使用 Google 的 Gson 将 Json 转换为 java 对象

Converting Json to java objects using Google's Gson

提问by Vignesh Gopalakrishnan

I am using Spring Social FqlQuery to get data's from facebook. Here is the JSON response I am getting from facebook. My controller where i am getting Json output is here,

我正在使用 Spring Social FqlQuery 从 facebook 获取数据。这是我从 facebook 得到的 JSON 响应。我获取 Json 输出的控制器在这里，

fql = "SELECT work FROM user WHERE uid = me()";
facebook.fqlOperations().query(fql, new FqlResultMapper<Object>() {
    public Object mapObject(FqlResult result) {
        List list = (List) result.getObject("work");
        for (Object object : list) {
           JsonHelper jsonHelper = new JsonHelper();
           Gson gson = new GsonBuilder().setPrettyPrinting().create();
           String jsonOutput = gson.toJson(object);
           System.out.println(jsonOutput);
           gson.fromJson(jsonOutput, JsonHelper.class);
        }

System.out.println inside for loop Outputs multiple json as below.:

System.out.println 内 for 循环输出多个 json 如下：

{
  "employer": {
    "id": 129843057436,
    "name": "www.metroplots.com"
  },
  "location": {
    "id": 102186159822587,
    "name": "Chennai, Tamil Nadu"
  },
  "position": {
    "id": 108480125843293,
    "name": "Web Developer"
  },
  "start_date": "2012-10-01",
  "end_date": "2013-05-31"
}
{
  "employer": {
    "id": 520808381292985,
    "name": "Federation of Indian Blood Donor Organizations"
  },
  "start_date": "0000-00",
  "end_date": "0000-00"
}

Here is my Helper Class:

这是我的助手类：

import java.util.List;

public class JsonHelper {

class Employer{
    private int id;
    private String name;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

}
class Location{
    private int id;
    private String name;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }   

}
class Position{
    private int id;
    private String name;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}
//Edited After here
private String start_Date;
private String end_Date;
private Employer employer;
private Location location;
private Position position;
public String getStart_Date() {
    return start_Date;
}
public void setStart_Date(String start_Date) {
    this.start_Date = start_Date;
}
public String getEnd_Date() {
    return end_Date;
}
public void setEnd_Date(String end_Date) {
    this.end_Date = end_Date;
}
public Employer getEmployer() {
    return employer;
}
public void setEmployer(Employer employer) {
    this.employer = employer;
}
public Location getLocation() {
    return location;
}
public void setLocation(Location location) {
    this.location = location;
}
public Position getPosition() {
    return position;
}
public void setPosition(Position position) {
    this.position = position;
}
}

When I try to convert the json objects to java object as done above I am getting this exception.

当我尝试如上所述将 json 对象转换为 java 对象时，出现此异常。

HTTP Status 500 - Request processing failed; nested exception is com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was BEGIN_OBJECT at line 6 column 16

Can any one help me where I am wrong. Please help me converting json to java objects. Hope my question is clear. Thanks in advance.

任何人都可以帮助我哪里出错了。请帮我将 json 转换为 java 对象。希望我的问题很清楚。提前致谢。

EDIT MADE TO CONTROLLER:

对控制器进行编辑：

facebook.fqlOperations().query(fql, new FqlResultMapper<Object>() {
public Object mapObject(FqlResult result) {
List<JsonHelper> json = new ArrayList<JsonHelper>();
List list = (List) result.getObject("work");

for (Object object : list) {
    Gson gson = new GsonBuilder().setPrettyPrinting().create();
    String jsonOutput = gson.toJson(object);
    System.out.println(jsonOutput);
    JsonHelper jsonHelper = gson.fromJson(jsonOutput, JsonHelper.class);
    json.add(jsonHelper);
    System.out.println(jsonHelper.getStart_Date());
}

for (JsonHelper jsonHelper : json) {
    System.out.println(jsonHelper.getStart_Date());
}

return list;
}

});

回答by Jhanvi

Since i am not having the actual api access, so i am trying it with static value in the example. Firstly in your JsonHelperclass, replace all intby long, as the values mentioned in the json are of type longand String. Then try it like mentioned below:

由于我没有实际的 api 访问权限，所以我在示例中尝试使用静态值。首先在你的JsonHelper班级中，全部替换int为long，因为 json 中提到的值是类型long和String。然后像下面提到的那样尝试：

            String str = "{\n"
            + "  \"employer\": {\n"
            + "    \"id\": 129843057436,\n"
            + "    \"name\": \"www.metroplots.com\"\n"
            + "  },\n"
            + "  \"location\": {\n"
            + "    \"id\": 102186159822587,\n"
            + "    \"name\": \"Chennai, Tamil Nadu\"\n"
            + "  },\n"
            + "  \"position\": {\n"
            + "    \"id\": 108480125843293,\n"
            + "    \"name\": \"Web Developer\"\n"
            + "  },\n"
            + "  \"start_date\": \"2012-10-01\",\n"
            + "  \"end_date\": \"2013-05-31\"\n"
            + "}";


    List<JsonHelper> json = new ArrayList<JsonHelper>();
    Gson gson = new Gson();
    JsonHelper users = gson.fromJson(str, JsonHelper.class);
    json.add(users);


    for (JsonHelper js_obj : json) {
        System.out.println(js_obj.getEmployer().getId());
        System.out.println(js_obj.getEmployer().getName());
    }