JavaServer Pages, Second Edition

Data Types

A variable is always of a specific Java type. In addition to the standard Java types for numeric, Boolean, and text values, the EL provides special support for custom classes developed according to the JavaBeans guidelines, java.util.Map object, java.util.List objects, and arrays.

Bean properties can be accessed using the special property accessor operator (a dot) and be nested to any length:

${aBean.aProperty.aPropertyOfTheProperty.andSoOn}

Map entries can be accessed the same way:

${aMap.aKey}

List and array elements can be accessed using the array accessor operator (square brackets):

${aList[0]}
${anArray[0]}
${anArrayOrList[anExressionWithANumbericValue]}

The array accessor operator can also access bean properties and Map entries when the property name must be composed by an expression, or the property name is a reserved word or contains characters used for operators:

${aMap[param.customerName]}
${aBean['empty']}
${aMap['com.mycomp.logo']}

Coercion Rules

The EL automatically converts, or coerces, variable values and the result of an expression to the type required by an attribute or an operator:

To Java type	Conversion rule
String	null: to empty string (” “). All other types: to the corresponding String value.
Primitive number or Number	null: 0. Character or char: to the value represented by the character code. String: parse as an Integer or floating-point literal. Numeric types: coerce to the requested precision.
boolean or Boolean	null ...