RestTemplate反序列化嵌套List异常：如何实现完整映射？

使用RestTemplate将JSON映射为Java对象时，仅能反序列化得到reservations为空数组的LockerReservations对象；当reservations列表包含数据时，反序列化直接失败。

相关代码与数据 #

LockerReservations实体类 #

@Data
@AllArgsConstructor
@NoArgsConstructor
public class LockerReservations {
    Locker locker;
    List<Reservation> reservations;
}

返回的JSON数据 #

[
    {
        "locker": {
            "id": 0,
            "size": "S"
        },
        "reservations": []
    },
    {
        "locker": {
            "id": 1,
            "size": "S"
        },
        "reservations": []
    },
    {
        "locker": {
            "id": 4,
            "size": "S"
        },
        "reservations": [
            {
                "id": 17,
                "start": "2023-03-14T06:37:07.006",
                "end": "2023-03-14T12:37:07.006",
                "user": {
                    "id": 1,
                    "name": "Kiemoon"
                },
                "locker": {
                    "id": 4,
                    "size": "S"
                }
            },
            {
                "id": 36,
                "start": "2023-03-14T14:37:07.006",
                "end": "2023-03-14T15:37:07.006",
                "user": {
                    "id": 1,
                    "name": "Kiemoon"
                },
                "locker": {
                    "id": 4,
                    "size": "S"
                }
            }
        ]
    } 
]

RestTemplate调用代码 #

public List<LockerReservations> getReservationsCheck2(Size size, LocalDateTime start, LocalDateTime end) {

    HttpHeaders httpHeaders = new HttpHeaders();
    httpHeaders.setContentType(MediaType.APPLICATION_JSON);
    Map<String, Object> sizeTimeMap = new HashMap<>();
    sizeTimeMap.put("size", size.toString());
    sizeTimeMap.put("start", start.toString());
    sizeTimeMap.put("end", end.toString());
    HttpEntity<Map<String, Object>> httpEntity = new HttpEntity<>(sizeTimeMap, httpHeaders);
    LockerReservations[] exchange = restTemplate.postForObject(url + "reservationsCheck", httpEntity, LockerReservations[].class);
    return Arrays.asList(exchange);
}

1. 完善所有嵌套实体类的序列化配置 #

确保Locker、Reservation、User类都满足以下要求：

• 有无参构造器（通过@NoArgsConstructor注解生成）
• 字段具备可访问性（通过@Data生成getter/setter，或直接设为public）
• 日期字段适配JSON格式

示例实体类实现：

// Locker类
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Locker {
    private Integer id;
    private String size;
}

// User类
@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private Integer id;
    private String name;
}

// Reservation类
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Reservation {
    private Integer id;
    @JsonProperty("start")
    private LocalDateTime startTime;
    @JsonProperty("end")
    private LocalDateTime endTime;
    private User user;
    private Locker locker;
}

2. 配置RestTemplate的Jackson消息转换器 #

Jackson默认不支持LocalDateTime类型的序列化/反序列化，需添加JavaTimeModule并配置对应日期格式：

@Bean
public RestTemplate restTemplate() {
    RestTemplate restTemplate = new RestTemplate();
    
    MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
    ObjectMapper objectMapper = new ObjectMapper();
    // 注册Java 8时间处理模块
    objectMapper.registerModule(new JavaTimeModule());
    // 禁用时间戳格式，使用字符串格式化
    objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
    // 匹配JSON中的日期格式
    objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS"));
    
    converter.setObjectMapper(objectMapper);
    // 替换默认的Jackson转换器
    restTemplate.getMessageConverters().replaceAll(c -> 
        c instanceof MappingJackson2HttpMessageConverter ? converter : c
    );
    
    return restTemplate;
}

3. 异常排查与调试 #

在调用代码中捕获异常并打印详细栈信息，精准定位反序列化失败的具体字段：

public List<LockerReservations> getReservationsCheck2(Size size, LocalDateTime start, LocalDateTime end) {
    try {
        HttpHeaders httpHeaders = new HttpHeaders();
        httpHeaders.setContentType(MediaType.APPLICATION_JSON);
        Map<String, Object> sizeTimeMap = new HashMap<>();
        sizeTimeMap.put("size", size.toString());
        sizeTimeMap.put("start", start.toString());
        sizeTimeMap.put("end", end.toString());
        HttpEntity<Map<String, Object>> httpEntity = new HttpEntity<>(sizeTimeMap, httpHeaders);
        LockerReservations[] exchange = restTemplate.postForObject(url + "reservationsCheck", httpEntity, LockerReservations[].class);
        return Arrays.asList(exchange);
    } catch (RestClientException e) {
        e.printStackTrace();
        throw new RuntimeException("反序列化失败", e);
    }
}

4. 字段匹配验证 #

确保实体类字段名与JSON中的键完全一致，若存在命名差异，使用@JsonProperty显式指定映射关系（例如JSON键为start，实体类字段为startTime时，添加@JsonProperty("start")注解）。

内容的提问来源于stack exchange，提问作者Kiemoon