如何在Java中将Spring MVC JSON视图对象转换为字符串？

Question

This is my first Stackoverflow post. I'm new to Java and have been thrown into the deep end of the pool so to speak.

My company has set up a big framework that is already working well extracting data from databases on an ERP system into JSON view objects to be used for their Web UI. They are using the Spring MVC framework and the MappingJacksonJsonView Class to render what they are passing in into JSON formatted View objects.

I need to retrieve the data in JSON format and instead insert it into MongoDB.

Ideally I'd just call their methods that are returning the JSON View objects and convert them into JSON Strings that I can then insert into MongoDB. Otherwise I'm disassembling their existing code to try to emulate what they are doing just prior to creating the view object (not a bad thing for learning, but time consuming).

Is there a straight forward way to convert a Spring MVC View object to a String? All my google searches are returning nothing useful, although I've found a handful of similar responses regarding MVC and ASP.net. I also found an example of rendering a hashMap as a Json string. Maybe I should be just looking for some mechanism to do that instead using the HashSet below?

/*
 Here the data is being retrieved in a certain format from our databases using existing 
 infrastructure and the data gets converted into a View object named view.
*/
ResultSet rs = getBrowseData(newBrowseId, newQueryParameters);

model.addAttribute(MODEL_ATTRIBUTE_DATA, rs);

model.addAttribute(MODEL_ATTRIBUTE_AUX_DATA, rs.getAuxillaryData());


View view = createJsonView(new HashSet<String>(Arrays.asList(MODEL_ATTRIBUTE_AUX_DATA, MODEL_ATTRIBUTE_DATA)));

/*
 Ideally, after that last line, I would just convert the new View object view into a 
 String and pass it into our MongoDB database because all the work formatting the data 
 as Json has been done.
 OR - I could take the HashSet<String> and convert that to a JsonString instead of calling
 the createJsonView method, but I'm only seeing where I can pass in a HashMap to 
 objectmapper if I use org.codehaus.jackson.map.ObjectMapper (as an example). 
 Is there an objectMapper for HashSet? How could I create a HashMap instead of HashSet?
 Otherwise, I'm going to need to do everything the following code does except instead 
 return the code as a string.
*/


public View createJsonView(Set<String> renderedAttributes) {
  MappingJacksonJsonView view = JsonUtil.CreateJsonMapperView(null);
  view.setRenderedAttributes(renderedAttributes);
  return view;
}


/**
* Creates a Json-mapping-view object configured with the specified FilterProvider for controlling serialization 
* of objects from the model to JSON data.
* @param filters Filter provider to specify JSON data filtering. Can be null if no filtering is desired.
* @return Spring View that will return serialized JSON data to client.
*/
public static MappingJacksonJsonView CreateJsonMapperView(FilterProvider filters) {
    MappingJacksonJsonView view = new MappingJacksonJsonView();
    view.setObjectMapper(CreateJsonMapper(filters));

    return view;
    }

/**
* Creates a Json-object-mapper object configured with the specified FilterProvider for controlling serialization 
* of objects to JSON data using filtering (e.g for security by hiding fields).
* @param filters Filter provider to specify JSON data filtering. Can be null if no filtering is desired.
* @return ObjectMapper that can be used to serialize JSON data from objects.
*/
public static ObjectMapper CreateJsonMapper(FilterProvider filters) {
    ObjectMapper objectMapper = new ObjectMapper();

    objectMapper.setDateFormat(SerializationUtil.getStandardDateFormat());
    // Ignore any unknown properties received in JSON objects
    objectMapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);

    if (filters != null) {
    // use our own custom filter introspector so that we do not need to pollute our data beans with filter annotations
    JsonFilterIntrospector filterIntrospector = new JsonFilterIntrospector();       
    objectMapper.setSerializationConfig(objectMapper.getSerializationConfig().withAnnotationIntrospector(filterIntrospector));

    // apply input filters
    objectMapper.setFilters(filters);
    }

  return objectMapper;
}

Answer 1

Use gson.jar to convert json to java object. 

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import com.google.gson.Gson;

public class GsonExample {
    public static void main(String[] args) {

    Gson gson = new Gson();

    try {

        BufferedReader br = new BufferedReader(
            new FileReader("c:\\file.json"));

        //convert the json string back to object
        DataObject obj = gson.fromJson(br, DataObject.class);

        System.out.println(obj);

    } catch (IOException e) {
        e.printStackTrace();
    }

    }
}