[SNIPPET] Json Parsing

[cesco]

Ciao ragazzi
In giro si trova davvero poco riguardo il parsing dei Json e dato che ho avuto la necessità di utilizzare questi metodi, ritengo opportuno condividere con voi questi frammenti di codice

Necessario:
Libreria Gson: https://code.google.com/p/google-gson/


Importate la libreria nel progetto di eclipse (io non uso AndroidStudio ma suppongo esista un repository su maven per Gson)

Procuratevi un Json (file sul dispositivo o tramite inputstream da Url)

Qui un esempio di Json:

	{
	"text": "RT @PostGradProblem: In preparation for the NFL lockout, I will be spending twice as much time analyzing my fantasy baseball team during ...",
	"truncated": true,
	"in_reply_to_user_id": null,
	"in_reply_to_status_id": null,
	"favorited": false,
	"source": "<a href=\"http://twitter.com/\" rel=\"nofollow\">Twitter for iPhone</a>",
	"in_reply_to_screen_name": null,
	"in_reply_to_status_id_str": null,
	"id_str": "54691802283900928",
	"entities": {
	"user_mentions": [
	{
	"indices": [
	3,
	19
	],
	"screen_name": "PostGradProblem",
	"id_str": "271572434",
	"name": "PostGradProblems",
	"id": 271572434
	}
	],
	"urls": [ ],
	"hashtags": [ ]
	},
	"contributors": null,
	"retweeted": false,
	"in_reply_to_user_id_str": null,
	"place": null,
	"retweet_count": 4,
	"created_at": "Sun Apr 03 23:48:36 +0000 2011",
	"retweeted_status": {
	"text": "In preparation for the NFL lockout, I will be spending twice as much time analyzing my fantasy baseball team during company time. #PGP",
	"truncated": false,
	"in_reply_to_user_id": null,
	"in_reply_to_status_id": null,
	"favorited": false,
	"source": "<a href=\"http://www.hootsuite.com\" rel=\"nofollow\">HootSuite</a>",
	"in_reply_to_screen_name": null,
	"in_reply_to_status_id_str": null,
	"id_str": "54640519019642881",
	"entities": {
	"user_mentions": [ ],
	"urls": [ ],
	"hashtags": [
	{
	"text": "PGP",
	"indices": [
	130,
	134
	]
	}
	]
	},
	"contributors": null,
	"retweeted": false,
	"in_reply_to_user_id_str": null,
	"place": null,
	"retweet_count": 4,
	"created_at": "Sun Apr 03 20:24:49 +0000 2011",
	"user": {
	"notifications": null,
	"profile_use_background_image": true,
	"statuses_count": 31,
	"profile_background_color": "C0DEED",
	"followers_count": 3066,
	"profile_image_url": "http://a2.twimg.com/profile_images/1285770264/PGP_normal.jpg",
	"listed_count": 6,
	"profile_background_image_url": "http://a3.twimg.com/a/1301071706/images/themes/theme1/bg.png",
	"description": "",
	"screen_name": "PostGradProblem",
	"default_profile": true,
	"verified": false,
	"time_zone": null,
	"profile_text_color": "333333",
	"is_translator": false,
	"profile_sidebar_fill_color": "DDEEF6",
	"location": "",
	"id_str": "271572434",
	"default_profile_image": false,
	"profile_background_tile": false,
	"lang": "en",
	"friends_count": 21,
	"protected": false,
	"favourites_count": 0,
	"created_at": "Thu Mar 24 19:45:44 +0000 2011",
	"profile_link_color": "0084B4",
	"name": "PostGradProblems",
	"show_all_inline_media": false,
	"follow_request_sent": null,
	"geo_enabled": false,
	"profile_sidebar_border_color": "C0DEED",
	"url": null,
	"id": 271572434,
	"contributors_enabled": false,
	"following": null,
	"utc_offset": null
	},
	"id": 54640519019642880,
	"coordinates": null,
	"geo": null
	},
	"user": {
	"notifications": null,
	"profile_use_background_image": true,
	"statuses_count": 351,
	"profile_background_color": "C0DEED",
	"followers_count": 48,
	"profile_image_url": "http://a1.twimg.com/profile_images/455128973/gCsVUnofNqqyd6tdOGevROvko1_500_normal.jpg",
	"listed_count": 0,
	"profile_background_image_url": "http://a3.twimg.com/a/1300479984/images/themes/theme1/bg.png",
	"description": "watcha doin in my waters?",
	"screen_name": "OldGREG85",
	"default_profile": true,
	"verified": false,
	"time_zone": "Hawaii",
	"profile_text_color": "333333",
	"is_translator": false,
	"profile_sidebar_fill_color": "DDEEF6",
	"location": "Texas",
	"id_str": "80177619",
	"default_profile_image": false,
	"profile_background_tile": false,
	"lang": "en",
	"friends_count": 81,
	"protected": false,
	"favourites_count": 0,
	"created_at": "Tue Oct 06 01:13:17 +0000 2009",
	"profile_link_color": "0084B4",
	"name": "GG",
	"show_all_inline_media": false,
	"follow_request_sent": null,
	"geo_enabled": false,
	"profile_sidebar_border_color": "C0DEED",
	"url": null,
	"id": 80177619,
	"contributors_enabled": false,
	"following": null,
	"utc_offset": -36000
	},
	"id": 54691802283900930,
	"coordinates": null,
	"geo": null
	}

