如何在Java中将Spring MVC JSON视图对象转换为字符串？

Question

这是我的第一个Stackoverflow帖子。 我是Java的新手，可以这么说。

我公司已经建立了一个大型框架，该框架已经很好地运行，可以将ERP系统上数据库中的数据提取到JSON视图对象中以用于其Web UI。 他们正在使用Spring MVC框架和MappingJacksonJsonView类来呈现将它们传递到JSON格式的View对象中。

我需要以JSON格式检索数据，而不是将其插入MongoDB。

理想情况下，我只调用返回JSON View对象的方法，并将它们转换为JSON字符串，然后将其插入MongoDB。 否则，我将分解他们现有的代码，以尝试模拟他们在创建视图对象之前所做的事情（这对学习不是一件坏事，但很耗时）。

是否有直接方法将Spring MVC View对象转换为String？ 我的所有Google搜索都没有返回任何有用的信息，尽管我发现了一些关于MVC和ASP.net的类似响应。 我还找到了一个将hashMap呈现为Json字符串的示例。 也许我应该只是在寻找某种机制来代替使用下面的HashSet呢？

/*
 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();
    }

    }
}