Deserialize JSON to Map<String,String> using jackson databind

Question

I'm using spring 4.0.5.RELEASE and jackson-databind 2.2.3 in my web application. When sending this JSON:

{"keyField1":"57579","keyField2":"sdf","someField":"sdasd","parameters":[{"parameterName":"dfgdfg","parameterValue":"sdf"},{"parameterName":"erwer","parameterValue":"sdfsdf"}]}

to the controller all I get is a HTTP 400 Bad Request at browser, I don't see any error at local websphere log, but after some tests I saw that the problem is with deserialization of the JSON array to the map. I never get into the save method at the controller. Tried some annotation like @JsonDeserialize(as=HashMap.class) without success. How can I resolve this?

My POJO:

class MyClassId implements Serializable {
private static final long serialVersionUID = 5022985493208399875L;
String keyField1;
String keyField2;
}

@Entity
@IdClass(MyClassId.class)
public class MyClass {
@Id
String keyField1;

@Id
String keyField2;

String someField;

@ElementCollection
@MapKeyColumn(name="parameterName")
@Column(name="parameterValue", length=400)
Map<String, String> parameters;
... Getters and Setters ...

My controller:

@RestController
@RequestMapping("/myclass/**")
public class MyClassController {

@Transactional
@RequestMapping(value = "/save", method = RequestMethod.POST, consumes={"application/json"})
public @ResponseBody ServiceResponce<MyClass> save(@RequestBody MyClass processToSave) {
    ... Code ...
}
}

Answer 1

I see two solutions to your problem:

• You distinguish the entity class that is persistent to the representation class that is sent back to the client. The drawback is that you need to make the representation creation explicitely in your code from the entity

• If you use Jackson to serialize your response in the respone (JSON, ...), you can leverage it feature "custom serializer" to adapt the structure of the returned payload according to your needs. See this answer for more details:

  • Spring 3.2 and Jackson 2 custom object mapper - Spring 3.2 and Jackson 2: add custom object mapper
  • Register a custom Jackson ObjectMapper using Sprint JavaCconfig - http://magicmonster.com/kb/prg/java/spring/webmvc/jackson_custom.html
  • Restlet Complex Object to XML serializaton - Restlet Complex Object to XML serializaton

Hope it helps you, Thierry

Answer 2

In the JSON, parameters is not an object but an array of objects:

"parameters":[{"parameterName":"dfgdfg","parameterValue":"sdf"}, ...

You can not map this on a

Map<String, String> parameters;

Use at least

List<Map<String, String>> parameters;