通过 RestTemplate 交换不适用于自定义类

Question

我想实现两个微服务之间的通信。为此，在微服务 1 中，我尝试使用 RestTemplate 与微服务 2 交换数据。当我尝试使用 ResponseEntity<Greeting> 时，它不起作用。但是，当我使用ResponseEntity<Object> 时，它确实有效。显然使用第一种方法会好很多，因为我需要 Response 作为Greeting 的实例。

错误信息：

There was an unexpected error (type=Internal Server Error, status=500).
Type definition error: [...Greeting]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: 
Cannot construct instance of `...Greeting` (no Creators, like default constructor, exist):
Cannot deserialize from Object value (no delegate- or property-based Creator) at [Source: (PushbackInputStream); line: 1, column: 2]
org.springframework.http.converter.HttpMessageConversionException:
Type definition error: [simple type, class ...Greeting];
nested exception is .fasterxml.jackson.databind.exc.InvalidDefinitionException:
Cannot construct instance of Greeting` (no Creators, like default constructor, exist):
cannot deserialize from Object value (no delegate- or property-based Creator)

我的问题：我错过了什么？使用Greeting 启动和运行它有什么问题？

代码

在微服务 1 中调用的函数（在 GreetingsController 类中）：

...
@Autowired
private RestTemplate restTemplate;

@Bean
public RestTemplate getRestTemplate() {
    return new RestTemplate();
}

@ResponseBody
public Greeting getGreeting() {
    ....
    HttpHeaders requestHeaders = new HttpHeaders();
    requestHeaders.setContentType(MediaType.APPLICATION_JSON);
    HttpEntity<String> requestEntity = new HttpEntity<>(requestHeaders);
    // This one does not work
    //ResponseEntity<Greeting> response = restTemplate.exchange("http://localhost:8081/greetings", HttpMethod.GET, requestEntity, Greeting.class, "get");
    // only the following works
    ResponseEntity<Object> response = restTemplate.exchange("http://localhost:8081/greetings", HttpMethod.GET, requestEntity, Object.class, "get");
    ...
    return response.getBody(); 
}

我的问候班：

// some imports here
@Data
@AllArgsConstructor
public class Greeting {
    @NotBlank
    private Integer id;
    @NonNull
    private String text;
}

到目前为止我尝试了什么？

我给了不同的在线教程一个机会。我尝试使用restTemplate.getForObject()、restTemplate.getForEntity() 和restTemplate.exchange()。它们都没有使用Greetings。

Answer 1

试试这个。这应该可以。

    HttpHeaders requestHeaders = new HttpHeaders();
    requestHeaders.setContentType(MediaType.APPLICATION_JSON);            
    HttpEntity<?> requestEntity=new HttpEntity<>(requestHeaders);             
    ParameterizedTypeReference<Greeting> responseType =  new ParameterizedTypeReference<Greeting>() {};    
    ResponseEntity<Greeting> responseEntity = restTemplate.exchange(yourUrl,HttpMethod.GET, requestEntity,responseType); 
    return response.getBody();