GsonFromJson：如何使用数组结构进行序列化和反序列化

Question

Im working on a project where we used jsonfile as its database since SQLite doesnt meet the requirement. The project has a portion when an object fron the wordbank is use it will change the status(such as 1-4). I made use of JSONArray to access the data. When i tried to change/edit the status, it doesnt save or write back to the jsonfile. Instead it only works on the momentary use of the application.

From searches, alot of stuff pop out that using gson. I concluded to use gson.

I am new to gson and just started learning it the other day. And i am having troubles with it.

This is the structure of my jsonfile. It has 2 objects(users and wordbank) that are arrayed

{ 
"users" :
  [{
    "username": "free",
    "password": "free",
    "email": "free@gmail.com",
    "type": "1"
  },
  {
    "username": "premium",
    "password": "premium",
    "email": "premium@gmail.com",
    "type": "2"
  }],
"wordbank" : 
  [{
      "English": "able",
      "Cebuano": "kaya",
      "Pronunciation": "ká-ya",
      "POS": "adjective",
      "Audio": "kaya.mp3",
      "Status": "0"
  },
  {
      "English": "advice",
      "Cebuano": "tambag",
      "Pronunciation": "tam-bag",
      "POS": "noun",
      "Audio": "tambag.mp3",
      "Status": "0"
  }]
}

From what I've seen in tutorial videos is that you create a different java class for its model. So i create 3 java class. user, wordbank and dictionary (combining them both).

public class dictionary{
  users[] user;
  wordbanks[] word;
}

Im using an existing jsonfile already so i parsed it and got its jsonstring. After which i tried to deserialize it using

jsonstring = readFromFile();//returns string from jsonfile
dictionary list = new Gson().fromJson(jsonstring, dictionary.class);

runned it and debug it. but when i got the results. it was null.

QUESTIONS: 1.Will I be able to edit and save the changes in json file by using gson? 2.Is my structure correct for the distionary class? 3.how to serialize and deserialize it?

Answer 1

• If your member variables of pojo Classes(users,workdbank,dictionary) don't match with JSON key, consider using @SerializedName provided by GSON. In your case, i was able to deserialise the string using gson by using @SerializedName as shown below

User Class

 public class User {

       @SerializedName("username")
    private String userName;
    @SerializedName("password")
    private String password;
    @SerializedName("email")
    private String email;
    @SerializedName("type")
    private String type;

    // Add Getters and Setters
}

WordBank Class

public class Wordbank {

    @SerializedName("English")
    private String english;
    @SerializedName("Cebuano")
    private String cebuano;
    @SerializedName("Pronunciation")
    private String pronunciation;
    @SerializedName("POS")
    private String pos;
    @SerializedName("Audio")
    private String audio;
    @SerializedName("Status")
    private String status;

    // Add getters and Setters
}

Dictionary Class

    public class Dictonary {

    @SerializedName("users")
    User[] userArray;
    @SerializedName("wordbank")
    Wordbank[] wordbankArray;

    public User[] getUserArray() {
        return userArray;
    }

    public void setUserArray(User[] userArray) {
        this.userArray = userArray;
    }

    public Wordbank[] getWordbankArray() {
        return wordbankArray;
    }

    public void setWordbankArray(Wordbank[] wordbankArray) {
        this.wordbankArray = wordbankArray;
    }
}

After making necessary changes as explained above, I was able to deserialise the string

 Dictonary dictonary =  new Gson().fromJson(input,Dictonary.class);

Answer 2

Yes you can use Gson for all your requirements. First create matching Pojo for your json structure. you can use tools such as this pojo generator . Just paste the json there (don't select json schema) and generate. Assuming you have three classes Result (contains to lists, similar to your dictionary class), User and Wordbank class. You can read (deserialize) and write (serialize) back into a file as follows.

try {
    // deserialize
    Result result = gson.fromJson(new FileReader(new File("src/test/resources/sample.json")), Result.class);
    // ... update result as required
    // result.users.remove(0);
    // serialize
    String json = gson.toJson(result);
    Files.write(new File("src/test/resources/sample.json").toPath(), json.getBytes());
} catch (FileNotFoundException e) {
    e.printStackTrace();
} catch (IOException e) {
    e.printStackTrace();
}