java+jdbc+mysql+socket搭建局域网聊天室

 void linkdb() {
    try {
      Class.forName("com.mysql.jdbc.Driver");

      conn = DriverManager.getConnection(url,user,password);
      DatabaseMetaData dbmd=conn.getMetaData();

      ResultSet tableRS = dbmd.getTables(null, null, "chatusr", null );

      if (tableRS.next())
        System.out.println(" the table is exsited");
      else {
        String sql = "CREATE TABLE chatusr(";  
        sql+= " ip char(15),";  
        sql+= " port int(6),";  
        sql+= " name char(255),";
        sql+="PRIMARY KEY(ip))";
        pst=conn.prepareStatement(sql);
        pst.executeUpdate();
      }
    } catch (SQLException e) {
      // TODO 自动生成的 catch 块
      e.printStackTrace();
    } catch (ClassNotFoundException e) {
      // TODO 自动生成的 catch 块
      e.printStackTrace();
    }
    System.out.println("连接数据库成功");
  }

public int getlength(byte[] conf) {
    int c=0,i;
    for(i=0;i<250;++i)
      if(conf[i]==10)//'\0'的编码为10，表示数组结尾
        break;
    return i+1;
  }
public void send(String message) {

      String string=m_port; 
      //string+=sendcontent.getText();
      string+=message;
      byte[] databyte = new byte[250];
      try {
        databyte=string.getBytes("GBK");
      } catch (UnsupportedEncodingException e1) {
        // TODO 自动生成的 catch 块
        e1.printStackTrace();
      }
      //string.getBytes(0, string.length(), databyte, 0);
      int len=getlength(databyte);
    //发送给自己
    try {
      DatagramPacket sendPacket = new DatagramPacket(databyte,len, java.net.InetAddress.getByName(m_ip), Integer.parseInt(m_port));
      sendSocket=new DatagramSocket();
      sendSocket.send(sendPacket);
    } catch (IOException ioe) {
      record.append("网络通信出现错误，问题在于" + ioe.toString());
    }
    //发送给其他人
    for(int ti=0;ti<num;++ti) {
      try {
        DatagramPacket sendPacket = new DatagramPacket(databyte, len, java.net.InetAddress.getByName(ip[ti]), Integer.parseInt(port[ti]));

        sendSocket=new DatagramSocket();
        sendSocket.send(sendPacket);
      } catch (IOException e) {
        // TODO 自动生成的 catch 块
        e.printStackTrace();
      }
    }
  }

public void run() {
    // TODO 自动生成的方法存根
    while (true) {

      try {
        byte buf[] = new byte[250];
        receivePacket = new DatagramPacket(buf, buf.length);
        receiveSocket.receive(receivePacket);
        String t_ip = receivePacket.getAddress().toString().trim();
        t_ip=t_ip.substring(1);//获取ip
        String t_name="unname";
        Date date=new Date();
        byte[] data = receivePacket.getData();
        String receivedString = new String(data, "GBK");
        String t_port = receivedString.substring(0,4);//获取端口
        receivedString=receivedString.substring(4);
        if(t_ip.equals(m_ip)) {
          t_name=m_name;
          record.append("来自本机:\\" + t_ip + "\n端口:" + receivePacket.getPort()+"\n时间:"+ date.toString());
          record.append("\n"+t_name+":\t");
        }
        else {
          int ti=0;
          for(ti=0;ti<num;++ti) {
            if(t_ip.equals(ip[ti])) {
              break;
            }
          }
          if(ti==num) {
            mysql="Insert Into chatusr Values ('"+t_ip+"','"+Integer.parseInt(t_port)+"','"+t_name+"')";
            if(mm.add(mysql))
              System.out.println("插入成功");
            t_name="unnamed";
          }
          else {
            t_name=name[ti];
          }
          record.append("\n来自主机:\\" + t_ip + "\n端口:" + receivePacket.getPort()+"\n时间:"+ date.toString());
          record.append("\n"+t_name+":\t");
        }
        record.append(receivedString+"\n");
      } catch (IOException e) {
        record.append("网络通信出现错误,问题在于" + e.toString());
      }
      record.selectAll();
    }
  }