Spring Boot默認啓動的時候會注入一個專門處理異常的自動配置類:
@Configuration
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class })
// Load before the main WebMvcAutoConfiguration so that the error View is available
@AutoConfigureBefore(WebMvcAutoConfiguration.class)
@EnableConfigurationProperties({ ServerProperties.class, ResourceProperties.class })
public class ErrorMvcAutoConfiguration {
private final ServerProperties serverProperties;
private final List<ErrorViewResolver> errorViewResolvers;
public ErrorMvcAutoConfiguration(ServerProperties serverProperties,
ObjectProvider<List<ErrorViewResolver>> errorViewResolversProvider) {
this.serverProperties = serverProperties;
this.errorViewResolvers = errorViewResolversProvider.getIfAvailable();
}
@Bean
@ConditionalOnMissingBean(value = ErrorAttributes.class, search = SearchStrategy.CURRENT)
public DefaultErrorAttributes errorAttributes() {
return new DefaultErrorAttributes(
this.serverProperties.getError().isIncludeException());
}
@Bean
@ConditionalOnMissingBean(value = ErrorController.class, search = SearchStrategy.CURRENT)
public BasicErrorController basicErrorController(ErrorAttributes errorAttributes) {
return new BasicErrorController(errorAttributes, this.serverProperties.getError(),
this.errorViewResolvers);
}
//.................
}
查看源碼發現其會注入一個默認的BasicErrorController來處理異常，所以主要看這個Controller：
@Controller
@RequestMapping("${server.error.path:${error.path:/error}}")
public class BasicErrorController extends AbstractErrorController {
@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<>(body, status);
}
}
這裏根據返回類型不同分爲了兩個方法，errorHtml方法返回ModelAndView，error方法返回ResponseEntity，熟悉SpringMvc的同學應該對這兩個類不陌生。其中errorHtml方法中的resolveErrorView方法由父類實現：
public abstract class AbstractErrorController implements ErrorController {
private final ErrorAttributes errorAttributes;
private final List<ErrorViewResolver> errorViewResolvers;
protected ModelAndView resolveErrorView(HttpServletRequest request,
HttpServletResponse response, HttpStatus status, Map<String, Object> model) {
for (ErrorViewResolver resolver : this.errorViewResolvers) {
ModelAndView modelAndView = resolver.resolveErrorView(request, status, model);
if (modelAndView != null) {
return modelAndView;
}
}
return null;
}
}
這裏具體是由ErrorViewResolver去處理的，這裏當SpringBoot啓動的時候會自動裝載一個默認的ErrorViewResolver進來，其還實現了Ordered接口，優先級最低，如下：
public class DefaultErrorViewResolver implements ErrorViewResolver, Ordered {
private static final Map<Series, String> SERIES_VIEWS;
static {
Map<Series, String> views = new EnumMap<>(Series.class);
views.put(Series.CLIENT_ERROR, "4xx");
views.put(Series.SERVER_ERROR, "5xx");
SERIES_VIEWS = Collections.unmodifiableMap(views);
}
private ApplicationContext applicationContext;
private final ResourceProperties resourceProperties;
private final TemplateAvailabilityProviders templateAvailabilityProviders;
private int order = Ordered.LOWEST_PRECEDENCE;
@Override
public ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status,
Map<String, Object> model) {
ModelAndView modelAndView = resolve(String.valueOf(status), model);
if (modelAndView == null && SERIES_VIEWS.containsKey(status.series())) {
modelAndView = resolve(SERIES_VIEWS.get(status.series()), model);
}
return modelAndView;
}
private ModelAndView resolve(String viewName, Map<String, Object> model) {
String errorViewName = "error/" + viewName;
TemplateAvailabilityProvider provider = this.templateAvailabilityProviders
.getProvider(errorViewName, this.applicationContext);
if (provider != null) {
return new ModelAndView(errorViewName, model);
}
return resolveResource(errorViewName, model);
}
private ModelAndView resolveResource(String viewName, Map<String, Object> model) {
for (String location : this.resourceProperties.getStaticLocations()) {
try {
Resource resource = this.applicationContext.getResource(location);
resource = resource.createRelative(viewName + ".html");
if (resource.exists()) {
return new ModelAndView(new HtmlResourceView(resource), model);
}
}
catch (Exception ex) {
}
}
return null;
}
}
ResourceProperties中包含了默認的四個靜態資源路徑：
@ConfigurationProperties(prefix = "spring.resources", ignoreUnknownFields = false)
public class ResourceProperties {
private static final String[] CLASSPATH_RESOURCE_LOCATIONS = {
"classpath:/META-INF/resources/", "classpath:/resources/",
"classpath:/static/", "classpath:/public/" };
/**
* Locations of static resources. Defaults to classpath:[/META-INF/resources/,
* /resources/, /static/, /public/].
