Question

I am using JSON Jackson 2.0 to write a data Model to file and then load it back into the application. I can successfully write the object into a string but I encounter the following error message when trying to marshal it back into a object:

No suitable constructor found for type [simple type, class ImportAttributeModel]: can not instantiate from JSON object (need to add/enable type information?)
at [Source: user; line: 1, column: 111] (through reference chain: ImportTemplateModel[“modelList”])

This is a code snippet of my classes:

public class ImportTemplateModel 
{  
  private Map<Integer, AttributeModel> m_modelList;
  private GraphElementType m_type; 

  public ImportTemplateModel() 
  {

  }
// getters  & setters
}

public class AttributeModel 
{
   private String m_label;
   private String m_key;
   private ElementDefinition m_definition;

   public AttributeModel(String label, String key, ElementDefinition def)
   {
      m_label = label;
      m_key = key;
      m_definition = def;
   }
// getters  & setters
}

Here is the calls I make to write & read the model:

// Write model
ObjectMapper mapper = new ObjectMapper();
ImportTemplateModel itm = new ImportTemplateModel()
// set model atttributes
...
//

try {
  mapper.writeValue(new File(filepath), itm);

} 
catch (IOException e) {

}
.... 

// Read Model
ObjectMapper mapper = new ObjectMapper();
try {
  mapper.readValue(new File(filepath), ImportTemplateModel.class);

}
catch (IOException e) {

}

I am not sure what I am doing wrong at the moment… Is it because AttributeModel is not a POJO? or is it I can’t use Maps for this implementation? If so, how do I get around this?

Answer 1

It needs to have a no-argument constructor so Jackson can instantiate it.