网络编程

1.1概述

计算机网络：
将不同位置的电脑通过某种协议连接起来，实现通信资源共享
网络编程的目的：
无线电台--传播交流信息，数据交流、通信
想要达到这个点需要什么：

如何准确的定位网络上的一台主机？ IP地址+port口，定位到计算机上的某个资源（如QQ）
找到这个主机，如何传输数据呢？（协议）

javaweb:网页编程 B/S
网络编程：TCP/IP C/S
TCP&UDP 类比
打电话 -- 连接--接了--通话 TCP
发短信--发送就完事--接收 UDP （不稳定，会丢包）

1.2 网络通信的要素

人工智能：智能汽车：工厂、人少。目前不能量产涉及伦理
如何实现网络的通信？
通信双地址：

ip
端口号 (www.baidu.com域名和IP是对应的)
规则：网络通信的协议

1.3 IP

ip地址：类InetAddress 不能new,api里构造函数灰色
唯一定位一台网络上计算机
127.0.0.1 本机localhost
ip地址的分类

Ip地址分类Ipv4/ipv6
- ipv4:127.0.0.1 4个字节组成，共 0-255， 42亿~，30亿在北美，亚洲4亿，2011年用尽
- ipv6:fe80::915d:470e:d522:4339%16,共128位，8个无符号整数，四个数字一组=16位，每个整数用16进制表示，当有连续多个0可以用:省略代替，但是只可以用一次[https://zhidao.baidu.com/question/748939481379152052.html]()
公网（互联网）-私网（局域网）
- ABCD类地址,字段分开给不同组织用
- 192.168.xx.xx 专门给组织内部使用的
  *域名：记忆IP问题！
- IP：www.vip.com 越短越贵

1.4 端口

端口表示计算机傻瓜一个程序的进程（类比一栋楼是一个IP，每一户是一个IP，物资里的东西是资源）

不同的进程有不同的端口号，不能冲突，用来区分软件
被规定 0-65535
TCP/UDP: 65535*2 单个协议下端口不能冲突
端口分类
- 公有端口 0-1023
  - HTTP:80
  - HTTPS:443
  - FTP：21
  - Telnet:23
- 程序注册端口：1024-49151，分配用户或者程序
  - Tomcat:8080
  - MySQL:3306
  - Oracle: 1521
- 动态、私有：49152-65535
```
netstat -ano # 查看所有的端口
netstat -anao|findstr "5900" # 查看指定的端口
tasklist|findstr "8696"  # 查看指定端口对应的应用进程
```
InetSocketAddress
InetSocaketAddress soketAddress2 = new InetSocketAddress("localhost",8080);
socketAddress.getHostName();//对应window系统C:\Windows\System32\drivers\etc\host里面可以设置IP和域名的对应关系

1.5 通信协议

协议：约定通信规则
网络通信协议：速率，传输马路，代码结构，传输控制...
问题：非常复杂
大事化小：分层
TCP/IP协议（实际上是一组协议）
TCP：用户传输协议
UDP：用户传输协议
IP: 网络互连协议
TCP:打电话
- 连接，稳定
- 三次握手，四次挥手

  握手最少需要三次，保证稳定连接
  A:你瞅啥？
  B:瞅你咋地？
  A:干一场！

  分开四次
  A:我要走了！
  B:你要走了？
  B:你真的要走了？
  A:我真的要走了！

区分客户端，服务端
传输完成,释放连接，效率低
UDP:发短信
- 不连接，不稳定
- 客户端服务端，没有明确的界限
- 不管有没有准备号，都可以发送给你
- 导弹，DDOS 洪水攻击，造成端口堵塞（饱和攻击）

1.6 TCP

客户端

连接服务器socket
发送消息
服务器
建立服务的端口 ServerSocket
通过accept等待客户端连接
接收消息

例1 发送接收消息

TcpServerDemo01.java

package demo1;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class TcpServerDemo01 {

	public TcpServerDemo01() {
		// TODO Auto-generated constructor stub
	}

	public static void main(String[] args) {
		ServerSocket serverSocket = null;
		Socket accept = null;
		InputStream is = null;
		ByteArrayOutputStream baos = null;
		try {
			// 1. should have a address, test on same computer local host
			serverSocket = new ServerSocket(9999);
			while (true) {
				// 2. wait clent to connect
				accept = serverSocket.accept();
				// 3.read client message
				is = accept.getInputStream();

