错误信息：Exception in thread main java.lang.ClassCastException: com.alibaba.fastjson.JSONObject cannot be cast to com.xh.demo.UserDO泛型类：@Datapublic class ResultSetDTO { private Integer totalSize; private Integer count; }
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<T> {
private Integer totalSize;
private Integer count;
private List<T> 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<UserDO> resultSetDTO = new ResultSetDTO<UserDO>();
resultSetDTO.setTotalSize(10);
resultSetDTO.setCount(10);
List<UserDO> 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<XsyUserDO> resultSet = JSON.parseObject(jsonString, ResultSetDTO.class);
List<UserDO> 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<JSONObject> 类型，不是 ArrayList<UserDO> 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<UserDO> records = JSON.parseArray(parseObject.getString("records"), UserDO.class);
for (UserDO user : records) {
System.out.println(user.getName());
}
// 方法二
ResultSetDTO<XsyUserDO> resultSet = JSON.parseObject(jsonString, ResultSetDTO.class);
List<UserDO> records = JSONObject.parseArray(resultSet.getRecords().toString(), UserDO.class);
for (UserDO user : records) {
System.out.println(user.getName());
}
// 方法三
ResultSetDTO<XsyUserDO> resultSet = JSON.parseObject(jsonString, new TypeReference<ResultSetDTO<UserDO>>(){});
List<UserDO> records = resultSet.getRecords();
for (UserDO user : records){
System.out.println(user.getName());}
}
错误信息：Exception in thread main java.lang.ClassCastException: com.alibaba.fastjson.JSONObject cannot be cast to com.xh.demo.UserDO泛型类：@Datapublic class ResultSetDTO { private Integer totalSize; private Integer count; }
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<T> {
private Integer totalSize;
private Integer count;
private List<T> 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<UserDO> resultSetDTO = new ResultSetDTO<UserDO>();
resultSetDTO.setTotalSize(10);
resultSetDTO.setCount(10);
List<UserDO> 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<XsyUserDO> resultSet = JSON.parseObject(jsonString, ResultSetDTO.class);
List<UserDO> 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<JSONObject> 类型，不是 ArrayList<UserDO> 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<UserDO> records = JSON.parseArray(parseObject.getString("records"), UserDO.class);
for (UserDO user : records) {
System.out.println(user.getName());
}
// 方法二
ResultSetDTO<XsyUserDO> resultSet = JSON.parseObject(jsonString, ResultSetDTO.class);
List<UserDO> records = JSONObject.parseArray(resultSet.getRecords().toString(), UserDO.class);
for (UserDO user : records) {
System.out.println(user.getName());
}
// 方法三
ResultSetDTO<XsyUserDO> resultSet = JSON.parseObject(jsonString, new TypeReference<ResultSetDTO<UserDO>>(){});
List<UserDO> records = resultSet.getRecords();
for (UserDO user : records){
System.out.println(user.getName());}
}
