OmniFaces approach for writing custom ELContexts

If you are in the situation of writing a custom ELContext, then you need to extend the ELContext and override the abstract methods. But, if you have OmniFaces available in your project, then you can extend the org.omnifaces.el.ELContextWrapper, which provides a simple implementation of ELContext that can be sub-classed by developers wishing to provide specialized behavior to an existing ELContext instance. The default implementation of all methods is to call through to the wrapped ELContext. The source code of ELContextWrapper is:

package org.omnifaces.el;

import java.util.Locale;

import javax.el.ELContext;

import javax.el.ELResolver;

import javax.el.FunctionMapper;

import javax.el.VariableMapper;

import javax.faces.FacesWrapper;

import javax.faces.application.ViewHandler;

public class ELContextWrapper extends ELContext implements FacesWrapper<ELContext> {

 private ELContext elContext;

 public ELContextWrapper() {}

 public ELContextWrapper(ELContext elContext) {

  this.elContext = elContext;

 }

 @Override

 public ELContext getWrapped() {

  return elContext;

 }

 @Override

 public void setPropertyResolved(boolean resolved) {

  getWrapped().setPropertyResolved(resolved);

 }

 @Override

 public boolean isPropertyResolved() {

  return getWrapped().isPropertyResolved();

 }

 @Override

 public void putContext(@SuppressWarnings("rawtypes") Class key, Object contextObject) {

  getWrapped().putContext(key, contextObject);

}

 @Override

 public Object getContext(@SuppressWarnings("rawtypes") Class key) {

  return getWrapped().getContext(key);

 }

 @Override

 public ELResolver getELResolver() {

  return getWrapped().getELResolver();

 }

 @Override

 public FunctionMapper getFunctionMapper() {

  return getWrapped().getFunctionMapper();

 }

 @Override

 public Locale getLocale() {

  return getWrapped().getLocale();

 }

 @Override

 public void setLocale(Locale locale) {

  getWrapped().setLocale(locale);

 }

 @Override

 public VariableMapper getVariableMapper() {

  return getWrapped().getVariableMapper();

 }

}

Now, you can write a custom ELContext by following the next two skeletons:

·         extend ELContextWrapper and override #getWrapped() to return the instance wrapped by ELContextWrapper

import javax.el.ELContext;

import org.omnifaces.el.ELContextWrapper;

public class MyELContext extends ELContextWrapper {

 // override the desired ELContext methods

   

 //extend ELContextWrapper and override #getWrapped() to return the instance wrapped by ELContextWrapper

 @Override

 public ELContext getWrapped() {

  return super.getWrapped();

 }

}

·         provide ELContext instance to the overloaded constructor

import javax.el.ELContext;

import org.omnifaces.el.ELContextWrapper;

public class MyELContext extends ELContextWrapper {

 public MyELContext(ELContext elContext) {

  super(elContext);

 }   

   

 // override the desired ELContext methods 

}

Further, you can check the OmniFaces custom ELContexts:

ValueToInvokeElContext

InspectorElContext

These provides valuable lessons about how to correctly write a custom ELContext.