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JavaEE进阶知识学习----Java NIO-2

原文 http://blog.csdn.net/qq_27922023/article/details/79237040

2018-02-03 02:00:30阅读(272)

分散读取和聚集写入

分散读取:将通道中的数据分散到多个缓冲区中。
聚集写入:将多个缓冲区中的数据聚集到通道中。
分散读取实例

@Test
public void test4() throws IOException{
    RandomAccessFile rFile = new RandomAccessFile("1.txt", "rw");
    //获取通道
    FileChannel channel = rFile.getChannel();
    //分配指定大小的缓冲区
    ByteBuffer buffer1 = ByteBuffer.allocate(100);
    ByteBuffer buffer2 = ByteBuffer.allocate(1024);
    //分散读取
    ByteBuffer[] bufs = {buffer1,buffer2};
    channel.read(bufs);
    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()));

聚集写入实例

@Test
public void test4() throws IOException{
    RandomAccessFile rFile = new RandomAccessFile("1.txt", "rw");
    //获取通道
    FileChannel channel = rFile.getChannel();
    //分配指定大小的缓冲区
    ByteBuffer buffer1 = ByteBuffer.allocate(100);
    ByteBuffer buffer2 = ByteBuffer.allocate(1024);
    //分散读取
    ByteBuffer[] bufs = {buffer1,buffer2};
    channel.read(bufs);
    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 rfile2 = new RandomAccessFile("2.txt", "rw");
    FileChannel channel2 = rfile2.getChannel();
    channel2.write(bufs);
}
NIO的字符集

查看支持的字符集

@Test
public void test5(){
    //支持的字符集
    Map<String, Charset> map = Charset.availableCharsets();
    //遍历map
    Set<Entry<String, Charset>> set = map.entrySet();
    for (Entry<String, Charset> entry : set) {
        System.out.println(entry.getKey()+"==="+entry.getValue());
    }
}

通过一个字符集得到的编码器和解码器就不会出现乱码,如下

@Test
public void test6() throws IOException{
    Charset cs1 = Charset.forName("GBK");
    //获取编码器
    CharsetEncoder ce = cs1.newEncoder();
    //获取解码器
    CharsetDecoder cd = cs1.newDecoder();
    //创建buffer,并存入文字
    CharBuffer cBuff = CharBuffer.allocate(1024);
    cBuff.put("疾风知劲草");
    cBuff.flip();
    //编码,字符-字节
    ByteBuffer bBuf =  ce.encode(cBuff);
    //查看是否编码成功
    for(int i = 0; i < 10; i++){
        System.out.println(bBuf.get());
    }
    //解码,字节-字符
    bBuf.flip();
    CharBuffer cBuf2 = cd.decode(bBuf);
    System.out.println(cBuf2.toString());// 疾风知劲草
}

如果使用GBK进行编码,使用UTF-8进行解码,就会出现乱码,如下所示。

@Test
public void test6() throws IOException{
    Charset cs1 = Charset.forName("GBK");
    //获取编码器
    CharsetEncoder ce = cs1.newEncoder();
    //获取解码器
    CharsetDecoder cd = cs1.newDecoder();
    //创建buffer,并存入文字
    CharBuffer cBuff = CharBuffer.allocate(1024);
    cBuff.put("疾风知劲草");
    cBuff.flip();
    //编码,字符-字节
    ByteBuffer bBuf =  ce.encode(cBuff);
    //查看是否编码成功
    for(int i = 0; i < 10; i++){
        System.out.println(bBuf.get());
    }
    //解码,字节-字符
    bBuf.flip();
    CharBuffer cBuf2 = cd.decode(bBuf);
    System.out.println(cBuf2.toString());// 疾风知劲草
    System.out.println("=========================");
    //如果按照UTF-8解码,就会出现乱码
    Charset cs2 = Charset.forName("UTF-8");
    bBuf.flip();
    CharBuffer cBuf3 = cs2.decode(bBuf);
    System.out.println(cBuf3.toString());
}
以上都是使用通道解决本地的数据传输,NIO的核心是网络数据传输。 NIO的非阻塞网络通信

选择器(Selector):将每一个通道注册到选择器上,选择器就是监控每一个通道的IO状况(读,写,连接等情况)。只有当通道中的请求时间准备就绪时,才会将任务分配到服务端的一个线程或者多个线程上运行。
NIO非阻塞模式图解如下:
<a href=JavaEE进阶知识学习----Java NIO-2" src="https://i.imgur.com/4fRFbv9.png" alt="" title="">
使用NIO非阻塞式进行网络通信,我们先来看一个阻塞式的网络通信。
使用NIO完成网络通信的三个核心:
1. 通道(channel):负责连接,实现类有SocketChannel、ServerSocketChanel、DatagramChannel。
2. 缓冲区:负责数据的读取。
3. 选择器:是是SelectableChannel的多路复用器,用于监控selectablechannel的IO状况。

