Killing SSJS - Passing a parameter using Expression Language - Part 1

Expression Language is a powerful and useful tool, but it doesn't handle parameterized methods (other than Map.get(Object) and DataObject.getValue(Object)). That means if you need to do anything more complicated than simple data retrieval, you have to jump through some hoops. I'm going help you get started here.

I've posted this code before, but here is one simple trick:

public class BaseDataModel implements DataObject, Serializable {
    private static final long serialVersionUID = 1L;

    private Map<Object, Object> values;

    public Class<?> getType(Object key) {
        Object o = getValue(key);
        return o == null ? null : o.getClass();
    }

    public final Object getValue(Object key) {
        try {
            return customGetter(key);
        }
        catch (NoSuchMethodException e) {
            return getMapValue(key);
        }
    }

    protected Object customGetter(Object keyObj) throws NoSuchMethodException {
        if (keyObj instanceof String) {
            String key = (String) keyObj;
            if (key.startsWith("isReadOnly") && key.length() > "isReadOnly".length()) {
                String property = key.substring("isReadOnly".length());
                property = property.substring(0, 1).toLowerCase() + property.substring(1);
                }
                return isReadOnly(property);
            }
        }
        throw new NoSuchMethodException();
    }

    public final void setValue(Object key, Object value) {
        if (isReadOnly(key)) return;
        try {
            customSetter(key, value);
        }
        catch (NoSuchMethodException e) {
            setMapValue(key, value);
        }
    }

    protected void customSetter(Object key, Object value) throws NoSuchMethodException {
        throw new NoSuchMethodException();
    }

    public boolean isReadOnly(Object key) {
        return false;
    }

    protected Map<Object, Object> getValues() {
        if (values == null) {
            values = new HashMap<Object, Object>();
        }
        return values;
    }

    public final Object getMapValue(Object key) {
        return getValues().get(key);
    }

    public final void setMapValue(Object key, Object value) {
        getValues().put(key, value);
    }

    private Set<Object> getKeys() {
        return this.getValues() == null ? null : this.getValues().keySet();
    }
}

This allows you to use an EL expresssion like "#{bean.isReadOnlyFirstName}". This is extendable so you can extend the customGetter() to support prefixes like hasPermissionEdit or getRelatedData. The customGetter intercepts the getValue method and if any patterns are matched, it supplies the result, otherwise the value from the Map is returned. I have been using this for great effect for months since I worked it out.

However, there are some big limitations to this technique:

1) You can't compute any part of the expression. You can't really use this technique in a custom control where you have to use a passed value. You can't really do something like #{getNameFromDoc(DocumentId)}. Caveat: There is a hack I've seen that allows you to do something like ${javascript:'#{isReadOnly'+compositeData.fieldName+'}'"}, but now we're using SSJS to compute EL and that seems to make things worse rather than better.

2) You can't use a hierarchical EL expression like {bean.getFullName.getUserDirectory.getFolderMyDocuments}.

In Part 2: a better solution.