项目中出行java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to xxx(实体类)异常的原因：
参数如下：

{
	"appId": 101,
	"tokenId": 201,
	"sign": 1,
	"userId": 45,
    "traineeInfo":"{\"name\":\"马继涛\",\"gender\":1,\"birth\":\"19930906\",\"idCardNo\":\"2012050614\",\"school\":\"北京第三中学\",\"contact\":\"18866666666\"}",
    "relationship":"母子",
	"orders": [{
			"amount": 200,
            "totalAmount":200,
            "payMethod":2,
            "isTeacherQualified":"true",
			"courseCode": "51bf186450d8bc11ebb49b005056a7973c",
			"orderId": 20210708006,
            "merRecvInfo":"{\"merchantPayBal\":\"21343323\"}",
            "teacherInfo":"{\"isTeacherCertain\":1, \"teacherName\":\"王XX\", \"isTeacherQualified\":1 }"
		},
        {
			"amount": 300,
            "totalAmount":300,
            "payMethod":1,
            "isTeacherQualified":"false",
			"courseCode": "87f06c1211d94f11eb9c8f68545a856785",
			"orderId": 20210708005,
            "merRecvInfo":"{\"merchantPayBal\":\"1112222333\"}",
            "teacherInfo":"{\"isTeacherCertain\":1, \"teacherName\":\"马XX\", \"isTeacherQualified\":0 }"
		}
	]

}

后端如果用BeanUtils.populate(contractInfo, body);会导致orders内部结构是List<LinkedHashMap>而不是List,遇到这种情况，不要着急，我们不是拿不到它的值，而是跟我们预期的不太理想，那我们就想办法让它达到预期的效果，就要用到fastjson来处理了。

List<OrderDo> orderDos = JSON.parseArray(JSON.toJSONString(contractInfo.getOrders()), OrderDo.class);
contractInfo.setOrders(orderDos);

JSON、java对象、list之间的相互转换

1：pom引入

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.2.44</version>
</dependency>

2 常见转换

//1. List<Map<String, String>> list 转 JSONArray
JSONArray jsonArray = JSONArray.parseArray(JSONObject.toJSONString(list));  /**list为 List<Map<String, String>>**/
//2.JSON 转成List
List<ChannelItem> channelItemList  = JSON.parseArray(itemJson,ChannelItem.class);  /** itemJson: JsonArray  ChannelItem ： 对象bean类**/
//3. Map<String, String> 转 JSON
JSONObject itemJSONObj = JSONObject.parseObject(JSON.toJSONString(itemMap)); /** itemMap 为 Map<String, String>**/
//4.JSON 转 Map<String, String>
Map<String, Object> itemMap = JSONObject.toJavaObject(itemJSONObj, Map.class);  /** itemJSONObj  JSONObject**/
//5. JSONObject 转 JavaBean
Student student = JSON.parseObject(JSONObjectStr, new TypeReference<Student>() {});  //因为JSONObject继承了JSON，所以这样也是可以的
//6.JSONObject 转 Map<String , String>
Map<String ,String> param =  JSONObject.parseObject(jsonObject.toJSONString(), new TypeReference<Map<String, String>>(){});

json转换来自于：https://blog.csdn.net/sinat_35626559/article/details/78919736

标签：lang,Map,java,JSONObject,List,JSON,list,ClassCastException
来源： https://blog.csdn.net/qq_34254462/article/details/118570231