You might want to create & use an EL function.
If you're using facelets, you can look at Rick Hightower's article for an example of EL functions.

I think this should be done in a Converter in JSF. With seam this should not be a problem with the great support annotations.

The first implementation I would think of:

@Name("your.package.name.StringAddAndRemoveCharacter")
@org.jboss.seam.annotations.faces.Converter(id = "characterSuffix")
public class StringAddAndRemoveCharacter implements Converter {

     /** @see Converter#getAsObject(FacesContext, UIComponent, String) */
     public Object getAsObject(FacesContext ctx, UIComponent comp, String s) {
          return s == null ? s : s + 'A';
     }

     /** @see Converter#getAsString(FacesContext, UIComponent, Object) */
     public String getAsString(FacesContext ctx, UIComponent comp, Object o) {
          if (o == null) {
               return null;
          }
          String s = o.toString();
          return s.substring(0, s.length() - 1);
     }

}

Of course this only works, if you don't have too many different characters to add.

Sorry, I think I have misinterpreted your use case. A converter is usually used to do custom data conversion. I just searched for a tutorial on converters and found something here. In your case, you actually need to add or remove characters from a single field.

Please forget my previous advice.

Could you perhaps elaborate on your current design? This would make it easier for others to answer.

Is your <f:param … enclosed in a h:commandButton or s:link? I'd say you could just call an action that removes the last character from an injected context variable, but it really depends on how you add characters.

Peter, I'm not entirely sure of the use case, but would it make sense to create an Enum that maps the possible keynames and keywords?  You can then use an EnumConverter to convert stuff.

You want chop the last character from a string in EL? Jakarta Commons Lang's StringUtils has a chop() method.

You can turn this - and any static method really - into a JSF function with a custom tag lib, e.g. META-INF/custom.taglib.xml:

<?xml version="1.0"?>
<!DOCTYPE facelet-taglib PUBLIC "-//Sun Microsystems, Inc.//DTD Facelet Taglib 1.0//EN" "facelet-taglib_1_0.dtd">
<facelet-taglib>
 <namespace>http://org.apache.commons.lang/StringUtils</namespace>
 <function>
  <function-name>chop</function-name>
  <function-class>org.apache.commons.lang.StringUtils</function-class>
  <function-signature>java.lang.String chop(java.lang.String)</function-signature>
 </function>
</facelet-taglib>

You may need to alter your build.xml to ensure the custom.taglib.xml finds its way to your WAR's META-INF folder.

And use it as such:

value="#{stringutils:chop(keyword)}"

Be sure to bind the stringutils prefix to http://org.apache.commons.lang/StringUtils - add this xmlns attribute to the root element of the page:

xmlns:stringutils="http://org.apache.commons.lang/StringUtils"

Are you sure that:

#{empty keyword ? '' : keyword.substring(0,keyword.length()-1)}

Doesn't work? I think you just got the method name wrong.

Note that there is also a built-in fn:substringAfter() function (at least in JSP, not 100% sure if it is there in Facelets).

You can see a list of all built-in EL functions here.

Just out of interest, is there anything particularly wrong with writing your own Bean that does this?

eg:

@Name("stringUtility")
@BypassInterceptors
public class StringUtility {

     public String backspace(String in) {
          return in.substring(0, in.length() -1);
     }
}

<a:commandButton value="Backspace"
action="#{stringUtility.backspace(keyword)}" 
ajaxSingle="true" 
reRender="keyword"/>

I use this StringUtility to do things like padding, converting line breaks to <br/> etc. What advantage does an EL function give me?

Cheers,

Damian.

Having done any testing but there is likely a performance difference between using the JavaBean approach and JSF function.

Also, if you're concerned about standards, the JavaBean method is a Seam extension to EL.

And finally, it all depends on what kind of link it is.  See Christian's comments on GET/POST/DELETE