view raw twitter.json hosted with ❤ by GitHub

Prima di iniziare il parsing è importante anche stabilire quali oggetti sono presenti all'interno del file (JsonObject o JsonArray). Esiste un comodissimo tool online che categorizza il contenuto del Json: Json Parser Online

Incollate il codice e nelle opzioni in alto a destra selezionate "Show JS Types", otterrete qualcosa di questo tipo:



Ora entra in gioco Gson. Questa libreria infatti, permette il parsing dell'intero Json, semplicemente fornendogli una classe java appositamente creata a patto che il contenuto della classe rifletta il contenuto del Json.

Un semplice esempio basato su questo file (riporto solo una parte):

MyJsonObject.java
public class MyJsonObject {<br /> <br /> @SerializedName("text")<br /> public String text;<br /> <br /> @SerializedName("truncated")<br /> public boolean truncated;<br /> <br /> @SerializedName("source")<br /> publci String source;<br /> <br /> @SerializedName("entities")<br /> public MyJsonEntities entities;<br /> <br /> //Getters/setters<br /> <br /> }

​x

 

1

public class MyJsonObject {

2

​

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@SerializedName("text")

4

public String text;

5

​

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@SerializedName("truncated")

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public boolean truncated;

8

​

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@SerializedName("source")

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publci String source;

11

​

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@SerializedName("entities")

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public MyJsonEntities entities;

14

​

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//Getters/setters

16

​

17

}

MyJsonEntities.java
<br /> public class MyJsonEntities {<br /> <br /> @SerializedName("user_mentions")<br /> public List<MyMentions> user_mentions;<br /> <br /> //Getters/Setters<br /> <br /> }<br />

10

 

1

​

2

public class MyJsonEntities {

3

​

4

@SerializedName("user_mentions")

5

public List<MyMentions> user_mentions;

6

​

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//Getters/Setters

8

​

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}

10

​

MyMentions.java
<br /> <br /> public class MyMentions {<br /> <br /> @SerializedName("indices")<br /> public ArrayList<Integer> indices;<br /> <br /> @SerializedName("screen_name")<br /> public String screen_name;<br /> <br /> @SerializedName("id_str")<br /> public String id_str;<br /> <br /> @SerializedName("name")<br /> public String name;<br /> <br /> @SerializedName("id")<br /> public int id;<br /> <br /> //Getters/setters<br /> }<br /> <br />

23

 

1

​

2

​

3

public class MyMentions {

4

​

5

@SerializedName("indices")

6

public ArrayList<Integer> indices;

7

​

8

@SerializedName("screen_name")

9

public String screen_name;

10

​

11

@SerializedName("id_str")

12

public String id_str;

13

​

14

@SerializedName("name")

15

public String name;

16

​

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@SerializedName("id")

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public int id;

19

​

20

//Getters/setters

21

}

22

​

23

​

Una volta create queste classi il parsing diventa un giochetto di poche righe di codice:

<br /> Gson gson = new Gson();<br /> Reader reader = new InputStreamReader(source);<br /> MyJsonObject response = gson.f<span class="forTooltip">rom</span>Json(reader, MyJsonObject.class);<br />

5

 

1

​

2

Gson gson = new Gson();

3

Reader reader = new InputStreamReader(source);

4

MyJsonObject response = gson.fromJson(reader, MyJsonObject.class);

5

​

e voilà! Parsing del Json eseguito correttamente
Va sottolineato che la gerarchia e la struttura delle classi che create deve rispecchiare quella del file Json ricevuto! (MyJsonObject > MyJsonEntities > MyMentions)

Inutile dire che il parsing non va eseguito nel thread della UI ma eventualmente in un thread separato o in un AsyncTask

