Java网络编程——NIO三大组件Buffer、Channel、Selector

ByteBuffer byteBuffer = ByteBuffer.allocate(12);
byteBuffer.put((byte)'a');
byteBuffer.put((byte)'b'); 

ByteBuffer heapBuffer = ByteBuffer.allocate(1024);

ByteBuffer directBuffer = ByteBuffer.allocateDirect(1024); 

public class BufferTest {
    public static void main(String[] args) throws IOException {
        // 1、初始化Buffer，先初始化一个长度为12的ByteBuffer，也就是创建了类型为byte一个长度为12的数组：
        ByteBuffer byteBuffer = ByteBuffer.allocate(12);
        System.out.println("【初始化ByteBuffer】 capacity: " + byteBuffer.capacity() + " position: " + byteBuffer.position() + " limit: " + byteBuffer.limit());

        // 2、写数据，写的过程中，每写入一个字节，position自增1，当写入8个字节数据后，position=8
        for (int i = 0; i < 8; i++) {
            byteBuffer.put((byte) i);
        }
        System.out.println("【ByteBuffer写完数据】 capacity: " + byteBuffer.capacity() + " position: " + byteBuffer.position() + " limit: " + byteBuffer.limit());

        // 3、将Buffer由写模式转化为读模式
        byteBuffer.flip();
        System.out.println("【ByteBuffer调flip】 capacity: " + byteBuffer.capacity() + " position: " + byteBuffer.position() + " limit: " + byteBuffer.limit());

        // 4、读数据，如果依次读取了6个字节，那现在position就指向下标为6的位置，limit不变
        for (int i = 0; i < 6; i++) {
            if (i == 3) {
                byteBuffer.mark();
            }
            byte b = byteBuffer.get();
        }
        System.out.println("【ByteBuffer读完数据】 capacity: " + byteBuffer.capacity() + " position: " + byteBuffer.position() + " limit: " + byteBuffer.limit());

        // 5、重置position
        byteBuffer.reset();
        System.out.println("【ByteBuffer调reset】 capacity: " + byteBuffer.capacity() + " position: " + byteBuffer.position() + " limit: " + byteBuffer.limit());
    }
}

byteBuffer.put((byte) 'a'); //在position位置存入字符a对应的字节
byteBuffer.put(1, (byte) 5); //在1位置存入数字5对应的字节
byteBuffer.get();// 从position的位置读取一个字节的数据，读完后会导致position加1
byteBuffer.get(i);// 从position=i的位置读取一个字节的数据，读完后不会导致position加1
byteBuffer.reset(); // 重置position的值为mark
byteBuffer.position(5); // 重置position的值为5
byteBuffer.flip(); // 写完数据后，切换到读模式，把limit置为position的值，position置为0，
byteBuffer.clear(); // 清空ByteBuffer，position=0，limit=capacity
byteBuffer.compact(); // 读了一部分数据后，切换到写模式，会把未读的数据向前压缩，只留下有效数据（一般认为position~limit之间的数据为有效数据），比如原来pos=2，limit=8，capacity=12，执行compact()后，pos=6，limit=12，capacity=12

public class FileChannelTest {
    public static void main(String[] args) throws IOException {
        FileChannel fileChannel = FileChannel.open(Paths.get("/Users/danny/data/file/file.txt"), StandardOpenOption.WRITE, StandardOpenOption.READ);
        // 通过FileChannel从文件中读数据
        ByteBuffer readBuffer=ByteBuffer.allocate(10);
        while (fileChannel.read(readBuffer) != -1){
            while (readBuffer.hasRemaining()){
                byte b=readBuffer.get();
            }
        }
        // 通过FileChannel向文件中写数据
        ByteBuffer writeBuffer=ByteBuffer.allocate(10);
        writeBuffer.put("Data".getBytes());
        writeBuffer.flip();
        while (writeBuffer.hasRemaining()){
            fileChannel.write(writeBuffer);
        }
    }
}

public class ServerSocketChannelTest {
    public static void main(String[] args) throws IOException {
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.configureBlocking(true); // 设置阻塞模式为阻塞，默认就是true
        serverSocketChannel.bind(new InetSocketAddress(8080));
        ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
        SocketChannel socketChannel = serverSocketChannel.accept(); // 如果没有接收到新的客户端连接，这里会阻塞
        System.out.println("收到到客户端连接");
        int length = socketChannel.read(byteBuffer); // 如果读不到数据，这里会阻塞，无法处理其他Channel的读操作和连接请求
        System.out.println("读取到客户端数据：" + new String(byteBuffer.array(), 0, length));
    }
}

public class SocketChannelTest {
    public static void main(String[] args) throws IOException {
    	Socket socket = new Socket();
    	socket.connect(new InetSocketAddress("127.0.0.1", 8080));
    	System.out.println("连接服务端完成");
    	socket.getOutputStream().write(Constant.MESSAGE_128B.getBytes());
    	System.out.println("向服务端发送数据完成");
    	socket.close();
	}
}