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The role of Servlets: techniques for developing dynamic resources in the Java language
The role of JSP: the technology of developing dynamic resources in the Java language (+html language)
JSP is the servlet
Features of 1.2JSP1) The operation of the JSP must be given to the Tomcat server
Tomcat's work directory: the Tomcat server holds temporary files for the JSP runtime
2) JSP page can write HTML code, also can write Java code
(HTML pages cannot write Java code, and JSP pages can write Java code)
1.3 Experience JSP page functionRequirements: Display the current time to the browser
1<%@ Page Language="Java"Import="java.util.*,java.text.*"pageencoding="Utf-8"%>2 <!DOCTYPE HTML PUBLIC "-//w3c//dtd HTML 4.01 transitional//en">3 <HTML>4 <Head> 5 <title>First JSP page</title> 6 </Head>7 <Body>8<%9 //Write Java codeTen //Get current Time One SimpleDateFormat SDF= NewSimpleDateFormat (); A Stringcurdate=Sdf.format (New Date()); - //output content to browser - //response.getwriter (). Write (""); the Out.write ("the current time is 2:"+curdate); -%> - </Body> - </HTML>1.4jsp Execution Process
Execution process
1) access to 01.hello.jsp page,tomcat scan to jsp file, in %tomcat %/work translating JSP files into java source files
(01.hello.jsp-_01_hello_jsp.java) (translation)
2)thetomcat Server compiles the Java source files into a class bytecode file (compile)
(_01_hello_jsp.java-_01_hello_jsp.class)
3)Tomcat Server constructs _01_hello_jsp class object
4)thetomcat Server calls the _01_hello_jsp class inside the method, and the return content is displayed to the browser.
Attention:
1)jsp file modified or jsp Temporary files are deleted, to re-walk translation (1) and compile (2 ) of the process
1.5jsp and servlet relationships
JSP translation of java files:
Public final class _01_hello_jsp extends Org.apache.jasper.runtime.HttpJspBase
Implements Org.apache.jasper.runtime.JspSourceDependent {
Httpjspbase class: Public abstract class Org.apache.jasper.runtime.HttpJs PBase
Extends Javax.servlet.http.HttpServlet implements Javax.servlet.jsp.HttpJspPage {
Conclusion: JSP is a servlet program!!!
Servlet technology can be used in JSP programs
JSP technology is not all applicable to the servlet program!
The life cycle of a servlet:
1) Construction method (1th visit)
2) Init method (1th visit)
3) Service method
4) Destroy method
The life cycle of a JSP
1) Translation: Jsp->java file
2) Compile: Java file->class file (servlet program)
3) Construction method (1th visit)
4) Init method (1th visit): _jspinit ()
5) Service method: _jspservice ()
6) Destroy method: _jspdestroy ()
2.jsp Syntax 2.1jsp templatesThe HTML code in the JSP page is the template for the JSP
2.2jsp-expressionSyntax: <%= variable or expression%>
Effect: The value of an output variable to the browser or the result of an expression calculation
Attention:
1) The principle of expression is to translate into out.print ("variable"), write the content to the browser by this method
2) No semicolon is required after expression
Script for 2.3jspSyntax: <%java code%>
Role: Executing Java code
Note: The principle is that the Java Code in the script is copied intact into the _jspservice method.
Statement of the 2.4JSPSyntax: <%! variable or method%>
Function: A variable or method that declares a JSP
Note: variables are translated into member variables and methods are translated into member methods
2.5jsp annotationsSyntax: <%!--jsp Comment--%>
Note: HTML annotations are translated and executed, and JSP annotations cannot be translated and executed
3.jsp of the three instructions 3.1include instructionsRole: Used in the current page to include other pages
Syntax: <% @include file= "common/header.jsp"%>
Note: 1) The principle is to translate the contents of the included pages into the included pages, merge into a translation of a Java source file, in the compilation run, this contains called static inclusion (source code contains)
2) If a static inclusion is used, the global HTML tag is not required in the included page. such as (Html,head,body)
3.2page instructionRole: Tell the Tomcat server how to translate the JSP file
<%@ Page Language="Java" --tell the server what dynamic language to use to translate the JSP file import="java.util.*" --tell the server what package the Java file uses to import the package, with multiple packages separated by commas pageencoding="Utf-8" --tell the server what encoding to use to translate JSP files (into Java files) ContentType="text/html; Charset=utf-8"Server Send browser data type and content encoding note: In the development tool, only need to set pageencoding in the future to solve the Chinese garbled problem errorpage="error.jsp"Iserrorpage="false"Buffer="8kb"Session="true"iselignored="false"%>3.3taglib instruction
Learn the basics of everyday notes <day12>jsp
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