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Expression Language (EL)

What? Another language?

Definition and Syntax

  • EL is a simple way to access variables in a JSP page in a Java Web Application.
    • Syntax: ${some variable or attribute name here}
  • Examples
    • For a variable named “pageTitle”, you would access it like this:
      • ${pageTitle}
    • A variable named “employee” with a field named “firstName” would be accessed like this:
      • ${employee.firstName}
    • An element in a List or array is accessed like this:
      • ${color[3]}
    • A value from a Map with a given key:
      • ${states["WI"]}
  • We use these variables in our JSP code so that we can substitute values in a template.

EL Demos

Demo 1

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html>
  <head>
    <meta name="generator" content="HTML Tidy, see www.w3.org">

    <title>${pageTitle}</title>
  </head>

  <body>
    <h3>Nothing to see here, look at the title.</h3>

    <a href="/java112/java112/">Home</a>
  </body>
</html>

Demo 2

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html>
  <head>
    <meta name="generator" content="HTML Tidy, see www.w3.org">

    <title>EL Demo 2</title>
  </head>

  <body>
    <h3>The full list</h3>
    <ul><li>${colors}</li></ul>

    <h3>One list element</h3>
    <ul><li>${colors[2]}</li></ul>

    <a href="/java112/java112/">Home</a>

  </body>
</html>

Demo 3

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html>
  <head>
    <meta name="generator" content="HTML Tidy, see www.w3.org">

    <title>EL Demo 3</title>
  </head>

  <body>
    <h3>Employee ID</h3>
    <ul><li>${employee.id}</li></ul>

    <h3>Employee Name</h3>
    <ul><li>${employee.firstName} ${employee.lastName}</li></ul>

    <a href="/java112/java112/">Home</a>

  </body>
</html>