				/*
				 * if has chinese word,broke 1024 may broke word into garbled
				 * word 
                                 * byte[] buffer = new byte[1024]; 
                                 * int len;
				 *  while ((len = is.read(buffer))!=-1)
                                 * { String msg = new String(buffer,0,len);
				 * System.out.print(msg); }
				 */
				// Pipestream ---ByteArrayOutputStream
				baos = new ByteArrayOutputStream();
				byte[] buffer = new byte[1024];
				int len;
				while ((len = is.read(buffer)) != -1) {
					baos.write(buffer, 0, len);
				}
				// all the bytes are written into pipestream, and output at one
				// time.
				System.out.print(baos.toString());
			}

		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} finally {
			// close resource

			try {
				if (baos != null) {
					baos.close();
				}
				if (is != null) {
					is.close();
				}
				if (accept != null) {
					is.close();
				}
				if (serverSocket != null) {
					serverSocket.close();
				}

			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}

		}
	}

}

TcpClientDemo01.java

package demo1;

import java.io.IOException;
import java.io.OutputStream;
import java.net.InetAddress;
import java.net.Socket;

public class TcpClientDemo01 {

	public TcpClientDemo01() {
		// TODO Auto-generated constructor stub
	}
	public static void main(String[] args){
		
		Socket socket = null;
		OutputStream os = null;
		try {
			//1.should know server address,port
			InetAddress serverIP = InetAddress.getByName("127.0.0.1");
			int port = 9999;
			//2. create a socket connnection
			socket = new Socket(serverIP,port);
			//3. send message
			os = socket.getOutputStream();
			
			os.write("hello, welcome to learn java".getBytes());
			
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} finally {
			try {
				if(os != null){
					os.close();
				}
				if(socket!=null){
					socket.close();
				}
				
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		
		
	}

}

扩展：
server端读数据打印到屏幕上，第二种方法不同于注释掉的第一种方法，使用了管道。
将所有数据读入管道流，然后再一次性输出，不会出现中文占两位被截断，输出乱码的问题。

例2 发送接收文件

TcpClientDemo02.java


package demo1;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.InetAddress;
import java.net.Socket;

public class TcpClientDemo02 {

	public static void main(String[] args) throws Exception{
		//1. create socket connection
		Socket socket = new Socket(InetAddress.getByName("127.0.0.1"),9000);
		OutputStream os = socket.getOutputStream();
		
		//2. prepare fileinputStream
		FileInputStream fis = new FileInputStream(new File("food.png"));
		
		//3. read and write file
		byte[] buffer = new byte[1024];
		int len;
		while((len = fis.read(buffer))!= -1){
			os.write(buffer, 0, len);
		}
		
		//notify server output is over
		socket.shutdownOutput();
		
		InputStream is = socket.getInputStream();
		ByteArrayOutputStream baos = new ByteArrayOutputStream();
		
		byte[] buffer2 = new byte[1024];
		int len2;
		// ensure server finish reception
		while ((len2 = is.read(buffer2))!=-1){
				baos.write(buffer2, 0, len2);
		}
		System.out.println(baos.toString());
		baos.close();
		fis.close();
		os.close();
		socket.close();
	}

}

TcpServerDemo02.java

package demo1;

import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class TcpServerDemo02 {
	public static void main(String[] args) throws Exception {
		//1. create service, IP is local PC, only need port
		ServerSocket serverSocket = new ServerSocket(9000);
		Socket accept = serverSocket.accept();
		// 3. get inputstream
		InputStream is = accept.getInputStream();
		
		//4. get outputStream.
		//refer to project, picture and src directory is in same level.
		FileOutputStream fos = new FileOutputStream(new File("copy.png"));
		byte[] buffer = new byte[1024];
		int len;
		while((len = is.read(buffer))!= -1){
			fos.write(buffer, 0, len);
		}
		// nofify client has finished
		OutputStream os = accept.getOutputStream();
		os.write("Have received all".getBytes());
		
		fos.close();
		is.close();
		serverSocket.close();
	}
}

扩展：

socket.shutdownOutput/shutdownInput作用
在C/S基本结构中，为了防止同一个流中，会出现输入/输出流发生交叉影响，会先设置好输出输入的先后顺序，然后在写入客户端或者服务端的时候，要将优先使用过的输入输出流进行暂时性关闭，保证输入输出流的数据流畅和准确性（解释refer 吾爱破解）
此处client端先socket.shutdownOutput,通知server端写完了。（关闭流没特别懂，后续懂了补详细解释）
Tomcat
服务端

