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copied!<p>From <a href="http://wiki.fasterxml.com/JacksonInFiveMinutes" rel="nofollow">http://wiki.fasterxml.com/JacksonInFiveMinutes</a> (but also look at TypeFactory in Jackson 1.3+) : </p> <blockquote> <p><strong>Data Binding with Generics</strong></p> </blockquote> <p>In addition to binding to POJOs and "simple" types, there is one additional variant: that of binding to generic (typed) containers. This case requires special handling due to so-called Type Erasure (used by Java to implement generics in somewhat backwards compatible way), which prevents you from using something like Collection.class (which does not compile).</p> <p>So if you want to bind data into a Map you will need to use:</p> <pre><code> Map<String,User> result = mapper.readValue(src, new TypeReference<Map<String,User>>() { }); </code></pre> <p>where TypeReference is only needed to pass generic type definition (via anynomous inner class in this case): the important part is > which defines type to bind to.</p> <p>If you don't do this (and just pass Map.class), call is equivalent to binding to Map (i.e. "untyped" Map), as explained above.</p> <hr> <p>If you mean polymorphic deserialization, check this link <a href="http://programmerbruce.blogspot.com/2011/05/deserialize-json-with-jackson-into.html" rel="nofollow">http://programmerbruce.blogspot.com/2011/05/deserialize-json-with-jackson-into.html</a> which discusses using the jackson annotations to assist the mapper in picking the right object for the job.</p> <hr> <p>I wrote this today (I'm sure it can be improved) for simply taking a JSON string and always converting it into a List of DTOs (or whatever it can be converted into). This could be called with any type, and could be modified to return a single instance, or List, or whatever you wished. OBJECT_MAPPER is a static ObjectMapper variable.</p> <pre><code> public static <T> List<T> getFromJSONCollection(String jsonString, final Class<T> type) throws IOException { try { return OBJECT_MAPPER.readValue(jsonString, TypeFactory.defaultInstance().constructCollectionType(ArrayList.class, type)); } catch (JsonMappingException e) { return getFromJSON(jsonString, type); } } public static <T> List<T> getFromJSON(final String jsonString, final Class<T> type) throws IOException { return new ArrayList<T>() {{ add(OBJECT_MAPPER.readValue(jsonString, type));}}; } </code></pre>

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