SpringBoot2.1.4中的错误处理机制 SpringBoot2.1.4中的错误处理机制

SpringBoot 2.1.4 错误处理机制

SpringBoot错误机制原理

SpringBoot 2.1.3 错误处理机制

引用的问题做个标记
错误处理机制

SpringBoot 2.1.4 错误处理机制 springboot的自动配置中帮我们配置了相关的错误处理组件，例如访问一个不存在的页面，就会出现下面的错误页面，上面也会显示相应的信息

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在Postman软件中模拟移动端访问，会获取如下响应的json数据：

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可以发现springboot的错误处理机制很好的适应了不同客户端访问，浏览器返回页面，移动端返回json，那这背后springboot是如何处理的，显示的页面我想自己设计，或者返回的这些信息我们自己能够定制吗？

SpringBoot错误机制原理

springboot版本：2.1.4.RELEASE

1、默认错误页面生成机制
当我们在访问一个不存在的路径时，会出现上面的错误页面，这个页面不是我们自己创建的，而是由springboot帮我们生成的，那下面我们首先弄清楚这个默认的错误页面（Whitelabel Error Page）是怎么生成的。
1.1 springboot关于error的自动配置
在package org.springframework.boot.autoconfigure.web.servlet.error包下有如下的类：

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BasicErrorController、AbstractErrorController：错误请求控制器
DefaultErrorViewResolver：错误视图解析器
ErrorMvcAutoConfiguration：error的自动配置类

【SpringBoot2.1.4中的错误处理机制】ErrorMvcAutoConfiguration
在这个配置类中注册了一些组件：

@Bean@ConditionalOnMissingBean(value = https://www.it610.com/article/{ErrorAttributes.class},search = SearchStrategy.CURRENT)// 关于error错误信息的相关类public DefaultErrorAttributes errorAttributes() {return new DefaultErrorAttributes(this.serverProperties.getError().isIncludeException()); }@Bean@ConditionalOnMissingBean(value = {ErrorController.class},search = SearchStrategy.CURRENT)// 处理错误请求的控制器public BasicErrorController basicErrorController(ErrorAttributes errorAttributes) {return new BasicErrorController(errorAttributes, this.serverProperties.getError(), this.errorViewResolvers); }@Bean// 错误页面定制器public ErrorMvcAutoConfiguration.ErrorPageCustomizer errorPageCustomizer() {return new ErrorMvcAutoConfiguration.ErrorPageCustomizer(this.serverProperties, this.dispatcherServletPath); }

第一步：ErrorPageCustomizer

private static class ErrorPageCustomizer implements ErrorPageRegistrar, Ordered {private final ServerProperties properties; private final DispatcherServletPath dispatcherServletPath; protected ErrorPageCustomizer(ServerProperties properties, DispatcherServletPath dispatcherServletPath) {this.properties = properties; this.dispatcherServletPath = dispatcherServletPath; }public void registerErrorPages(ErrorPageRegistry errorPageRegistry) {// getPath()获取到一个路径“/error”ErrorPage errorPage = new ErrorPage(this.dispatcherServletPath.getRelativePath(this.properties.getError().getPath())); // 关键点：这里讲将/error的errorPage注册到了servlet，在发生异常时就会转发到/errorerrorPageRegistry.addErrorPages(new ErrorPage[]{errorPage}); }public int getOrder() {return 0; }}

注意上面的注释，这里是为什么发生错误就会发起/error，很多博客都未说明，当然这里没有讨论其内部原理。
第二步：BasicErrorController
在错误发生后，发起 “/error” 请求，那这个 “/error” 就会由上面已经注册的BasicErrorController 接收处理。

@Controller // 表明是个控制器@RequestMapping({"${server.error.path:${error.path:/error}}"}) // 映射的路径：/errorpublic class BasicErrorController extends AbstractErrorController {private final ErrorProperties errorProperties; public BasicErrorController(ErrorAttributes errorAttributes, ErrorProperties errorProperties) {this(errorAttributes, errorProperties, Collections.emptyList()); }public BasicErrorController(ErrorAttributes errorAttributes, ErrorProperties errorProperties, List errorViewResolvers) {super(errorAttributes, errorViewResolvers); Assert.notNull(errorProperties, "ErrorProperties must not be null"); this.errorProperties = errorProperties; }public String getErrorPath() {return this.errorProperties.getPath(); } // 处理浏览器的请求@RequestMapping(produces = {"text/html"})public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response) {HttpStatus status = this.getStatus(request); Map model = Collections.unmodifiableMap(this.getErrorAttributes(request, this.isIncludeStackTrace(request, MediaType.TEXT_HTML))); response.setStatus(status.value()); ModelAndView modelAndView = this.resolveErrorView(request, response, status, model); return modelAndView != null ? modelAndView : new ModelAndView("error", model); } // 处理移动端的请求@RequestMappingpublic ResponseEntity error(HttpServletRequest request) {Map body = this.getErrorAttributes(request, this.isIncludeStackTrace(request, MediaType.ALL)); HttpStatus status = this.getStatus(request); return new ResponseEntity(body, status); }protected boolean isIncludeStackTrace(HttpServletRequest request, MediaType produces) {IncludeStacktrace include = this.getErrorProperties().getIncludeStacktrace(); if (include == IncludeStacktrace.ALWAYS) {return true; } else {return include == IncludeStacktrace.ON_TRACE_PARAM ? this.getTraceParameter(request) : false; }}protected ErrorProperties getErrorProperties() {return this.errorProperties; }}

