Java基础入门之网络编程教程

TCP 网络编程

-- tcp 分为客户端和服务端

-- 客户端对应的对象是 Socket

-- 服务端对应的对象是 ServerSocket

-- 如果客户端先启动,则出现 connection refused 异常  //refused 拒绝

客户端创建Socket 对象时,就可以连接服务器,连接成功后,即形成通路,进行数据交换

import java.net.*;import java.io.*;        //TCP客户端class TClient{public static void main(String [] args) throws Exception
            {
                Socket socket=new Socket("127.0.0.1",9000);                //取得 Socket 中的输出流OutputStream out =socket.getOutputStream();
                out.write("这是客户端向主机输出的数据".getBytes());                //取得服务端发回的数据InputStream in=socket.getInputStream();byte [] buff=new byte[1024];int len =in.read(buff);
                String str=new String(buff,0,len);
                System.out.println("服务端返回的数是:"+str);
                
                out.close();
                in.close();
                socket.close();
            }
        }

//TCP服务端/* 1 创建ServerSocket ,指定要监听的端口
         2 通过 ServerSocket 的 accept 方法 (它是阻塞模式的) 取得连接上来的客户端对象
         3 与客户端连通后,就可以得到客户端对象,并使用客户端对象读取流来取得数据
         4 如果有必要,释放资源*/import java.io.*;import java.net.*;class TServer
        {public static void main(String [] args) throws Exception
            {
                ServerSocket serverSocket=new ServerSocket(9000);  //指定监听的端口Socket clientSocket=serverSocket.accept();                //通过客户端的Socket对象可以取得信息String clientIp=clientSocket.getInetAddress().getHostAddress();int clientPort=clientSocket.getPort();
                
                System.out.println(clientIp+":"+clientPort +"连接成功");
                
                InputStream in= clientSocket.getInputStream();byte[] buff=new byte[1024];int len=in.read(buff);  //len 表示读了多少个字节   注意,这个read 是阻塞的                
                String msg=new String(buff,0,len);
                
                System.out.println(msg);                //往回发送数据OutputStream out=clientSocket.getOutputStream();
                out.write("小样的客户端,你竞敢骂人?,我也能".getBytes()); */
                out.close();
                in.close();
                serverSocket.close();
                clientSocket.close();
        
            }
        }

例子 从客户端向服务端发字母,变成大写后反回

/*客户端:
            1 建立服务
            2 获取键盘录入
            3 将数入的数据发给服务端
            4 接收服务端返回的大写字母
            5 关闭资源
            备注: 使用带缓冲的字符流进行操作 */import java.io.*;import java.net.*;class TransClient
        {public static void main(String [] args) throws Exception
            {
                    Socket socket=new Socket("127.0.0.1",8000);                    //定义输入流,读取键盘数据BufferedReader br=new BufferedReader(new InputStreamReader(System.in));                    //定义输出流对象(用于将键盘数据写入到输出流中)BufferedWriter bw=new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));                    //定义一个socket 读取流,读取服务器返回的大写字母BufferedReader brResult=new BufferedReader(new InputStreamReader(socket.getInputStream()));
                    
                    String str=null;while((str=br.readLine())!=null){ //从键盘开始读取bw.write(str);  //向服务端输出                        bw.newLine();
                        bw.flush(); //千万别忘了                        
                      System.out.println("服务端返回的数据是"+brResult.readLine()); //取出变大写后的字符串                    }
                    
                    socket.close();
                    br.close();
                    bw.close();
                    brResult.close();        
            }
        }

//服务端  import java.net.*;import java.io.*;class TransServer
        {public static void main(String [] args) throws Exception
                {
                     ServerSocket serverSocket=new ServerSocket(8000);
                     Socket clientSocket=serverSocket.accept();                     
                     //读取socket流中的数据(从客户端发过来的小写字母) BufferedReader br=new BufferedReader(new InputStreamReader( clientSocket.getInputStream()));                     
                     //创建输出流对象,往clientSocket 的流中写入转换后的大写字母 BufferedWriter bw=new BufferedWriter(new OutputStreamWriter( clientSocket.getOutputStream()));
                     
                     String str=null;                     while((str=br.readLine())!=null)  //注意 readLine 的特性,它是要一直读取回车换行才返回                     {
                             bw.write(str.toUpperCase());
                             bw.newLine();
                             bw.flush(); //千万别忘了                     }
                     
                    br.close();
                    bw.close();
                    clientSocket.close();
                    serverSocket.close();
                }
        
        }

例子 上传文件

//客户端  import java.io.*;import java.net.*;class UPClient
        {public static void main(String [] args) throws Exception
            {
                    Socket socket=new Socket("127.0.0.1",7000);
                    BufferedReader br=new BufferedReader(new FileReader("C:\\作业\\名单.txt"));  //用来读文件的输入流BufferedWriter bw=new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));  //用来把文件往服务端传                    //往scoket中一行一行的写入数据String content=null;while((content=br.readLine())!=null){
                        bw.write(content);
                        bw.newLine();
                        bw.flush();
                    }
                    
                    socket.shutdownOutput(); //关闭客端的输出流同,当相于加入一个结束标记(-1),要不然服务端会不停的等                                //取出服务端返回的信息BufferedReader brResult=new BufferedReader(new InputStreamReader(socket.getInputStream())) ;
                    System.out.println(    brResult.readLine());
                        
                    bw.close();
                    br.close();
                    socket.close();
            }
        }

