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This article mainly introduces the Java back-end how to use EL expression to improve JSP related knowledge, the content is detailed and easy to understand, the operation is simple and fast, has a certain reference value, I believe that everyone after reading this Java back-end how to use EL expression to improve JSP article will have a harvest, let's take a look.

EL expression improves the shortcomings of JSPJSP

Because both HTML tags and java code can be defined within the jsp page, the following problems are caused

1. Trouble with writing: especially complex pages

2. Trouble reading

3. High complexity: operation depends on a variety of environments, JRE. JSP container (tomcat server).

4. Take up memory and disk: JSP automatically generates .java and .class files to occupy the disk, and runs .class files to occupy memory.

5. Debugging is difficult: after an error, you need to find the automatically generated .java file for debugging

6. disadvantageous team writing: front and rear staff

...

JSP has gradually retired from the stage of history, replaced by html and Ajax

Evolution process:

It's best not to write java code directly in jsp.

EL expression

Expression Language expression language for simplifying java code in JSP pages

Main function: access to data

Syntax: ${expression}

For example: ${brands}: get the data stored in the domain whose key is brands

Common problems when using Maven in idea maven is used in idea unable to create packages / classes

There is no source file, add one of these files as the source file, you can create a package or class (blue in the project structure)

Maven project that configures web in idea

Cannot create servlet in web created by maven

Deploy the tomcat plug-in in maven

Write to the pom.xml file

Org.apache.tomcat.maven tomcat7-maven-plugin 2.2 8080 / jsp-demo02 EL expression walkthrough

Create a com.web.ServletDemo1 class

Package com.web; import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;import java.util.ArrayList;import java.util.List; @ WebServlet ("/ demo1") public class ServletDemo1 extends HttpServlet {protected void doGet (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {/ / add data List list=new ArrayList () List.add ("zhangSan1"); list.add ("zhangSan2"); list.add ("zhangSan3"); list.add ("zhangSan4"); list.add ("zhangSan5"); System.out.println (list); / / 2, stored in the request field, which can be forwarded to the jsp page to use the EL expression request.setAttribute ("lists", list) / / 3. Forward to el-demo.jsprequest.getRequestDispatcher ("/ el-demo.jsp") .forward (request, response);}}

Create an el-demo.jsp under the web.app directory and write ${lists} in it

Insert title here$ {lists}

Running result

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