Java网络编程

概述

        Java是通过使用流模式来实现网络信息交互的，一个接口同时拥有两个流：输入流和输出流。

        当一个进程向另一进程发送数据时，只需要将数据写入到相应接口的输出流上，而另一进程在接口的“另一端”从输入流上读取数据。

        Java所提供的网络功能按层次及使用方法分为三大类：

            URL：通过URL的网络资源表达形式确定数据在网络中的位置，利用URL对象中提供的相关方法，直接读入网络中的数据，或者将本地数据传送倒网络的另一端。

           Socket: Socket是指两个程序在网络上的通信连接，这个经常用到的一种方式。

           Datagram(数据报):Datagram方式是三种网络功能中最低级的一种，它是一种面向非连接的，以数据报方式工作的通信，使用在网络状况不可靠环境下的数据传输和访问。

               URL

                    程序Example

import  java.net.URL;
import  java.net.MalformedURLException;

public   class  UseURL
... {
           public static void main( String args[] )
           ...{
                     URL url = null;
                     try
                     ...{
                                 url = new URL("http://www.163.com/fff/java.html");
                     }
                     catch( MalformedURLExcetpion e )
                     ...{
                                 System.out.println("MalformedURLException:" + e);
                      }
                      System.out.println("The URL is:");
                      System.out.println(url);
                      System.out.println("Use toString():" + url.toString());
                      System.out.println("Protocol is:" + url.getProtocol());
                      System.out.println("Host is:" + url.getHost());
                      System.out.println("Port is:" + url.getPort());
                      System.out.println("File is:" + url.getFile());
           }
}

              读入URL数据

                      URL类中定义了openStream()方法，用以读取URL位置的数据，其返回值是一个InputStream数据流。

import  java.net.URL;
import  java.net.MalformedURLException;
import  java.io. * ;

public   class  ReadFromURL
... {
          public static void main( String args[] )
          ...{
                    URL root = null;
                    URL url = null;
                    String readString;
                    try
                    ...{
                              root = new URL("file:///e:/lxt008/javacode/");
                              url = new URL(root, "ReadFromURL.java");
                              BufferedReader br = new BufferedReader( new InputStreamReader(url.openStream()));
                              while((readString = br.readLine()) != null)
                              ...{
                                        System.out.println( readString );
                              }
                              System.out.println("*********** end of the file ****************");
                              br.close();
                    }
                    catch( MalformedURLException e )
                    ...{
                                System.out.println("MalformedURLException:" + e);
                    }
                    catch(IOException e)
                    ...{
                                 System.out.println("IOException:" + e);

                    }
          }
}

               Socket

                          Server端口与Client端建立连接的过程

                         先生成一个ServerSocket实例对象，随时监听Client端的连接请求，当Client端需要连接时，相应地要生成一个Socket实例对象，并发出连接请求，其中host参数指明该主机名，port#参数指明该主机端口号。Server端通过accept()方法接收倒Client端的请求后，开辟一个接口与之进行连接，并生成所需的I/O数据流。Client端和Server端的通信都是通过一对InputStream和OutputStream进行的。通信结束后，两端分别关闭对应的Socket接口。

                  Server端程序

import  java.net. * ;
import  java.io. * ;
public   class  SimpleServer
... {
          public static void main( String args[] )
          ...{
                     s = new ServerSocket(5432);
                     System.out.println("Server started! Listener port 5432!!!");
          }
          catch( IOException e )
          ...{
                    e.printStackTrace();
          }
          while( true )
          ...{
                   try
                   ...{
                                Socket s1 = s.accept();
                                System.out.println("Client connected!!!!");
                                OutputStream s1out = s1.getOutputStream();
                                BufferedOutputStream bw = new BufferedOutputStream(s1out);
                                ObjectOutputStream oos = new ObjectOutputStream(bw);
                                oos.writeObject("Hello Net World!  ");        //返回Client信息
                                oos.close();
                                bw.close();
                                s1.close();
                   }
                   catch( IOException e )
                   ...{
                              e.printStackTrace();
                   }
          }
}

                   Client端程序

import  java.net. * ;
import  java.io. * ;
public   class  SimpleClient
... {
          public static void main( String args[] )
          ...{
                    try
                    ...{
                              Socket s1 = new Socket("127.0.0.1", 5432);
                              InputStream is = s1.getInputStream();

                                  BufferedInputStream bis = new BufferedInputStream(is);
                              ObjectInputStream ois = new ObjectInputStream( bis );
                              System.out.println( ois.readObject() );
                              ois.close();

                                  bis.close();

                                  is.close();
                              s1.close();
                    }
                    catch( ConnectException connExc )
                    ...{
                              System.out.println("Could not connect to the server.");
                    }
           }
}