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POJersey JSON marshalling of nested generic produces null
 

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  1. POJersey JSON marshalling of nested generic produces null
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    <p>Having an issue trying to marshall into JSON a HashMap nested in a List using Jersey 1.11.</p> <p>Here's a snippet of a Jersey endpoint which produces MediaType.APPLICATION_JSON via the returned Response object:</p> <p><strong>DataDTO.java</strong></p> <pre><code>@XmlRootElement public class DataDTO { ... private List&lt;GenericEntity&lt;HashMap&lt;String, String&gt;&gt; dataHierarchy; public List&lt;GenericEntity&lt;HashMap&lt;String, String&gt;&gt; getDataHierarchy() { return dataHierarchy; } public void setDataHierarchy(List&lt;GenericEntity&lt;HashMap&lt;String, String&gt;&gt; dh) { dataHierarchy = dh; } } </code></pre> <p><strong>Jersey resource class:</strong></p> <pre><code>@Get @Produces(MediaType.APPLICATION_JSON) @Path("/summary") public Response getSummary() { .... DataDTO dto = new DataDTO(); List&lt;GenericEntity&lt;HashMap&lt;String,String&gt;&gt;&gt; genericEntityList = new ArrayList&lt;&gt;(); for (HashMap&lt;String, String&gt; hashMapEntity : summary.getDataHierarchy()) { GenericEntity&lt;HashMap&lt;String, String&gt;&gt; genericEntity = new GenericEntity&lt;HashMap&lt;String, String&gt;&gt;(hashMapEntity) {}; genericEntityList.add(genericEntity); } dto.setDataHierarchy(genericEntityList); return Response.ok(dto).build(); } </code></pre> <p>The DTO is part of the 'natural class set' and its JAXBContext resolver context is configured to use natural notation and root unwrapping as so:</p> <pre><code>new JSONJAXBContext(JSONConfiguration.natural().rootUnwrapping(true).build(), naturalClassSet.toArray(new Class[naturalClassSet.size()])); </code></pre> <p>When, for example there are 5 entries in the list, the response JSON ends up looking like so:</p> <pre><code>{"dataHierarychy":[null, null, null, null, null]} </code></pre> <p>I've also tried changing the dataHierarchy property of DataDTO so that each generic data structure is wrapped in a GenericEntity:</p> <pre><code>private GenericEntity&lt;List&lt;GenericEntity&lt;HashMap&lt;String,String&gt;&gt;&gt;&gt; </code></pre> <p>This results in simply:</p> <pre><code>{"dataHierarychy":null} </code></pre>
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    1. COSolution: I ended working around this by creating DTOs to replace these ADTs.
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