//服务端  import java.io.*;import java.net.*;class UPServer
        {public static void main(String [] args) throws Exception
            {
                    ServerSocket serverSocket=new ServerSocket(7000);
                    Socket clientSocket=serverSocket.accept();
                    
                    System.out.println(clientSocket.getInetAddress().getHostAddress()+"已经连接..."); //打印一下客户端连上的的信息                    //读取客户端发过的来的数据BufferedReader br=new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
                    BufferedWriter bw=new BufferedWriter(new FileWriter("e:/xxx.exe"));
                    
                    String str=null;while((str=br.readLine())!=null){  //如果客户端不发结束标记,它就不会返回                        bw.write(str);
                        bw.newLine();
                        bw.flush();
                    }                    //再向发送端返回一条提示息                    
                    BufferedWriter bwResult=new BufferedWriter(new OutputStreamWriter(clientSocket.getOutputStream()));
                    bwResult.write("文件上传成功");
                    bwResult.flush();
                    
                    serverSocket.close();
                    clientSocket.close();
                    bwResult.close();
                    bw.close();
                    br.close();
                        
            }

例子 上传图片

客户端import java.net.*;import java.io.*;class ImgClient
            {public static void main(String [] ars) throws Exception
                    {
                            Socket socket=new Socket("127.0.0.1",7000);
                            FileInputStream fis=new FileInputStream("C:\\image\\0.jpg");  //文件输入流OutputStream out=socket.getOutputStream();                            byte [] buff  =new byte[1024];int len=0;while((len=fis.read(buff))!=-1){  //一边读数据,一边传数据out.write(buff,0,len);    //字节流,不用flush, 和 newLine()                            }
                            
                            socket.shutdownOutput(); //加一个结束标记,表示输入流结束                            //取出服务端发过来的信息BufferedReader brResult=new BufferedReader(new InputStreamReader(socket.getInputStream()));
                            System.out.println(brResult.readLine());
                            
                            socket.close();
                            fis.close();
                    }
            }

服务端import java.net.*;import java.io.*;class ImgServer
            {public static void main(String [] args) throws Exception
                {
                        ServerSocket serverSocket=new ServerSocket(7000);
                        
                        Socket clientSocket=serverSocket.accept();
                        
                        System.out.println(clientSocket.getInetAddress().getHostAddress()+" 已连接");
                        
                        InputStream in=clientSocket.getInputStream(); //取数据用的流FileOutputStream fos=new FileOutputStream("e:\\xxx.jpg");                        byte [] buff=new byte[1024];int len=0;while((len=in.read(buff))!=-1){
                            fos.write(buff,0,len); //不用flush 因为是字节流                        }
                        
                        BufferedWriter br=new BufferedWriter(new OutputStreamWriter(clientSocket.getOutputStream()));
                        br.write("图片上传成功");
                        br.flush(); //别忘了                        
                        serverSocket.close();
                        clientSocket.close();
                        br.close();
                        fos.close();    
                }
            }

例子 多线程并发上传图片

服务端     import java.net.*;class PICServer
        {public static void main(String [] args) throws Exception 
                {
                    ServerSocket serverSocket=new ServerSocket(9000);                    while(true)
                    {
                            Socket clientSocket=serverSocket.accept();new Thread(new PICThread(clientSocket)).start();
                    }
                }
        }

import java.io.*;import java.net.*;class PICThread implements Runnable{private Socket clientSocket;public PICThread(Socket socket)
            {
                clientSocket=socket;
            }public void run()
            {try{
                    
                    String clientIp=clientSocket.getInetAddress().getHostAddress();
                    FileOutputStream fos=new FileOutputStream("e:\\"+clientIp);
                    InputStream in =clientSocket.getInputStream();  //从套接字中取出数据byte[] buff=new byte[1024];int len=0;while((len=in.read(buff))!=-1)  //把数据从流中读出,写入文件                    {
                         fos.write(buff,0,len);
                    }
                    
                    BufferedWriter br=new BufferedWriter(new OutputStreamWriter(clientSocket.getOutputStream()));
                    br.write("图片上传成功");
                    br.flush();
                    
                    
                    clientSocket.close();
                    fos.close();
                    in.close();
                    
                }catch(Exception ex){
                    System.out.println("出错了");
                }            
            }
        }

客户端        import java.io.*;import java.net.*;class PICClient{public static void main(String [] args) throws Exception
            {
                
                   String fileName=args[0];//String fileName="c:\\Image\\2.jpg";                
                    //进行验证File file=new File(fileName);if(!(file.exists()&&file.isFile()))  //验证文件是不是存在                    {
                        System.out.println("输入的文件名错误或是个目录");return;
                    }                    if( !file.getName().endsWith(".jpg")){
                        System.out.println("文件类型不正确");return ;
                    }                    if( file.length() >1024*1024){
                        System.out.println("你想干啥,整这么大的文件上来? 不行");return; 
                    }
                    
                  Socket socket=new Socket("127.0.0.1",9000);
                
                    FileInputStream fis=new FileInputStream(fileName);  //构建文件输入流OutputStream out=socket.getOutputStream(); //输出流byte [] buff=new byte[1024]; int len=0;while((len=fis.read(buff))!=-1)  //一边读入,一边往文件中写出                    {
                         out.write(buff,0,len);
                    }
                    
                    socket.shutdownOutput();                    //取出服务端发过来的信息BufferedReader brResult=new BufferedReader(new InputStreamReader(socket.getInputStream()));
                    System.out.println(brResult.readLine());
                    
                    socket.close();
                    fis.close();
                    brResult.close();
                    out.close();    
            }
        }

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