JavaSE学习笔记——网络编程

• 要想实现网络传输，需要考虑哪些问题

  1. 如何准确地定位到网络上的一台主机
  2. 如何才能进行可靠高效的传输

• Java如何实现网络通信

  1. 使用IP地址定位主机，使用端口号定位主机上的应用 ---> InetAddress类
  2. InetAddress类对象使用

     InetAddress inet = InetAddress.getByName(""127.0.0.1);
     inet.getLocalHost();//获取本机的InetAddress对象
     inet.getHostName();//获取域名
     inet.getHostAddress();//获取主机地址
     

  3. 如何实现通信 ---> TCP/UDP

     public class TestUDP {
         @Test
         public void send(){
             DatagramSocket ds = null;
             try {
                 ds = new DatagramSocket();
                 byte[] b = "data to be send".getBytes();
                 //创建一个数据报，每个数据报不能大于64k，每个都记录着数据信息+发送端IP及端口号+接收端IP及端口号
                 DatagramPacket packet = new DatagramPacket(b,0, b.length,
                         InetAddress.getByName("127.0.0.1"), 9090);
     
                 ds.send(packet);
             } catch (IOException e) {
                 e.printStackTrace();
             }finally{
                 if (ds != null)
                     ds.close();
             }
     
         }
     
         @Test
         public void receive(){
             DatagramSocket ds = null;
             try {
                 ds = new DatagramSocket(9090);
                 byte[] b = new byte[1024];
                 DatagramPacket packet = new DatagramPacket(b, 0, b.length);
                 ds.receive(packet);
                 String str = new String(packet.getData(), 0,packet.getLength() );
                 System.out.println(str);
             } catch (IOException e) {
                 e.printStackTrace();
             } finally {
                 ds.close();
             }
         }
     }
     

     //TCP编程例一：客户端给服务端发送信息，服务端输出此信息到控制台上
     public class TestTCP1 {
         //client
         @Test
         public void client() {
             Socket socket = null;
             OutputStream os = null;
             try {
                 //1.创建一个Socket的对象，通过构造器指明服务端的IP地址+端口号
                 socket = new Socket(InetAddress.getByName("127.0.0.1"), 9090);
                 //2. getOutputStream()，发送数据，该方法返回一个OutputStream对象
                 os = socket.getOutputStream();
                 //3.具体的输出过程
                 os.write("I am client".getBytes());
             } catch (IOException e) {
                 e.printStackTrace();
             }finally {
                 //4.关闭相应的流
                 if(os != null)
                     try {
                         os.close();
                     } catch (IOException e) {
                         e.printStackTrace();
                     }
                 if(socket != null)
                     try {
                         socket.close();
                     } catch (IOException e) {
                         e.printStackTrace();
                     }
             }
         }
     
         //server
         @Test
         public void server() {
             ServerSocket ss = null;
             InputStream is = null;
             Socket s = null;
             try {
                 //1. 创建serversocket对象，通过构造器指明自身的端口号
                 ss = new ServerSocket(9090);
                 //2.调用accept方法返回一个socket对象
                 s = ss.accept();
                 //3.调用socket对象的getInputStream方法获取同客户端发送过来的输入流
                 is = s.getInputStream();
                 //4 对获取的流进行的具体操作
                 byte[] b = new byte[20];
                 int len;
                 while((len = is.read(b)) != -1){
                     String str = new String(b,0,len);
                     System.out.print(str);
                 }
                 System.out.println("\n receive message from " + s.getInetAddress().getHostAddress());
             } catch (IOException e) {
                 e.printStackTrace();
             }finally {
                 //5.关闭相应的流、socket、serversocket的对象
                 if(is != null)
                     try {
                         is.close();
                     } catch (IOException e) {
                         e.printStackTrace();
                     }
                 if(s != null)
                     try {
                         s.close();
                     } catch (IOException e) {
                         e.printStackTrace();
                     }
                 if(ss != null)
                     try {
                         ss.close();
                     } catch (IOException e) {
                         e.printStackTrace();
                     }
             }
         }
     }
     

  4. URL编程

     public class TestURL {
         public static void main(String[] args) {
             InputStream is = null;
             URL url = null;
             try {
                 url = new URL("https://www.runoob.com/java/java-collections.html");//类似于File类的初始化
     //        url.getProtocol();//获取该URL的协议名
     //        url.getHost();//获取该URL的主机名
     //        url.getPort();//获取该URL的端口号
     //        url.getPath();//获取该URL的文件路径
     //        url.getFile();//获取该URL的文件名
     //        url.getRef();//获取该URL在文件中的相对位置
     //        url.getQuery();//获取该URL的查名
                 //如何将服务端数据读入:openStream()
                 is = url.openStream();
                 byte[] b = new byte[20];
                 int len;
                 while ((len = is.read(b)) != -1) {
                     String str = new String(b, 0, len);
                     System.out.println(str);
                 }
             } catch (IOException e) {
                 e.printStackTrace();
             } finally {
                 try {
                     if (is != null)
                         is.close();
                 } catch (IOException e) {
                     e.printStackTrace();
                 }
             }
     
             //如果既有数据输入又有数据输出，考虑使用URLConnection
             InputStream is1 = null;
             FileOutputStream fos = null;
             try {
                 URLConnection urlConnection = url.openConnection();
                 is1 = urlConnection.getInputStream();
                 fos = new FileOutputStream(new File("abc.txt"));
                 byte[] b = new byte[20];
                 int len1;
                 while((len1 = is1.read(b))!=-1){
                     fos.write(b,0,len1);
                 }
             } catch (IOException e) {
                 e.printStackTrace();
             }finally {
                 try {
                     if(fos != null)
                         fos.close();
                     if(is1 != null)
                         is1.close();
                 } catch (IOException e) {
                     e.printStackTrace();
                 }
             }
     
         }
     }