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POImmutable/polymorphic POJO <-> JSON serialization with Jackson
 

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    <p>I'm trying to serialize a immutable POJO to and from JSON, using Jackson 2.1.4, without having to write a custom serializer and with as few annotations as possible. I also like to avoid having to add unnecessary getters or default constructors just to satisfy the Jackson library.</p> <p>I'm now stuck on the exception:</p> <p>JsonMappingException: No suitable constructor found for type [simple type, class Circle]: can not instantiate from JSON object (need to add/enable type information?)</p> <p>The code:</p> <pre><code>public abstract class Shape {} public class Circle extends Shape { public final int radius; // Immutable - no getter needed public Circle(int radius) { this.radius = radius; } } public class Rectangle extends Shape { public final int w; // Immutable - no getter needed public final int h; // Immutable - no getter needed public Rectangle(int w, int h) { this.w = w; this.h = h; } } </code></pre> <p>The test code:</p> <pre><code>ObjectMapper mapper = new ObjectMapper(); mapper.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL, JsonTypeInfo.As.PROPERTY); // Adds type info Shape circle = new Circle(10); Shape rectangle = new Rectangle(20, 30); String jsonCircle = mapper.writeValueAsString(circle); String jsonRectangle = mapper.writeValueAsString(rectangle); System.out.println(jsonCircle); // {"@class":"Circle","radius":123} System.out.println(jsonRectangle); // {"@class":"Rectangle","w":20,"h":30} // Throws: // JsonMappingException: No suitable constructor found. // Can not instantiate from JSON object (need to add/enable type information?) Shape newCircle = mapper.readValue(jsonCircle, Shape.class); Shape newRectangle = mapper.readValue(jsonRectangle, Shape.class); System.out.println("newCircle = " + newCircle); System.out.println("newRectangle = " + newRectangle); </code></pre> <p>Any help is greatly appreciated, thanks!</p>
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