Web and network basics, HTTP packets, working principles, HTTP Communication Technology in Java, java Communication Technology

Web and network basics, HTTP packets, working principles, HTTP Communication Technology in Java, java Communication Technology

I. web and network Basics

1. HTTP history

1.1 concept of HTTP:

HTTP (Hyper Text Transfer Protocol) is a communication Protocol that allows the Transfer of Hypertext Markup Language (HTML) documents from a Web server to a client browser.

It is an application layer protocol that carries over TCP. A standard client server model consisting of requests and responses

1.2. HTTP development history:

As the HTTP protocol for Web file transfer, the version update is very slow. Currently, only three versions are updated:

HTTP/0.9: no standard was set up in 1990

HTTP/1.0: August 1, May 1996,

HTTP/1.1: January 1997, the current mainstream HTTP Version

1.2 importance of HTTP in Web applications:

HTTP is the foundation of the entire Web, and many applications do not need to understand the HTTP protocol:

WebService = HTTP + XML

Reset = HTTP + JSON

Implementation of various APIs: HTTP + XML/JSON

Collection and thieves site

Desktop applications such as QQ and thunder

2. Basic Network TCP/IP protocol

2.1. Concepts of protocols:

Protocols refer to the regulations or rules that must be followed when two computers communicate in a computer communication network.

There are various protocols in the computer network, such as TCP, IP, HTTP, FTP, and so on, it becomes the TCP/IP protocol family.

2.2 hierarchical management of TCP/IP

Application Layer: processes specific applications, such as FTP, DNS, and HTTP.

Transport Layer: provides data connections between two computers in a network connection to the upper application layer. This layer has two Protocols: TCP and UDP.

Network Layer: processes the flow of data packets on the network. The layer protocols include IP, ICMP, and IGMP.

Data link layer: process the hardware part of the connected network. Including the operating system, hardware driver, Nic, and optical fiber.

2.3 TCP/IP communication and transmission process

3. close relationship between IP, TCP, DNS and HTTP

3.1 concepts and functions of IP protocol

IP (Internet Protocol), Internet Protocol, at the network layer

Send various data packets to the other party. The two most important conditions are the IP address and MAC address (the MAC address will not change, but it can be changed through software)

ARP Address Resolution Protocol: detects MAC addresses based on IP addresses

3.2 concepts and functions of TCP

TCP (Transmission Control Protocol), which is located at the transport layer.

Provides reliable byte stream service and uses a three-way handshake Policy

3.3 TCP three-way handshake

3.4 concept and role of DNS

DNS (Domain Name System) is located at the application layer.

Provides resolution services between domain names and IP addresses

3.5. Relationship between HTTP and TCP, IP, and DNS

To generate HTTP request packets, you must use DNS resolution to find the server and transmit requests over TCP.

4. Concepts of URI and URL

4.1 concepts of URI:

URI (Uniform Resource Identifier), a unified Resource Identifier, is a string used to identify an Internet Resource Name.

4.2 concept of URL:

URL (Uniform Resource Location), which specifies the Location of a specific Resource on a specific server.

4.3 relationship between URI and URL:

URI identifies an Internet resource with a string, and a URL represents the address of the resource. It can be seen that a URL is a subset of the URI.

A URI consists of two major subsets: URL and URN.

4.4 URI format, which consists of nine parts

1. For example URI: https: // user: pass@www.example.com: 80/home/index.html? Age = 11 # mask

Http: protocol solution name. To obtain resources, specify the protocol type.

User: pass: logon information (authentication). This parameter specifies the user name and password. Optional.

Www.example.com: server address

80: port number. Optional.

/Home/index.html: file path

Age = 11: parameter component that provides the application with additional information needed to access resources

Query string: for resources in the specified file path, you can use the query string to input any parameter. Optional (case by page)

Mask: The fragment identifier. It can mark the sub-Resources in the obtained Resource (a location in the Document). Optional.

Ii. elaborate on the HTTP message format and workflow

1. Formats of HTTP request messages and response packets

1.1 concepts of HTTP transactions and message streams

HTTP transaction = Request command + response result

1.2 Request Message format (packet capture tool, fiddler)

Request Line: Request Method (uppercase) request URL version

Request Header: Name: Value

Empty rows:

Message Body:

The request header is also called a message header. The field names are case-insensitive and are used to the camper mode. The fields can be arranged in any order. Some fields can have multiple value options, and some fields can appear multiple times.

1.2.1 request methods: GET, POST, HEAD, OPTIONS, DELETE, PUT

By default, GET requests are sent. For example, if you directly enter an address in the browser to access the site, and click the hyperlink to access the site, you can change the Request Method to post by changing the form submission method. The difference between POST and GET Methods: The method for passing parameters; the size of data transferred

1.2.2 common request headers:

Accept: the MIME type acceptable to the browser */* (large type)/(small type)

Accept-Charset: Tell the server which character set is supported by the browser

Accept-Encoding: The data Encoding method that the browser can decode, such as gzip.

Accept-Language: the Language type that the browser wants.

Host: Host and port in the initial URL

Referer: contains a URL from which the user sends a page representing the current request.

Content-Type: Content Type

If-Modified-Since: The value is a GMT standard time. If the requested file has not changed Since this time, the server informs the browser that the file can be directly read from the cache.

User-Agent: User's browser type, operating system, and other information

Content-Length: the Length of the Request Message Body.

