Catalog

JSP summary

JSP The essence

JSP and Servlet The difference between

JSP Basic grammar of

Digression

（1） Why? jsp The first access to the file is slow ？

（2）JSP The extension of must be xxx.jsp Do you ？

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JSP summary

JSP yes java Program , yes JavaServer Pages Abbreviation .（ be based on Java Language implementation of the server-side page ）

JSP It's a set of norms . be-all web Containers /web Servers follow this set of specifications , every last web Containers /web The server will have a built-in JSP Translation engine .

Yes JSP When debugging errors , To open it directly JSP File corresponding java file , Check java Code .

JSP If you don't understand , Make a proposal to jsp Translate into java Code , You can read it .

JSP The essence

JSP It's essentially a Servlet

index.jsp At the time of the visit , Will automatically translate and generate index_jsp.java, Will automatically compile and generate index_jsp.class, that index_jsp It's a class .

index_jsp Class inheritance HttpJspBase, and HttpJspBase Class inherits HttpServlet. therefore index_jsp A class is just a Servlet class .

•  jsp The life cycle of Servlet The life cycle of is exactly the same .
•  jsp and servlet equally , It's all singletons .（ False single case ）

JSP and Servlet The difference between

Different responsibilities

• Servlet： collecting data （ Logical processing , Business processing , Then connect to the database , obtain / collecting data ）
• JSP： Display data

JSP Basic grammar of

1. stay jsp Write text directly in the document , Will be automatically translated to where ？

Translate to servlet Class service Methodical out.write(" Translate here "), Translate directly into double quotation marks , By java The program prints out to the browser as an ordinary string .

stay JSP Writing in the HTML,CSS,JS Code , These codes are for JSP It's just an ordinary string . however JSP Once this ordinary string is output to the browser , The browser will respond to HTML,CSS,JS To interpret and execute , To show an effect . 

2.page Instructions

（1） Chinese garbled code in response ：

adopt contentType Property is used to set the content type of the response , Add... At the end of the content type ：charset=UTF-8

<%@page contentType="text/html;charset=UTF-8"%>

 The content type of the response is text/html, Adopted character set UTF-8

（2） Guide pack

<%@page import="java.util.List,java.util.ArrayList"%>

3. stay JSP Written in Java Program ：

（1）<% java sentence ; %>

• What is written in this symbol is considered java Program , Translated to Servlet Class service Methods the internal .
• stay <% %> This symbol says java Code time , You should always remember that you are “ Method body ” Write code in it , What can be written in the method body , You can't write anything ？
  • service Static code blocks cannot be written in methods , Cannot write method , Member variables cannot be defined
• The code in the method body should be executed line by line from top to bottom .
• In the same JSP among <%%> This symbol can appear more than one .

（2）<%! %>

• Written in this symbol java The program will automatically translate to service Out of the way .
• Not recommended , Because in service Write static variables and instance variables outside the method , There will be thread safety problems .servlet Is a singleton , Multithreading concurrent environment , Once the static variable and instance variable are modified , There must be thread safety issues .

4.JSP The output statement of
（1） Output a... To the browser java Variable

<%

String name = “Tom”;  

out.write("name = " + name);

%>

out yes JSP One of the nine built-in objects . Can be directly in service Method used internally
（2） If there is no... In the output to the browser java Code , For example, output a fixed string , Can be directly in jsp Written in , There is no need to write <%%> here .

（3） If the output contains java Code

<%= %>

• stay = Write the content to be output after .
• Will translate to service Among the methods , It's this java Code ：out.print();

5.JSP Notes

（1）<%--JSP Professional notes , Will not be translated into java In the source code .--%>
（2）<!-- Belong to HTML Notes , The annotation information will still be translated into java In the source code , Don't suggest .-->

Digression

（1） Why? jsp The first access to the file is slow ？

Most o & M personnel demonstrate the project to customers , I'll put all the... In advance jsp Access the file first .
for the first time ：

• To put jsp File translation generation java Source file
• java The source file should be compiled to generate class Bytecode file
• And then through class To create servlet object
• And then call servlet Object's init Method
• Last call servlet Object's service Method .

The second time is faster
Call the singleton directly servlet Object's service The method can .

（2）JSP The extension of must be xxx.jsp Do you ？

jsp The extension of the file can be configured . Not fixed .

stay CATALINA_HOME/conf/web.xml, Configure... In this file jsp Extension of the file .

<servlet-mapping>
    <servlet-name>jsp</servlet-name>
    <url-pattern>*.jsp</url-pattern>
    <url-pattern>*.jspx</url-pattern>
</servlet-mapping>

xxx.jsp File for Tomcat Come on , Just an ordinary text file ,web The container will xxx.jsp Final file generation java Program , The final call is java Object related methods , When it's actually implemented , and jsp The document doesn't matter .