EL expressions will coerce the type automatically. Here is the summary of the coercion rules.

Note: The coercion is also applied to function arguments. For example, {c:doSomething(null)} will cause doSomething("") being called if it expects a String object.

  Boolean Character Number String
Boolean obj1 ERROR ERROR obj.toString()
Character ERROR obj (short)obj obj.toString()
Number obj ERROR (char)obj obj.toString()
String (not empty) Boolean.valueOf(obj) obj.charAt(0) Number2.valueOf(x) obj
String (empty) false (char)0 0 ”” (obj)
null false (char)0 0 ””
Other ERROR ERROR ERROR obj.toString()
  • The handling of an empty string and null is the same

  1. obj represents the object being corerced ↩

  2. The real class is determined at run time, such as Integer and Float. ↩