16.4 Using Expressions

A JSP expression element is used to insert the result of a scripting code expression into the response. It's the Java scripting equivalent to an EL expression directly in template text. An expression starts with <%= and ends with %>. Note that the only syntax difference compared to a scriptlet is the equal sign (=) in the start identifier. Examples are:

<%= userInfo.getUserName(  ) %>
<%= 1 + 1 %>
<%= new java.util.Date(  ) %>

The result of the expression is written to the response body, converted to a String if needed. One thing is important to note: as opposed to statements in a scriptlet, the code in an expression must not end with a semicolon. This is because the JSP container combines the expression code with code for writing the result to the response body. If the expression ends with a semicolon, the combined code will not be syntactically correct.

As with EL expressions, a Java expression can also be used to assign a dynamic value to an action element attribute, but with a few restrictions as described later in this chapter.