Creating JSON From Selected Objects

Question

I want to create JSON object of selected options. I've already written java code but it creates JSON of all the database values.

The JSON code is:

rs = stmt.executeQuery("SELECT file_id,fid from nonspatial_data  where file_id=1");

JSONArray jArray = new JSONArray();

while (rs.next())
{  
    String  FileID_json=rs.getString("file_id");
    String fid_json=rs.getString("fid");
    JSONObject jobj = new ``JSONObject();
    jobj.put("file_id", FileID_json);
    jobj.put("fid", fid_json);
    jArray.add(jobj);
}

JSONObject features = new JSONObject();
features.put("features", jArray);

I want to create json of selected file_id.

Any assistance is appreciated.

Answer 1

I'm not sure the format you want the json to be in but you should really use a library like jackson (has serializers/mappers that help). The way to use that is: create a domain object representing a json object and pass it through this serializer and you have json.

NOTE: to keep code brief, I don't use best practices of java (eg making string constants, etc). I have also not tested this code but you should get a very good idea of what I'm suggesting.

public class SomeObject{ 
  Map<String,Object> model;
  public void setFoo( String foo ) {...}
  public String getFoo() {
    return model.get( "foo" );
  }

  // if you have more than one model, consider moving this method to a superclass
  public String toJson() {
    Map<String, Object> result = new HashMap<String, Object>();
    String status;
    List<String> errors = new ArrayList<String>();

    ObjectMapper mapper = new ObjectMapper();
    result.put("status", status);
    result.put("errors", errors);
    StringWriter sw = new StringWriter();
    mapper.writeValue(sw, result);
    return sw.toString();
  }
}

This helps keep your code object-oriented...and your app logic can then refer to domain objects instead of manipulating basic strings.

Answer 2

我用冬眠做很多时间，然后用flexjson将集合的对象转换成json