我創(chuàng)建了一個轉(zhuǎn)換為另一個類的字段，通過它我得到了json，問題發(fā)生在哪里，但我不明白我做錯了什么User班級public class User extends BaseEntity<Integer> {  private String firstName;  private String lastName;  @Column(name = "username")  private String username;  @Convert(converter = PurshasedProductConverter.class)  private PurshasedProductConverter purshasedProducts;}PurshasedProductConverter班級public class PurshasedProductConverter implements AttributeConverter<PurshasedProduct, String> {  private static final Logger LOG = (Logger) LoggerFactory.getLogger(PurshasedProductConverter.class);  private final ObjectMapper mapper = new ObjectMapper();  @Override  public String convertToDatabaseColumn(PurshasedProduct attribute) {    try {        if (attribute != null)            return mapper.writeValueAsString(attribute);        else        return null;    } catch (JsonProcessingException e) {        LOG.error(e.getMessage(), e);        throw new RuntimeException(e);    }  }  @Override  public PurshasedProduct convertToEntityAttribute(String dbData) {    TypeReference<HashMap<String, String>> typeRef            = new TypeReference<HashMap<String, String>>() {    };    try {        PurshasedProduct purshasedProduct = new PurshasedProduct();        if (dbData != null)            purshasedProduct.strings = mapper.readValue(dbData, typeRef);        return purshasedProduct;    } catch (IOException e) {        LOG.error(e.getMessage(), e);        throw new RuntimeException(e);    }  }}PurshasedProduct班級public class PurshasedProduct {  public Map<String, String> strings = new HashMap<>();  public static PurshasedProduct create(String key, String value) {    PurshasedProduct purshasedProduct = new PurshasedProduct();    purshasedProduct.set(key, value);    return purshasedProduct;  }  public void set(String lang, String text) {    if (text == null || lang == null) {        return;    }    strings.put(lang, text);  }