel inChannel = FileChannel.open(Paths.get("D:/123.txt"), StandardOpenOption.READ);
    FileChannel outChannel = FileChannel.open(Paths.get("D:/456.txt"), StandardOpenOption.WRITE, StandardOpenOption.READ, StandardOpenOption.CREATE);

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

    inChannel.close();
    outChannel.close();
}

// 使用直接缓冲区完成文件的复制(内存映射文件)
@Test
public void byteBuffCopy() {
    long start = System.currentTimeMillis();

    try (FileChannel inChannel = FileChannel.open(Paths.get("D:/123.txt"), StandardOpenOption.READ);
         FileChannel outChannel = FileChannel.open(Paths.get("D:/456.txt"), StandardOpenOption.WRITE, StandardOpenOption.READ, StandardOpenOption.CREATE)) {

        // 内存映射文件
        MappedByteBuffer inMappedBuf = inChannel.map(MapMode.READ_ONLY, 0, inChannel.size());
        MappedByteBuffer outMappedBuf = outChannel.map(MapMode.READ_WRITE, 0, inChannel.size());

        // 直接对缓冲区进行数据的读写操作
        byte[] dst = new byte[inMappedBuf.limit()];
        inMappedBuf.get(dst);
        outMappedBuf.put(dst);
    } catch (IOException e) {
        e.printStackTrace();
    }

    long end = System.currentTimeMillis();
    System.out.println("耗费时间为：" + (end - start));
}

// 利用通道完成文件的复制（非直接缓冲区）
@Test
public void fileCopy() {
    long start = System.currentTimeMillis();

    try (FileInputStream fis = new FileInputStream("D:/123.txt");
         FileOutputStream fos = new FileOutputStream("D:/456.txt");
         // 获取通道
         FileChannel inChannel = fis.getChannel();
         FileChannel outChannel = fos.getChannel()) {

        // 分配指定大小的缓冲区
        ByteBuffer buf = ByteBuffer.allocate(1024);

        // 将通道中的数据存入缓冲区中
        while (inChannel.read(buf) != -1) {
            // 切换读取数据的模式
            buf.flip();
            // 将缓冲区中的数据写入通道中
            outChannel.write(buf);
            // 清空缓冲区
            buf.clear();
        }
    } catch (IOException e) {
        e.printStackTrace();
    }

    long end = System.currentTimeMillis();
    System.out.println("Time：" + (end - start));
}

// 分散和聚集
@Test
public void scatterAndGather() throws IOException {
    RandomAccessFile raf1 = new RandomAccessFile("D:/123.txt", "rw");

    // 获取通道
    FileChannel channel1 = raf1.getChannel();
    // 分配指定大小的缓冲区
    ByteBuffer buf1 = ByteBuffer.allocate(100);
    ByteBuffer buf2 = ByteBuffer.allocate(1024);
    // 分散读取
    ByteBuffer[] bufs = {buf1, buf2};
    channel1.read(bufs);

    // 转换模式
    for (ByteBuffer byteBuffer : bufs) {
        byteBuffer.flip();
    }

    System.out.println(new String(bufs[0].array(), 0, bufs[0].limit()));
    System.out.println("-----------------");
    System.out.println(new String(bufs[1].array(), 0, bufs[1].limit()));

    // 聚集写入
    RandomAccessFile raf2 = new RandomAccessFile("D:/456.txt", "rw");
    FileChannel channel2 = raf2.getChannel();
    channel2.write(bufs);
}