Created attachment 29898 [details]
JasperELInterpreter implementation

Jasper ELInterpreter Implementation

 Simple ELInterpreter. It can transfer simple ELs to java code directly.
 EL is a big bottleneck of JSP. EL resolving takes much CPU expense.
 
 The performance is better when simple ELs were transfered to java code.
  
 However the code will by pass all ELResolvers. This interpreter is not a standard of JSP specification. 
 When activate this ELInterpreter. User must know how it works.
 
 Here are the cases of Simple ELs,
 
 1.Simple EL, only contains one part of expression, for example ${elemId}. This kind of EL will be generated as
 
 this.getJspContext().findAttribute("elemId")
 
 2.EL with two parts of expression and type of first part is specified by attribute in Tag File. 
   For example, ${model.location} .  "model" is specified on the top of tag file, 
   
   <%@ attribute name="model" required="true" type="org.apache.jasper.model.results.ItemModel" %>.
   
   It is generated as (getModel() != null ? getModel().getLocation() : null)
   
 3.EL with logic or arithmetic and the value part can be generated.
   For example: ${(intlExpansion eq 'true' && not empty model.location) || sortType==7}
   
   It is generated as 
   (org.apache.jasper.runtime.ELRuntimeUtil.equals(getIntlExpansion(), "true")&&(!org.apache.jasper.runtime.ELRuntimeUtil.isEmpty((getModel() != null ? getModel().getLocation() : null))))
 
 How to apply this ELInterpreter?
 
 It is based on BUG 54239.