springboot异常处理之404

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源码分析

在springboot中默认有一个异常处理器接口ErrorContorller，该接口提供了getErrorPath()方法，此接口的BasicErrorController实现类实现了getErrorPath()方法，如下：

/* * AbstractErrorController是ErrorContoller的实现类 */ @Controller @RequestMapping("${server.error.path:${error.path:/error}}") public class BasicErrorController extends AbstractErrorController { private final ErrorProperties errorProperties; ... @Override public String getErrorPath() { return this.errorProperties.getPath(); }@RequestMapping(produces = MediaType.TEXT_HTML_VALUE) 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) ? modelAndView : new ModelAndView("error", model); }@RequestMapping public ResponseEntity<Map<String, Object>> error(HttpServletRequest request) { HttpStatus status = getStatus(request); if (status == HttpStatus.NO_CONTENT) { return new ResponseEntity<>(status); } Map<String, Object> body = getErrorAttributes(request, isIncludeStackTrace(request, MediaType.ALL)); return new ResponseEntity<>(body, status); } .... }

errorProperties类定义如下：

public class ErrorProperties {/** * Path of the error controller. */ @Value("${error.path:/error}") private String path = "/error"; ... }

由此可见，springboot中默认有一个处理/error映射的控制器，有error和errorHtml两个方法的存在，它可以处理来自浏览器页面和来自机器客户端（app应用）的请求。

当用户请求不存在的url时，dispatcherServlet会交由ResourceHttpRequestHandler映射处理器来处理该请求，并在handlerRequest方法中，重定向至/error映射，代码如下：

@Override public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// For very general mappings (e.g. "/") we need to check 404 first Resource resource = getResource(request); if (resource == null) { logger.debug("Resource not found"); response.sendError(HttpServletResponse.SC_NOT_FOUND); // 404 return; } ... }

getResource(request)会调用this.resolverChain.resolveResource(request, path, getLocations())方法，getLocations()方法返回结果如下：

接着程序会执行到getResource(pathToUse, location)方法如下：

@Nullable protected Resource getResource(String resourcePath, Resource location) throws IOException { // 新建一个resource对象，url为 location + resourcePath，判断此对象（文件）是否存在 Resource resource = location.createRelative(resourcePath); if (resource.isReadable()) { if (checkResource(resource, location)) { return resource; } else if (logger.isWarnEnabled()) { Resource[] allowedLocations = getAllowedLocations(); logger.warn("Resource path \"" + resourcePath + "\" was successfully resolved " + "but resource \"" +resource.getURL() + "\" is neither under the " + "current location \"" + location.getURL() + "\" nor under any of the " + "allowed locations " + (allowedLocations != null ? Arrays.asList(allowedLocations) : "[]")); } } return null; }