How to improve JSP with EL expression in Java backend
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
This is the end of the article on "how Java backend uses EL expressions to improve JSP". Thank you for reading! I believe that everyone has a certain understanding of "Java back-end how to improve JSP with EL expressions". If you want to learn more, you are welcome to follow the industry information channel.
