Just Spring Integration

Custom Transformers

Now that we have seen out-of-the-box transformers, it is time to see how we can create our own Transformers should the need arise.

Let us look at an example of a TradePublisher that will produce Trade messages with a Trade POJO as a payload. In the example, the consumer is not interested in receiving a Java Object but is expecting a name-value paired map. Can we tweak the TradePublisher to produce the Trade data compatible with that of a receiver? Yes, we can, but what if we have another receiver that may come up a few weeks later and be interested in consuming XML-formatted Trade messages?

Ideally, the producers should be unaware of consumers or their requirements. They only talk via an intermediary called message. This enables the applications to be decoupled, too. Our TradePublisher produces the Trades in a universal format—a POJO.

Before the message hits the receiver, a transformer needs to be plugged in.

Trade Map Transformer

Because the receiver is expecting name-value pairs of the Trade data, we need to transform the message into the expected format before sending to the consumer. One way to do this is to create a class that transforms the POJO to a name-value pair. The TradeMapTransformer class defined below satisfies this requirement:

public class TradeMapTransformer { public Map<String, String> transform(Trade t) { Map<String,String> tradeNameValuesMap = new HashMap<String,String>(); tradeNameValuesMap.put("TRADE_ID", t.getId()); tradeNameValuesMap.put("TRADE_ACCOUNT", ...