这里可以解决一个疑惑，springboot怎么区分是浏览器还是移动端的，主要看这个方法的注解 produces={“text/html”} ，表示响应的数据是以html形式返回，这样当浏览器访问时就会调用这个方法

@RequestMapping(produces = {"text/html"})public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response){ ...

客户端访问时就会调用下面的error方法。

@RequestMappingpublic ResponseEntity error(HttpServletRequest request) {

下面再来具体分析默认错误页面如何生成，还是来看到errorHTML方法：

public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response) {// 获取错误状态码，封装到HttpStatus里面HttpStatus status = this.getStatus(request); // 获取错误信息，以map形式返回，这个后面我们具体来看，到底我们能获取到哪些数据Map model = Collections.unmodifiableMap(this.getErrorAttributes(request, this.isIncludeStackTrace(request, MediaType.TEXT_HTML))); // 设置响应体中状态码response.setStatus(status.value()); // 关键点：这里就是在创建视图对象ModelAndView modelAndView = this.resolveErrorView(request, response, status, model); return modelAndView != null ? modelAndView : new ModelAndView("error", model); }

下面来看这个resolveErrorView方法，这个方法是父类AbstractErrorController 中的：

protected ModelAndView resolveErrorView(HttpServletRequest request, HttpServletResponse response, HttpStatus status, Map model) { // errorViewResolvers是一个list，存放ErrorViewResolver对象Iterator var5 = this.errorViewResolvers.iterator(); ModelAndView modelAndView; // 遍历集合do {if (!var5.hasNext()) {return null; }ErrorViewResolver resolver = (ErrorViewResolver)var5.next(); // 关键点：解析器对象进行视图解析modelAndView = resolver.resolveErrorView(request, status, model); } while(modelAndView == null); return modelAndView; }

这里的resolveErrorView方法属于DefaultErrorViewResolver：

public ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status, Map model) {// 调用下面的方法解析视图，传入参数为错误状态码，错误信息的mapModelAndView modelAndView = this.resolve(String.valueOf(status.value()), model); if (modelAndView == null && SERIES_VIEWS.containsKey(status.series())) {modelAndView = this.resolve((String)SERIES_VIEWS.get(status.series()), model); }return modelAndView; }private ModelAndView resolve(String viewName, Map model) {// 定义视图名，这里我们可以确定视图名：error/错误码，例如：error/404，String errorViewName = "error/" + viewName; // 这里结合上面的errorViewName，其实就是在template目录下的error目录进行查找// 我们默认情况下是没有error目录，这里的provide最终值为null，代码较多就不一一展示，有兴趣的可以跟下去TemplateAvailabilityProvider provider = this.templateAvailabilityProviders.getProvider(errorViewName, this.applicationContext); // 根据判定，这里会接着调用下面的resolveResource方法return provider != null ? new ModelAndView(errorViewName, model) : this.resolveResource(errorViewName, model); }private ModelAndView resolveResource(String viewName, Map model) {//getStaticLocations()获取的是静态资源路径："classpath:/META-INF/resources/", "classpath:/resources/","classpath:/static/", "classpath:/public/"String[] var3 = this.resourceProperties.getStaticLocations(); int var4 = var3.length; // 遍历上面的4个静态资源路径for(int var5 = 0; var5 < var4; ++var5) {String location = var3[var5]; try {Resource resource = this.applicationContext.getResource(location); // 创建resource对象，例如error/404.htmlresource = resource.createRelative(viewName + ".html"); // 查找在对应静态资源目录下是否有上面的这个资源对象，有就创建视图对象if (resource.exists()) {return new ModelAndView(new DefaultErrorViewResolver.HtmlResourceView(resource), model); }} catch (Exception var8) {; }}// 都没找到就返回null，默认情况下是不存在error目录的，所以这里最终返回nullreturn null; }

