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JSP Call to Bean Getter Malfunction

Posted on 2004-08-25
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Last Modified: 2012-05-05
I am not understanding something about calling bean methods from JSP.  All calls to the bean "getter" return nothing!  Here's my jsp...

   <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
   <HTML>
   <HEAD>
   <TITLE>Reusing JavaBeans in JSP</TITLE>
   </HEAD>
   <BODY>
   <jsp:useBean id="test" class="myBeans.SimpleBean"/>
   <jsp:setProperty name="test" property="message" value="Hello WWW" />
   Message 1:  <jsp:getProperty name="test" property="message" />
   <br>
   <% test.setMessage("New Message"); %>
   Message 2: <jsp:getProperty name="test" property="message" />
   <br>
   Message 3: <% test.getMessage(); %>
   <br>
   <jsp:setProperty name="test" property="message" value="Final Message" />
   Message 4-1: <% test.getMessage(); %>
   <br>
   Message 4-2: <jsp:getProperty name="test" property="message" />
   </BODY>
   </HTML>

Here's my bean class...
   
   package myBeans;
      public class SimpleBean
   {
       private String message = "No message specified";
          public String getMessage()
       {
       return(message);
       }
          public void setMessage(String message)
       {
       this.message = message;
       }
   }
   
 (By the way, I created a test class with a main method and successfully tested calls to setMessage and getMessage.)

Here's my output...
 
   Message 1: Hello WWW
   Message 2: New Message          <-- proof that test.setMessage call worked...
   Message 3:                               <-- call to test.getMessage() failure...
   Message 4-1:                            <-- call to test.getMessage() failure...
   Message 4-2: Final Message

Nothing prints for Message #3 and #4-1 above.  Why?  The commonality is that both call test.getMessage().

Recently, I asked a question about using beans.  My problem ended up being path related.  This question is different than my previous question, but you can refer to http://www.experts-exchange.com/Web/Web_Languages/JSP/Q_21106099.html if I haven't provided enough background info above.
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Question by:LarryAndro
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9 Comments
 
LVL 19

Accepted Solution

by:
ramazanyich earned 230 total points
ID: 11892445
Use <%=test.getMessage()%>
0
 
LVL 27

Assisted Solution

by:rrz
rrz earned 20 total points
ID: 11892492
><% test.getMessage(); %>
Please use  instead
<%=test.getMessage()%>    rrz
0
 
LVL 27

Expert Comment

by:rrz
ID: 11892503
Sorry ramazanyich I didn't see your post.
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LVL 1

Author Comment

by:LarryAndro
ID: 11892715
I initially tried <%=...%> as you both suggested and it didn't work.  So, I tried <%...%>, as you saw in my first message.  When I changed back to <%=...%> as suggested, it still didn't work.  Here's the error I got...

   C:\Tomcat_JWSDP_1.4.1.0\work\Catalina\localhost\SCS_Prototype\org\apache\jsp\SimpleBean_jsp.java:71: ')' expected out.print(test.getMessage(););

But, I noticed you didn't append a semicolon to <%=test.getMessage();%> like I did.  So, I removed my semicolon to make it exactly match your suggestion(s), and it worked.

Here's the working code...

   <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
   <HTML>
   <HEAD>
   <TITLE>Reusing JavaBeans in JSP</TITLE>
   </HEAD>
   <BODY>
   <jsp:useBean id="test" class="myBeans.SimpleBean"/>
   <jsp:setProperty name="test" property="message" value="Hello WWW" />
   Message 1:  <jsp:getProperty name="test" property="message" />
   <br>
   <% test.setMessage("New Message"); %>
   Message 2: <jsp:getProperty name="test" property="message" />
   <br>
   Message 3: <%=test.getMessage()%>
   <br>
   <jsp:setProperty name="test" property="message" value="Final Message" />
   Message 4-1: <%= test.getMessage() %>
   <br>
   Message 4-2: <jsp:getProperty name="test" property="message" />
   </BODY>
   </HTML>

But, now I'm mystified about the use or non-use of semicolons!  There are two locations in the above code I am referring two:

   (1) <% test.setMessage("New Message"); %>
   (2) <%= test.getMessage() %>

If I remove the semicolon from #1 I get an "expected semicolon" error.  If I add a semicolon to #2, I get an error!

What are the rules?  (Add semicolon if code is being executed, and don't if output is being returned?)
0
 
LVL 19

Assisted Solution

by:ramazanyich
ramazanyich earned 230 total points
ID: 11892816
As you know JSP pages during request converted to Java source and compiled.
<% %> in JSP are used to insert Java code into generated Java source as is.
<%=expr%> is used to get value of  expression between that tags and put it into resulting HTML page. Usually in Java source it is replaced by out.print(expr);
0
 
LVL 35

Expert Comment

by:TimYates
ID: 11892864
<%  use them

<%= don't (and only put one expression)
0
 
LVL 35

Expert Comment

by:TimYates
ID: 11892879
sorry.. ramazanyich...  I didn't refresh before I posted...

Please ignore my comment LarryAndro

:-)

Tim
0
 
LVL 27

Expert Comment

by:rrz
ID: 11892901
Please look in Tomcat's work folder you will find the translated file that Tomcat produced from your JSP file.  You can see that
<%= test.getMessage() %>   ( this is a JSP scripting element called an JSP expression)
is translated to
out.print(test.getMessage());  

><% test.setMessage("New Message"); %>  ( this is called a scriptlet )
This is just put into the code as is, so it needs  the  ;           rrz

0
 
LVL 27

Expert Comment

by:rrz
ID: 11892996
Thanks for the points Larry.  
Be sure to start looking at the translated file(in work folder) for debugging clues.   rrz
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