Connection: If the value is Keep-Alive, a persistent Connection is required. HTTP 1.1 performs a persistent Connection by default.

Cookie: This is one of the most important request header information. However, this function is replaced by Session due to security risks and other reasons.

Date: The value is GMT, indicating the request time.

1.3. Response Message format

Response line: Protocol version status code reason phrase

Response Header:

Empty rows:

Message Body:

1.3.1. Status Code: Used to indicate various processing results and statuses of the server's requests. It is a three-digit decimal number. Response status codes fall into five categories:

1.3.2. Common status codes:

200: normal

301: Permanent redirection

302/307: Temporary redirection

304: not modified. You can use the cache without modifying it again.

404: resource not found

500: Internal Server Error

1.3.3 common response headers:

Location: https://cn.bing.com/indicates the new resource Location.

Server: apache tomcat indicates the Server type

Content-Encoding: Encoding type used by the gzip server to send data

Content-Length: 80 indicates the Length of the browser body.

Content-Language: Language of the text sent by the zh-cn Server

Content-Type: text/html; charset = GB2312 the MIME Type of the Content sent by the server

Last-Modified: The Last modification time of the GMT time file

Refresh: 1; url = https://www.baidu.com indicates the client Refresh frequency, in seconds

Content-Disposition: attachment?filename=aaa.zip instructs the client to download the file

Set-Cookie: SS = Q0 = 5Lb_nQ; path =/Cookie sent by the search Server

Expires: GMT indicates the expiration time. The value 0 or-1 indicates that cache is disabled.

Cache-Control: no-cache (1.1) indicates the hexadecimal Cache.

Connection: close/Keep-Alive

Date: GMT

2. HTTP Workflow

2.1 process steps

2.2 domain name resolution process

2.3 three-way handshake

2.4 initiate an HTTP request

2.5 respond to HTTP requests and get HTML code

2.6 parse HTML code in a browser

2.7 rendering the page by the browser to the user

3. Differences between HTTP1.0 and HTTP1.1

3.1 basic running mode of HTTP1.0:

A transaction is divided into four processes: establishing a connection, sending a request from a browser, sending a response from the server, and closing a connection. Each connection only processes one request and response. A separate connection must be established between the browser and the server to access each file.

3.2. Features of HTTP1.1

A TCP connection can send the HTTP request and response of the lock brother.

Multiple requests and responses can overlap.

Added more request headers and response headers, such as Host and If-Unmodified-Since request headers.

4. Use Telnet to connect to an instance

The Telnet protocol is a member of the TCP/IP protocol family and is the standard protocol and main method of the Internet remote Logon Service. It provides users with the ability to complete remote host work on local computers. Use the telnet program on the terminal computer to connect to the server

Iii. HTTP Communication in Java

1. Use HTTP Get to read Network Data

Class ReadByGet extends Thread {@ Override public void run () {URL url = new URL ("url"); // if there is a parameter, URLConnection conn = URL is included in the url. openConnection (); InputStream is = conn. getInputStream (); InputStreamReader isr = new InputStreamReader (is); BufferedReader br = new BufferedReader (isr); String line; StringBuilder builder = new StringBuilder (); while (line = br. readLine ())! = Null) {builder. append (line);} br. close (); isr. cloae (); is. close (); System. out. println (builder. toString) ;}} public static void main (String [] args) {new ReadByGet (). start ();}

2. Use HTTP Post to communicate with the network

Class ReadByPost extends Thread {@ override public void run () {URL url = new URL ("url"); HttpURLConnection conn = (HttpURLConnection) URL. openConnection (); conn. addRequestProperty ("encoding", "UTF-8"); conn. setDoInput (true); Conn. setDoOutput (true); conn. setRequestMethod ("POST"); OutputStream OS = conn. getOutputStream (); OutputStreamWriter osw = new OutputStreamWriter (OS); BufferedWriter bw = new Buffer EdWriter (osw); bw. write ("parameters passed to the server"); bw. flush (); InputStream is = conn. getInputStream (); InputStreamReader isr = new InputStreamReader (is); BufferedReader br = new BufferedReader (isr); String line; StringBuilder builder = new StringBuilder (); while (line = br. readLine ())! = Null) {builder. append (line);} // closes the resource System. out. println (builder. toString) ;}} public static void main () {new ReadByPost (). start ();}

3. Use HttpClient for Get Communication

Apache has an HttpClient package

1. class Get extends Thread{       HttpClient client = HttpClients.createDefault();    @Override    public void run(){                HttpGet get = new HttpGet("https://www.baidu.com");                  HttpResponse response = client.execute(get);         HttpEntity entity = response.getEntity();         String result = EntityUtils.toString(entity,"UTF-8");                  System.out.println(result);             }}public static void main(String[] args){    new Get().start();}

4. Use HttpClient for Post Communication

Class Post extends Thread {HttpClient cilent = HttpClients. createDefault (); @ Override public void run () {HttpPost post = new HttpPost ("url"); // you can specify the List of parameters to be uploaded.
 
  
Parameters = new ArratList (); parameters. add (new BasicNameValuePair ("key", "value"); post. setEntity (new UrlEncodeFormEntity (parameters, "UTF-8"); HttpResponse response = client.exe cute (post); HttpEntity entity = response. getEntity (); String result = EntityUtils. roString (entity, "UTF-8"); System. out. println (result) ;}} main () {new Post (). start ();}