Expression Language (EL)

Expression language makes it possible to easily access application data stored in JavaBeans components. For example, the JSP expression language allows a page author to access a bean using simple syntax such as ${name} for a simple variable or ${name.foo.bar} for a nested property.

Type Operators/Syntax Description
1 Arithmetic Operators +, –, *, /, %
2 Relational Operators == ( eq), != (ne), < (lt), > (gt), <= (le), >= (ge)
3 Logical Operators &&(and), ||(or), !(not)
4 The empty Operator ${empty x} If operand is null then return true.
5 Conditionally expression ${ test ? expression1 : expression2 } ${1==2 ? “a” : “b”}

Deactivating Expression Evaluation

To deactivate the evaluation of EL expressions, you specify the isELIgnored attribute of the page directive:

<%@ page isELIgnored =”true|false” %>

The valid values of this attribute are true and false. If it is true, all EL expressions are ignored within the page.

Or make it globally in the web application in web.xml

In the following example, we use EL to access java bean in request scope.

Step 1 Create New Dynamic Web Project

Step 1.1 Create New Project

Go to File->New->Others… Select Dynamic Web Project under Web category then click Next. TypeServletDemo or whatever name you want in the Project name field.

Step 1.2 Configure Target Runtime

  • Click New Runtime… button under Target Runtime.
  • Select Apache Tomcat v7.0. Click Next.
  • Click Browse button to specify Tomcat Server installation directory. The select the folder then click Ok.
  • Click Installed JREs… button to add/remove or edit JRE definition. Remove existing one; then click Add button to configure new one. Select Standard VM; then click Next. Click Directory button to select the root folder of JDK installation. Select the folder then click Ok. Click Finish.
  • Check the JDK then click Ok.
  • Change JRE to the JDK then click Finish.
  • Click Finish the finish the project creation.

Step 2 Create Java Bean

  • Right click to the project or src folder, select New -> Class from the menu.
  • Type User in name field and info.java.tips.to in Package field
  • Click Finish.
  • Add the following code to the file:

Note: simply copy the code below to clipboard, select src folder of your project in Eclipse IDE then press CTRL + V.

Step 3 Create New JSP File

  • Right click to the project or WebContent folder, select New -> JSP File from the menu.
  • You can choose any name, for example elDemo.jsp
  • Click Finish.
  • Eclipse IDE will generate some boilerplate code. We just clear all its content and replace with the followings code:

Step 4 Clean & Build

Clean & build the project to clean old classes file (if any) & force the IDE to recompile java code.

  • Go to Project on menu bar; select Clean…
  • Select Clean all projects (default)
  • Click Ok to proceed clean & build.

Step 5 Configure Tomcat

Select Servers window; in case it’s not there, go to Windows -> Show View-> Others… Select Server -> Servers; then click Ok.

If this is the first time you are creating a server, in the Servers area you will see a link as No servers are available click this link to create a new server. Click the link.

Define a New Server window will be opened, In Select the server type. Select Apache -> Tomcat v7.0 Server. Then click Finish.

Step 6 Deploy The Application

  • Right click to the Tomcat Server select Add and Remove.
  • Move the application (JSPDemo) from Available column to Configured. Then click on Finish to deploy it to tomcat server.

Step 7 Start Tomcat Server

Right click on the tomcat server and choose Start or simply click on the green start icon to start the server.

Step 8 Run The Servlet

We assume that you install tomcat on default port (8080) and project name is ServletDemo. Open web browser and type:

http://localhost:8080/JspDemo/elDemo.jsp

Output

Note: for JSP, you don’t need to Clean & Build the project or restart the tomcat server before running. You just change the code, save the changes and run.

For java classes, you need to Clean & Build the project to re-compile the code. In case register new servlet, change settings in web.xml or server.xml… you need to Clean & Build the project and restart tomcat server.