Trouble retrieving data from web service using GSON

问题

I have tried a lot of samples and tutorials about GSON and how things would work using it such as:

http://www.softwarepassion.com/android-series-parsing-json-data-with-gson/
http://androidsmith.com/2011/07/using-gson-to-parse-json-on-android/

and etc.

My problem is that I have this json value returned by my http://localhost:3000/users/1.json, which is:

{
  "created_at": "2012-09-20T01:43:15Z",
  "id": 1,
  "name": "kevin",
  "updated_at": "2012-09-20T01:43:15Z"
}

Another is in this url http://localhost:3000/users.json which has a json value

[ {
    "created_at": "2012-09-20T01:43:15Z",
    "id": 1,
    "name": "kevin",
    "updated_at": "2012-09-20T01:43:15Z"
  }, {
    "created_at": "2012-09-20T01:43:33Z",
    "id": 2,
    "name": "pineda",
    "updated_at": "2012-09-20T01:43:33Z"
  }, {
    "created_at": "2012-09-20T01:46:08Z",
    "id": 3,
    "name": "raphael",
    "updated_at": "2012-09-20T01:46:08Z"
  }, {
    "created_at": "2012-09-20T16:13:42Z",
    "id": 4,
    "name": null,
    "updated_at": "2012-09-20T16:13:42Z"
  }, {
    "created_at": "2012-09-20T16:18:03Z",
    "id": 5,
    "name": null,
    "updated_at": "2012-09-20T16:18:03Z"
  }, {
    "created_at": "2012-09-20T16:19:23Z",
    "id": 6,
    "name": null,
    "updated_at": "2012-09-20T16:19:23Z"
  }, {
    "created_at": "2012-09-20T16:20:41Z",
    "id": 7,
    "name": null,
    "updated_at": "2012-09-20T16:20:41Z"
  } 
]

I am having a bit of a hard time parsing such data and getting it for storage purposes.

回答1:

In order to parse your JSON, you first need to create a class to wrap your data. In your case:

public class Item {
  @SerializedName("created_at")
  private String createdAt;
  @SerializedName("id")
  private int id;
  @SerializedName("name")
  private String name;
  @SerializedName("updated_at")
  private String updatedAt;
  //getters and setters
}

Then, in order to parse your 1st JSON reponse, you just have to do:

Gson gson = new Gson();
Item item = gson.fromJson(your1stJsonString, Item.class);

Your 2nd JSON response is a bit more tricky, because it's an array. The problem is that you can't simply do:

List<Item> item = gson.fromJson(your1stJsonString, List<Item>.class); //wrong!

The previous code fails because Java can't know the class of List<Item> due to type erasure.

So you have to do it this way:

Type itemListType = new TypeToken<List<Item>>() {}.getType();
List<User> itemList = gson.fromJson(your2stJsonString, itemListType);

And that's all, once you have parsed your JSON response in your object (or list of objects) you can access all the retrieved data as usual:

String name = itemList.get(i).getName();

Note 1: Notice that I've set the types of attributes created_at and updated_at as just String, because it makes things easier. I usually do it this way, and then I parse the Date or any other confictive type. Anyway, if you want to directly parse the dates, I think you can use a Custom Deserializer following Gson's User Guide.

Note2: The use of the annotation @SerializedName is interesting to separate the name of a field in the JSON response and in your app, in order to follow Java naming conventions...

来源：https://stackoverflow.com/questions/12568954/trouble-retrieving-data-from-web-service-using-gson

标签

android

json

gson

webservice-client

arrays