网络通信如下:

public class TestBlockingNIO {
    //客户端
    @Test
    public void client(){
        SocketChannel sChannel = null;
        FileChannel inChannel = null;
        try {
            sChannel = SocketChannel.open(new InetSocketAddress("127.0.0.1",9898));
            inChannel = FileChannel.open(Paths.get("1.jpg"), StandardOpenOption.READ);
            //分配指定大小的缓冲区
            ByteBuffer buf = ByteBuffer.allocate(1024);
            //读取本地文件,并发送到服务端
            while(inChannel.read(buf) != -1){
                buf.flip();
                sChannel.write(buf);
                buf.clear();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally{
            if(inChannel != null){
                try {
                    inChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(sChannel != null){
              try {
                sChannel.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            }
        }
    }
    //服务端(异常处理应该使用try-catch)
    @Test
    public void server() throws IOException{
        //获取通道
        ServerSocketChannel ssChannel = ServerSocketChannel.open();
        FileChannel outChannel = FileChannel.open(Paths.get("44.jpg"), StandardOpenOption.WRITE,StandardOpenOption.CREATE);
        //绑定连接
        ssChannel.bind(new InetSocketAddress(9898));
        //获取客户端连接的通道
        SocketChannel sChannel = ssChannel.accept();
        //分配指定大小的缓冲区
        ByteBuffer buf = ByteBuffer.allocate(1024);
        //接收客户端的数据,并保存在本地
        while(sChannel.read(buf) != -1){
            buf.flip();
            outChannel.write(buf);
            buf.clear();
        }
        //关闭通道
        sChannel.close();
        outChannel.close();
        ssChannel.close();
    }
}

说明:先启动服务端,在启动客户端,就会发现项目中多了一个文件。这就是使用socket进行网络通信的一个实例,如果我们想客户端运行成功后,服务端返回一个信息,表明已经成功了。看如下程序

//客户端
@Test
public void client() throws IOException{
    SocketChannel sChannel = SocketChannel.open(new InetSocketAddress("127.0.0.1",9898));
    FileChannel inChannel = FileChannel.open(Paths.get("1.jpg"), StandardOpenOption.READ);
    ByteBuffer buf = ByteBuffer.allocate(1024);
    while (inChannel.read(buf) != -1) {
        buf.flip();
        sChannel.write(buf);
        buf.clear();
    }
    //接收服务端返回的信息
    int len = 0;
    while(sChannel.read(buf)!= -1){
        buf.flip();
        System.out.println(new String(buf.array(),0,len));
        buf.clear();
    }
    inChannel.close();
    sChannel.close();
}
//服务端(异常处理应该使用try-catch)
@Test
public void server() throws IOException{
    ServerSocketChannel ssChannel = ServerSocketChannel.open();
    FileChannel outChannel = FileChannel.open(Paths.get("66.jpg"), StandardOpenOption.WRITE,StandardOpenOption.CREATE);
    ssChannel.bind(new InetSocketAddress(9898));
    SocketChannel sChannel = ssChannel.accept();
    ByteBuffer buf = ByteBuffer.allocate(1024);
    while (sChannel.read(buf)!= -1) {
        buf.flip();
        outChannel.write(buf);
        buf.clear();
    }
    //发送反馈请求给客户端
    buf.put("服务端接收数据成功".getBytes());
    buf.flip();
    sChannel.write(buf);
    sChannel.close();
    outChannel.close();
    ssChannel.close();
}

说明:以上程序运行后就会导致阻塞,服务端不知道客户端是否发送结束,解决办法有两种,一种是使用shutdownOutPut,另外一种就是换成非阻塞模式。
使用sChannel.shutdownOutput();方法。

//客户端
@Test
public void client() throws IOException{
    SocketChannel sChannel = SocketChannel.open(new InetSocketAddress("127.0.0.1",9898));
    FileChannel inChannel = FileChannel.open(Paths.get("1.jpg"), StandardOpenOption.READ);
    ByteBuffer buf = ByteBuffer.allocate(1024);
    while (inChannel.read(buf) != -1) {
        buf.flip();
        sChannel.write(buf);
        buf.clear();
    }
    sChannel.shutdownOutput();
    //接收服务端返回的信息
    int len = 0;
    while((len = sChannel.read(buf))!= -1){
        buf.flip();
        System.out.println(new String(buf.array(),0,len));
        buf.clear();
    }
    inChannel.close();
    sChannel.close();
}
//服务端(异常处理应该使用try-catch)
@Test
public void server() throws IOException{
    ServerSocketChannel ssChannel = ServerSocketChannel.open();
    FileChannel outChannel = FileChannel.open(Paths.get("66.jpg"), StandardOpenOption.WRITE,StandardOpenOption.CREATE);
    ssChannel.bind(new InetSocketAddress(9898));
    SocketChannel sChannel = ssChannel.accept();
    ByteBuffer buf = ByteBuffer.allocate(1024);
    while (sChannel.read(buf)!= -1) {
        buf.flip();
        outChannel.write(buf);
        buf.clear();
    }
    //发送反馈请求给客户端
    buf.put("服务端接收数据成功".getBytes());
    buf.flip();
    sChannel.write(buf);
    sChannel.close();
    outChannel.close();
    ssChannel.close();
}
未完,待续

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