SpringBoot初始教程之统一异常处理详解

1.介绍

在日常开发中发生了异常，往往是需要通过一个统一的异常处理处理所有异常，来保证客户端能够收到友好的提示。SpringBoot在页面发生异常的时候会自动把请求转到/error，SpringBoot内置了一个BasicErrorController对异常进行统一的处理，当然也可以自定义这个路径

application.yaml

server:
 port: 8080
 error:
 path: /custom/error

BasicErrorController提供两种返回错误一种是页面返回、当你是页面请求的时候就会返回页面，另外一种是json请求的时候就会返回json错误

 @RequestMapping(produces = "text/html")
 public ModelAndView errorHtml(HttpServletRequest request,
   HttpServletResponse response) {
  HttpStatus status = getStatus(request);
  Map<String, Object> model = Collections.unmodifiableMap(getErrorAttributes(
    request, isIncludeStackTrace(request, MediaType.TEXT_HTML)));
  response.setStatus(status.value());
  ModelAndView modelAndView = resolveErrorView(request, response, status, model);
  return (modelAndView == null ? new ModelAndView("error", model) : modelAndView);
 }

 @RequestMapping
 @ResponseBody
 public ResponseEntity<Map<String, Object>> error(HttpServletRequest request) {
  Map<String, Object> body = getErrorAttributes(request,
    isIncludeStackTrace(request, MediaType.ALL));
  HttpStatus status = getStatus(request);
  return new ResponseEntity<Map<String, Object>>(body, status);
 }

分别会有如下两种返回

{
 "timestamp": 1478571808052,
 "status": 404,
 "error": "Not Found",
 "message": "No message available",
 "path": "/rpc"
}

2.通用Exception处理

通过使用@ControllerAdvice来进行统一异常处理，@ExceptionHandler(value = Exception.class)来指定捕获的异常

下面针对两种异常进行了特殊处理分别返回页面和json数据，使用这种方式有个局限，无法根据不同的头部返回不同的数据格式，而且无法针对404、403等多种状态进行处理

 @ControllerAdvice
 public class GlobalExceptionHandler {
  public static final String DEFAULT_ERROR_VIEW = "error";
  @ExceptionHandler(value = CustomException.class)
  @ResponseBody
  public ResponseEntity defaultErrorHandler(HttpServletRequest req, CustomException e) throws Exception {
   return ResponseEntity.ok("ok");
  }
  @ExceptionHandler(value = Exception.class)
  public ModelAndView defaultErrorHandler(HttpServletRequest req, Exception e) throws Exception {
   ModelAndView mav = new ModelAndView();
   mav.addObject("exception", e);
   mav.addObject("url", req.getRequestURL());
   mav.setViewName(DEFAULT_ERROR_VIEW);
   return mav;
  }
 }

3.自定义BasicErrorController 错误处理

在初始介绍哪里提到了BasicErrorController，这个是SpringBoot的默认错误处理，也是一种全局处理方式。咱们可以模仿这种处理方式自定义自己的全局错误处理

下面定义了一个自己的BasicErrorController，可以根据自己的需求自定义errorHtml()和error()的返回值。

 @Controller
 @RequestMapping("${server.error.path:${error.path:/error}}")
 public class BasicErrorController extends AbstractErrorController {
  private final ErrorProperties errorProperties;
  private static final Logger LOGGER = LoggerFactory.getLogger(BasicErrorController.class);
  @Autowired
  private ApplicationContext applicationContext;

  /**
   * Create a new {@link org.springframework.boot.autoconfigure.web.BasicErrorController} instance.
   *
   * @param errorAttributes the error attributes
   * @param errorProperties configuration properties
   */
  public BasicErrorController(ErrorAttributes errorAttributes,
         ErrorProperties errorProperties) {
   this(errorAttributes, errorProperties,
     Collections.<ErrorViewResolver>emptyList());
  }

