Customized exception handling returns an error page
a) PassErrorMvcAutoConfigurationAutomatic configuration class to understand the principle of exception handling
There are four core processing methods in this automatic configuration class, as follows:
1）ErrorPageCustomizer
//第一步：系统出现错误以后来到error请求进行处理
private static class ErrorPageCustomizer implements ErrorPageRegistrar, Ordered {
private final ServerProperties properties;
protected ErrorPageCustomizer(ServerProperties properties) {
this.properties = properties;
}
@Override
public void registerErrorPages(ErrorPageRegistry errorPageRegistry) {
ErrorPage errorPage = new ErrorPage(this.properties.getServletPrefix()
+ this.properties.getError().getPath());//系统出现错误以后来到error请求进行处理
/*
@Value("${error.path:/error}")
private String path = "/error";
public String getPath() {
return this.path;
}
*/
errorPageRegistry.addErrorPages(errorPage);
}
@Override
public int getOrder() {
return 0;
}
}
2）BasicErrorController
//第二步：处理/error请求，根据请求判断响应格式
@Controller
@RequestMapping("${server.error.path:${error.path:/error}}")//处理/error请求
public class BasicErrorController extends AbstractErrorController {
@RequestMapping(produces = "text/html")//产生html类型的数据；浏览器发送的请求来到这个方法处理
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());
//去哪个页面作为错误页面；包含页面地址和页面内容
ModelAndView modelAndView = resolveErrorView(request, response, status, model);
return (modelAndView == null ? new ModelAndView("error", model) : modelAndView);
}
@RequestMapping
@ResponseBody //产生json数据，其他客户端来到这个方法处理；
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);
}
3）DefaultErrorViewResolver
//第三步：根据视图解析跳转页面
public class DefaultErrorViewResolver implements ErrorViewResolver, Ordered {
private static final Map<Series, String> SERIES_VIEWS;
static {
Map<Series, String> views = new HashMap<Series, String>();
views.put(Series.CLIENT_ERROR, "4xx");
views.put(Series.SERVER_ERROR, "5xx");
SERIES_VIEWS = Collections.unmodifiableMap(views);
}
@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);//调用resolve方法
}
return modelAndView;
}
private ModelAndView resolve(String viewName, Map<String, Object> model) {
//默认SpringBoot可以去找到一个页面？ error/404
String errorViewName = "error/" + viewName;
//模板引擎可以解析这个页面地址就用模板引擎解析
TemplateAvailabilityProvider provider = this.templateAvailabilityProviders
.getProvider(errorViewName, this.applicationContext);
if (provider != null) {
//模板引擎可用的情况下返回到errorViewName指定的视图地址
return new ModelAndView(errorViewName, model);
}
//模板引擎不可用，就在静态资源文件夹下找errorViewName对应的页面 error/404.html
return resolveResource(errorViewName, model);
}
}
4）DefaultErrorViewResolver
//在错误页面共享信息
@Order(Ordered.HIGHEST_PRECEDENCE)
public class DefaultErrorAttributes
implements ErrorAttributes, HandlerExceptionResolver, Ordered {
@Override
public Map<String, Object> getErrorAttributes(RequestAttributes requestAttributes,
boolean includeStackTrace) {
Map<String, Object> errorAttributes = new LinkedHashMap<String, Object>();
errorAttributes.put("timestamp", new Date());
addStatus(errorAttributes, requestAttributes);
addErrorDetails(errorAttributes, requestAttributes, includeStackTrace);
addPath(errorAttributes, requestAttributes);
return errorAttributes;
}
private void addStatus(Map<String, Object> errorAttributes,
RequestAttributes requestAttributes) {
Integer status = getAttribute(requestAttributes,
"javax.servlet.error.status_code");
if (status == null) {
errorAttributes.put("status", 999);
errorAttributes.put("error", "None");
return;
}
errorAttributes.put("status", status);
try {
errorAttributes.put("error", HttpStatus.valueOf(status).getReasonPhrase());
}
catch (Exception ex) {
// Unable to obtain a reason
errorAttributes.put("error", "Http Status " + status);
}
}
}
