JavaServer Pages, 3rd Edition

Automatic Type Conversions

The beans used in this chapter have properties of the Java type String, meaning they have plain-text values. But as I mentioned in the beginning of this chapter, a bean property can be of any Java type. As a JSP page author, you typically don’t have to worry too much about this, though, since the container can convert text values to other Java types. It handles the most common types all by itself, but for more complex types, it needs a little help from the Java programmer who develops the bean class.

When you use the <jsp:setProperty> or the JSTL <c:set> action, the container takes care automatically of the conversion from text values to the Java types shown in Table 6-3.

Table 6-3. Conversion of text value to property type

Property type	Conversion method
boolean or Boolean	Boolean.valueOf(String)
byte or Byte	Byte.valueOf(String)
char or Character	String.charAt(0)
double or Double	Double.valueOf(String)
int or Integer	Integer.valueOf(String)
float or Float	Float.valueOf(String)
long or Long	Long.valueOf(String)
short or Short	Short.valueOf(String)
Object	new String(String)

For other types, such as a java.util.Date, the JSP specification defines how a Java programmer can develop a so-called "property editor” to handle the conversion. A property editor associated with a bean can convert a string such as 2002-05-10 to a Date object that represents this date. How to do so is described in Chapter 22.

The value returned by ...