Esistono anche librerie che possono semplificarvi la vita, quali ION (https://github.com/koush/ion) soprattutto se per ricevere il Json avete bisogno di autenticazione (Nel repo di ION date un'occhiata all'esempio relativo a twitter)


Semplice esempio di parsing tramite Url
<br /> <br /> MyJsonObject mJObject;<br /> <br /> ...<br /> <br /> class LoadJson extends<br /> AsyncTask<Void, Boolean, MyJsonObject> {<br /> <br /> ProgressDialog p;<br /> <br /> @Override<br /> protected void onPreExecute() {<br /> p = new ProgressDialog(context);<br /> p.setMessage("Loading...please wait");<br /> p.setIndeterminate(true);<br /> p.show();<br /> <br /> }<br /> <br /> @Override<br /> protected JSObject doInBackground(Void... v) {<br /> <br /> InputStream source = retrieveStream(url);<br /> <br /> Gson gson = new Gson();<br /> <br /> Reader reader = new InputStreamReader(source);<br /> <br /> MyJsonObject response = gson.fromJson(reader, JSObject.class);<br /> return response;<br /> }<br /> <br /> @Override<br /> protected void onPostExecute(MyJsonObject result) {<br /> <br /> mJObject = result;<br /> <br /> p.cancel();<br /> super.onPostExecute(result);<br /> }<br /> }<br /> new LoadJson().execute();<br /> <br /> <br /> private InputStream retrieveStream(String url) {<br /> <br /> DefaultHttpClient client = new DefaultHttpClient(); <br /> <br /> HttpGet getRequest = new HttpGet(url);<br /> <br /> try {<br /> <br /> HttpResponse getResponse = client.execute(getRequest);<br /> final int statusCode = getResponse.getStatusLine().getStatusCode();<br /> <br /> if (statusCode != HttpStatus.SC_OK) { <br /> Log.w(context.getClass().getSimpleName(), <br /> "Error " + statusCode + " for URL " + url); <br /> return null;<br /> }<br /> <br /> HttpEntity getResponseEntity = getResponse.getEntity();<br /> return getResponseEntity.getContent();<br /> <br /> } <br /> catch (IOException e) {<br /> getRequest.abort();<br /> Log.w(context.getClass().getSimpleName(), "Error for URL " + url, e);<br /> }<br /> <br /> return null;<br /> <br /> }<br /> <br />

76

 

1

​

2

​

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MyJsonObject mJObject;

4

​

5

...

6

​

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class LoadJson extends

8

        AsyncTask<Void, Boolean, MyJsonObject> {

9

​

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            ProgressDialog p;

11

​

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            @Override

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            protected void onPreExecute() {

14

                p = new ProgressDialog(context);

15

                p.setMessage("Loading...please wait");

16

                p.setIndeterminate(true);

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                p.show();

18

​

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            }

20

​

21

            @Override

22

            protected JSObject doInBackground(Void... v) {

23

​

24

                InputStream source = retrieveStream(url);

25

​

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                Gson gson = new Gson();

27

​

28

                Reader reader = new InputStreamReader(source);

29

​

30

                MyJsonObject response = gson.fromJson(reader, JSObject.class);

31

                return response;

32

            }

33

​

34

            @Override

35

            protected void onPostExecute(MyJsonObject result) {

36

​

37

                mJObject = result;

38

​

39

                p.cancel();

40

                super.onPostExecute(result);

41

            }

42

        }

43

     new LoadJson().execute();

44

​

45

​

46

private InputStream retrieveStream(String url) {

47

​

48

        DefaultHttpClient client = new DefaultHttpClient(); 

49

​

50

        HttpGet getRequest = new HttpGet(url);

51

​

52

        try {

53

​

54

            HttpResponse getResponse = client.execute(getRequest);

55

            final int statusCode = getResponse.getStatusLine().getStatusCode();

56

​

57

            if (statusCode != HttpStatus.SC_OK) { 

58

                Log.w(context.getClass().getSimpleName(), 

59

                        "Error " + statusCode + " for URL " + url); 

60

                return null;

61

            }

62

​

63

            HttpEntity getResponseEntity = getResponse.getEntity();

64

            return getResponseEntity.getContent();

65

​

66

        } 

67

        catch (IOException e) {

68

            getRequest.abort();

69

            Log.w(context.getClass().getSimpleName(), "Error for URL " + url, e);

70

        }

71

​

72

        return null;

73

​

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    }

75

​

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​

Buon coding

[TheCopacabanaMan]

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