Embed JSON values in Solr fields and auto unmarshall it when converting from a document to a bean

ExtendedHttpSolrServer.java

import org.apache.http.client.HttpClient;
import org.apache.solr.client.solrj.ResponseParser;
import org.apache.solr.client.solrj.beans.DocumentObjectBinder;
import org.apache.solr.client.solrj.impl.HttpSolrServer;

public class ExtendedHttpSolrServer extends HttpSolrServer {

	private static final long serialVersionUID = -5355794252201598225L;
	
	private DocumentObjectBinder binder;

	public ExtendedHttpSolrServer(String baseURL) {
		super(baseURL);
	}

	public ExtendedHttpSolrServer(String baseURL, HttpClient client, ResponseParser parser) {
		super(baseURL, client, parser);
	}

	public ExtendedHttpSolrServer(String baseURL, HttpClient client) {
		super(baseURL, client);
	}

	@Override
	public DocumentObjectBinder getBinder() {
		if (binder == null) {
			binder = new JsonDocumentObjectBinder();
		}
		return binder;
	}

}

JsonDocumentObjectBinder.java

import java.lang.reflect.Field;
import java.lang.reflect.Type;
import java.util.Collection;
import java.util.List;

import org.apache.solr.client.solrj.beans.DocumentObjectBinder;
import org.apache.solr.common.SolrDocument;
import org.apache.solr.common.SolrDocumentList;

import com.google.gson.Gson;

public class JsonDocumentObjectBinder extends DocumentObjectBinder {
	
	public <T> List<T> getBeans(Class<T> clazz, SolrDocumentList solrDocList) {
		List<T> beans = super.getBeans(clazz, solrDocList);
		for (int i = 0; i < beans.size(); i++) {
			try {
				mapJsonFields(beans.get(i), solrDocList.get(i));
			} catch (Exception e) {
				throw new RuntimeException(e);
			}
		}
		
		return beans;
	}
	
	public <T> T getBean(Class<T> clazz, SolrDocument solrDoc) {
		T bean = super.getBean(clazz, solrDoc);
		try {
			return mapJsonFields(bean, solrDoc);
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}
	
	private <T> T mapJsonFields(T bean, SolrDocument document) throws IllegalArgumentException, IllegalAccessException {
		Class<?> clazz = bean.getClass();
		
		for (Field field : clazz.getDeclaredFields()) {
			if(field.getAnnotation(JSONField.class) != null){
				JSONField annotation = field.getAnnotation(JSONField.class);
				String solrField = annotation.value();
				
				if(solrField.equals(JSONField.DEFAULT))
					solrField = field.getName();
				
				String json = (String)document.getFieldValue(solrField);
				if(json == null || json.trim().length() == 0)
					continue;
				
				Type type = field.getType();
				field.setAccessible(true);
				
				if(Collection.class.isAssignableFrom((Class<?>)type))
					type = field.getGenericType();
					
				Object value = new Gson().fromJson(json, type);
				field.set(bean, value);
			}
		}
		
		return bean;
	}
	
}

JSONField.java

import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

import java.lang.annotation.Retention;
import java.lang.annotation.Target;

@Target({FIELD})
@Retention(RUNTIME)
public @interface JSONField {
	public static final String DEFAULT ="#default";
	String value() default DEFAULT;
}