在 Spring Boot Webflux 中管理 NullPointerException

Question

我的代码从 Flux 元素库（已创建）中调用 Mono 元素。包括带有“getJobById”的@Repository 类和@Component 类“Handler”来处理getAll、getJobById、post、put、delete 等请求。如果我输入错误的 id - 无法处理异常并收到 NullPointerException 错误。 我想捕获异常。

错误：

java.lang.NullPointerException: null at com.javasampleapproach.webflux.repo.impl.JobClientRepositoryImpl.getJobById(JobClientRepositoryImpl.java:32) ~[classes/:na]
    at com.javasampleapproach.webflux.functional.handler.JobClientHandler.getJobById(JobClientHandler.java:52) ~[classes/:na]

已经试过了：

@ControllerAdvice
public class ClientExceptionController  {
@ExceptionHandler(value = ClientNotfoundException.class)
public ResponseEntity<Object> exception(ClientNotfoundException exception) {return new ResponseEntity<>("Id not found", HttpStatus.NOT_FOUND);}

+

public class ClientNotfoundException extends NullPointerException{
    public ClientNotfoundException() {}
    public ClientNotfoundException(String s) {
        super(s);
    }

and in Handler and Repository classes:

if(jobClientRepository.getJobById(jobId).equals(null)) throw new ClientNotfoundException();

我也试过这样：

 Mono<JobClient> jobMono = jobClientRepository.getJobById(jobId)
.onErrorResume(e->Mono.empty());
 @Component
    public Mono<ServerResponse> getJobById(ServerRequest request) {
            long jobId = Long.valueOf(request.pathVariable("id"));
            Mono<ServerResponse> notFound = ServerResponse.notFound().build();

我试过这个：

  if(jobClientRepository.getJobById(jobId).equals(null)) throw new ClientNotfoundException();

此处出现错误：

Mono<JobClient> jobMono = jobClientRepository.getJobById(jobId).onErrorResume(e->Mono.empty());
return jobMono.flatMap(job -> ServerResponse.ok().contentType(MediaType.APPLICATION_JSON).body(fromObject(job))).switchIfEmpty(notFound).onErrorResume(ClientNotfoundException.class, e -> notFound);

@Repository 
@Override
public Mono<JobClient> getJobById(Long id)  {if(jobStores.get(id).equals(null)) throw new ClientNotfoundException();
return Mono.just(jobStores.get(id)).onErrorResume(e -> Mono.error(new ClientNotfoundException("Correct ID is required"+e)));

Answer 1

您需要将常规编程与反应式编程分开。试试这个。

@Repository 
@Override
public Mono<JobClient> getJobById(Long id)  {
    return Optional.ofNullable(jobStore.get(id))
            .map(Mono::just)
            .orElseGet(Mono::empty);
}

//Then call it
getJobById(1L).map(jobClient -> ServerResponse.ok()
            .contentType(MediaType.APPLICATION_JSON)
            .syncBody(jobClient)
        ).switchIfEmpty(Mono.error(ClientNotfoundException::new));

不要运行在移动设备上编写的代码。

Answer 2

试试这个：

@Repository 
@Override
public Mono<JobClient> getJobById(Long id)  {
    if(jobStores.get(id) == null) throw new ClientNotfoundException();
    return Mono.just(jobStores.get(id)).onErrorResume(e -> Mono.error(new ClientNotfoundException("Correct ID is required"+e)));
}

在 java 中，你可以避免NullPointerException，首先检查给定对象是否为空，然后继续调用它的方法

if (obj != null) {
    obj.doSomething();
}