Jackson JSON, REST Data Binding & HashMaps problem

I implemented a RESTful web service with Spring and am using Jackson JSON as the serializer / deserializer for JSON objects.

However I run into Error 41开发者_如何学Python5's when the object that is to be deserialized contains a HashMap:

private Map<String, String> requestMap = new HashMap<String, String>();

If I remove this, everything works perfectly. Is this a known issue? Are there any fixes?

Thanks, Sri

Strictly speaking, Jackson serializes from Interface-type references just fine. The following demonstrates this point.

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.codehaus.jackson.map.ObjectMapper;

public class Foo
{
  public static void main(String[] args) throws Exception
  {
    ObjectMapper mapper = new ObjectMapper();

    Map<String, String> requestMap = new HashMap<String, String>();
    requestMap.put("one", "1");
    requestMap.put("two", "2");

    System.out.println(mapper.writeValueAsString(requestMap));
    // output: {"two":"2","one":"1"}

    List<UserPermission> userPermissions = new ArrayList<UserPermission>();
    userPermissions.add(new UserPermissionImpl("domain1"));
    userPermissions.add(new UserPermissionImpl("domain2"));

    System.out.println(mapper.writeValueAsString(userPermissions));
    // output: [{"scope":"domain1"},{"scope":"domain2"}]

    Container container = new ContainerImpl(requestMap, userPermissions);

    // From an Interface-type reference, where the implementation is an object with two Interface-type references:
    System.out.println(mapper.writeValueAsString(container));
    // {"requestMap":{"two":"2","one":"1"},"userPermissions":[{"scope":"domain1"},{"scope":"domain2"}]}
  }
}

interface UserPermission {}

class UserPermissionImpl implements UserPermission
{
  public String scope;
  UserPermissionImpl(String scope) { this.scope = scope; }
}

interface Container {}

class ContainerImpl implements Container
{
  public Map<String, String> requestMap;
  public List<UserPermission> userPermissions;

  ContainerImpl(Map<String, String> requestMap, List<UserPermission> userPermissions)
  { this.requestMap = requestMap; this.userPermissions = userPermissions; }
}

There's some other problem in the system you're using.

Discovered the problem. Jackson JSON has difficulties with Interfaces. So in the definitions, use HashMaps and ArrayLists instead of Maps and Lists. Not sure if this is a perfect solution, but it works for me.