网络编程

Posted 2020-12-21 hunter-w

URL对象

• URL类

  1. URL(Uniform Resource Locator)

     一致资源定位器的简称，表示Internet上某一资源的地址

  2. URL的组成

     protocol:resourceNamae

     协议名指明获取资源所使用的的传输协议，如http、ftp等，资源名则是资源的完整地址，包括主机名、端口号或文件内部的一个引用。

  3. 获取URL对象属性

     Public String getProtocol()
     
     Public String getHost()
     
     public String getPort()
     
     public String getFile()
     

URLConnection对象

• 一个URLConnection对象代表一个URL资源与Java程序的通讯连接，可以通过它对这个URL资源读或写。

• 与URL的区别

  1. URL是单向的，URLConnection是双向的

  2. 可以查看服务器的响应消息的首部

  3. 可以设置客户端请求消息的首部

• 使用示例

  关键步骤：构造一个URL对象，调用URL对象的openConnection()方法获取对应该URL的URLConnection对象。

  public class URLConnector {
      public static void main(String[] args) {
          try {
              URL cs = new URL("http://www.sina.com/");
              URLConnection tc = cs.openConnection();
              BufferedReader in = new BufferedReader(new InputStreamReader(tc.getInputStream()));
              String inputLine;
              while((inputLine = in.readLine()) != null) {
                  System.out.println(inputLine);
              }
              in.close();
          } catch (MalformedURLException e) {
              e.printStackTrace();
          } catch (IOException e) {
              e.printStackTrace();
          }
      }
  }
  

Get与Post请求

• 示例

  public static String sendGet(String url, String param) {
      String result = "";
      BufferedReader in = null;
      try {
          String urlNameString = url + "?" +param;
          URL realUrl = new URL(urlNameString);
          URLConnection connection = realUrl.openConnection();
          connection.setRequestProperty("accept", "*/*");
          connection.setRequestProperty("connection", "Keep-Alive");
          connection.connect();
          in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
          String line;
          while((line=in.readLine()) != null) {
              result += line;
          }
      } catch (MalformedURLException e) {
          e.printStackTrace();
      } catch (IOException e) {
          e.printStackTrace();
      } finally {
          try {
              if (in != null) {
                  in.close();
              }
          } catch (IOException e) {
              e.printStackTrace();
          }
          return result;
      }
  }
  
  public static String sendPost(String url, String param) {
      PrintWriter out = null;
      BufferedReader in = null;
      String result = "";
      try {
          URL realUrl = new URL(url);
          URLConnection connection = realUrl.openConnection();
          connection.setRequestProperty("accept", "*/*");
          connection.setRequestProperty("connection", "Keep-Alive");
          connection.setDoOutput(true);
          out = new PrintWriter(connection.getOutputStream());
          out.print(param);
          out.flush();
          in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
          String line;
          while((line=in.readLine()) != null) {
              result += line;
          }
      } catch (MalformedURLException e) {
          e.printStackTrace();
      } catch (IOException e) {
          e.printStackTrace();
      } finally {
          try {
              if (in != null) {
                  in.close();
              }
          } catch (IOException e) {
              e.printStackTrace();
          }
          return result;
      }
  }
  

• HttpURLConnection类

  在URLConnection的基础上提供一系列针对http请求的内容

  1. HTTP状态码（例如HTTP_OK:200)
  2. setRequestMethod（设置请求方法GETPOST等)
  3. getResponseCode（获取HTTP的响应）

Socket通信原理

• TCP传输协议（Transport Control Protocol）

  面向连接的能够提供可靠的流式数据传输的协议

  URL，URLConnection，Sokcet，ServerSocket等类都使用TCP协议进行网络通讯。

• socket通讯

  网络上的两个程序通过一个双向的通讯连接实现数据的交换，这个双向链路的一端称为一个socket。

Socket通信实现

• 创建socket

  使用Socket类构造

• 客户端socket的建立

• 服务端socket的建立

• 打开输入输出流

• 关闭socket

  注意先关闭流再关闭socket

  @TalkClient.java

  import java.net.*;
  import java.io.*;
  
  public class TalkClient {
      public static void main(String[] args) {
          System.out.println("Client Start...");
          try {
              Socket socket = new Socket("127.0.0.1", 8888);
              BufferedReader sin = new BufferedReader(new InputStreamReader(System.in));
              PrintWriter os = new PrintWriter(socket.getOutputStream());
              BufferedReader is = new BufferedReader(new InputStreamReader(socket.getInputStream()));
              String readline;
              readline = sin.readLine();
              while (!readline.equals("bye")) {
                  os.println(readline);
                  os.flush();
                  System.out.println("Client:" + readline);
                  System.out.println("Server:" + is.readLine());
                  readline = sin.readLine();
              }
              os.close();
              is.close();
              socket.close();
          } catch (UnknownHostException e) {
              e.printStackTrace();
          } catch (IOException e) {
              e.printStackTrace();
          }
      }
  }
  

  @TalkServer.java

  public class TalkServer {
      public static void main (String[] args) {
          System.out.println("Server start...");
          try {
              ServerSocket server = new ServerSocket(8888);
              Socket socket = server.accept();
              String readline;
              BufferedReader is = new BufferedReader(new InputStreamReader(socket.getInputStream()));
              PrintWriter os = new PrintWriter(socket.getOutputStream());
              BufferedReader sin = new BufferedReader(new InputStreamReader(System.in));
              System.out.println("Client: "+is.readLine());
              readline = sin.readLine();
              while (!readline.equals("bye")) {
                  os.println(readline);
                  os.flush();
                  System.out.println("Server:" + readline);
                  System.out.println("Client:" + is.readLine());
                  readline = sin.readLine();
              }
              os.close();
              is.close();
              socket.close();
          } catch (Exception e) {
              e.printStackTrace();
          }
      }
  }
  

  注意os.print()与os.println()的区别，不要被回车符坑了!!!