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Unable to trace

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  Unable to trace RVic <rvince99@hotmail.com> - 2013-05-09 09:53 -0700
    Re: Unable to trace Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-05-09 13:04 -0400
    Re: Unable to trace markspace <markspace@nospam.nospam> - 2013-05-09 15:39 -0700
    Re: Unable to trace Arne Vajhøj <arne@vajhoej.dk> - 2013-05-09 21:45 -0400
    Re: Unable to trace RVic <rvince99@hotmail.com> - 2013-05-09 19:32 -0700
    Re: Unable to trace RVic <rvince99@hotmail.com> - 2013-05-09 19:41 -0700
      Re: Unable to trace Arne Vajhøj <arne@vajhoej.dk> - 2013-05-12 21:51 -0400
    Re: Unable to trace RVic <rvince99@hotmail.com> - 2013-05-10 07:26 -0700
      Re: Unable to trace Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-05-10 10:43 -0400
        Re: Unable to trace Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2013-05-10 09:52 -0700
          Re: Unable to trace Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2013-05-10 19:03 +0200
            Re: Unable to trace Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2013-05-10 11:02 -0700
              Re: Unable to trace Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2013-05-10 23:37 +0200
    Re: Unable to trace RVic <rvince99@hotmail.com> - 2013-05-12 19:10 -0700

#23968 — Unable to trace

Related to my previous post here, I have a simple piece of code in a servlet:

HttpServletRequest request = RequestData.getRequest();
HttpServletResponse response = RequestData.getResponse();
request.getRequestDispatcher("/something").forward(request, response);

The last line of which throws an error (below) which I am unable to trace further from this line in the stack. The error is :

javax.el.ELException: Cannot convert beta of type class java.lang.String to class com.cblnet.web.data.Env

and com.cblnet.web.data.Env is:

public enum Env {
    local,
    mirror,
    production;
}

But if you look at the stack trace, below (the last line in it is the last line in my simple three lines of code, the request.getRequestDispatcher().forward() ) I have no way to trace what is causing this -- can anyone shed any light here for me on how to track down this frustrating offender? Thanks in advance, RVic


2013-05-09 11:22:23,425 ERROR [ajp-bio-9509-exec-4] [Page] Error forwarding request to display JSP.
org.apache.jasper.JasperException: javax.servlet.ServletException: javax.servlet.jsp.JspException: javax.servlet.jsp.JspException: javax.el.ELException: Cannot convert beta of type class java.lang.String to class com.cblnet.web.data.Env
	at org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:549)
	at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:455)
	at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
	at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
	at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:749)
	at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:487)
	at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:412)
	at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:339)
	at com.cblnet.web.view.Page.forward(Page.java:73)

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#23969

On 5/9/2013 12:53 PM, RVic wrote:
> Related to my previous post here, I have a simple piece of code in a servlet:
>
> HttpServletRequest request = RequestData.getRequest();
> HttpServletResponse response = RequestData.getResponse();
> request.getRequestDispatcher("/something").forward(request, response);
>
> The last line of which throws an error (below) which I am unable to trace further from this line in the stack. The error is :
>
> javax.el.ELException: Cannot convert beta of type class java.lang.String to class com.cblnet.web.data.Env
>
> and com.cblnet.web.data.Env is:
>
> public enum Env {
>      local,
>      mirror,
>      production;
> }

     Just a guess: What happens if you change the Env enum to

	public enum Env {
	    local,
	    mirror,
	    production,
	    beta;  // this is the guess
	}

?  If somebody somewhere calls Env.valueOf("beta") they should get
an IllegalArgumentException (using the original Env), but perhaps
they're catching it and throwing an ElException instead.

-- 
Eric Sosman
esosman@comcast-dot-net.invalid

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#23970

On 5/9/2013 9:53 AM, RVic wrote:
> The last line of which throws an error (below) which I am unable to
> trace further from this line in the stack. The error is :

>
> But if you look at the stack trace,


I have to somewhat doubt your premise.  If you look at the stack trace,
it looks to me like the dispatch succeeded, and you got an error
somewhere after that.

