解决了。
我有一个关于用Gson写读取对象列表的问题。我有一个Product类。
public class Product {
private String name;
private double price;
private int quantity;
public Product(String name, double price, int quantity) {
this.name = name;
this.price = price;
this.quantity = quantity;
}
......
然后我有一个ProductList的类
public class ProductMenu {
public List<Product> productList;
public ProductMenu() {
productList = new ArrayList<>();
}
......
我在另一个类中初始化我的产品列表。
public class ShoppingOperations {
ProductUpdater import = new ProductUpdaterFromJson();
private ProductMenu shopItems = import.importProducts();
.....
我想做的是,在构造函数中初始化我的产品列表,像这样。
public class ProductMenu {
public List<Product> productList;
public ProductMenu() {
ProductUpdater getList = new ProductUpdaterFromJson();
productList = getList.importProducts();
}
......
这是我的方法,它将对象列表写入.json文件。
public class ProductUpdaterFromJson implements ProductUpdater {
public final static String PATH = "src\\shop\\products\\promenu.json5";
@Override
public void updateWarehouseData(ProductMenu shopItems) {
Gson gson = new GsonBuilder().setPrettyPrinting().create();
try {
Writer writer = new FileWriter(PATH);
gson.toJson(shopItems, writer);
writer.flush();
writer.close();
} catch (IOException e) {
System.out.println("file not found");
e.printStackTrace();
}
}
.json文件是这样的: 它是用Gson生成的。
{
"productList": [
{
"name": "Cheese",
"price": 1.37,
"quantity": 6
},
{
"name": "Milk",
"price": 1.16,
"quantity": 7
},
{
"name": "Milka",
"price": 0.66,
"quantity": 2
},
{
"name": "Potatoes",
"price": 0.7,
"quantity": 7
},
{
"name": "Tea",
"price": 2.1,
"quantity": 4
}
]
}
但是我在读取这个文件的时候出现了错误 构造函数期望的是List,但是我的文件写入器写的是ProductMenu(和产品的列表是一样的),但是我有这个错误--在线程 "main "com.google.gson.JsonSyntaxException中出现异常:java.lang.IllegalStateException: 期待BEGIN_ARRAY,但在第1行第1列路径是STRING $而这是从.json文件中读取的方法。
public final static String PATH = "src\\shop\\products\\promenu.json5";
public List<Product> importProducts2() {
Gson gson = new Gson();
Type userListType = new TypeToken<ArrayList<Product>>(){}.getType();
return gson.fromJson(PATH, userListType);
}
我如何才能解决这个问题。Writer写入,但无法读取文件和初始化产品列表。
我发现的解决方案与成员的帮助。
public class ProductUpdaterFromJson implements ProductUpdater {
public final static String PATH = "src\\shop\\products\\promenu.json5";
@Override
public void updateWarehouseData(ProductMenu shopItems) {
Gson gson = new GsonBuilder().setPrettyPrinting().create();
try {
Writer writer = new FileWriter(PATH);
gson.toJson(shopItems.productList, writer);
writer.flush();
writer.close();
} catch (IOException e) {
System.out.println("file not found");
e.printStackTrace();
}
}
public List<Product> importProducts() {
Gson gson = new Gson();
List<Product> list = null;
try {
Reader reader = new FileReader(PATH);
Type userListType = new TypeToken<ArrayList<Product>>(){}.getType();
list = gson.fromJson(reader, userListType);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
return list;
}
}
还有构造函数
public class ProductMenu {
public List<Product> productList;
public ProductMenu() {
ProductUpdater listFromJson = new ProductUpdaterFromJson();
productList = listFromJson.importProducts();
}
尝试使用ProductMenu作为序列化
public List<Product> importProducts2() {
Gson gson = new Gson();
ProductMenu productMenu = gson.fromJson(new InputStreamReader(...), ProductMenu.class);
return productMenu.productList
}
或将普通列表序列化
gson.toJson(shopItems.productList, writer);