ClojureUberspectImpl.java

package clojure.velocity;

import org.apache.velocity.util.introspection.UberspectImpl;
import org.apache.velocity.util.introspection.VelPropertyGet;
import org.apache.velocity.util.introspection.Info;
import org.apache.velocity.runtime.parser.node.AbstractExecutor;
import clojure.lang.APersistentMap;
import clojure.lang.Keyword;

import java.lang.reflect.InvocationTargetException;

public class ClojureUberspectImpl extends UberspectImpl {

    @Override
    public VelPropertyGet getPropertyGet(Object obj, String identifier, Info i) throws Exception {
        if (obj instanceof APersistentMap) {
            final APersistentMap map = (APersistentMap)obj;
            final Keyword key = Keyword.intern(null, identifier);
            return new VelGetterImpl(new AbstractExecutor() {
                public Object execute(Object o) throws IllegalAccessException, InvocationTargetException {
                    return map.get(key);
                }
            });
        } else {
            return super.getPropertyGet(obj, identifier, i);
        }
    }
}

velocity.clj

(in-ns 'clojure.velocity)
(clojure/refer 'clojure)

(import '(org.apache.velocity.util.introspection UberspectImpl VelPropertyGet Info))
(import '(org.apache.velocity.runtime.parser.node AbstractExecutor))

(defn ClojureUberspectImpl-getPropertyGet-Object-String-Info [this obj id info] 
  (if (instance? clojure.lang.APersistentMap) 
    (new org.apache.velocity.util.introspection.UberspectImpl$VelGetterImpl 
	 (proxy [AbstractExecutor] [] (execute [obj] (obj id))))
    (proxy-super getPropertyGet obj id info)))

(gen-and-load-class 'clojure.velocity.ClojureUberspectImpl :extends UberspectImpl)

(in-ns 'velocity)
(clojure/refer 'clojure)

(import '(org.apache.velocity.app VelocityEngine))
(import '(org.apache.velocity.context Context))
(import '(java.io StringWriter))

(defn make-context [context]
  (proxy [Context] [] 
    (containsKey [key] (contains? context (keyword key)))    
    (get [key] (context (keyword key)))
    (getKeys [] (keys context))
    (put [key value] false)
    (remove [key] false)))

(defn render [template context]
  (let 
      [ve (new VelocityEngine)
       ctx (make-context context)       
       out (new StringWriter)
       props (new java.util.Properties)]
    (.setProperty props "runtime.introspector.uberspect" "clojure.velocity.ClojureUberspectImpl")
    (.init ve props)
    (.evaluate ve ctx out "clojure" template)
    (.toString out)))