Java Reference
In-Depth Information
User
is created using the
<jsp:useBean>
action. The
user
was set as the
request
attribute in the servlet code.
Line 2: In Line 2, the value of name, which is a property of the User object is
Line 1: In Line 1, the class
accessed using
${user.name}
.
The variable
user
in the expression
${user.name}
is an attribute stored in the
request
scope. The
variable in the EL expression to which the dot operator is applied could be one of two kinds.
An attribute that is stored in any of the four scopes, as it is in this case
An EL implicit object, as explained later in this chapter
Whether this variable is an EL implicit object or an attribute stored in any of the four scopes, it
can be either a JavaBean or a map. In Listing 3-13, this variable is a JavaBean that was set as an
attribute in the
request
scope, and therefore
name is
the property of the JavaBean referenced by
the variable
user
. Had the
user
variable been a map set as an attribute in any of the four scopes, the
name would-be the key of the map.
Note
The variable in the EL expression to which the dot operator is applied could be either an attribute
set in any of the four scopes or an EL implicit object. Furthermore, regardless of whether this variable is an
attribute set in any of the four scopes or is an EL implicit object, it could be either a JavaBean or a Map. If the
variable is a JavaBean, it is followed by its property right after the dot operator; if the variable is a Map, it is
followed by its key right after the dot operator.
So, now it should be clear that the variable in the EL expression is either a JavaBean or a Map. But
what if you want to set an array as an attribute in any of the four scopes and access its elements
using an EL expression? Or what if you want to set a list as an attribute in any of the four scopes and
access its elements using an EL expression? The answer lies with the
[]
operator provided by EL.
The
[]
operator is used for accessing arrays, lists, JavaBeans, and maps. That is, the variable to
which the [ ] operator is applied can be an array, list, JavaBean, or map.
Inside the Brackets
There can be one of following inside the brackets of the [ ] operator:
An index with or without quotes.
A String literal.
An EL implicit object or an attribute in any of the four scopes. The EL implicit
object is explained later in this chapter.
A nested expression.
If there is an index with or without quotes inside the brackets of the[ ] operator, the variable to which
the [ ] operator is applied is either an array or a list. Listing 3-14 illustrates how to use the [ ] operator
with a list or an array.
