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PODeserializing JSON based on object type
 

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    <p>I am creating a service that receives requests in the form of JSON messages. I need to parse the message and take the appropriate action based on the request type. For example (in pseudo code):</p> <pre><code>switch(request.type) { case "NewOrder": createNewOrder(order); break; case "CancelOrder" cancelOrder(orderId); break; } </code></pre> <p>It seems that most JSON APIs (at least those that do the object mapping for you) need the root object type to deserialize. Is there any elegant way around this?</p> <p>As an example, in the Jackson API (using full object mapping), I need to call the mapper as follows:</p> <pre><code>NewOrder newOrder = mapper.readValue(src, NewOrder.class); CancelOrder cancelOrder = mapper.readValue(src. CancelOrder.class); </code></pre> <p>Which means that I need to know the object's class even before I have parsed it. What I really need is some way to peek into the JSON string, determine the request type and then call the appropriate readValue() method - something like this:</p> <pre><code>String requestType = getRequestType(src); switch(request.type) { case "NewOrder": NewOrder newOrder = mapper.readValue(src, NewOrder.class); createNewOrder(newOrder.order); break; case "CancelOrder" CancelOrder cancelOrder = mapper.readValue(src. CancelOrder.class); cancelOrder(cancelOrder.orderId); break; } </code></pre> <p>Is it possible to do this using Jackson or any other Java JSON parser? I am sure I can go to a lower level and use a streaming API or a node based API, but trying to avoid that complexity if I can.</p>
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