14.4 Example: StringBean

Listing 14.1 presents a simple class called StringBean that is in the coreservlets package. Because the class has no public instance variables (fields) and has a zero-argument constructor since it doesn't declare any explicit constructors, it satisfies the basic criteria for being a bean. Since StringBean has a method called getMessage that returns a String and another method called setMessage that takes a String as an argument, in beans terminology the class is said to have a String property called message .

Listing 14.2 shows a JSP file that uses the StringBean class. First, an instance of StringBean is created with the jsp:useBean action as follows .

 <jsp:useBean id="stringBean" class="coreservlets.StringBean" />

After this, the message property can be inserted into the page in either of the following two ways.

 <jsp:getProperty name="stringBean" property="message" /> <%= stringBean.getMessage() %>

The message property can be modified in either of the following two ways.

 <jsp:setProperty name="stringBean"                  property="message"                  value="some message" /> <% stringBean.setMessage("some message"); %>

Please note that we do not recommend that you really mix the explicit Java syntax and the XML syntax in the same page; this example is just meant to illustrate the equivalent results of the two forms.

Core Approach

Whenever possible, avoid mixing the XML-compatible jsp:useBean tags with JSP scripting elements containing explicit Java code.

Figure 14-2 shows the result.

Listing 14.1 StringBean.java

 package coreservlets; /** A simple bean that has a single String property  *  called message.  */ public class StringBean {   private String message = "No message specified";   public String  getMessage  () {     return(message);   }   public void  setMessage  (String message) {     this.message = message;   } }

Listing 14.2 StringBean.jsp

 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML> <HEAD> <TITLE>Using JavaBeans with JSP</TITLE> <LINK REL=STYLESHEET       HREF="JSP-Styles.css"       TYPE="text/css"> </HEAD> <BODY> <TABLE BORDER=5 ALIGN="CENTER">   <TR><TH CLASS="TITLE">       Using JavaBeans with JSP</TABLE>  <jsp:useBean id="stringBean" class="coreservlets.StringBean" />  <OL> <LI>Initial value (from jsp:getProperty):     <I>  <jsp:getProperty name="stringBean"   property="message" />  </I> <LI>Initial value (from JSP expression):     <I>  <%= stringBean.getMessage() %>  </I> <LI>  <jsp:setProperty name="stringBean"   property="message"   value="Best string bean: Fortex" />  Value after setting property with jsp:setProperty:     <I>  <jsp:getProperty name="stringBean"   property="message" />  </I> <LI>  <% stringBean.setMessage("My favorite: Kentucky Wonder"); %>  Value after setting property with scriptlet:     <I>  <%= stringBean.getMessage() %>  </I> </OL> </BODY></HTML>

Figure 14-2. Result of `StringBean.jsp` .

graphics/14fig02.jpg

Listing 14.1 StringBean.java

Listing 14.2 StringBean.jsp

Figure 14-2. Result of StringBean.jsp .

Figure 14-2. Result of `StringBean.jsp` .