asked on

JSP Call to Bean Getter Malfunction

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" />
 
<% test.setMessage("New Message"); %>
Message 2: <jsp:getProperty name="test" property="message" />
 
Message 3: <% test.getMessage(); %>
 
<jsp:setProperty name="test" property="message" value="Final Message" />
Message 4-1: <% test.getMessage(); %>
 
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 https://www.experts-exchange.com/questions/21106099/useBean-Problem.html if I haven't provided enough background info above.

ASKER CERTIFIED SOLUTION

ramazanyich

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SOLUTION

rrz

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rrz

Sorry ramazanyich I didn't see your post.

LarryAndro

ASKER

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" />
 
<% test.setMessage("New Message"); %>
Message 2: <jsp:getProperty name="test" property="message" />
 
Message 3: <%=test.getMessage()%>
 
<jsp:setProperty name="test" property="message" value="Final Message" />
Message 4-1: <%= test.getMessage() %>
 
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?)

SOLUTION

ramazanyich

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TimYates

<% use them

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

TimYates

sorry.. ramazanyich... I didn't refresh before I posted...

Please ignore my comment LarryAndro

:-)

Tim

rrz

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

rrz

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