*/
private String[] staticLocations = CLASSPATH_RESOURCE_LOCATIONS;
}
所以分析源碼可以發現，SpringBoot會依次從"classpath:/META-INF/resources/", "classpath:/resources/","classpath:/static/", "classpath:/public/"這四個目錄下面尋找是否存在error目錄，然後根據錯誤碼errorCode去尋找具體的errorCode.html頁面，如果找到則構造成ModelAndView對象返回，我們可以通過添加自定義ErrorViewResolver可以構造自己的異常目錄：
@Component
public class CustomErrorViewResolver implements ErrorViewResolver,Ordered,ApplicationContextAware {
private final String CUSTOM_RESOURCE_LOCATION = "classpath:/static/custom_error/";
private ApplicationContext applicationContext;
@Override
public int getOrder() {
return 0;
}
/**
* 返回null的時候會由後續的ErrorViewResolver去解析
* @see org.springframework.boot.autoconfigure.web.servlet.error.AbstractErrorController#resolveErrorView(HttpServletRequest, HttpServletResponse, HttpStatus, Map)
* @param request
* @param status
* @param model
* @return
*/
@Override
public ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status, Map<String, Object> model) {
if(status.equals(HttpStatus.INTERNAL_SERVER_ERROR)){
try {
Resource resource = this.applicationContext.getResource(CUSTOM_RESOURCE_LOCATION);
resource = resource.createRelative(String.valueOf(status) + ".html");
if (resource.exists()) {
return new ModelAndView(new HtmlResourceView(resource), model);
}
} catch (IOException e) {
e.printStackTrace();
}
}
return null;
}
@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
this.applicationContext = applicationContext;
}
class HtmlResourceView implements View {
private Resource resource;
HtmlResourceView(Resource resource) {
this.resource = resource;
}
@Override
public String getContentType() {
return MediaType.TEXT_HTML_VALUE;
}
@Override
public void render(Map<String, ?> model, HttpServletRequest request,
HttpServletResponse response) throws Exception {
response.setContentType(getContentType());
FileCopyUtils.copy(this.resource.getInputStream(),
response.getOutputStream());
}
}
}
還可以使用常規的Spring MVC特性，比如@ExceptionHandler方法和@ControllerAdvice解析需要處理的異常。其他未處理的異常由ErrorController來解析。
@ControllerAdvice
public class CustomControllerAdvice extends ResponseEntityExceptionHandler {
@ExceptionHandler(CustomException.class)
@ResponseBody
ResponseEntity<?> handleControllerException(HttpServletRequest request, Throwable ex) {
HttpStatus status = getStatus(request);
Map<String, Object> map = new HashMap<>();
map.put("status",status.value());
map.put("msg",ex.getMessage());
return new ResponseEntity<>(map, status);
}
private HttpStatus getStatus(HttpServletRequest request) {
Integer statusCode = (Integer) request.getAttribute("javax.servlet.error.status_code");
if (statusCode == null) {
return HttpStatus.INTERNAL_SERVER_ERROR;
}
return HttpStatus.valueOf(statusCode);
}
}