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Java developers probably know that there are two ways to introduce other files in a JSP into a project.
<% @include file= "xxx.jsp"%> <jsp:include page= "xxx.jsp" ></jsp:include>
We may use both of these methods, but perhaps many people do not name the difference between the two ways. Let's take a look at the following two examples
2 straight to the point(1)/include/include.jsp
<%@ Page Language="Java"pageencoding="UTF-8"%><%StringPath=Request.getcontextpath ();%><H1>Include Page</H1>
(2)/index1.jsp page
<%@ Page Language="Java"pageencoding="UTF-8"%><%StringPath=Request.getcontextpath ();%><!DOCTYPE HTML><HTML> <Head> </Head> <Body> <H1>Index page</H1> <%@include File="/include/include.jsp"%> </Body></HTML>
(3)/index2.jsp
<%@ Page Language="Java"pageencoding="UTF-8"%><%StringPath=Request.getcontextpath ();%><!DOCTYPE HTML><HTML> <Head> </Head> <Body> <H1>Index page</H1> <Jsp:includepage= "/include/include.jsp"></Jsp:include> </Body></HTML>
Now we have access to index1.jsp and the results are as follows
So we continue to visit index2.jsp and the results are as follows
Why, how index1.jsp why visit error, ah, it seems @include and Jsp:include is a difference it. Only by understanding the underlying differences between the two ways of @include and jsp:include, we know why the index1.jsp page is wrong. Just keep looking and you'll understand.
3 @include and Jsp:include internal differencesTo demonstrate the correct effect of @include, we'll write two more pages
(1)/include/include1.jsp
<%@ Page Language="Java"pageencoding="UTF-8"%><H1>Include1 page</H1>
(2)/index3.jsp
<%@ Page Language="Java"pageencoding="UTF-8"%><%StringPath=Request.getcontextpath ();%><!DOCTYPE HTML><HTML> <Head> </Head> <Body> <H1>Index page</H1> <%@include File="/include/include1.jsp" %> </Body></HTML>
We visit the index3.jsp page
OK, we found the result is correct, can compare the include1.jsp and include.jsp see where the change. We know that when we visit a JSP page, the servlet container (such as Tomcat) compiles the JSP into the servlet Java code. Let's look at the servlet Java code generated by Tomcat for Index1.jsp and index3.jsp. In Tomcat we can find the code for Tomcat to compile the JSP into a servlet in the "/tomcat directory/work/catalina/localhost/project name/".
(1) index3.jsp corresponding servlet code
(2) The servlet code corresponding to the index2.jsp page
The include.jsp corresponding servlet code was also generated when accessing ndex2.jsp
Servlet code generated from Tomcat we can draw the difference between the two
4 Conclusion@include: Pre-compiling the page request, all the code is included, processed together, all the code together, compiled into a servlet
Jsp:include all the code is processed separately, compiled when the page is requested, compiled into multiple servlets, the page syntax is relatively independent, and the results of the code (processing results) are combined after processing is complete.
5 back to the question againWhy this article in the beginning of the question index1.jsp page error, you know, because the include.jsp page and index1.jsp page contains the following code.
<% = request.getcontextpath (); %>
Because we adopt the Include method, so that the page request before all the code is included in the first and then processed together, so that the code has two path variables. This does not conform to the Java syntax. All of them reported 500 mistakes. Why index2.jsp is not wrong, because the use of the jsp:include way, such two pages are compiled separately, and finally the compilation results are merged. All will not go wrong.
Knock it off, get it done, finish!
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