自定义 S
Tomcat服务器 S: JAVA后台开发用别人的服务器
客户端
自定义 C
浏览器 B

1.7 UDP

发短信，不用连接，但需要知道对方的地址

例1. UDP发送消息

接收端

package demo1;

import java.net.DatagramPacket;
import java.net.DatagramSocket;

public class UdpServerDemo01 {

	public static void main(String[] args) throws Exception {
		//1. open the port 
		DatagramSocket socket = new DatagramSocket(9000);
		
		//2. receive packet
		byte[] buffer = new byte[1024];
		DatagramPacket packet =new DatagramPacket(buffer,0,buffer.length);
		
		socket.receive(packet);
		System.out.println(new String(packet.getData(),0,packet.getLength()));
		socket.close();
	}
}

发送端

package demo1;

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;

public class UdpClientDemo01 {

	public static void main(String[] args) throws Exception {
		//1. create socket
		DatagramSocket socket = new DatagramSocket();
		//2. create packet
		String msg = "hello server";
		InetAddress IP = InetAddress.getByName("localhost");
		int port = 9000;
		
		
		DatagramPacket packet = new DatagramPacket(msg.getBytes(),0,msg.getBytes().length,IP,port);
		
		//2. send packet
		socket.send(packet);
		
		socket.close();
	}

}

例2 UDP聊天（应用网页上咨询客服对话框）

例2.1咨询

UdpSenderDemo01.java

package demo1;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetSocketAddress;

public class UdpSenderDemo01 {

	public static void main(String[] args) throws Exception {

		DatagramSocket socket = new DatagramSocket(8888);
		while(true){
		// prepare data from console
		BufferedReader reader =  new BufferedReader(new InputStreamReader(System.in));
		String data = reader.readLine();
		byte[] datas = data.getBytes();
		
	
		DatagramPacket packet = new DatagramPacket(datas, 0, datas.length, new InetSocketAddress("localhost",6666));
		socket.send(packet);
		if("bye bye".equals(data)){
			socket.close();
			break;
		}
		
		}
		
	}

}

UdpReceiverDemo01.java

package demo1;

import java.net.DatagramPacket;
import java.net.DatagramSocket;

public class TcpReceiverDemo01 {
	public static void main(String[] args) throws Exception {
		DatagramSocket socket = new DatagramSocket(6666);

		while (true) {
			byte[] datas = new byte[1024];
			DatagramPacket packet = new DatagramPacket(datas, datas.length);
			socket.receive(packet);// block until receive packet
			String receiveData = new String(packet.getData());
                        /* 错了这样写，byte[]数组长度为1024转化位字符串长度也是1024，前面是有效字符后面追加的都是空个'\0'
                           应调用trim把空格剪除再进行比较
			if ("bye bye".equals(receiveData)){
				socket.close();
				break;
			}
                        */
			System.out.println(receiveData);

			if ("bye bye".equals(receiveData.trim())){
				socket.close();
				break;
			}
		}
	}
}

例2.2在线咨询

两个人都可以是发送方，也是接收方，因为有while(true)在循环接收发送，所以要启动两个线程来实现

建立连接一定在run方法外面，然后初始化赋值的都在构造器里，run方法里真正主体是循环等待发送接收
抽象两个工具类实现runnable接口，一个线程专门用来发消息，一个专门用来接收消息
一个线程占用一个端口，发送的端口号随意，但是接收的端口要保证一致

TalkReceive.java

package demo1;

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

public class TalkReceive implements Runnable {
	DatagramSocket socket = null;
	int fromPort;
	private String msgFrom;
	public TalkReceive(int fromPort, String msgFrom) {
		super();
		this.fromPort = fromPort;
		this.msgFrom = msgFrom;
		try {
			// Constructor can't throw exception out, except deal inside
			socket = new DatagramSocket(fromPort);
		} catch (SocketException e) {

			e.printStackTrace();
		}

	}

	public void run() {

		while (true) {
			try {
				byte[] datas = new byte[1024];
				DatagramPacket packet = new DatagramPacket(datas, datas.length);
				socket.receive(packet);// block until receive packet
				String receiveData = new String(packet.getData());
				System.out.println(msgFrom+": "+receiveData);
				if ("bye bye".equals(receiveData.trim())) {
					socket.close();
					break;
				}
			} catch (Exception e) {
				e.printStackTrace();

