Java NIO

public class TestBuffer {
    @Test
    public void test1(){
        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()----------------");
        System.out.println(buf.position());//0
        System.out.println(buf.limit());//1024
        System.out.println(buf.capacity());//1024
        
        //2. 利用 put() 存入数据到缓冲区中
        buf.put(str.getBytes());
        
        System.out.println("-----------------put()----------------");
        System.out.println(buf.position());//5
        System.out.println(buf.limit());//1024
        System.out.println(buf.capacity());//1024
        
        //3. 切换读取数据模式
        buf.flip();
        
        System.out.println("-----------------flip()----------------");
        System.out.println(buf.position());//0
        System.out.println(buf.limit());//5
        System.out.println(buf.capacity());//1024
        
        //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));//abcde
        System.out.println("-----------------get()----------------");
        System.out.println(buf.position());//5
        System.out.println(buf.limit());//5
        System.out.println(buf.capacity());//1024
        
        //5. rewind() : 可重复读
        buf.rewind();
        
        System.out.println("-----------------rewind()----------------");
        System.out.println(buf.position());//0
        System.out.println(buf.limit());//5
        System.out.println(buf.capacity());//1024
        
        //6. clear() : 清空缓冲区. 但是缓冲区中的数据依然存在，但是处于“被遗忘”状态
        buf.clear();
        
        System.out.println("-----------------clear()----------------");
        System.out.println(buf.position());//0
        System.out.println(buf.limit());//1024
        System.out.println(buf.capacity());//1024
        System.out.println((char)buf.get());//a
    }
    
    @Test
    public void test2(){
        String str = "abcde";
        ByteBuffer buf = ByteBuffer.allocate(1024);
        buf.put(str.getBytes());
        
        buf.flip();
        
        byte[] dst = new byte[buf.limit()];
        buf.get(dst, 0, 2);
        System.out.println(new String(dst, 0, 2));//ab
        System.out.println(buf.position());//2
        
        //mark() : 标记
        buf.mark();
        
        buf.get(dst, 2, 2);
        System.out.println(new String(dst, 2, 2));//cd
        System.out.println(buf.position());//4
        
        //reset() : 恢复到 mark 的位置
        buf.reset();
        System.out.println(buf.position());//2
        
        //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());//3
        }
    }

}

public class TestChannel {
    //使用直接缓冲区完成文件的复制(内存映射文件)
    @Test
    public void test2() throws IOException{//2127-1902-1777
        long start = System.currentTimeMillis();
        
        FileChannel inChannel = FileChannel.open(Paths.get("d:/1.mkv"), StandardOpenOption.READ);
        FileChannel outChannel = FileChannel.open(Paths.get("d:/2.mkv"), 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);
        
        inChannel.close();
        outChannel.close();
        
        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 test1(){//10874-10953
        long start = System.currentTimeMillis();
        
        FileInputStream fis = null;
        FileOutputStream fos = null;
        //①获取通道
        FileChannel inChannel = null;
        FileChannel outChannel = null;
        try {
            fis = new FileInputStream("d:/1.mkv");
            fos = new FileOutputStream("d:/2.mkv");
            
            inChannel = fis.getChannel();
            outChannel = fos.getChannel();
            
            //②分配指定大小的缓冲区
            ByteBuffer buf = ByteBuffer.allocate(1024);
            
            //③将通道中的数据存入缓冲区中
            while(inChannel.read(buf) != -1){
                buf.flip(); //切换读取数据的模式
                //④将缓冲区中的数据写入通道中
                outChannel.write(buf);
                buf.clear(); //清空缓冲区
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(outChannel != null){
                try {
                    outChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            
            if(inChannel != null){
                try {
                    inChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            
            if(fos != null){
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            
            if(fis != null){
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        
        long end = System.currentTimeMillis();
        System.out.println("耗费时间为：" + (end - start));
        
    }

}