Learning Java - Network Programming

network programming

Notes content:

• Network Programming Overview
• Three elements of network programming
• UDP Programming
• TCP programming

Network Programming Overview:

computer network

是指将地理位置不同的具有独立功能的多台计算机及其外部设备，通过通信线路连接起来，在网络操作系统，网络管理软件及网络通信协议的管理和协调下，实现资源共享和信息传递的计算机系统。

network programming

就是用来实现网络互连的==不同计算机上==运行的程序间可以进行数据交换。

Network model:

计算机网络之间以何种规则进行通信，就是网络模型研究问题。

Generally refers to the network model

    OSI（Open System Interconnection开放系统互连）参考模型
    TCP/IP参考模型

Network reference model of FIG.

Three elements of network programming

1. IP address: InetAddress
   identifies the network device, easy to remember, the host name is available
2. Port number
   identifies the logical address, the process used to identify the different processes
3. Transfer Protocol
   communications rules
   common protocols: TCP, UDP

IP addresses

To get the network computers can communicate with each other, must specify an identification number == == for each computer to identify computers and computer designated to receive data transmitted by the identification number in the TCP / IP protocol, this identification number is the IP address.

The computer can only recognize binary data, our IP address should be a binary data, but we configured IP address is not binary, in order to facilitate representation on the IP address, so I have put it on every byte of the IP address the data is converted into decimal, then "" shown separately, this method is referred to as "dotted decimal"

IP composition: a host network number section number section +

Classification IP address:

Composition IP address: the network host number section number section +
class A: segment number is a first network segment number + the number segment three sections host
a network number: 256 256 256 = 16,777,216
Class B: before the network segment No. II host segment number + period after the Sec
a network number: 256 * 256 = 65536
class C: Three segments before the network segment number + number segment host after a period of
a network number: 256
classification IP address:
a class 1.0. 0.1 --- 127.255.255.254 (1) 10.XXX is a private address (private address is not used on the Internet, and is used in local area network address) (2) 127.XXX is reserved addresses, used cycle test use.
Class B 128.0.0.1 --- 191.255.255.254 172.16.0.0 --- 172.31.255.255 is a private address. 169.254.XX is reserved addresses.
Class C 192.0.0.1 --- 223.255.255.254 192.168.XX is a private address
like 224.0.0.1 --- 239.255.255.254 D
E class 240.0.0.1 --- 247.255.255.254

Two DOS command:

    ipconfig 查看本机ip地址
    ping 后面跟ip地址。测试本机与指定的ip地址间的通信是否有问题

Special IP addresses:

    127.0.0.1 回环地址(表示本机)
    x.x.x.255 广播地址
    x.x.x.0 网络地址

So, if we acquire and operate IP address?
In order to facilitate our acquisition and operation of the IP address, java provides a class InetAddress for our use.

MAC address :( ID number):

网卡的硬件标识

Use of InetAddress

No constructor, then how to make it functional classes offered?
To grasp the function:
static InetAddress the getByName (String Host): According to the host name or IP address of the string representation of the object to get the IP address
to get the host name: getHostName ()
Gets the host Ip address: getHostAddress ()

public static void main(String[] args) throws UnknownHostException {
        // public static InetAddress getByName(String host)
        // InetAddress address = InetAddress.getByName("liuyi");
        // InetAddress address = InetAddress.getByName("192.168.12.92");
        InetAddress address = InetAddress.getByName("192.168.12.63");

        // 获取两个东西：主机名，IP地址
        // public String getHostName()
        String name = address.getHostName();
        // public String getHostAddress()
        String ip = address.getHostAddress();
        System.out.println(name + "---" + ip);
    }

The port number

Physical port NIC port

We refer to logical port is a logical port

A:每个网络程序都会至少有一个逻辑端口
B:用于标识进程的逻辑地址，不同进程的标识
C:有效端口：0~65535，其中0~1024系统使用或保留端口。

TCP and UDP protocols

UDP

将数据源和目的==封装成数据包==中，不需要建立连接；每个数据报的大小在限制在64k；因无连接，是不可靠协议；不需要建立连接，速度快

TCP

建立连接，形成传输数据的通道，在连接中进行大数据量传输；通过三次握手完成连接，是可靠协议；必须建立连接，效率会稍低

to sum up:

UDP:

• Connectionless-oriented.
• Unreliable.
• high speed.
• The data packet transmission, the maximum data packet 64k.
  Example:
  chat messages, online video, video conferencing, text messaging, post office parcel.

TCP:

• Connection-oriented (the established connection path).
• Unlimited data
• Safe and reliable

• Less efficient.

• By three-way handshake to ensure the establishment of the connection.
  For example:
  download, phone calls,
  

Socket

Socket programming, network programming, socket programming is the same.

Socket socket:

网络上具有唯一标识的==IP地址和端口号组合==在一起才能构成唯一能识别的标识符套接字。
Socket包含了： IP地址+端口号

Socket principle mechanisms:

• Ends of the communication has Socket.
• In fact, network traffic is communication between the Socket.
• Socket IO between the two data transmission.

Scoket illustrating the principles of communication:

UDP transmission

• DatagramSocket: This class represents a socket for sending and receiving datagram packets.

• DatagramPacket: This class represents a datagram packet.

• Establishing the transmitting side, the receiving end.

• Set-up packet.

• Socket method of sending and receiving calls.

• Close Socket.

• Transmission and the receiver are two separate program.

