@Override
    protected void doXContent(XContentBuilder builder) throws IOException {
        builder.startArray("filter");
        for (QueryBuilder query : filters) {
            query.toXContent(builder);
        }
        builder.endArray();
    }
@see io.apiman.manager.api.es.util.AbstractQueryBuilder#doXContent(io.apiman.manager.api.es.util.XContentBuilder)
manager/api/es/src/main/java/io/apiman/manager/api/es/util/FilterBuilder.java