1.0 Iterate JSON Object in Apache Velocity

Well this is slightly json implementation (ex: gson, jettison, json) dependent solution. 

For example :

     

• jsonObject.entrySet()  //  returns Set<Entry<String, JsonElement>> for gson 
•  jsonObject.keys()         // returns Iterator<String>   for jettison

 So we are gonna write a Custom apache velocity Uberspector exploiting the above facts.

1. Create a class MyUberspector which extends SecureUberspector 

import java.util.Iterator;
import org.apache.velocity.util.introspection.Info;
import org.apache.velocity.util.introspection.SecureUberspector;
import com.google.gson.JsonObject;

public class MyUberspector extends SecureUberspector {

    @Override
    public Iterator getIterator(Object object, Info info) throws Exception {
        if (object instanceof JsonObject) {
            return new VelJSONObjectIerator((JsonObject) object);
        } else {
            return super.getIterator(object, info);
        }
    }
}

 2. Create a class VelJSONObjectIerator which implements Iterator<Object>

import java.nio.channels.UnsupportedAddressTypeException;
import java.util.Iterator;
import java.util.Map.Entry;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;

public class VelJSONObjectIerator implements Iterator<Object> {
    private Iterator<Entry<String, JsonElement>> iterator;

    public VelJSONObjectIerator(JsonObject object) {
        this.iterator = object.entrySet().iterator();
    }

    public boolean hasNext() {
        return iterator.hasNext();
    }

    public Object next() {
        return iterator.next();
    }

    public void remove() {
        throw new UnsupportedAddressTypeException();
    }
}

3. Set property "runtime.introspector.uberspect" to class name of MyUberspector class.

Thats it ..!!! 

 for jsonObject = {"1":"un","2":"deux","3":"trois","4":"quatre"} 

Velocity template :
 #foreach ($x in $jsonObject)
   $x.key | $x.value
#end

Output:

   1 | "un"
   2 | "deux"
   3 | "trois"
   4 | "quatre"



For  jsonObject.keys() solution, look for blog 1.1