HashMap 到 POJO 使用 GSON 或 Jackson

Question

My code for conversion:

public MyEntity convert(){
            HashMap<String,String> map = new HashMap<>();
            map.put("name","akshay");
            map.put("mobile","xxxxxxx");
            map.put("soap","lux");
            map.put("noodles","maggi");
            Gson gson = new Gson();
            JsonElement jsonElement = gson.toJsonTree(map);
            MyEntity pojo = gson.fromJson(jsonElement, MyEntity.class);
            System.out.println(gson.toJson(pojo));
            return pojo;
       }

My Entity class:

public class MyEntity {
    private String name;
    private int mobile;
    private HashMap<String,String> utility;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getMobile() {
        return mobile;
    }

    public void setMobile(int mobile) {
        this.mobile = mobile;
    }

    public HashMap<String, String> getUtility() {
        return utility;
    }

    public void setUtility(HashMap<String, String> utility) {
        this.utility = utility;
    }
}

What I am getting using my code:

{
    "name" : "akshay",
    "mobile" : 1234567890
}

But I want output like:

{
    "name" : "akshay",
    "mobile" : 1234567890,
    "utility" : {
        "soap" : "lux",
        "noodles" : "maggi"
    }
}

GSON does not map SOAP and noodles because there is no corresponding matching object in POJO. That's why I took hashmap. I want GSON to put all the unmatching fields into a hashmap.

One noticeable thing the key-value pair under utility is not fixed depends upon customer purchase. I mean it might be something else like below.

{
    "name" : "akshay",
    "mobile" : 1234567890,
    "utility" : {
        "toothpaste" : "colgate",
        "noodles" : "maggi"
    }
}

Answer 1

This will do the trick:

    HashMap<String, Object> map = new HashMap<>();
    map.put("name", "akshay");
    map.put("mobile", "xxxxxxx");
    HashMap<String, String> utility = new HashMap<>();
    utility.put("soap", "lux");
    utility.put("noodles", "maggi");
    map.put("utility", utility);

GSON ignores soap and noodles since they are not on the right level. They need to be children of "utility".

If you would like a "flat" JSON structure to be parsed in a specific way as you describe (matching fields are mapped 1:1, unmatched fields go into utility), you can write a custom (de)serializer. See this question for an example: GSON - Custom serializer in specific case . However, I would not recommend this as it probably ends up being more work.