JavaBeans and JSPs

• We've talked a lot about JavaBeans.  Now they are finally going to make our lives easier.
• First a review:
• JavaBeans are simply Java classes that have private instance fields, or attributes.
• These fields are accessed via public getter and setter methods.  These methods control access to the variables.
• JavaBeans have a zero-argument constructor.
• JavaBeans should be used whenever possible.  It's really a good coding methodology.
• Now, using them with our JSPs.
• Use the <jsp:usebean id="name" class="package.class" scope="scope" /> tag to use the bean in the JSP.
• This instantiates the bean named in the class argument to a variable with the name in the id argument.
• Scope is optional; the values permitted are outlined on page 303 of the book/
• This tag uses the XML syntax, so the attributes are case-sensitive; quotes, whether single or double, must be used; and the tag ends with />
• Once we've added the first tag, we can add the following tags to get or set values in our beans:
• <jsp:setProperty name="name" property = "property" value = "value" /> sets the value of the value parameter to the property (setter method) specified in property for the bean named in name.  In other words, name.setProperty(value) in this example.
• Alternatively, <jsp:setProperty name="name" property = "*" /> automatically sets the properties in the bean where the bean properties match the incoming request parameter properties.  Wow!  You only need one of these to call all of those getters.
• <jsp:getProperty name="name" property="property"> calls the getter method matching the property value in the bean named in name.  In other words, name.getProperty().
• As you can see, this is makes our application much more object oriented.  Let's re-engineer our previous application to take advantage of this.
• Student.java and sessionshtml.html do not change.
• For the others, we completely eliminate our references to session, because our bean will be a session bean.
• We simply add the useBean, setProperty, and getProperty tags.
• sessionsexample new source

<%-- <jsp:useBean id="beanInstanceName" scope="session" class="package.class" /> --%>
<%-- <jsp:getProperty name="beanInstanceName"  property="propertyName" /> --%>
 

<jsp:useBean id="student" class="jsp.Student" scope="session" />
<jsp:setProperty name="student" property="*"/>

Congratulations <%= student.getName() %>, your registration is complete!
<br>
<a href = "beanresults.jsp">Continue</a>

</body>
</html>

• beanresults new source

<%-- <jsp:useBean id="beanInstanceName" scope="session" class="package.class" /> --%>
<%-- <jsp:getProperty name="beanInstanceName"  property="propertyName" /> --%>
 

<jsp:useBean id="student" class="jsp.Student" scope="session" />

    Your data:<BR>
    Name: <jsp:getProperty name="student" property = "name" /> <BR>
    Year: <jsp:getProperty name="student" property = "year" /> <BR>
    Degree: <jsp:getProperty name="student" property = "degree" /> <BR>

</body>
</html>
 

• Incredibly simple, isn't it?

Created by:  Brandan Jones December 17, 2001