Getting started with Servlet

1、 What is? servlet

servlet It's a Java Program , Is to run the processed client request on the server and respond

servlet The core is javax.servlet.Servlet Interface , be-all servlet This interface must be implemented

Self defined servlet Mostly from genericServlet or HttpServlet Class to implement

2、servlet Life cycle of

Load and instantiate  

servlet initialization   

Client request processing  

servlet The destruction

3.get、post The difference between

1.get Get data from the server ,post Is to send data to the server .

2.get The parameter data queue is added to the submission form ACTION Attribute refers to URL in , Value corresponds to each field in the form one by one , stay URL Can be seen in .post It's through HTTPpost Mechanism , Place the fields and their contents in the HTML HEADER Transfer to ACTION Attribute refers to URL Address . Users don't see the process .

3. about get The way , Server side Request.QueryString Get the value of the variable , about post The way , Server side Request.Form Get submitted data .

4.get Small amount of data transmitted , Not greater than 2KB.post Large amount of data transmitted , It is generally defaulted to unlimited . But in theory, ,IIS4 The maximum quantity is 80KB,IIS5 In Chinese, it means 100KB.（ Here are other articles about get and post The size of the transmission data with each browser 、 Operating system and server restrictions ）

5.get Very low security ,post High security .

4、JSP The four scopes of （ From small to large ）
1.pageContext : Page scope
2.request : Request scope
3.Session: Conversation scope
4.application: Project scope