Question

我尝试了以下代码来生成json

        public void GenJson(){
            HostDetails hostDetails = new HostDetails();
            hostDetails.status = true;
            hostDetails.deviceAddedTime = "2018-02-07 05:44:21.196541";
            hostDetails.hostname = "MyHost";
            hostDetails.id = 1;

            Gson gson = new GsonBuilder().serializeNulls().create();
            JsonElement je = gson.toJsonTree(hostDetails);
            JsonObject jo = new JsonObject();
            jo.add(hostDetails.getClass().getSimpleName(), je);
            String jstr = jo.toString();
            System.out.println(jstr);
        }

        class HostDetails {
            public boolean status;
            public String deviceAddedTime;
            public String hostname;
            public int id;
        }

生成的Json输出

{
    "HostDetails":{
        "deviceAddedTime":"2018-02-07 05:44:21.196541",
        "hostname":"MyHost",
        "status":true,
        "id":1
    }
}

我想使用Gson将上面的json数据转换为类。我尝试下面的代码。而hostDetails1类的调试成员返回 null 。我该如何解决

public void GenClass(){
    Gson gson1 = new GsonBuilder().serializeNulls().create();
    HostDetails hostDetails1 = gson1.fromJson(jstr, HostDetails.class);
}

Answer 1

此行不是必需的。

jo.add(hostDetails.getClass().getSimpleName(), je);

jo变量都不是。

您为JSON添加了一个额外的级别，您可以在一行中立即创建JSON字符串...

如果要生成正确的JSON字符串，请尝试

 Gson gson = new GsonBuilder().serializeNulls().create();

 String jstr = gson.toJSON(hostDetails);
 System.out.println(jstr);

原因

使用此行

gson1.fromJson(jstr, HostDetails.class);

Gson期待这个

{
    "deviceAddedTime":"2018-02-07 05:44:21.196541",
    "hostname":"MyHost",
    "status":true,
    "id":1
}

如果要解析给定的JSON，则需要另一个包装类

class Foo {
    public Foo() {}

    @SerializedName("HostDetails")
    public HostDetails hostDetails;
}

然后

HostDetails hostDetails1  = gson1.fromJson(jstr, Foo.class).hostDetails;

你需要一个默认的无参数构造函数

    class HostDetails {

        public HostDetails() {}

        public boolean status;
        public String deviceAddedTime;
        public String hostname;
        public int id;
    }

也许是一些二传手和吸气鬼。

Answer 2

尝试getter/setters，这种做法。

 class HostResponse{
     @SerializedName("HostDetails")
     HostDetails  hostDetails;
    }


class HostDetails {
            public boolean status;
            public String deviceAddedTime;
            public String hostname;
            public int id;
        }


 HostResponse hostResponse= new Gson().fromJson(json.toString(), HostResponse.class);

用gson解析json值返回null

2 个答案:

原因