UDP protocol to send and receive data illustrate

UDP transmission - transmitting end Thinking

1. Establish udp socket server
2. The data to be transmitted is encapsulated into packets
3. By udp socket server, the packet is sent out
4. Close Resources

public static void main(String[] args) throws IOException {
       //1.创建发送端Socket对象
    //发送端的Socket对象不需要指定端口
       DatagramSocket ds=new DatagramSocket();
       //2.创建数据，并把数据打包
       byte[] bytes="hello,java".getBytes();
       //长度
       int length=bytes.length;
       //IP地址对象
       InetAddress address=InetAddress.getByName("z-atu-72");
       //端口
       int port=10086;
       DatagramPacket dp=new DatagramPacket(bytes,length,address,port);
       //3.调用Socket对象的发送方法发送数据包
       ds.send(dp);
       //4.释放资源
       ds.close();


   }

Code optimization:

public class SendDemo {
    public static void main(String[] args) throws IOException {
        // 创建发送端的Socket对象
        DatagramSocket ds = new DatagramSocket();

        // 创建数据并打包
        byte[] bys = "helloworld".getBytes();
        DatagramPacket dp = new DatagramPacket(bys, bys.length,
        InetAddress.getByName("192.168.12.92"), 12345);
        // 发送数据
        ds.send(dp);
        // 释放资源
        ds.close();
    }
}

UDP transmission - reception side ideas:

1. Create a UDP Socket object receiving end
2. Receiving packet data for creating
3. Socket object method call receiver to receive data
4. Resolution Packet
5. Release resources

import java.io.IOException;
import java.net.*;

public class SendDemo {
    public static void main(String[] args) throws IOException {
        //1.创建发送端Socket对象
        DatagramSocket ds=new DatagramSocket();
        //2.创建数据，并把数据打包
        byte[] bytes="hello,java".getBytes();
        //长度
        int length=bytes.length;
        //IP地址对象
        InetAddress address=InetAddress.getByName("z-atu-72");
        //端口
        int port=10086;
        DatagramPacket dp=new DatagramPacket(bytes,length,address,port);
        //3.调用Socket对象的发送方法发送数据包
        ds.send(dp);

        //4.释放资源
        ds.close();
    }
}

Code optimization:

public class ReceiveDemo {
    public static void main(String[] args) throws IOException {
        // 创建接收端的Socket对象
        DatagramSocket ds = new DatagramSocket(12345);

        // 创建一个包裹
        byte[] bys = new byte[1024];
        DatagramPacket dp = new DatagramPacket(bys, bys.length);

        // 接收数据
        ds.receive(dp);

        // 解析数据
        String ip = dp.getAddress().getHostAddress();
        String s = new String(dp.getData(), 0, dp.getLength());
        System.out.println("from " + ip + " data is : " + s);

        // 释放资源
        ds.close();
    }
}

注意：

多次启动接受端会报java.net.BindException：Address already in use:Cannot bind 异常，表示端口别占用

UDP案例

从键盘录入数据进行发送，如果输入的是886那么客户端就结束输入数据。

TCP传输

Socket和ServerSocket
建立客户端和服务器端
建立连接后，通过Socket中的IO流进行数据的传输
关闭socket
同样，客户端与服务器端是两个独立的应用程序。

TCP传输-客户端思路：

Socket 客户端Socket套接字

1:建立客户端的Socket服务,并明确要连接的服务器。 （这一步如果创建成功，就说明连接已经创建成功）
2:如果连接建立成功,就表明,已经建立了数据传输的通道.就可以在该通道通过IO进行数据的读取和写入.该通道称为Socket流,Socket流中既有读取流,也有写入流.
3:通过Socket对象的方法,可以获取这两个流
4:通过流的对象可以对数据进行传输
5:如果传输数据完毕,关闭资源

/*
 * TCP协议发送数据：
 * A:创建发送端的Socket对象
 *      这一步如果成功，就说明连接已经建立成功了。
 * B:获取输出流，写数据
 * C:释放资源
 * 
 * 连接被拒绝。TCP协议一定要先开启服务器。
 * java.net.ConnectException: Connection refused: connect
 */
public class ClientDemo {
    public static void main(String[] args) throws IOException {
        // 创建发送端的Socket对象
        // Socket(InetAddress address, int port)
        // Socket(String host, int port)
        // Socket s = new Socket(InetAddress.getByName("192.168.12.92"), 8888);
        Socket s = new Socket("192.168.12.92", 8888);

        // 获取输出流，写数据
        // public OutputStream getOutputStream()
        OutputStream os = s.getOutputStream();
        os.write("hello,tcp,我来了".getBytes());

        // 释放资源
        s.close();
    }
}

TCP传输-服务器端思路

ServerSocket 服务端Socket套接字

1:建立服务器端的socket服务，需要一个端口，
2:服务端没有直接流的操作,而是通过accept方法获取客户端对象，在通过获取到的客户端对象的流和客户端进行通信
3:通过客户端的获取流对象的方法,读取数据或者写入数据
4:如果服务完成,需要关闭客户端,然后关闭服务器，但是,一般会关闭客户端,不会关闭服务器,因为服务端是一直提供服务的

TCP传输案例

服务器给客户端反馈

客户端键盘录入，服务器输出到控制台

客户端键盘录入，服务器输出文本文件

客户端文本文件，服务器输出到控制台

客户端文本文件，服务器输出文本文件

上传图片案例

服务器的代码用线程进行封装，这样可以模拟一个同时接收多人上传文件的服务器。(用循环也可以但是效率低，是单线程的程序)

TCP协议发送和接收数据图解

TCP传输容易出现的问题

客户端连接上服务端，两端都在等待，没有任何数据传输。
通过例程分析：
因为read方法或者readLine方法是阻塞式。
解决办法：
自定义结束标记
使用shutdownInput，shutdownOutput方法。