Ed Burns's Blog

Using JSP Immediate Expressions to access JSF Data

Here is an ultra-quick blog entry sharing something in JSF 1.2 about which I'm not sure many people are aware. Thanks to the unified EL, it is possible to refer to JSF managed beans and other JSF concepts using plain old JSP expressions in the page. For example, let's say you have a JSF app that is a bookstore. In the app is a managed bean that is a Map where the keys are ISBN numbers and the values are Book JavaBeans that have properties like author, title, ISBN, etc.

In JSF 1.1, to display any information from the book Map, you had to use JSF components. In JSF 1.2, you can use plain old JSP ${} expressions to access this data, like this:

The title is ${books["0072262400"].title}.  

Even though books is a managed bean, you can still access it without JSF.

Keep in mind that you can also access all the implicit objects, including JSF ones, in this manner. For example, if you wanted to use EL to get the locale of the current view, you could say:

${view.locale}

As a final example, if you wanted to get the remote user name of the current user using standard Servlet authentication APIs you could say:

${facesContext.externalContext.remoteUser}

Basically anything that conforms to JavaBeans naming conventions and is accessible from the FacesContext or UIViewRoot can be reached via the EL in this way.

Comments

• actually, to clarify this, you can't use contextual EL in this manner-- like inlining ${employee.name} within a dataTable. This can be done with a simple fix to JSF's implementation and setting the 'deferredSyntaxAllowedAsLiteral' page property in JSP 2.1 to get 'render-time' evaluation of inlined text w/ #{...} vs. build-time evaluation with the common ${...} syntax.

  Posted by: jhook on March 15, 2006 at 01:05 PM

• hey,Edburns,when do JSF 1.2 release?I have waited it for two years.
  Actually,I think hybrid Programming(EL\JSTL\JSF) is very important in JSF 1.2.But must waiting for Glassfish or JBoss seam,still waiting...

  Posted by: forsoft on March 16, 2006 at 06:39 AM

• JSF 1.2 will have its final release this Spring. As you know, however, it is currently available in the Java EE SDK at http://java.sun.com/javaee/downloads/

  Ed

  Posted by: edburns on March 16, 2006 at 11:22 AM

• 
  JH> actually, to clarify this, you can't use contextual EL in this
  JH> manner-- like inlining ${employee.name} within a dataTable. This
  JH> can be done with a simple fix to JSF's implementation and setting
  JH> the 'deferredSyntaxAllowedAsLiteral' page property in JSP 2.1 to
  JH> get 'render-time' evaluation of inlined text w/ #{...}
  JH> vs. build-time evaluation with the common ${...} syntax.

  
  Yes, I see, Jacob. I have simply inlining ${customer.name} into a
  dataTable demo I have and found that it does not work in the data table
  case. However, I do want to point out that one can use immediate
  expressions to reference JSF managed beans in all other cases than the
  data table case.

  Ed - JSF co-spec lead
  

  Posted by: edburns on March 31, 2006 at 05:29 AM

• 
  JH> actually, to clarify this, you can't use contextual EL in this
  JH> manner-- like inlining ${employee.name} within a dataTable. This
  JH> can be done with a simple fix to JSF's implementation and setting
  JH> the 'deferredSyntaxAllowedAsLiteral' page property in JSP 2.1 to
  JH> get 'render-time' evaluation of inlined text w/ #{...}
  JH> vs. build-time evaluation with the common ${...} syntax.

  
  Well, Jacob, I played around a bit with your suggestion and found
  that the fix to the JSF impl isn't so simple. I gather you're
  suggesting we special-case the ValueExpression callsites in the JSF tag
  layer to check:

  
  if isLiteral
  then
  See if the literal happens to be a real #{ } expression. If it does
  create a real (non-literal) expression from it, the way we do
  in jsf 1.1.

  
  This approach has problems because the places where you'd have to do
  this check are numerous. Furthermore, once you do the check you'd need
  some way to have the #{employee.name} value actually get turned into a
  real (non-literal) expression. I think we could do this
  because of the content-interweaving solution where the template text
  would be turned into a UIOutput. Therefore, we could modify the code
  that turns the template text into a UIOutput to actually turn it into an
  ValueExpression and set that as the value of the UIOutput. As a
  performance optimization, we could have that code inspect the literal
  text value to see if it contains any #{ characters and only then turn it
  into an expression.

  This is worth investigating further. I've created issue 164
  in the jsf-api public issue tracker and attached my change-bundle so
  far.

  Ed (JSF co-spec-lead)

  Posted by: edburns on March 31, 2006 at 06:30 AM

• This approach has problems because the places where you'd have to do this check are numerous. Furthermore, once you do the check you'd need some way to have the #{employee.name} value actually get turned into a real (non-literal) expression. I think we could do this because of the content-interweaving solution where the template text would be turned into a UIOutput. Therefore, we could modify the code that turns the template text into a UIOutput to actually turn it into an ValueExpression and set that as the value of the UIOutput. As a performance optimization, we could have that code inspect the literal text value to see if it contains any #{ characters and only then turn it into an expression.

  
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  Posted by: keriolder on March 04, 2007 at 02:55 PM

• This is really great. I think Unified EL + content interweaving in JSF 1.2 bring a LOT of value a HTML and dynamic content generated by JSF artifacts are so easy to integrate in a JSF page. No more verbatim just plain HTML. Wonderful !!!

  Currently we are using JSF 1.1 and to address this handicap of not being able to use JSF EL in template text we did this:
  1. Created a TLD function that returns an Object and has a String argument
  2. Function creates a ValueBinding out of the argument and ultimately evaluates the expression.

  
  it looks something like

  ${e:jsfEL('#{MyBean.name}')}

  and can be used anywhere in the page. The syntax is a bit long, but it solves the problem but with JSF 1.2 and JSP 2.1 goodies we can use this much more naturally.

  Thank you,
  Marius
  

  Posted by: marius_danciu on August 12, 2007 at 04:26 AM

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