线程“main”中的异常 java.lang.ClassCastException：class org.json.simple.JSONObject 无法转换为 class java.util.List

Question

我想读取一个 json 文件并将其存储到对象中，以便我可以在我的逻辑中使用它。 经过多次尝试，我能够将 json 提取到 Map 中。但我希望将值存储在 object 中，而不是 map 中。

下面是我尝试获取它并以货币 object 存储的代码。

package com.springboot.currencyExchange;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.*;
import com.springboot.currencyExchange.model.*;
import com.springboot.currencyExchange.model.Currency;

import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import com.springboot.currencyExchange.service.MarketStrategyImpl;

@SpringBootApplication
public class CurrencyExchangeApplication {

    @SuppressWarnings({ "rawtypes", "unchecked" })
    public static void main(String[] args) throws FileNotFoundException, IOException, ParseException {
        // SpringApplication.run(CurrencyExchangeApplication.class, args);

        Object obj = new JSONParser().parse(new FileReader(
                "*absolute path*\AvailableMarket.json"));

        JSONObject jobj = (JSONObject) obj;
        JSONArray ja = (JSONArray) jobj.get("currencies");
        Iterator<Currency> itr1 = null;
        Iterator<CurrentMarket> itr2 = ja.iterator();
        while (itr2.hasNext()) {
            itr1 = (Iterator<Currency>) (((List) itr2.next()).iterator());
            while (itr1.hasNext()) {
                Currency pair = itr1.next();
            //  System.out.println(pair.getKey() + " : " + pair.getValue());

            }
        }

    }

}

下面是我的 JSON 文件

{
    "currencies": [
        {
            "currencyName": "Euro",
            "price": 80
        },
        {
            "currencyName": "Pound",
            "price": 90
        },
        {
            "currencyName": "USD",
            "price": 75
        }
    ],
    "trades": [
        {
            "take": "Euro",
            "give": "USD"
        },
        {
            "take": "USD",
            "give": "Pound"
        }
    ]
}

下面是我创建的用于存储 JSON 值的 POJO 类：

package com.springboot.currencyExchange.model;

import java.util.List;

public class CurrentMarket {

    public List<Currency> currency;
    public List<Trade> trade;

    public CurrentMarket() {
        super();
    }

    public List<Currency> getCurrency() {
        return currency;
    }

    public void setCurrency(List<Currency> currency) {
        this.currency = currency;
    }

    public List<Trade> getTrade() {
        return trade;
    }

    public CurrentMarket(List<Currency> currency, List<Trade> trade) {
        super();
        this.currency = currency;
        this.trade = trade;
    }

    @Override
    public String toString() {
        return "CurrentMarket [currency=" + currency + ", trade=" + trade + "]";
    }

    public void setTrade(List<Trade> trade) {
        this.trade = trade;
    }

}

货币.java

package com.springboot.currencyExchange.model;

import java.io.Serializable;

@SuppressWarnings("serial")
public class Currency implements Serializable{
    String currencyName;
    Double price;

    public String getCurrencyName() {
        return currencyName;
    }

    public void setCurrencyName(String currencyName) {
        this.currencyName = currencyName;
    }

    public Double getPrice() {
        return price;
    }

    public void setPrice(Double price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "Currency [currencyName=" + currencyName + ", price=" + price + "]";
    }

    public Currency(String currencyName, Double price) {
        super();
        this.currencyName = currencyName;
        this.price = price;
    }
}

贸易.java

package com.springboot.currencyExchange.model;

import java.util.ArrayList;

public class Trade {
    ArrayList<String> take;
    ArrayList<String> give;

    public ArrayList<String> getTake() {
        return take;
    }

    public Trade(ArrayList<String> take, ArrayList<String> give) {
        super();
        this.take = take;
        this.give = give;
    }

    public void setTake(ArrayList<String> take) {
        this.take = take;
    }

    public ArrayList<String> getGive() {
        return give;
    }

    public void setGive(ArrayList<String> give) {
        this.give = give;
    }

}

我还尝试了 GSON 方法，但无法以所需格式获取它。

以下是我在当前设置中收到的错误消息：

Exception in thread "main" java.lang.ClassCastException: class org.json.simple.JSONObject cannot be cast to class java.util.List (org.json.simple.JSONObject is in unnamed module of loader 'app'; java.util.List is in module java.base of loader 'bootstrap')
    at com.springboot.currencyExchange.CurrencyExchangeApplication.main(CurrencyExchangeApplication.java:32)

我不确定我还能如何进行。 任何帮助，将不胜感激。

Answer 1

您首先需要进行一些更改。

正如 Abrar Ansari 所说，将变量的类型从 ArrayList 更改为 Trade class 中的 String。同时将 CurrencyMarket class 中的货币和贸易变量重命名为货币和交易。 在所有 model 类中将所有字段设为私有，并确保在所有 model 类中都有默认构造函数。 然后使用 Jackson 的 ObjectMapper 将 json 文件反序列化为 CurrentMarket 类型的 object：

ObjectMapper objectMapper = new ObjectMapper();
CurrentMarket currentMarket = objectMapper.readValue(new ClassPathResource("AvailableMarket.json").getFile(),
        CurrentMarket.class);