我使用Spring MVC为一个简单的JSON API,使用@ResponseBody的方法,如下所示。(我已经有了一个直接生成JSON的服务层。)
@RequestMapping(value = "/matches/{matchId}", produces = "application/json")
@ResponseBody
public String match(@PathVariable String matchId) {
String json = matchService.getMatchJson(matchId);
if (json == null) {
// TODO: how to respond with e.g. 400 "bad request"?
}
return json;
}
在给定的场景中,响应HTTP 400错误的最简单、最干净的方法是什么?
我确实遇到过这样的方法:
return new ResponseEntity(HttpStatus.BAD_REQUEST);
...但我不能在这里使用它,因为我的方法的返回类型是字符串,而不是ResponseEntity。
另一种方法是使用@ExceptionHandler和@ControllerAdvice将所有处理程序集中在同一个类中。如果不是,则必须将处理程序方法放入希望为其管理异常的每个控制器中。
你的处理程序类:
@ControllerAdvice
public class MyExceptionHandler extends ResponseEntityExceptionHandler {
@ExceptionHandler(MyBadRequestException.class)
public ResponseEntity<MyError> handleException(MyBadRequestException e) {
return ResponseEntity
.badRequest()
.body(new MyError(HttpStatus.BAD_REQUEST, e.getDescription()));
}
}
您的自定义异常:
public class MyBadRequestException extends RuntimeException {
private String description;
public MyBadRequestException(String description) {
this.description = description;
}
public String getDescription() {
return this.description;
}
}
现在,您可以从任何控制器抛出异常,并且可以在通知类中定义其他处理程序。
正如在一些回答中提到的,可以为您想要返回的每个HTTP状态创建一个异常类。我不喜欢为每个项目的每个状态创建一个类的想法。这是我想出的替代方案。
创建接受HTTP状态的通用异常
创建一个Controller Advice异常处理程序
让我们来看看代码
package com.javaninja.cam.exception;
import org.springframework.http.HttpStatus;
/**
* The exception used to return a status and a message to the calling system.
* @author norrisshelton
*/
@SuppressWarnings("ClassWithoutNoArgConstructor")
public class ResourceException extends RuntimeException {
private HttpStatus httpStatus = HttpStatus.INTERNAL_SERVER_ERROR;
/**
* Gets the HTTP status code to be returned to the calling system.
* @return http status code. Defaults to HttpStatus.INTERNAL_SERVER_ERROR (500).
* @see HttpStatus
*/
public HttpStatus getHttpStatus() {
return httpStatus;
}
/**
* Constructs a new runtime exception with the specified HttpStatus code and detail message.
* The cause is not initialized, and may subsequently be initialized by a call to {@link #initCause}.
* @param httpStatus the http status. The detail message is saved for later retrieval by the {@link
* #getHttpStatus()} method.
* @param message the detail message. The detail message is saved for later retrieval by the {@link
* #getMessage()} method.
* @see HttpStatus
*/
public ResourceException(HttpStatus httpStatus, String message) {
super(message);
this.httpStatus = httpStatus;
}
}
然后我创建一个控制器通知类
package com.javaninja.cam.spring;
import com.javaninja.cam.exception.ResourceException;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.ExceptionHandler;
/**
* Exception handler advice class for all SpringMVC controllers.
* @author norrisshelton
* @see org.springframework.web.bind.annotation.ControllerAdvice
*/
@org.springframework.web.bind.annotation.ControllerAdvice
public class ControllerAdvice {
/**
* Handles ResourceExceptions for the SpringMVC controllers.
* @param e SpringMVC controller exception.
* @return http response entity
* @see ExceptionHandler
*/
@ExceptionHandler(ResourceException.class)
public ResponseEntity handleException(ResourceException e) {
return ResponseEntity.status(e.getHttpStatus()).body(e.getMessage());
}
}
使用它
throw new ResourceException(HttpStatus.BAD_REQUEST, "My message");
http://javaninja.net/2016/06/throwing-exceptions-messages-spring-mvc-controller/
这里有一个不同的方法。创建一个带有@ResponseStatus注解的自定义Exception,如下所示。
@ResponseStatus(code = HttpStatus.NOT_FOUND, reason = "Not Found")
public class NotFoundException extends Exception {
public NotFoundException() {
}
}
需要的时候扔出去。
@RequestMapping(value = "/matches/{matchId}", produces = "application/json")
@ResponseBody
public String match(@PathVariable String matchId) {
String json = matchService.getMatchJson(matchId);
if (json == null) {
throw new NotFoundException();
}
return json;
}
我将稍微改变一下实现:
首先,我创建了一个UnknownMatchException:
@ResponseStatus(HttpStatus.NOT_FOUND)
public class UnknownMatchException extends RuntimeException {
public UnknownMatchException(String matchId) {
super("Unknown match: " + matchId);
}
}
注意@ResponseStatus的使用,它将被Spring的ResponseStatusExceptionResolver识别。如果抛出异常,它将创建具有相应响应状态的响应。(我还擅自将状态代码更改为404 - Not Found,我认为这更适合这个用例,但您可以坚持使用HttpStatus。BAD_REQUEST如果你喜欢。)
接下来,我将更改MatchService具有以下签名:
interface MatchService {
public Match findMatch(String matchId);
}
最后,我将更新控制器并委托给Spring的MappingJackson2HttpMessageConverter来自动处理JSON序列化(如果您将Jackson添加到类路径中,并将@EnableWebMvc或<mvc:annotation-driven />添加到配置中,则默认添加JSON序列化。请参阅参考文档):
@RequestMapping(value = "/matches/{matchId}", produces = MediaType.APPLICATION_JSON_VALUE)
@ResponseBody
public Match match(@PathVariable String matchId) {
// Throws an UnknownMatchException if the matchId is not known
return matchService.findMatch(matchId);
}
注意,将域对象与视图对象或DTO对象分离是非常常见的。这可以通过添加一个小型DTO工厂来轻松实现,该工厂返回可序列化的JSON对象:
@RequestMapping(value = "/matches/{matchId}", produces = MediaType.APPLICATION_JSON_VALUE)
@ResponseBody
public MatchDTO match(@PathVariable String matchId) {
Match match = matchService.findMatch(matchId);
return MatchDtoFactory.createDTO(match);
}