json 转换成 带泛型的对象 , 报错问题解决

场景

当我们将json转换成带泛型的对象时, 再获取该泛型属性时会报错
java.util.LinkedHashMap cannot be cast to xxx(你的泛型的类型)

解决办法

1 先将该泛型属性的值, 转为json字符串
2 再将该json字符串, 转成泛型的类型

错误演示

// bean 类
public class HttpResult {
    private boolean success;
    private T result;
    private String error;
    
    // get,set ,tostring
}

public static void main(String[] args) throws Exception {
	String json = "你的json字符串";
	// json转bean
	ObjectMapper mapper = new ObjectMapper();
	HttpResult response = mapper.readValue(stockInfoResponseJson, HttpResult.class);
	
	System.out.println(response); // 此时不会报错
	System.out.println(response.getResult()); // 此时也不会报错
	QueryResult queryResult = response.getResult(); // 此时会报错
}

解决办法演示

public static void main(String[] args) throws Exception {
	String json = "你的json字符串";
	// json转bean
	ObjectMapper mapper = new ObjectMapper();
	HttpResult response = mapper.readValue(stockInfoResponseJson, HttpResult.class);
	
	// 开始解决 报错问题 --------------------------------------
	// 泛型 属性 转 json字符串
	String conStr= mapper .writeValueAsString(response.getResult());
	//  json字符串 再转 泛型 属性
	QueryResult queryResult = mapper.readValue(conStr, QueryResult.class);
	System.out.println(queryResult); // 此时就没问题了
}

json & bean 互转

上述转换过程 , 可以使用下面工具类 JsonUtil 中的 conveterObject 方法来实现
QueryResult queryResult = JsonUtil.conveterObject(response.getResult(), QueryResult.class);

package com.nspark.utils;

import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;
import java.util.Map;

/**
 * @Description: json 工具类
 * @Author: North Spark
 */
public class JsonUtil {


    /**
     * 对象转JSON字符串
     */
    public static String object2Json(Object obj) {
        String result = null;
        try {
            ObjectMapper objectMapper = new ObjectMapper();
            result = objectMapper.writeValueAsString(obj);
        } catch (IOException e) {
            e.printStackTrace();
        }
        return result;
    }

    /**
     * @Function: bean 转 map
     */
    public static Map object2Map(Object obj) {
        String object2Json = object2Json(obj);
        Map result = jsonToMap(object2Json);
        return result;
    }

    /**
     * JSON字符串转Map对象
     */
    public static Map jsonToMap(String json) {
        return json2Object(json, Map.class);
    }

    /**
     * JSON转Object对象
     */
    public static  T json2Object(String json, Class cls) {
        T result = null;
        try {
            ObjectMapper objectMapper = new ObjectMapper();
            result = objectMapper.readValue(json, cls);
        } catch (IOException e) {
            e.printStackTrace();
        }

        return result;
    }

    /**
     * @Process : 泛型 转 json , json 再转 bean
     * @Function: 泛型属性, 转成指定的类
     */
    public static  T conveterObject(Object srcObject, Class destObjectType) {
        String jsonContent = object2Json(srcObject);
        return json2Object(jsonContent, destObjectType);
    }

}