如果返回类型是list，那么如何在春季引导中返回getmapping中的字符串

Question

@GetMapping("/library/book/{genre}")
private List<Library> getBookByGenre(@PathVariable("genre") String genre) {
   if (libraryService.getBookByGenre(genre).isEmpty()) {
       return ;
   } else {
       return libraryService.getBookByGenre(genre);
   }
}

这是我的控制器代码。当没有特定类型的数据时，它返回一个空列表，但我想返回一个字符串，该字符串显示“在邮递员中找不到这种类型的数据”。

/*
* 提示：该行代码过长，系统自动注释不进行高亮。一键复制会移除系统注释 
* "trace": "org.springframework.web.client.HttpClientErrorException$NotFound: 404 : [{\"errorCode\":404,\"errorMessage\":\"No data found for this genre\"}]\r\n\tat org.springframework.web.client.HttpClientErrorException.create(HttpClientErrorException.java:113)\r\n\tat org.springframework.web.client.DefaultResponseErrorHandler.handleError(DefaultResponseErrorHandler.java:186)\r\n\tat org.springframework.web.client.DefaultResponseErrorHandler.handleError(DefaultResponseErrorHandler.java:125)\r\n\tat org.springframework.web.client.ResponseErrorHandler.handleError(ResponseErrorHandler.java:63)\r\n\tat org.springframework.web.client.RestTemplate.handleResponse(RestTemplate.java:819)\r\n\tat org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:777)\r\n\tat org.springframework.web.client.RestTemplate.execute(RestTemplate.java:711)\r\n\tat org.springframework.web.client.RestTemplate.exchange(RestTemplate.java:602)\r\n\tat com.example.student.adapter.outbound.Repository.getBookbyGenre(Repository.java:64)\r\n\tat com.example.student.adapter.outbound.Repository$$FastClassBySpringCGLIB$$c14fd765.invoke(<generated>)\r\n\tat org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)\r\n\tat org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:779)\r\n\tat org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)\r\n\tat org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:750)\r\n\tat org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:137)\r\n\tat org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)\r\n\tat org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:750)\r\n\tat org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:692)\r\n\tat com.example.student.adapter.outbound.Repository$$EnhancerBySpringCGLIB$$c8c38c72.getBookbyGenre(<generated>)\r\n\tat com.example.student.core.service.StudentService.getBookbyGenre(StudentService.java:43)\r\n\tat com.example.student.adapter.inbound.StudentController.getBookbyGenre(StudentController.java:30)\r\n\tat sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)\r\n\tat sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)\r\n\tat sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)\r\n\tat java.lang.reflect.Method.invoke(Method.java:498)\r\n\tat org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205)\r\n\tat org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:150)\r\n\tat org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:117)\r\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895)\r\n\tat org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808)\r\n\tat org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)\r\n\tat org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1067)\r\n\tat org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963)\r\n\tat org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)\r\n\tat org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898)\r\n\tat javax.servlet.http.HttpServlet.service(HttpServlet.java:655)\r\n\tat org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)\r\n\tat javax.servlet.http.HttpServlet.service(HttpServlet.java:764)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)\r\n\tat org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)\r\n\tat org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)\r\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)\r\n\tat org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)\r\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)\r\n\tat org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)\r\n\tat org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)\r\n\tat org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)\r\n\tat org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197)\r\n\tat org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)\r\n\tat org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:540)\r\n\tat org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135)\r\n\tat org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)\r\n\tat org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)\r\n\tat org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:357)\r\n\tat org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:382)\r\n\tat org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)\r\n\tat org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:893)\r\n\tat org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1726)\r\n\tat org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)\r\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)\r\n\tat org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)\r\n\tat org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)\r\n\tat java.lang.Thread.run(Thread.java:748)\r\n",
*/
    "message": "404 : [{\"errorCode\":404,\"errorMessage\":\"No data found for this genre\"}]",
    "path": "/Student/library/genre/lol"

Answer 1

最好的选择是抛出一个自定义异常：

@ResponseStatus(HttpStatus.NOT_FOUND)
public class NoBooksFoundException extends RuntimeException {

    private static final String ERROR_MESSAGE = "No data found for this genre";

    public NoBooksFoundException() {
        super(ERROR_MESSAGE);
    }
}

@GetMapping("/library/book/{genre}")
private List<Library> getBookByGenre(@PathVariable("genre") String genre) {
   if (libraryService.getBookByGenre(genre).isEmpty()) {
       throw NoBooksFoundException();
   } else {
       return libraryService.getBookByGenre(genre);
   }
}

然后将有一个全局异常处理程序来处理它：

@ControllerAdvice
public class GlobalExceptionHandler extends ResponseEntityExceptionHandler {

    @ExceptionHandler(value = {NoBooksFoundException.class})
    public ResponseEntity<Object> handleCustomExceptions(Exception exception, WebRequest webRequest) {
        HttpStatus errorCode = this.resolveAnnotatedResponseStatus(exception);
        return this.handleExceptionInternal(exception, new ErrorInfo(errorCode.value(), exception.getMessage()), new HttpHeaders(), errorCode, webRequest);
    }

    private HttpStatus resolveAnnotatedResponseStatus(Exception exception) {
        ResponseStatus annotation = findMergedAnnotation(exception.getClass(), ResponseStatus.class);

        return Objects.nonNull(annotation) ? annotation.value() : HttpStatus.INTERNAL_SERVER_ERROR;
    }
}

是ErrorInfo，如下所示：

public class ErrorInfo {
    private final int errorCode;
    private final String errorMessage;

    // getters, setters, constructor
}