JSP Expression Language (c:if>...)

Implicit Objects

The JSP expression language defines a set of implicit objects:

* pageContext: The context for the JSP page. Provides access to various objects including:
o servletContext: The context for the JSP page's servlet and any web components contained in the same application. See Accessing the Web Context.
o session: The session object for the client. See Maintaining Client State.
o request: The request triggering the execution of the JSP page. See Getting Information from Requests.
o response: The response returned by the JSP page. See Constructing Responses.

In addition, several implicit objects are available that allow easy access to the following objects:

* param: Maps a request parameter name to a single value
* paramValues: Maps a request parameter name to an array of values
* header: Maps a request header name to a single value
* headerValues: Maps a request header name to an array of values
* cookie: Maps a cookie name to a single cookie
* initParam: Maps a context initialization parameter name to a single value

Finally, there are objects that allow access to the various scoped variables described in Using Scope Objects.

* pageScope: Maps page-scoped variable names to their values
* requestScope: Maps request-scoped variable names to their values
* sessionScope: Maps session-scoped variable names to their values
* applicationScope: Maps application-scoped variable names to their values

When an expression references one of these objects by name, the appropriate object is returned instead of the corresponding attribute. For example, ${pageContext} returns the PageContext object, even if there is an existing pageContext attribute containing some other value.
Literals

The JSP expression language defines the following literals:

* Boolean: true and false
* Integer: as in Java
* Floating point: as in Java
* String: with single and double quotes; " is escaped as \", ' is escaped as \', and \ is escaped as \\.
* Null: null

Operators

In addition to the . and [] operators discussed in Variables, the JSP expression language provides the following operators:

* Arithmetic: +, - (binary), *, / and div, % and mod, - (unary)
* Logical: and, &&, or, ||, not, !
* Relational: ==, eq, !=, ne, <, lt, >, gt, <=, ge, >=, le. Comparisons can be made against other values, or against boolean, string, integer, or floating point literals.
* Empty: The empty operator is a prefix operation that can be used to determine whether a value is null or empty.
* Conditional: A ? B : C. Evaluate B or C, depending on the result of the evaluation of A.

The precedence of operators highest to lowest, left to right is as follows:

* [] .
* () - Used to change the precedence of operators.
* - (unary) not ! empty
* * / div % mod
* + - (binary)
* < > <= >= lt gt le ge
* == != eq ne
* && and
* || or
* ? :

Reserved Words

The following words are reserved for the JSP expression language and should not be used as identifiers.

and eq gt true instanceof
or ne le false empty
not lt ge null div mod

Note that many of these words are not in the language now, but they may be in the future, so you should avoid using them.
Examples

Table 12-2 contains example EL expressions and the result of evaluating them.
Table 12-2 Example Expressions
EL Expression

Result
${1 > (4/2)}

false
${4.0 >= 3}

true
${100.0 == 100}

true
${(10*10) ne 100}

false
${'a' < 'b'}

true
${'hip' gt 'hit'}

false
${4 > 3}

true
${1.2E4 + 1.4}

12001.4
${3 div 4}

0.75
${10 mod 4}

2
${empty param.Add}

True if the request parameter named Add is null or an empty string
${pageContext.request.contextPath}

The context path
${sessionScope.cart.numberOfItems}

The value of the numberOfItems property of the session-scoped attribute named cart
${param['mycom.productId']}

The value of the request parameter named mycom.productId
${header["host"]}

The host
${departments[deptName]}

The value of the entry named deptName in the departments map
${requestScope['javax.servlet.
forward.servlet_path']}

The value of the request-scoped attribute named javax.servlet.
forward.servlet_path

Functions