This line here seems to say that you're in a filter, running code:
> at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
> at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)


And then you seem to dispatch to a servlet:
> at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)


And then you run a JSP file.  Etc.  I'm not sure how to find out exactly
what file you're running though.  That might take a little research and
experimentation.

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#23973

On 5/9/2013 12:53 PM, RVic wrote:
> Related to my previous post here, I have a simple piece of code in a servlet:
>
> HttpServletRequest request = RequestData.getRequest();
> HttpServletResponse response = RequestData.getResponse();
> request.getRequestDispatcher("/something").forward(request, response);
>
> The last line of which throws an error (below) which I am unable to trace further from this line in the stack. The error is :
>
> javax.el.ELException: Cannot convert beta of type class java.lang.String to class com.cblnet.web.data.Env
>
> and com.cblnet.web.data.Env is:
>
> public enum Env {
>      local,
>      mirror,
>      production;
> }
>
> But if you look at the stack trace, below (the last line in it is the last line in my simple three lines of code, the request.getRequestDispatcher().forward() ) I have no way to trace what is causing this -- can anyone shed any light here for me on how to track down this frustrating offender? Thanks in advance, RVic
>
>
> 2013-05-09 11:22:23,425 ERROR [ajp-bio-9509-exec-4] [Page] Error forwarding request to display JSP.
> org.apache.jasper.JasperException: javax.servlet.ServletException: javax.servlet.jsp.JspException: javax.servlet.jsp.JspException: javax.el.ELException: Cannot convert beta of type class java.lang.String to class com.cblnet.web.data.Env
> 	at org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:549)
> 	at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:455)
> 	at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
> 	at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
> 	at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
> 	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
> 	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
> 	at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:749)
> 	at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:487)
> 	at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:412)
> 	at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:339)
> 	at com.cblnet.web.view.Page.forward(Page.java:73)

How does the JSP page you forward to look like?

Does it refer to "beta" anywhere?

Arne

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#23979

I have jsp's that DO refer to 'beta' but not the jsp's being forwarded to here. Simply, it is calling this jsp:

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib tagdir="/WEB-INF/tags" prefix="cn" %>
<%@ taglib tagdir="/WEB-INF/tags/admin" prefix="admin" %>
<%@ taglib tagdir="/WEB-INF/tags/footer" prefix="footer" %>
<%@ taglib tagdir="/WEB-INF/tags/header" prefix="header" %>
<%@ taglib tagdir="/WEB-INF/tags/sidebar" prefix="sidebar" %>

<%--@elvariable id="bodyUrl" type="java.lang.String"--%>
<%--@elvariable id="user" type="com.capablenet.domain.User"--%>


  
  
  

    

      
    
    


    

      
      

        ">view site
      
      
    
    

      

        
        

      
    
    
  
  


Where bodyUrl is this jsp:

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>

Administration | Access Denied


  
    

      ${text}
    
  
  
    

      We're sorry, the page you are trying to reach is part of a restricted portion of our site.
      You are not currently logged on with proper permissions to view it.
    

    

      If you believe you should have permissions to view this area, please send us ">Feedback.

