1. Two usages
The first type: include instruction:Specify the included page through the file attribute, when JSPIntroduce the specified file when converting to Servlet, generally no need to write a header
<%@ pagecontentType="text/html;charset=GB2312" language="java"errorPage=""%>
<%@ include file="hea"%>
<%@ include file=""%>
<%@ include file=""%>
The second type:The second type: <jsp:include> action element:Specify the included page through the page attribute, when the JSP page is requested, the specified file is introduced.Need to write a header
<%@ page contentType="text/html; charset=GB2312"language="java" errorPage=""%>
<jsp:include page=""/>
<jsp:include page=""/>
<jsp:include page=""/>
Note: The <jsp:include> action usually contains files that are frequently changed, because the included file changes will not affect the included file, so there is no need to recompile the included file.
2. Differences in usage
（1）The difference in the introduction;Difference in execution time
include directive，(statically included)The included file is inserted intact into the position where the instruction is used in the included page, and then the JSP compiler compiles the synthesized file, and finally there is only one compiled file.Execute in the translation stage
<jsp:include> (Dynamic Included)BagWhen including files, when the action flag is executed, the JSP program will forward the request to the included page (note that it is not a redirect) and output the execution result to the browser, and then return to the page to continue executing the subsequent code, thinking that the two files executed by the web container, so the JSP compiler will compile these two files respectively.Execute in the request processing phase.
3. How to bring the include page into parameters
<jsp:include> Action ElementIt can be used to use <jsp:param> to theContains page passing parameters, as follows:
<%@ page contentType="text/html; charset=GB2312"language="java" errorPage=""%>
<jsp:include page=""/>
<jsp:includepage="">
<jsp:param name="uid"value="username"/>
<jsp:param name="pwd"value="password"/>
</jsp:include>
<jsp:includepage=""/>
4. Description: Translation stage
Translation phase:
The Jsp container converts the jsp page into a servlet (called the jsp page implementation class - JSP Page implementation class) and compiles this servlet. These two steps form the translation stage.
Request processing phase:
JspDe-register containerjspPage conversion toservletoutside,Also calledjspPage implementation classes to process each request and generate a response.This stage is called the request processing stage.Only class documents are executed during the request processing phase.
5. Example
Server tomcatIntroduce pagequiltIntroduce a page
//===========//
<%@ page language=”java” contentType="text/html;charset=gb2312"%>
<%
date=new ();
String date_cn ="";
String dateStr = "";
switch(())
{
case 0:date_cn ="date"; break;
case 1:date_cn ="1"; break;
case 2:date_cn ="2"; break;
case 3:date_cn ="three"; break;
case 4:date_cn ="Four"; break;
case 5:date_cn ="five"; break;
case 6:date_cn ="Six"; break;
}
dateStr = (1900+()) + "year" + (()+1) + "month" + () + "day (week" + date_cn + ")";
%>
("<%=dateStr%>");
//==================//
<%@ page language=”java” contentType=”text/html;charset=gb2312”%>
<html>
<head>
<title>Two usages of include</title>
<jsp:include page=”” flush=”true”/>
<%--@ include file=”” %-->
<head>
<body>
<table><tr><td></td></tr></table>
</body>
</html>
First use <%@ include file="" %> to introduce it
500 Internal Error of Server –: /(0,0) Page directive: can't have multiple occurrences of contentType
Tip: You cannot specify multiple contentTypes in the page.
It is because during the translation stage, the code of the document is joined to the page as it is, thereby synthesizing a document. The synthesized document will be similar:
<%@ page language=”java” contentType=”text/html;charset=gb2312”%>
The solution is to delete this sentence from the document. Refresh and request the page, it's normal.
ChecktomcatThe temporary documentation under...\tomcat\work\Standalone\localhost\testYou will see it in the directorytest_jsp.javaandtest_jsp.classTwo documents,
The java document here is the test_jsp.java document obtained by converting jsp into servlets by the jsp container.
Open the generated servlet document (test_jsp.java). When the document is converted into a servlet document, the newly participated content in the output <haed> is the code inside.
Change <%@ include file=""%> to <jsp:include page="" flush="true"/>
There is garbled Chinese in the output date.
Reason: When introducing an include action element into the page, it is called as a separate document after execution before being called when the document is run.
Since there is no specified character encoding in the document, garbled code appears. The solution is to re-examine what I just removed in the document
<%@ page language=”java” contentType=”text/html;charset=gb2312”%>
Check the temporary document under tomcat again, test_jsp.java only added one code:
(request, response, "", out, true);
It does not introduce the code of the document into.