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288

Chapter 13 Using JavaBeans with JSP

change from English units to metric units internally, but still 

have 

getSpeedInMPH

 and 

getSpeedInKPH

 methods), and auto 

matically perform side effects when values change (e.g., update 

the user interface when 

setPosition

 is called).

3. Persistent values should be accessed through methods 

called 

getXxx

 and 

setXxx

. For example, if your 

Car

 class 

stores the current number of passengers, you might have meth 

ods named 

getNumPassengers

 (which takes no arguments and 

returns an 

int

) and 

setNumPassengers

 (which takes an 

int

and has a 

void

 return type). In such a case, the 

Car

 class is said to 

have a property named 

numPassengers

 (notice the lowercase n 

in the property name, but the uppercase N in the method 

names). If the class has a 

getXxx

 method but no corresponding 

setXxx

, the class is said to have a read only property named 

xxx

. 

The one exception to this naming convention is with boolean 

properties: they use a method called 

isXxx

 to look up their val 

ues. So, for example, your 

Car

 class might have methods called 

isLeased

 (which takes no arguments and returns a 

boolean

) 

and 

setLeased

 (which takes a 

boolean

 and has a 

void

 return 

type), and would be said to have a 

boolean

 property named 

leased

 (again, notice the lowercase leading letter in the property 

name). 

Although you can use JSP scriptlets or expressions to access arbi 

trary methods of a class, standard JSP actions for accessing beans 

can only make use of methods that use the 

getXxx

/

setXxx

 or 

isXxx

/

setXxx

 design pattern.

13.1 Basic Bean Use

The 

jsp:useBean

  action  lets  you  load  a  bean  to  be  used  in  the  JSP  page.

Beans provide a very useful capability because they let you exploit the reus 

ability of Java classes without sacrificing the convenience that JSP adds over

servlets alone.

The simplest syntax for specifying that a bean should be used is: 

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

Servlet and JSP training courses by book's author: courses.coreservlets.com.