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POIs Jackson really unable to deserialize json into a generic type?
 

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    <p>This is a duplicate question because the following questions are either messy or they are not answered at all:</p> <p><a href="https://stackoverflow.com/questions/13118798/deserializing-a-generic-type-with-jackson">deserializing-a-generic-type-with-jackson</a></p> <p><a href="https://stackoverflow.com/questions/12355742/jackson-deserialize-into-runtime-specified-class">jackson-deserialize-into-runtime-specified-class</a></p> <p><a href="https://stackoverflow.com/questions/11664894/jackson-deserialize-using-generic-class">jackson-deserialize-using-generic-class</a></p> <p><a href="https://stackoverflow.com/questions/11659844/jackson-deserialize-generic-class-variable">jackson-deserialize-generic-class-variable</a></p> <p>I hope that this question will finally find an answer that makes this clear for good.</p> <p>Having a model :</p> <pre><code>public class AgentResponse&lt;T&gt; { private T result; public AgentResponse(T result) { this.result = result; } public T getResult() { return result; } } </code></pre> <p>JSON input:</p> <pre><code>{"result":{"first-client-id":3,"test-mail-module":3,"third-client-id":3,"second-client-id":3}} </code></pre> <p>and two recommended ways of deserializing generic types :</p> <pre><code>mapper.readValue(out, new TypeReference&lt;AgentResponse&lt;Map&lt;String, Integer&gt;&gt;&gt;() {}); </code></pre> <p>or</p> <pre><code>JavaType javaType = mapper.getTypeFactory().constructParametricType(AgentResponse.class, Map.class); mapper.readValue(out, javaType); </code></pre> <p>Jackson is never able to deal with the generic type T, it figures it's a Map from JavaType, but it finds Object type constructor argument because of type erasure and throws an error. So is this a Jackson bug, or am I doing something wrong? What else is explicit specification of TypeReference or JavaType for?</p> <pre><code>com.fasterxml.jackson.databind.JsonMappingException: No suitable constructor found for type [simple type, class com.fg.mail.smtp.AgentResponse&lt;java.util.Map&lt;java.lang.String,java.lang.Integer&gt;&gt;]: can not instantiate from JSON object (need to add/enable type information?) at [Source: java.io.InputStreamReader@4f2d26d; line: 1, column: 2] at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:164) at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:984) at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:276) at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:121) at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2888) at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2064) </code></pre>
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    1. COYou should post that question on the jackson-users mailing list
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    2. COAlso, do you really try and deserialize _all_ that JSON or just this JSON's `result` member value?
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    3. COI'm deserializing the JSON input into AgentResponse. I don't know how and why would I deserialize it partially. It's just a response with status and result value, that may be Object, collection, map, etc. I modified the question so there is just the generic result,
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