当resolveResource方法执行完返回null，resolve方法也就返回null，在回到resolveErrorView

public ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status, Map model) {// 调用下面的方法解析视图，传入参数为错误状态码，错误信息的mapModelAndView modelAndView = this.resolve(String.valueOf(status.value()), model); // 上面分析得到modelAndView的值为null，下面的if中SERIES_VIEWS.containsKey(status.series())是在判断错误码的首位是否为1,2，3,4，5，这个大家下去可以跟一下if (modelAndView == null && SERIES_VIEWS.containsKey(status.series())) {modelAndView = this.resolve((String)SERIES_VIEWS.get(status.series()), model); }// if里面的resolve方法分析跟上面一样，默认情况下是没有4xx.html/5xx.html页面文件的，所以最终这里返回nullreturn modelAndView; }

这个resolveErrorView方法执行完后，我们就可以回到最开始处理 “/error” 请求的errorHtml方法了

@RequestMapping(produces = {"text/html"} )public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response) {HttpStatus status = this.getStatus(request); Map model = Collections.unmodifiableMap(this.getErrorAttributes(request, this.isIncludeStackTrace(request, MediaType.TEXT_HTML))); response.setStatus(status.value()); ModelAndView modelAndView = this.resolveErrorView(request, response, status, model); // modelAnView根据上面的分析其值为nullreturn modelAndView != null ? modelAndView : new ModelAndView("error", model); }

当modelAndView为null时，将会执行'new ModelAndView(“error”, model),那这个“error”又是什么呢？看下面WhitelabelErrorViewConfiguration 里面有个组件其 name就是error，这个组件是StaticView，就是一个View，里面的视图渲染方法render中的内容就是最开始我们看到的那个错误页面的内容。

@Conditional({ErrorMvcAutoConfiguration.ErrorTemplateMissingCondition.class})protected static class WhitelabelErrorViewConfiguration {private final ErrorMvcAutoConfiguration.StaticView defaultErrorView = new ErrorMvcAutoConfiguration.StaticView(); protected WhitelabelErrorViewConfiguration() {}@Bean(name = {"error"})@ConditionalOnMissingBean(name = {"error"})public View defaultErrorView() {return this.defaultErrorView; } ...}private static class StaticView implements View {private static final Log logger = LogFactory.getLog(ErrorMvcAutoConfiguration.StaticView.class); private StaticView() {}public void render(Map model, HttpServletRequest request, HttpServletResponse response) throws Exception {if (response.isCommitted()) {String message = this.getMessage(model); logger.error(message); } else {StringBuilder builder = new StringBuilder(); Date timestamp = (Date)model.get("timestamp"); Object message = model.get("message"); Object trace = model.get("trace"); if (response.getContentType() == null) {response.setContentType(this.getContentType()); }builder.append("Whitelabel Error Page").append("This application has no explicit mapping for /error, so you are seeing this as a fallback.
").append("").append(timestamp).append("").append("There was an unexpected error (type=").append(this.htmlEscape(model.get("error"))).append(", status=").append(this.htmlEscape(model.get("status"))).append(")."); if (message != null) {builder.append("").append(this.htmlEscape(message)).append(""); }if (trace != null) {builder.append("").append(this.htmlEscape(trace)).append(""); }builder.append(""); response.getWriter().append(builder.toString()); }}private String htmlEscape(Object input) {return input != null ? HtmlUtils.htmlEscape(input.toString()) : null; }private String getMessage(Map model) {Object path = model.get("path"); String message = "Cannot render error page for request [" + path + "]"; if (model.get("message") != null) {message = message + " and exception [" + model.get("message") + "]"; }message = message + " as the response has already been committed."; message = message + " As a result, the response may have the wrong status code."; return message; }public String getContentType() {return "text/html"; }}

所以，整个大致的过程到此结束了，默认情况下错误请求处理完成后就返回的这个StaticView定义的页面，下图做个基本的梳理。后续再来做自定义错误页面、自定义错误数据的原理分析。

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SpringBoot 2.1.3 错误处理机制
引用的问题做个标记
以前的引用好像在新版本中无法引用了

错误处理机制
其他的程序的类的声明直接用IDEA的提示来用就可以了。
如果还是有错误的话，就进入到lib中看看引用的类的方法就可以了

import org.springframework.boot.autoconfigration.web.DefaultErrorAttributes; //这是以前的import org.springframework.boot.web.servlet.error.DefaultErrorAttributes; //这是现在的

以上为个人经验，希望能给大家一个参考，也希望大家多多支持脚本之家。