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POHow do I give type hints to the Jackson deserializer?
 

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  1. POHow do I give type hints to the Jackson deserializer?
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    <p>I'm using Jackson as a tool to declare some objects whose classes I can't annotate (or modify at all). One of the classes has a setter and getter for an untyped list. Here's a sanitized version:</p> <pre><code>public class Family { private List members; public List getMembers() { return members; } public void setMembers(List members) { this.members = members; } //...many, many other properties } public class Member { private String name; public String getName() { return name; } public void setName(String name) { this.name = name; } } </code></pre> <p>Here's the JSON I'm trying to deserialize:</p> <pre><code>{ "members" : [ { "name" : "Mark" } ] } </code></pre> <p>The naive code I would use is this:</p> <pre><code>ObjectMapper mapper = new ObjectMapper(); Family family = mapper.readValue(json, Family.class); Member member = (Member) family.getMembers().get(0); System.out.println(member.getName()); </code></pre> <p>But of course this fails, as Jackson did not know to create a list of <code>Members</code> instead of its fallback, a list of <code>LinkedHashMap</code>s.</p> <p><strong>What's the easiest way to instruct Jackson to treat <code>members</code> as a <code>List&lt;Member&gt;</code>?</strong> I don't think I want to use a fully custom deserializer for the class, since there are many other properties that Jackson handles fine.</p> <p>Here's the best I could come up with, using BeanDeserializerModifier:</p> <pre><code>mapper.setDeserializerProvider(new StdDeserializerProvider() .withDeserializerModifier(new BeanDeserializerModifier() { @Override public BeanDeserializerBuilder updateBuilder(DeserializationConfig config, BasicBeanDescription beanDesc, BeanDeserializerBuilder builder) { if (beanDesc.getBeanClass() == Family.class) { CollectionType type = CollectionType.construct(ArrayList.class, SimpleType.construct(Member.class)); TypeDeserializer typeDeserializer = type.getTypeHandler(); SettableBeanProperty.MethodProperty membersProperty = (SettableBeanProperty.MethodProperty) builder.removeProperty("members"); builder.addProperty(new SettableBeanProperty.MethodProperty( "members", type, typeDeserializer, beanDesc.getClassAnnotations(), (AnnotatedMethod) membersProperty.getMember() )); } return builder; }})); </code></pre> <p>It works, but seems really low level (and verbose!) for what I'm trying to do. What am I missing here?</p> <h2>Edit</h2> <p>I should note, I'm using Jackson 1.8.2, but could update if there's a compelling reason to.</p>
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