使用RestAssured+Jackson反序列化时遇无构造器异常求助

我正在学习RestAssured框架，尝试结合Jackson与Lombok注解进行开发。已创建用于请求和响应的CreateUser模型类：

@Data
@Builder
@AllArgsConstructor
public class CreateUser {
        private String job;
        private String id;
        private String name;

        @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'")
        private Timestamp createdAt;
}

我在以下方法中尝试以createUser对象作为请求体发送POST请求，并将响应字符串反序列化为CreateUser对象返回：

public static CreateUser createUser(String name, String job) throws IOException {
    CreateUser createUser = CreateUser.builder()
            .name(name)
            .job(job)
            .build();

    String jsonResponse =  given()
            .when()
            .baseUri(baseUri)
            .contentType(ContentType.JSON)
            .body(createUser)
            .post("/users")
            .body()
            .asString();

    ObjectMapper mapper = new ObjectMapper();

    return mapper.readValue(jsonResponse, CreateUser.class);
}

运行时出现如下异常：

Cannot construct instance of `test.model.CreateUser` (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator)
 at [Source: (String)"{"job":"leader","id":"398","name":"morpheus","createdAt":"2023-07-10T18:04:35.486Z"}"; line: 1, column: 2]
com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `test.model.CreateUser` (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator)
 at [Source: (String)"{"job":"leader","id":"398","name":"morpheus","createdAt":"2023-07-10T18:04:35.486Z"}"; line: 1, column: 2]
    at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:67)
    at com.fasterxml.jackson.databind.DeserializationContext.reportBadDefinition(DeserializationContext.java:1452)
    at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1028)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1297)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:326)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:159)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4014)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3005)

解决方法 #

异常核心原因是Jackson找不到CreateUser类的合适构造方法完成反序列化，以下是三种可行解决方案：

方法1：添加无参构造函数

在CreateUser类上添加@NoArgsConstructor注解，让Lombok生成无参构造函数，Jackson默认会通过无参构造创建对象再赋值：

@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor // 添加该注解
public class CreateUser {
        private String job;
        private String id;
        private String name;

        @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'")
        private Timestamp createdAt;
}

方法2：启用Jackson的Lombok模块支持

引入jackson-datatype-lombok依赖，让Jackson识别Lombok生成的Builder：

1. 添加Maven依赖（版本需与项目中Jackson版本一致）：

<dependency>
    <groupId>com.fasterxml.jackson.datatype</groupId>
    <artifactId>jackson-datatype-lombok</artifactId>
    <version>你的Jackson版本号</version>
</dependency>

2. 配置ObjectMapper注册Lombok模块：

ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new LombokModule());
return mapper.readValue(jsonResponse, CreateUser.class);

方法3：给全参构造函数添加Jackson注解

通过@JsonCreator和@JsonProperty让Jackson直接使用全参构造函数实例化对象：

@Data
@Builder
@AllArgsConstructor(onConstructor = @__(@JsonCreator))
public class CreateUser {
        @JsonProperty("job")
        private String job;
        @JsonProperty("id")
        private String id;
        @JsonProperty("name")
        private String name;

        @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'")
        @JsonProperty("createdAt")
        private Timestamp createdAt;
}

内容的提问来源于stack exchange，提问作者anusree v