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 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> error(HttpServletRequest request) {

HttpStatus status = getStatus(request);

if (status == HttpStatus.NO_CONTENT) {

return new ResponseEntity<>(status);

}

Map 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;

}

在resource.isReadable()中，程序会在locations目录中寻找path目录下文件，由于不存在，返回null。

最终也就导致程序重定向至/error映射，如果是来自浏览器的请求，也就会返回/template/error/404.html页面,所以对于404请求，只需要在template目录下新建error目录，放入404页面即可。

使用注意在springboot4.x中我们可以自定义ControllerAdvice注解 + ExceptionHandler注解来助理不同错误类型的异常，但在springboot中404异常和拦截器异常由spring自己处理。