Make JSF access a Map<String, ?> values from an EL instead of a bean fields?

Question

Is there any proper way to override the way JSF accesses the beans fields from an Expression Language? The idea is to mimic this behavior in order to access a Map<String, ?> values, where the bean fields would be the map keys.

In other words, is it possible anyhow to use #{beanContainingNestedMap.keyOfSaidNestedMap}, just as if keyOfSaidNestedMap were a field of the beanContainingNestedMap?

If not, what other solution may I have?

---

Example:

Holder.java

public class Holder {

    private Map<String, Object> objects = new HashMap<String, Object>();

    public void add(String key, Object value) {
        objects.put(key, value);
    }

    public Object getObject(String key) {
        return objects.get(key);
    }

}

ExampleBean.java

public class ExampleBean {

    private Holder holder = new Holder();

    public ExampleBean() {
        holder.add("foo", 42);
        holder.add("bar", 'X');
    }

    public Holder getHolder() {
        return holder;
    }

}

example.xhtml

<c:out value="#{exampleBean.holder.foo}" /> <!-- should print "42" -->
<c:out value="#{exampleBean.holder.bar}" /> <!-- should print "X" -->

---

What would be great is if I could do something like (kind of pseudo-code since I don't know if such a method exists ;)):

@Override // override JSF's (if any...)
public Object resolveEl(String el) {
    try {
        super.resolveEl(el);
    } catch (ElException e) {
        Object bean = e.getBean();
        String fieldName = e.getFieldName();
        if (bean instanceof Holder) {
            Holder holder = (Holder) bean;
            Object value = holder.getObject(fieldName);
            if (value == null) {
                throw e;
            } else {
                return value;
            }
        }
    }
}

Scandinavia

This problem is not about JSF but EL. There's a map access section in the StackOverflow EL wiki. To cite two examples: ${someMap[dynamicKey]}, ${some['class'].simpleName} – Ketchum

@LuiggiMendoza Thank you for the tips, but the idea was first to know if it is possible anyhow to use #{beanContainingAMap.keyOfTheSaidMap} instead, just as if keyOfTheSaidMap were a field of the bean. – Scandinavia

If you check the link provided in my comment, you will see that's currently not possible. You have to use #{exampleBean.holder[foo]}. – Ketchum

@LuiggiMendoza It must be technically feasable anyhow, am I wrong? I'll wait a little bit to see other potential answers. But don't hesitate to add your own, since if you have the only right answer, I'll willingly accept it ;) – Scandinavia

Your question is confusing. EL already supports maps out the box using exactly the same syntax as javabeans. – Heyman

@Heyman Please have a look at my second comment to get more precisions. – Scandinavia

I'm not sure why you want to do it the harder way if a simple way already exist. – Heyman

Answer 1

You can directly use map by EL.

Holder.java

public class Holder {

    private Map<String, Object> objects = new HashMap<String, Object>();

    public void add(String key, Object value) {
        objects.put(key, value);
    }

    public Map<String, Object> getObjectsMap() {
        return objects;
    }

}

EL

#{exampleBean.holder.objectsMap[your-key]}

Disannul

Can [your-key] be a dynamic expression ? – Joyann

Can [your-key] be a dynamic expression ? Any help – Pisgah

@AnkitKumar: That depends on your logic, if you want to construct dynamic key you can use <c:set var="key" value="#{your dynamic value}" /> – Emplacement

Not working. NoSuchMethodException Holder.getObjectsMap[your-key](). – Snifter

Answer 2

This problem is not about JSF but EL. As noted in @BalusC comment, you can directly use the notation you already want/need with Map objects. I've prepared a basic example on this (note: this is just an example and should remain as is or improved since it uses scriptlets and we must avoid scriptlets usage but made it for a quick dirty test):

<%@page import="edu.home.model.entity.User"%>
<%@page import="java.util.HashMap"%>
<%@page import="java.util.Map"%>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
    <%
        //Scriptlets usage, sorry. This code must be moved to a Servlet or another controller component
        //defining the map
        Map<String, User> aMap = new HashMap<String, User>();
        //defining a value for the map
        User user = new User();
        user.setFirstName("Luiggi");
        user.setLastName("Mendoza");
        //adding the value in the map 
        aMap.put("userLM", user);
        //making the map accesible in EL through PageContext attribute
        pageContext.setAttribute("aMap", aMap);
    %>
    <!-- Accessing directly to the userLM key and its attributes -->
    ${aMap.userLM.firstName} - ${aMap.userLM.lastName}
</body>
</html>

User class code (minimized for test purposes):

public class User {
    private String firstName;
    private String lastName;
    //empty constructor
    //getters and setters
}

This generates a JSP page that prints:

Luiggi - Mendoza

Note that this (except the scriptlet part) will work on a Facelets page as well since this is EL and not JSF.

Ketchum