Annotations in java made our life easy for development!! In this post, I would explain how to parse JSON string from REST api using GSON, a google json parsing library. use user guide and refer this link to be familiar with more on gson(google json).
Assume, REST service will return following response
Here, CardNumber, CardStatusID, ExpiryDate, CardID etc will be the primitive types and the block of content in "{}" will represent one object and pushed into java objects. The block "[]" represents an array of elements or start & end of array. The name "Card" is the key/name to the array. Again, curly braces around "Card" represent one object.
So, I have created 2 classes "Card.java" & "CardData.java". class "Card.java" will store all the primitives here and represent each block. "CardData.java" represent the entire block.
GSON can parse only primitive and user-defined types but not arrays etc.. For this to handle, we have to provide de-serializer helper class. A simple example that I have used here is as below:
Below code snippet is for parsing the json response:
Below are the classes which have annotations to push respective primitives into variables.
Here is the wrapper class which holds the list of "Card" objects.
Assume, REST service will return following response
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 | {"Card": [
{
"CardNumber": "4544424719784129",
"CardStatusID": "3",
"ExpiryDate": "04/2017",
"CardID": "1",
"CardTypeID": "1",
"AccountID": "1",
"CardNotes": "",
"GetCash": "1"
},
{
"CardNumber": "4211472898719724",
"CardStatusID": "3",
"ExpiryDate": "05/2018",
"CardID": "2",
"CardTypeID": "2",
"AccountID": "3",
"CardNotes": "",
"GetCash": "1"
}]
}
|
Here, CardNumber, CardStatusID, ExpiryDate, CardID etc will be the primitive types and the block of content in "{}" will represent one object and pushed into java objects. The block "[]" represents an array of elements or start & end of array. The name "Card" is the key/name to the array. Again, curly braces around "Card" represent one object.
So, I have created 2 classes "Card.java" & "CardData.java". class "Card.java" will store all the primitives here and represent each block. "CardData.java" represent the entire block.
GSON can parse only primitive and user-defined types but not arrays etc.. For this to handle, we have to provide de-serializer helper class. A simple example that I have used here is as below:
1 2 3 4 5 6 7 8 9 10 | class CardListDeserializer implements JsonDeserializer<List<Card>> { public List<Card> deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException { List<Card> list = new ArrayList<Card>(); Gson gson = new Gson(); list.addAll( Arrays.asList(gson.fromJson(json.getAsJsonArray(),Card[].class)) ); return list; } } |
Below code snippet is for parsing the json response:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 | class RESTClient { private static String LOST_CARDS_GET_URL = "http://server:port/services/json/showallcards"; public static CardsData getLostCards(){ CardsData cardsData = null; try { URL url = new URL(LOST_CARDS_GET_URL); HttpURLConnection conn = (HttpURLConnection)url.openConnection(); conn.setRequestMethod("GET"); conn.setRequestProperty("Accept", "application/json"); if (conn.getResponseCode() != 200) { throw new RuntimeException("Failed : HTTP error code : " + conn.getResponseCode()); } BufferedReader br = new BufferedReader(new InputStreamReader((conn.getInputStream())));; GsonBuilder builder = new GsonBuilder(); builder.registerTypeAdapter(List.class, new CardListDeserializer()); Gson gson = builder.create(); cardsData = gson.fromJson(br, CardsData.class); conn.disconnect(); System.out.println(cardsData ); } catch (MalformedURLException e) { e.printStackTrace(); } catch (Exception e) { e.printStackTrace(); } return cardsData ; } } |
Below are the classes which have annotations to push respective primitives into variables.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 | import com.google.gson.annotations.SerializedName; public class Card { @SerializedName("CardNumber") private String cardNumber; @SerializedName("CardStatusID") private String cardStatusID; @SerializedName("ExpiryDate") private String expiryDate; @SerializedName("CardID") private String cardID; @SerializedName("CardTypeID") private String cardTypeID; @SerializedName("AccountID") private String accountID; @SerializedName("CardNotes") private String cardNotes; @SerializedName("GetCash") private String getCashFlag; public Card() { super(); } public void setCardID(String cardID) { this.cardID = cardID; } public String getCardID() { return cardID; } public void setAccountID(String accountID) { this.accountID = accountID; } public String getAccountID() { return accountID; } public void setCardNotes(String cardNotes) { this.cardNotes = cardNotes; } public String getCardNotes() { return cardNotes; } public void setCardNumber(String cardNumber) { this.cardNumber = cardNumber; } public String getCardNumber() { return cardNumber; } public void setExpiryDate(String expiryDate) { this.expiryDate = expiryDate; } public String getExpiryDate() { return expiryDate; } public void setCardStatusID(String cardStatusID) { this.cardStatusID = cardStatusID; } public String getCardStatusID() { return cardStatusID; } public void setCardTypeID(String cardTypeID) { this.cardTypeID = cardTypeID; } public String getCardTypeID() { return cardTypeID; } public void setGetCashFlag(String getCashFlag) { this.getCashFlag = getCashFlag; } public String getGetCashFlag() { return getCashFlag; } } |
Here is the wrapper class which holds the list of "Card" objects.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | public class CardData { @SerializedName("Card") private List<Card> cardsList; public CardList() { super(); } public void setCardsList(List<Card> cardsList) { this.cardsList = cardsList; } public List<Card> getCardsList() { return cardsList; } } |
