Given a scenario, write EL code that uses the following operators: property access (the '.' operator), collection access (the '[]' operator).

The EL borrows the JavaScript syntax for accessing structured data as either a property of an object (with the '.' operator) or as a named array element (with the ["name"] operator). JavaBeans component properties and java.util.Map entries, using the key as the property name, can be accessed this way. Here are some examples:

${myObj.myProperty}
${myObj["myProperty"]}
${myObj['myProperty']}
${myObj[varWithThePropertyName]}
					
As shown here, an EL expression must always be enclosed within '${' and '}' characters. The first three expressions access a property named myProperty in an object represented by a variable named myObj. The fourth expression access a property with a name that's held by a variable. Instead of a single variable, this syntax can be used with any expression that evaluates to the property name.

The ARRAY ACCESS operator is also used for data represented as a collection of indexed elements, such as a Java array or a java.util.List:

${myList[2]}
${myList[aVar + 1]}
					

Expressions with syntax '${identifier[subexpression]}' are evaluated as follows:

  1. Evaluate the identifier and the subexpression; if either resolves to null, the expression is null.

  2. If the identifier is a BEAN:

    The subexpression is coerced to a String value and that string is regarded as a name of one of the bean's properties. The expression resolves to the value of that property; for example, the expression ${name.["lastName"]} translates into the value returned by name.getLastName().

  3. If the identifier is an ARRAY:

    The subexpression is coerced to an int value and the expression resolves to identifier[subexpression]. For example, for an array named colors, colors[3] represents the fourth object in the array. Because the subexpression is coerced to an int, you can also access that color like this: colors["3"]; in that case, JSTL coerces "3" into 3.

  4. If the identifier is a LIST:

    The subexpression is also coerced to an int and the expression resolves to the value returned from identifier.get(subexpression), for example: colorList[3] and colorList["3"] both resolve to the fourth element in the list.

  5. If the identifier is a MAP:

    The subexpression is regarded as one of the map's keys. That expression is not coerced to a value because map keys can be any type of object. The expression evaluates to identifier.get(subexpression), for example, colorMap[Red] and colorMap["Red"]. The former expression is valid only if a scoped variable named Red exists in one of the four JSP scopes and was specified as a key for the map named colorMap.

Table 7.1. Summary of [] collection access operator

Identifier typeExample useMethod invoked
JavaBean

${colorBean.red}

${colorBean["red"]}

${colorBean['red']}

colorBean.getRed()
Array

${colorArray[2]}

${colorArray["2"]}

Array.get(colorArray, 2)
List

${colorList[2]}

${colorList["2"]}

colorList.get(2)
Map

${colorMap[red]}

colorMap.get(pageContext.findAttribute("red"))

${colorMap["red"]}

colorMap.get("red")

You access a map's values through its keys, which you can specify with the [] operator, for example, in table above, ${colorMap[red]} and ${colorMap["red"]}. The former specifies an IDENTIFIER for the key, whereas the latter specifies a STRING. For the identifier, the PageContext.findAttribute method searches all FOUR JSP scopes (searching the page, request, session, and application scopes) for a scoped variable with the name that you specify, in this case, red. On the other hand, if you specify a string, it's passed directly to the map's get method.

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