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#23980

I have jsp's that DO refer to 'beta' but not the jsp's being forwarded to here. Simply, it is calling this jsp:
'<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
'<%@ taglib tagdir="/WEB-INF/tags" prefix="cn" %>
'<%@ taglib tagdir="/WEB-INF/tags/admin" prefix="admin" %>
'<%@ taglib tagdir="/WEB-INF/tags/footer" prefix="footer" %>
'<%@ taglib tagdir="/WEB-INF/tags/header" prefix="header" %>
'<%@ taglib tagdir="/WEB-INF/tags/sidebar" prefix="sidebar" %>
'
'<%--@elvariable id="bodyUrl" type="java.lang.String"--%>
'<%--@elvariable id="user" type="com.capablenet.domain.User"--%>
'
'<cn:html>
'  <admin:head/>
'  <body id="admin">
'  <div id="container">
'    <div id="header" style="float:left;">
'      <admin:adminNav/>
'    </div>
'    <br class="clear"/>
'
'    <div id="site_info">
'      <header:communityBrand/>
'      <div id="site-links">
'        <a id="viewsite" href="<c:url value="/"/>">view site</a>
'      </div>
'      <admin:currentUser user="${user}"/>
'    </div>
'    <div id="main-content">
'      <div id="inner-content">
'        <c:import url="${bodyUrl}"/>
'        <br class="clear"/>
'      </div>
'    </div>
'    <footer:footer/>
'  </div>
'  </body>
'</cn:html>

Where ${bodyURL} is:

'<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
'
'<h1 class="title">Administration | <span>Access Denied</span></h1>
'
'<c:choose>
'  <c:when test="${!empty text}">
'    <p>
'      ${text}
'    </p>
'  </c:when>
'  <c:otherwise>
'    <p><strong>
'      We're sorry, the page you are trying to reach is part of a restricted 'portion of our site.
'      You are not currently logged on with proper permissions to view it.
'    </strong></p>
'
'    <p>
'      If you believe you should have permissions to view this area, please 'send us <a href="<c:url value="/help/feedback"/>">Feedback</a>.
'    </p>
'  </c:otherwise>
'</c:choose>

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#24023

On 5/9/2013 10:41 PM, RVic wrote:
> I have jsp's that DO refer to 'beta' but not the jsp's being forwarded to here. Simply, it is calling this jsp:
...

Apparently the problem has been solved.

But I am a bit puzzled.

The problem happened in some servlet code that forwarded to a JSP page.

If neither that servlet or that JSP page referred to beta - then where
did the call that try to parse "beta" occur??

Arne

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#23982

I got it. Thanks for pointing me in the right direction Eric -- the Env enum needed the enumeration 'beta' in it.

Thanks for your help guys, I am most grateful. RVic

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#23983

On 5/10/2013 10:26 AM, RVic wrote:
> I got it. Thanks for pointing me in the right direction Eric -- the Env enum needed the enumeration 'beta' in it.
>
> Thanks for your help guys, I am most grateful. RVic

     That's probably not the end of your problems, just a clue
about their mechanism.  Adding a `beta' value to the enum means
that Env.valueOf("beta") will now return Env.beta instead of
throwing an exception.  That's all fine and dandy, but what will
the rest of the code do when it encounters this new Env.beta
object?  For example, there may be something like

	Env env = Env.valueOf(someString);
	switch (env) {
	  case local:
	    // ...
	    break;
	  case mirror:
	    // ...
	    break;
	  case production:
	    // ...
	    break;
	}

A "beta" value will no longer cause an exception in this code,
but whatever was supposed to have been done by the switch block
will remain un-done ...  (This is one reason I think it's almost
always a good idea to have a `default:' label in every switch,
even if all it does is `assert false;'.)

     You don't have a cure yet (not for sure, anyhow): You just
have the beginnings of a diagnosis.

