我对此有疑问，但阅读了有关Stack Overflow的其他问题，并初步解决了这些问题。现在，我可以在客户端和服务器之间发送JSON，并在客户端中从该JSON创建对象。但是，我不断遇到一个特定对象的错误：
client.restaurant = gson.fromJson(obj.get("restaurant"), Restaurant.class); // works
client.postcodes = gson.fromJson(obj.get("postcodes"), new TypeToken<ArrayList<Postcode>>(){}.getType()); // works
client.orders = gson.fromJson(obj.get("orders"), new TypeToken<ArrayList<Order>>(){}.getType()); // java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at path $[0].dishes.updateListeners
所有JSON根据https://jsonlint.com有效。我不知道如何找到有关此问题的更多信息，但是我尝试的一件事是我提取了ArrayList<Order> orders的JSON并尝试手动解析它：
JsonObject testOrder = parser.parse("{\n" +
" \"orders\": [\n" +
" {\n" +
" \"user\": {\n" +
" \"userName\": \"Admin\",\n" +
" \"password\": \"password\",\n" +
" \"address\": \"University Road\",\n" +
" \"postcode\": {\n" +
" \"postcodeName\": \"SO17 1BJ\",\n" +
" \"latLong\": {\n" +
" \"lon\": 0.0,\n" +
" \"lat\": 0.0\n" +
" },\n" +
" \"distance\": 0,\n" +
" \"updateListeners\": []\n" +
" },\n" +
" \"updateListeners\": []\n" +
" },\n" +
" \"dishes\": {\n" +
" \"Sushi Roll\": 5,\n" +
" \"Side Rice\": 2\n" +
" },\n" +
" \"name\": \"07/05/2019 10:23:08\",\n" +
" \"updateListeners\": []\n" +
" }\n" +
" ]\n" +
"}").getAsJsonObject();
client.orders = gson.fromJson(testOrder, new TypeToken<ArrayList<Order>>(){}.getType()));
但是这也不起作用（错误略有不同-Expected BEGIN_ARRAY but was BEGIN_OBJECT）。
编辑：
Order.java
package comp1206.sushi.common;
import java.io.Serializable;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.HashMap;
import java.util.Map;
import comp1206.sushi.common.Order;
public class Order extends Model implements Serializable {
private String status;
private User user;
private HashMap<Dish, Number> dishes = new HashMap<Dish, Number>();
public Order() {
DateTimeFormatter dtf = DateTimeFormatter.ofPattern("dd/MM/YYYY HH:mm:ss");
LocalDateTime now = LocalDateTime.now();
this.name = dtf.format(now);
}
public Order(User user) {
DateTimeFormatter dtf = DateTimeFormatter.ofPattern("dd/MM/YYYY HH:mm:ss");
LocalDateTime now = LocalDateTime.now();
this.name = dtf.format(now);
setUser(user);
}
public Order(User user, Map<Dish, Number> basket) {
DateTimeFormatter dtf = DateTimeFormatter.ofPattern("dd/MM/YYYY HH:mm:ss");
LocalDateTime now = LocalDateTime.now();
this.name = dtf.format(now);
setUser(user);
basket.forEach((k,v)->addDishes(k,v));
}
public Number getDistance() {
return 1;
}
@Override
public String getName() {
return this.name;
}
public String getStatus() {
return status;
}
public void setStatus(String status) {
notifyUpdate("status",this.status,status);
this.status = status;
}
public void setUser(User user) {
this.user = user;
}
public User getUser() {
return this.user;
}
public void addDishes(Dish dish, Number quantity) {
// may need to call notifyUpdate?
dishes.put(dish, quantity);
}
public void editDishes(Dish dish, Number quantity) {
dishes.replace(dish, quantity);
}
public void clearDishes() {
dishes.clear();
}
public Number getCost() {
int total = 0;
for (Map.Entry<Dish, Number> entry : dishes.entrySet()) {
int temptotal1 = (int) entry.getKey().getPrice();
int temptotal2 = (int) entry.getValue();
total += (temptotal1*temptotal2);
}
return total;
}
public Map<Dish, Number> getOrderContents() {
return dishes;
}
}
Postcode.java：
package comp1206.sushi.common;
import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;
import comp1206.sushi.common.Postcode;
public class Postcode extends Model implements Serializable {
private static final long serialVersionUID = -2179416792423154920L;
private String postcodeName;
private Map<String,Double> latLong;
private Number distance;
public Postcode(String code) {
this.postcodeName = code;
calculateLatLong();
this.distance = Integer.valueOf(0);
}
public Postcode(String code, Restaurant restaurant) {
this.postcodeName = code;
calculateLatLong();
calculateDistance(restaurant);
}
@Override
public String getName() {
return this.postcodeName;
}
public void setName(String name) {
this.postcodeName = name;
}
public Number getDistance() {
return this.distance;
}
public Map<String,Double> getLatLong() {
return this.latLong;
}
protected void calculateDistance(Restaurant restaurant) {
//This function needs implementing
Postcode destination = restaurant.getLocation();
this.distance = Integer.valueOf(0);
}
protected void calculateLatLong() {
//This function needs implementing
this.latLong = new HashMap<String,Double>();
latLong.put("lat", 0d);
latLong.put("lon", 0d);
this.distance = new Integer(0);
}
}
答案 0 :(得分：0)
所以我认为您的问题出在这里：
"dishes": {
"Sushi Roll": 5,
"Side Rice": 2
}
它尝试调用顺序addDishes(Dish dish, Number quantity)的方法，但失败了，因为它具有"Sushi Roll"而不是代表Dish的整个对象。您需要更新Json而不是字符串，以具有与Dish的构造函数匹配的对象。像这样：
"dishes": {
{"name":"Sushi Roll","description":"", "price":0.0, "restockThreshold": 0, "restockAmount":0}: 5,
{"name":"Side Rice","description":"", "price":0.0, "restockThreshold": 0, "restockAmount":0}: 2
}
通常，在与Json打交道时，您需要遵循一些规则。