Append json object in existing json file using Java

问题

I'm trying to append JSON Object each time within an existing JSON Array. For that i'm using GSON libraries. Tried below code :

OrderIDDetailBean ord = new OrderIDDetailBean();
ord.uniqueID = "sadasdas0w021";
ord.orderID = "Nand";

ord.cartTotal = "50";
ord.date = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss.SSS").format(new Date());

try {
    JsonWriter writer = new JsonWriter(new FileWriter("D:\\file.json", true));

    writer.beginArray();
    writer.beginObject();

    writer.name("uniqueID").value(ord.uniqueID);
    writer.name("orderID").value(ord.orderID);
    writer.name("cartTotal").value(ord.cartTotal);
    writer.name("date").value(ord.date);
    writer.endObject();
    writer.endArray();

    writer.close();
} catch (IOException e) {
    e.printStackTrace();
}

But it created JSON array each time instead of appending.

Actual:

[  
   {  
      "uniqueID":"CHECKOUT_ES01",
      "orderID":"5001787761",
      "date":"07-02-2019 15:31:41.637",
      "cartTotal":"11.44"
   } 
]

[
   {  
      "uniqueID":"CHECKOUT_ES01",
      "orderID":"5001787767",
      "date":"07-02-2019 15:35:20.347",
      "cartTotal":"11.44"
   }
]

Expected :

[  
   {  
      "uniqueID":"CHECKOUT_ES01",
      "orderID":"5001787761",
      "date":"07-02-2019 15:31:41.637",
      "cartTotal":"11.44"
   },
   {  
      "uniqueID":"CHECKOUT_ES01",
      "orderID":"5001787767",
      "date":"07-02-2019 15:35:20.347",
      "cartTotal":"11.44"
   }
]

Any help would be great appreciated.

回答1:

With your approach you might have a file that has many arrays each having one object. I suggest using Gson.fromJson(..) & Gson.toJson(..) instead of JsonWriter.

Assume the object you want to add is like:

@AllArgsConstructor
@Getter @Setter
public class OrderIDDetailBean {
    private String uniqueID;
    private Integer orderID;
    private Date date;
    private Double cartTotal;        
}

then appending new object would go like:

@Test
public void test() throws Exception {
    Gson gson = new GsonBuilder().setPrettyPrinting().create();
    // construct Type that tells Gson about the generic type
    Type dtoListType = new TypeToken<List<OrderIDDetailBean>>(){}.getType();
    FileReader fr = new FileReader("test.json");
    List<OrderIDDetailBean> dtos = gson.fromJson(fr, dtoListType);
    fr.close();
    // If it was an empty one create initial list
    if(null==dtos) {
        dtos = new ArrayList<>();
    }
    // Add new item to the list
    dtos.add(new OrderIDDetailBean("23", 34234, new Date(), 544.677));
    // No append replace the whole file
    FileWriter fw  = new FileWriter("test.json");
    gson.toJson(dtos, fw);
    fw.close();        
}

来源：https://stackoverflow.com/questions/54574576/append-json-object-in-existing-json-file-using-java

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json

gson