-- 
Eric Sosman
esosman@comcast-dot-net.invalid

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#23985

On 5/10/13 7:43 AM, Eric Sosman wrote:
> On 5/10/2013 10:26 AM, RVic wrote:
>> I got it. Thanks for pointing me in the right direction Eric -- the
>> Env enum needed the enumeration 'beta' in it.
>>
>> Thanks for your help guys, I am most grateful. RVic
>
>      That's probably not the end of your problems, just a clue
> about their mechanism.  Adding a `beta' value to the enum means
> that Env.valueOf("beta") will now return Env.beta instead of
> throwing an exception.  That's all fine and dandy, but what will
> the rest of the code do when it encounters this new Env.beta
> object?  For example, there may be something like
>
>      Env env = Env.valueOf(someString);
>      switch (env) {
>        case local:
>          // ...
>          break;
>        case mirror:
>          // ...
>          break;
>        case production:
>          // ...
>          break;
>      }
>
> A "beta" value will no longer cause an exception in this code,
> but whatever was supposed to have been done by the switch block
> will remain un-done ...  (This is one reason I think it's almost
> always a good idea to have a `default:' label in every switch,
> even if all it does is `assert false;'.)
Or make the enum an abstract base class and have all behavior defined in 
the enum itself.

For example, using them as a flyweight:
<http://virtualinfinity.net/wordpress/program-design/2007/10/22/using-enums-as-a-flyweight-pattern/>

Switching on an enum is dangerous business, just for the reason Eric is 
demonstrating. Someone adds a new enum, and switch logic no longer 
handles every case.  If I do happen to use an enum and have a switch 
statement for it, I *always* have a default case. Sometimes that default 
is "throw new UnsupportedOperationException();" Other times that default 
is something that is "sensible" if an override isn't specified.

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#23987

On 10/05/2013 18:52, Daniel Pitts allegedly wrote:
> Switching on an enum is dangerous business, just for the reason Eric is
> demonstrating. Someone adds a new enum, and switch logic no longer
> handles every case.  If I do happen to use an enum and have a switch
> statement for it, I *always* have a default case. Sometimes that default
> is "throw new UnsupportedOperationException();" Other times that default
> is something that is "sensible" if an override isn't specified.

Crossing the street is dangerous business, too.

-- 
DF.

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#23989

On 5/10/13 10:03 AM, Daniele Futtorovic wrote:
> On 10/05/2013 18:52, Daniel Pitts allegedly wrote:
>> Switching on an enum is dangerous business, just for the reason Eric is
>> demonstrating. Someone adds a new enum, and switch logic no longer
>> handles every case.  If I do happen to use an enum and have a switch
>> statement for it, I *always* have a default case. Sometimes that default
>> is "throw new UnsupportedOperationException();" Other times that default
>> is something that is "sensible" if an override isn't specified.
>
> Crossing the street is dangerous business, too.

Switching on an enum is more likely to result in an accident.  One can 
look both ways before crossing the street, but the breaking of a switch 
statement can happen years after you wrote it.  It would be like getting 
hit by a bus a month after you crossed its path.

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#23996

On 10/05/2013 20:02, Daniel Pitts allegedly wrote:
> On 5/10/13 10:03 AM, Daniele Futtorovic wrote:
>> On 10/05/2013 18:52, Daniel Pitts allegedly wrote:
>>> Switching on an enum is dangerous business, just for the reason Eric is
>>> demonstrating. Someone adds a new enum, and switch logic no longer
>>> handles every case.  If I do happen to use an enum and have a switch
>>> statement for it, I *always* have a default case. Sometimes that default
>>> is "throw new UnsupportedOperationException();" Other times that default
>>> is something that is "sensible" if an override isn't specified.
>>
>> Crossing the street is dangerous business, too.
> 
> Switching on an enum is more likely to result in an accident.  One can
> look both ways before crossing the street, but the breaking of a switch
> statement can happen years after you wrote it.  It would be like getting
> hit by a bus a month after you crossed its path.

I would also strongly advise, when writing a switch on an enum, to
account for all possible (future) cases, possibly using a throw in the
default clause, or some similar means. That being said, this goes for
switches on other types as well; and either way a switch might
purposively and gracefully cover only part of the possible values.

What I disagree with is what I construe as an implication that one
should steer clear from switches on enums because of those "risks". Such
switches are no more and no less "dangerous" than the vast majority of
code constructs. And they rank firmly among the Very Useful ones.

-- 
DF.

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#24027

in <admin: head>

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