用Google Gson映射Mongo id字段 [英] Mapping Mongo id field with Google Gson

问题描述

我从MongoDB读取一个包含其唯一标识符的文档：

  {
_id： ObjectId（5526888bd3d56a86cea8ea12），
name：user1
} 
  

我想用java类映射它
$ b $ pre $ public class Mapper {
Object _id;
字符串名称;
}

由于执行fromJson的结果：

  Mapper m = gson.fromJson（string，Mapper.class）; 
  

...存储在_id字段中的值是 {$ oid = 5526888bd3d56a86cea8ea12} 。我想将ID字符串存储在其中。 （例如5526888bd3d56a86cea8ea12）

Gson可以自动为我做吗？

感谢您可以注册一个自定义适配器来告诉您解析器，您只需要在字符串值中的括号和引号之间获取值（请注意，id现在是 Mapper 类中的字符串）。

  class MapperAdapter实现了JsonDeserializer< Mapper> {
 
 private static final Pattern p = Pattern.compile（\\（\（[a-zA-Z\\d] +）\\\ ））; 
 $ b $ @Override 
 public Mapper反序列化（JsonElement json，类型typeOfT，JsonDeserializationContext上下文）throws JsonParseException {
 JsonObject jObj = json.getAsJsonObject（）; 
 String id = jObj.get（_ id）。getAsString（）; 
 String name = jObj.get（name）。getAsString（）; 
 
 Matcher m = p.matcher（id）; 
 if（！m.find（））{
 throw new IllegalArgumentException（id应该在括号和引号内。）; 
} 
返回新的映射器（m.group（1），name）; 
 
 
  

，然后在分析器中注册它：

  Gson gson = new GsonBuilder（）。registerTypeAdapter（Mapper.class，new MapperAdapter（））。create（）; 
 Mapper m = gson.fromJson（jsonString，Mapper.class）; 
  

这会产生输出：

  Mapper {id = 5526888bd3d56a86cea8ea12，name = user1} 
  

I'm reading a Document from MongoDB which contains its unique identifier:

{
    "_id" : ObjectId("5526888bd3d56a86cea8ea12"),
    "name" : "user1"
}

I'd like to map that with a java class

public class Mapper {
    Object _id;
    String name;
}

As a result of my fromJson execution:

Mapper m = gson.fromJson(string, Mapper.class);

...the value stored in the _id field is {$oid=5526888bd3d56a86cea8ea12}. I'd like to store the id String in it. (e.g. "5526888bd3d56a86cea8ea12")

Can Gson do it for me automatically ?

Thanks

解决方案

You can register a custom adapter to tell the parser that you only want to grab the value between parenthesis and quotes in the string value (note that id is now a String in your Mapper class). The regex can be changed to match the ids requirements that are generated.

class MapperAdapter implements JsonDeserializer<Mapper> {

    private static final Pattern p = Pattern.compile("\\(\"([a-zA-Z\\d]+)\"\\)");

    @Override
    public Mapper deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        JsonObject jObj = json.getAsJsonObject();
        String id = jObj.get("_id").getAsString();
        String name = jObj.get("name").getAsString();

        Matcher m = p.matcher(id);
        if(!m.find()) {
            throw new IllegalArgumentException("The id should be within parenthesis and quotes.");
        }
        return new Mapper(m.group(1), name);
    }
}

and you register it in your parser:

Gson gson = new GsonBuilder().registerTypeAdapter(Mapper.class, new MapperAdapter()).create();
Mapper m = gson.fromJson(jsonString, Mapper.class);

This yield the output:

Mapper{id=5526888bd3d56a86cea8ea12, name=user1}

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