			}

		}

	}

}

TalkSend.java

package demo1;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetSocketAddress;
import java.net.SocketException;

public class TalkSend implements Runnable {
	DatagramSocket socket = null;
	BufferedReader reader = null;
	
	private int fromPort;
	private String toIP;
	private int toPort;

	public TalkSend(int fromPort, String toIP, int toPort) {
		super();
		this.fromPort = fromPort;
		this.toIP = toIP;
		this.toPort = toPort;
		try {
			socket = new DatagramSocket(fromPort);
			reader = new BufferedReader(new InputStreamReader(
					System.in));
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	@Override
	public void run() {
		while (true) {

			try {
				// prepare data from console
				String data = reader.readLine();
				byte[] datas = data.getBytes();

				DatagramPacket packet;
				packet = new DatagramPacket(datas, 0, datas.length,
						new InetSocketAddress(this.toIP, this.toPort));
				socket.send(packet);
				if ("bye bye".equals(data)) {
					socket.close();
					break;
				}
			} catch (Exception e) {
				e.printStackTrace();
			}

		}
	}

}

调用线程聊天的二者，老师，学生
TalkTeacher.java

package demo1;

public class TalkTeacher {

	public static void main(String[] args) {
		new Thread(new TalkSend(6666,"localhost",9999)).start();
		new Thread(new TalkReceive(8888,"Student")).start();
	}

}

TalkStudent.java

package demo1;

public class TalkStudent {

	public static void main(String[] args) {
		
		// open two thread
		new Thread(new TalkSend(7777,"localhost",8888)).start();
		//one thread occupy one port, so fromIp is different
		new Thread(new TalkReceive(9999,"Teacher")).start();
	}

}

测试结果（用学的知识做个东西，感觉妙啊，视频里同学都刷秒）

1.8 URL

https://www.baidu.com/
统一资源定位符:定位资源的，定位互联网上的某一个资源
DNS域名解析 www.baidu.com xxx.xxx.xxx.xx IP地址
一个服务器里可以跑几个网站（几个项目）
URL组成部分如下，可以少，但是不可以多

协议：//IP地址：端口/项目名/资源

例1 URL类

public class URLDemo01 {

	public static void main(String[] args) throws MalformedURLException {
		
		URL url = new URL("http://localhost:8080/helloworld/index.jsp?"
				+ "username=xiaofang&password=123");
		System.out.println(url.getProtocol()); //协议
		System.out.println(url.getHost()); //IP
		System.out.println(url.getPort()); //Port
		System.out.println(url.getPath()); //文件
		System.out.println(url.getFile()); //文件全路径
		System.out.println(url.getQuery());//参数
	}

}

输出结果

public class URLDemo01 {

	public static void main(String[] args) throws MalformedURLException {
		
		URL url = new URL("http://localhost:8080/helloworld/index.jsp?"
				+ "username=xiaofang&password=123");
		System.out.println(url.getProtocol());
		System.out.println(url.getHost());
		System.out.println(url.getPort());
		System.out.println(url.getPath());
		System.out.println(url.getFile());
		//the URL parameter
		System.out.println(url.getQuery());
	}

}

例2测试URL下载文件

网络上所有的东西都是以流的形式存在的,可以爬取

package demo1;

import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class URLDown {

	public static void main(String[] args) throws Exception {
		//1.download address
		URL url = new URL("https://ss3.bdstatic.com/70cFv8Sh_Q1YnxGkpoWK1HF6hhy/it/u=2380135284,3640663381&fm=26&gp=0.jpg");
		
		//2. connect to this address
		HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
		
		//All the things in website are Stream
		InputStream inputStream = urlConnection.getInputStream();
		
		FileOutputStream fos = new FileOutputStream (new File("1.jpg"));
		
		byte[] buffer = new byte[1024];
		int len;
		while((len=inputStream.read(buffer))!=-1){
			fos.write(buffer, 0, len);
		}
		
		fos.close();
		inputStream.close();
		urlConnection.disconnect();
	}

}

posted @ 2021-03-17 15:26 晒网达人阅读(144) 评论(0) 收藏举报

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