@SuppressWarnings("unchecked")
	@Override
	protected Map<String, Object> transformPayload(String payload) throws Exception {
		if (columnNames.size() == 1 && "payload".equals(columnNames.get(0))) {
			Map<String, Object> fullPayload = new HashMap<String, Object>();
			fullPayload.put("payload", payload);
			return fullPayload;
		}
		Map<String, Object> payloadMap = this.jsonObjectMapper.fromJson(payload, Map.class);
		for (Map.Entry<String, Object> entry : payloadMap.entrySet()) {
			Object o = entry.getValue();
			if (o != null && !(o instanceof String || o instanceof Number)) {
				payloadMap.put(entry.getKey(), o.toString());
			}
		}
		for (String column : this.columnNames) {
			if (column.contains("_") && !payloadMap.containsKey(column)) {
				payloadMap.put(column, payloadMap.get(JdbcUtils.convertUnderscoreNameToPropertyName(column)));
			}
		}
		return payloadMap;
	}
Transforms a payload to a Map representation based on provided column names.

TODO: Right now it simply supports full payload under a 'payload' key or a JSON string with values stored with keys
corresponding to the column names specified. This could be expanded for additional payload types

@author Thomas Risberg
@author Gary Russell
@since 1.0
extensions/spring-xd-extension-jdbc/src/main/java/org/springframework/xd/jdbc/JdbcMessagePayloadTransformer.java