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JSP entry notes

2022-06-23 05:08:00 【Don't want to be a programmer】

JSP

1、 What is? JSP

Java Server Pages:Java Server side page , And also Servlet equally , For dynamic Web technology
The biggest feature ：

Write JSP It's like writing HTML
difference ：HTML Only static data is provided to users 、jsp Pages can embed JAVA Code , Provide users with dynamic data

2、JSP principle

Ideas ：JSP How did it happen

There are no problems at the code level
Work inside the server
tomcat There is one of them. work Catalog ;
IDEA Use Tomcat Of will be in IDEA Of Tomcat To create a work Catalog

Browser sends request to server , No matter what resources are accessed , In fact, they are all visiting Servlet！
JSP It will eventually be transformed into a Java class ！
JSP It's essentially one Servlet

// initialization 
public void_jspInit(){
    }
// The destruction 
public void_jspDestory(){
    }
//JSPService
public void _jspService(.HttpServletRequest request,HttpServletResponse response){
    }

Judge the request
Built in some objects
All of the above can be found in jsp Use in ！

stay JSP On the page ：
As long as it is JAVA The code will be output intact ;
If it is HTML Code , It will be converted to ：<out.write("<html>\r\n")> This format is output to the front end ！

3、JSP Basic grammar

Every language has its own grammar ,JAVA There is ,.
JSP expression

 <%--JSP expression 
  effect ： Used to convert the output of the program , Output to client 
 <%=  Variables or expressions %>
 --%>
 <%= new java.util.Date()%>

JSP Script

<%
    int sum = 0;
    for(int i = 1;i<=100;i++){
    
        sum+=i;
    }
    System.out.println("<h1>Sum="+sum+"</h1>");
%>

JSP Statement

<%!
static{
    
    System.out.println(" Statement ");
}
private int globalVar = 0;
%>

JSP Statement ： Will be compiled into JSP Generate Java In the two-point class ！ Other , Will be generated to _jspService In the method ！

<%@ page import="java.util.*"%>
<%@ page isErrorPage="true" %> // This is an error page 
<%@ page errorPage="error.jsp" %> // If it is an error page, go to error.jsp

web.xml Add the configuration error page Insert picture description here

4、9 Large built-in objects

PageContext To save things
Request To save things
Response
Session To save things
Application【ServletContext】 To save things
config【ServletConfig】
out
page
exception

JSP Page code

<%
    pageContext.setAttribute("name","jjj");// The saved data is only valid in one page 
    request.setAttribute("name2","jjj2");// The saved data is only valid in one request , Request forwarding will carry this data 
    session.setAttribute("name1","jjj1");// The saved data is valid only in one session , From open browser to close browser 
    application.setAttribute("name3","jjj3");// The saved data is only valid in the server , From turning on the server to turning off the server 
%>

<% pageContext.setAttribute("hello1","hello1",PageContext.SESSION_SCOPE);%>// Equate to 
<%--<% session.setAttribute("hello1","hello1");%>--%>

request： Client sends request to server , Data generated , It is useless after reading with the user , such as ： Journalism , It's useless for the user to read ！
session： Client sends request to server , Data generated , After the user runs out, there are still , such as ： The shopping cart ;
application： Client sends request to server , Data generated , One user ran out , Other users may also use , Such as chat data

5、JSP label 、JSTL label 、EL expression

EL expression ：（${ }）

get data
Perform an operation
obtain web Common objects for development

<jsp:forward page=" index.jsp">
	<jsp:param name="value1" value="value1"></jsp:param>
	<jsp:param name="value2" value="value2"></jsp:param>
</jsp:forward>`// Jump to a page

// Take out the parameters 
<%= request.getParam("value1")%>
<%= request.getParam("value2")%>

JSTL label
Rookie course study

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

JSTL The tag library is to make up for HTML The lack of labels ; It customizes many labels .

Core tags （ Master part ）：
Format label ：
xml label
Use steps ：

Introduce the corresponding taglib
Use the method
stay Tomcat We also need to introduce jstl package , Otherwise, an error will be reported ：JSTL Parse error （Tomcat Of lib in ）

<form action="coreif.jsp" method="get">
	<input type="text" name="value1" value="${param.value1}">
// Determine if the submitted user is an administrator , Login succeeded 
<c:if test="${param.value1=='value1'}" var="isAdmin">
	<c:out value=" The administrator welcomes you ！">
</c:if>
// Self closing label 
<c:out value="$(idAdmin)"/>

<c:set var="score" value="85"/>
<:choose>
	<c:when test="${score>90}">
	 You have to do well 
	</c:when>
	<c:when test="${score>=80}">
	 You have to do well 
	</c:when>
	<c:when test="${score>=70}">
	 Your grades are average 
	</c:when>
	<c:when test="${score<=60}">
	 You have to fail 
	</c:when>
</c:choose>

//var  Every time you traverse the variables 
//items  Object to traverse 
//begin  Where to start 
//end  Where to end 
//step  step 
<c:forEach var="***" items = ${
    list}>
	<c:out value="${people}"/><br>
</c:foreach>
<c:forEach var="" items="" begin="" end="" step=""></forEach>