  /**
   * Create a new {@link org.springframework.boot.autoconfigure.web.BasicErrorController} instance.
   *
   * @param errorAttributes the error attributes
   * @param errorProperties configuration properties
   * @param errorViewResolvers error view resolvers
   */
  public BasicErrorController(ErrorAttributes errorAttributes,
         ErrorProperties errorProperties, List<ErrorViewResolver> errorViewResolvers) {
   super(errorAttributes, errorViewResolvers);
   Assert.notNull(errorProperties, "ErrorProperties must not be null");
   this.errorProperties = errorProperties;
  }

  @Override
  public String getErrorPath() {
   return this.errorProperties.getPath();
  }

  @RequestMapping(produces = "text/html")
  public ModelAndView errorHtml(HttpServletRequest request,
          HttpServletResponse response) {
   HttpStatus status = getStatus(request);
   Map<String, Object> model = Collections.unmodifiableMap(getErrorAttributes(
     request, isIncludeStackTrace(request, MediaType.TEXT_HTML)));
   response.setStatus(status.value());
   ModelAndView modelAndView = resolveErrorView(request, response, status, model);
   insertError(request);
   return modelAndView == null ? new ModelAndView("error", model) : modelAndView;
  }

  @RequestMapping
  @ResponseBody
  public ResponseEntity<Map<String, Object>> error(HttpServletRequest request) {
   Map<String, Object> body = getErrorAttributes(request,
     isIncludeStackTrace(request, MediaType.ALL));
   HttpStatus status = getStatus(request);
   insertError(request);
   return new ResponseEntity(body, status);
  }

  /**
   * Determine if the stacktrace attribute should be included.
   *
   * @param request the source request
   * @param produces the media type produced (or {@code MediaType.ALL})
   * @return if the stacktrace attribute should be included
   */
  protected boolean isIncludeStackTrace(HttpServletRequest request,
            MediaType produces) {
   ErrorProperties.IncludeStacktrace include = getErrorProperties().getIncludeStacktrace();
   if (include == ErrorProperties.IncludeStacktrace.ALWAYS) {
    return true;
   }
   if (include == ErrorProperties.IncludeStacktrace.ON_TRACE_PARAM) {
    return getTraceParameter(request);
   }
   return false;
  }

  /**
   * Provide access to the error properties.
   *
   * @return the error properties
   */
  protected ErrorProperties getErrorProperties() {
   return this.errorProperties;
  }
 }

SpringBoot提供了一种特殊的Bean定义方式，可以让我们容易的覆盖已经定义好的Controller,原生的BasicErrorController是定义在ErrorMvcAutoConfiguration中的

具体代码如下：

 @Bean
 @ConditionalOnMissingBean(value = ErrorController.class, search = SearchStrategy.CURRENT)
 public BasicErrorController basicErrorController(ErrorAttributes errorAttributes) {
  return new BasicErrorController(errorAttributes, this.serverProperties.getError(),
    this.errorViewResolvers);
 }

可以看到这个注解@ConditionalOnMissingBean 意思就是定义这个bean 当 ErrorController.class 这个没有定义的时候， 意思就是说只要我们在代码里面定义了自己的ErrorController.class时，这段代码就不生效了，具体自定义如下：

 @Configuration
 @ConditionalOnWebApplication
 @ConditionalOnClass({Servlet.class, DispatcherServlet.class})
 @AutoConfigureBefore(WebMvcAutoConfiguration.class)
 @EnableConfigurationProperties(ResourceProperties.class)
 public class ConfigSpringboot {
  @Autowired(required = false)
  private List<ErrorViewResolver> errorViewResolvers;
  private final ServerProperties serverProperties;

  public ConfigSpringboot(
    ServerProperties serverProperties) {
   this.serverProperties = serverProperties;
  }

  @Bean
  public MyBasicErrorController basicErrorController(ErrorAttributes errorAttributes) {
   return new MyBasicErrorController(errorAttributes, this.serverProperties.getError(),
     this.errorViewResolvers);
  }
 }

在使用的时候需要注意MyBasicErrorController不能被自定义扫描Controller扫描到，否则无法启动。

3.总结

一般来说自定义BasicErrorController这种方式比较实用，因为可以通过不同的头部返回不同的数据格式，在配置上稍微复杂一些，但是从实用的角度来说比较方便而且可以定义通用组件

本文代码：SpringBoot-Learn_jb51.rar

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