错误信息

Exception in thread "main" java.lang.ClassCastException: com.alibaba.fastjson.JSONObject cannot be cast to com.xh.demo.UserDO

泛性类

@Data

public class ResultSetDTO {

private Integer totalSize;

private Integer count;

private List records;

}

实体类

@Data

public class UserDO {

private String id;

private String name;

}

Demo测试

public class AppDemo {

public static void main(String[] args) {

ResultSetDTO resultSetDTO = new ResultSetDTO();

resultSetDTO.setTotalSize(10);

resultSetDTO.setCount(10);

List list = new ArrayList<>();

UserDO userDO = null;

for (int i = 10000; i < 10003; i++) {

userDO = new UserDO();

userDO.setId(i + "");

userDO.setName("TEST_" + i);

list.add(userDO);

}

resultSetDTO.setRecords(list);

String jsonString = JSON.toJSONString(resultSetDTO);

System.out.println(jsonString);

ResultSetDTO resultSet = JSON.parseObject(jsonString, ResultSetDTO.class);

List records = resultSet.getRecords();

// 转换是报异常

for (UserDO user : records) {

System.out.println(user.getName());

}

}

debuge 调试时发现 resultSet.getRecords(); 返回的是 ArrayList 类型，不是 ArrayList 类型。由于类型引用必须强制指定目标对象，因此违背了 FastJson 规范，所以报：Exception in thread "main" java.lang.ClassCastException: com.alibaba.fastjson.JSONObject cannot be cast to com.xh.demo.UserDO。

解决方法

// 方法一

JSONObject parseObject = JSON.parseObject(jsonString);

List records = JSON.parseArray(parseObject.getString("records"), UserDO.class);

for (UserDO user : records) {

System.out.println(user.getName());

}

// 方法二

ResultSetDTO resultSet = JSON.parseObject(jsonString, ResultSetDTO.class);

List records = JSONObject.parseArray(resultSet.getRecords().toString(), UserDO.class);

for (UserDO user : records) {

System.out.println(user.getName());

}

// 方法三

ResultSetDTO resultSet = JSON.parseObject(jsonString, new TypeReference>(){});

List records = resultSet.getRecords();

for (UserDO user : records){

System.out.println(user.getName());}

}

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