Servlet core technology

C/S framework ： client / Server mode , The client is responsible for the interaction with the user , The server is responsible for data management ;

B/S framework ： browser / Server mode , The browser is responsible for interacting with users , The server is responsible for data management ;

JavaWeb：Web Web page , Here means the resources on the Internet for external access , It is divided into static resources and dynamic resources ,JavaWeb It's using Java Language goes on Web A general term for development , Is to solve related problems Web The sum of technologies in the field of Internet ;

HTTP agreement ： Hypertext transfer protocol , Application layer protocol , Used to regulate browsers and Web The data format of how servers communicate , It mainly involves the request format of the browser and the response format of the server ;

HTTP Request format ： Request line 、 Request header 、 Blank line 、 Request body ;

HTTP The response format ： Corresponding line , Response head , Blank line , Response body ;

Press F12 Key to view request and response information ;

Tomcat The default access is ROOT In the catalog index.html, Manual access is hostlocal:8080/ Directory name 、 file name ;

Servlet Is a class that runs on the server , Can respond to requests from browsers ;

Servlet There are three programming steps ：

Servlet Life cycle of ：

Instantiation	Servlet Container to create Servlet Example , First request Servlet Call the constructor to create Servlet example , Call it once
initialization	The container calls init() Method , The method Call it once , When creating a good Servlet The method is called immediately after the instance Servlet The initialization
service	If you ask for Servlet, Then the container calls service() Method ,service() Method is used multiple times call , Whenever there is a request, it will call service() Method for the response to the request
The destruction	Call before destroying instance destory() Method , This method is only used by Call once , When it's time to Servlet Instance Web The application calls the method before releasing it to release the resources currently occupied.
Unavailable	Destroy the instance and mark it for garbage collection

GET There are three ways to request ： Type in the browser URL Press enter ;

Click on <a> Hyperlinks ,<a href="hello4"> test Get request </a>;

Click on submit Button , Submit <form method="get"> Forms ;

<form action="hello4" method="get">
    <input type="submit">
</form>

GET Request characteristics ： The requested data will be added to URL After the address , Only a small amount of data can be submitted , unsafe ;

POST Request mode ： Click on submit Button , Submit <form method="get"> Forms ;（ multi-purpose ）

<form action="hello4" method="post">
    <input type="submit">
</form>

POST Request characteristics ： Request data to be added to HTTP Agreement , A large amount of data can be submitted , Good safety ;

ServletRequest The interface is mainly used to provide servlet Provide client request information , You can get any request information from ;

HttpServletRequest Interface is SercletRequest Sub interface of , Mainly used to provide HTTP The function of requesting information ;

Servlet Receive Chinese garbled code ： When the browser submits the form , Chinese parameter values will be automatically encoded , When Tomcat The server automatically decodes after receiving the browser request , When the encoding method is inconsistent with the decoding method, it will lead to garbled code ;

 ServletResponse Interface is used to define an object to help Servlet Send a response to the client ;

HttpServletResponse The interface provides a response specific to HTTP The function of ;

ServletConfig Interfaces are used to describe Servlet Relevant configuration information of itself , Used to pass information to during initialization Servlet Configuration object ;

ServletContext Interfaces are used to define a set of methods ,Servvlet Use these methods with its Servlet Vessel communication ;