SpringBoot错误处理----源码解析

1、默认机制

SpringBoot错误处理的自动配置都在ErrorMvcAutoConfiguration中，两大核心机制：

• 1.SpringBoot会自适应处理错误，响应页面或JSON数据；

• 2.SpringMVC的错误处理机制依然保留，MVC处理不了，才会交给SpringBoot进行处理。
  （图片来自尚硅谷）

2、使用@ExceptionHandler标识一个方法，处理用@Controller标注的该类发生的指定错误

（默认只能处理这个类的该指定错误）

// @ExceptionHandler源码
@Target({ElementType.METHOD})     // 指定了该注解仅能用于方法
@Retention(RetentionPolicy.RUNTIME)   //指定了注解会在运行时保留，这允许通过反射在运行时获取对注解的访问
@Documented      //注解应该被包含在生成的 JavaDoc 文档中
@Reflective({ExceptionHandlerReflectiveProcessor.class}) 
public @interface ExceptionHandler {Class<? extends Throwable>[] value() default {};       //它定义了一个名为 value 的属性，其类型是一个 Class 数组，这个数组的元素必须是 Throwable 类或其子类。通过使用这个注解时，可以为 value 属性提供一个 Throwable 类型的数组
}

1）.局部错误处理部分源码

@Controller         //适配服务端渲染    前后不分离模式开始
public class WelcomeController {//来到首页@GetMapping("/")public String index(){int i=10/0;    //制造错误return "index";}@ResponseBody     //返回的字符串应该直接作为 HTTP 响应体的内容，而不是作为视图名称解析。通常用于返回 JSON 或纯文本等非HTML内容@ExceptionHandler(Exception.class)   //传递到value数组中public String handleException(Exception e){return "Ohho~~~，原因："+e.getMessage();}}

2）.测试

• 1.启动项目，浏览器访问http://localhost:8080/

• 2.测试结果（成功处理错误）
  

3、 创建一个全局错误处理类集中处理错误，使用==@ControllerAdvice==注解标注

（这个类是集中处理所有@Controller 发生的错误）

//@ControllerAdvice源码
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component       //标记类为一个 Spring 组件
public @interface ControllerAdvice {@AliasFor(annotation = Component.class,attribute = "value")String name() default "";@AliasFor("basePackages")String[] value() default {};@AliasFor("value")String[] basePackages() default {};Class<?>[] basePackageClasses() default {};Class<?>[] assignableTypes() default {};Class<? extends Annotation>[] annotations() default {};
}

1）.全局错误处理部分源码

@ControllerAdvice        //这个类是集中处理所有@Controller发生的错误
public class GlobalExceptionHandler {@ResponseBody@ExceptionHandler(Exception.class)public String handleException(Exception e){return "Ohho~~~统一处理所有错误，原因："+e.getMessage();}
}

###2）.再创建一个类，使用@Controller注解标注

@Controller
public class HelloController {@GetMapping("/haha")public String haha(){int i = 10/0;        //制造错误return "index";}
}

3）.测试

• 1.启动项目，浏览器访问http://localhost:8080/
• 2.测试结果（成功处理错误）就近原则，执行的是@Controller类中标注了@ExceptionHandler方法的处理：
  
• 3.浏览器访问http://localhost:8080/haha：全局错误处理类进行处理
  

4、SpringMVC错误处理未能处理（上述处理不存在）

第一阶段的处理未解决，错误转发到/error，执行后续处理（图中第一阶段失效，第二阶段处理），以下测试过程中，注释掉上文中的全局和局部处理代码

1、SpringBoot中自动配置的错误处理机制，基于ErrorMvcAutoConfiguration自动配置实现

在ErrorMvcAutoConfiguration自动装配类中，SpringBoot在底层写好一个 ==BasicErrorController==的组件，专门处理/error这个请求，部分源码如下：

@AutoConfiguration(before = WebMvcAutoConfiguration.class) //指定了该自动配置类在 WebMvcAutoConfiguration 之前进行配置
@ConditionalOnWebApplication(type = Type.SERVLET)    //只有在当前应用是一个 Servlet Web 应用时，这个自动配置才会生效
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class })   //只有当类路径中存在 Servlet 和 DispatcherServlet 时，这个自动配置才会生效
@EnableConfigurationProperties({ ServerProperties.class, WebMvcProperties.class }) //启用指定类的配置属性绑定
public class ErrorMvcAutoConfiguration {private final ServerProperties serverProperties; //注入了 ServerProperties 实例。这样的构造方法注入是为了获取应用程序的服务器配置public ErrorMvcAutoConfiguration(ServerProperties serverProperties) {this.serverProperties = serverProperties;  //注入 ServerProperties 实例}//容器中不存在 ErrorAttributes 类型的 Bean 时，才会创建并注册当前方法所返回的 Bean@Bean@ConditionalOnMissingBean(value = ErrorAttributes.class, search = SearchStrategy.CURRENT)public DefaultErrorAttributes errorAttributes() {return new DefaultErrorAttributes();}//在容器中不存在 ErrorController 类型的 Bean 时，才会创建并注册当前方法所返回的 Bean@Bean@ConditionalOnMissingBean(value = ErrorController.class, search = SearchStrategy.CURRENT)public BasicErrorController basicErrorController(ErrorAttributes errorAttributes,ObjectProvider<ErrorViewResolver> errorViewResolvers) {return new BasicErrorController(errorAttributes, this.serverProperties.getError(),errorViewResolvers.orderedStream().toList());}...
}

2、 BasicErrorController组件

SpringBoot中默认的server.error.path=/error，即该类就是处理/error请求的，根据不同类型的请求，如果产生 HTML 内容的请求，匹配public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response) 这个方法；否则其他请求类型，匹配public ResponseEntity<Map<String, Object>> error(HttpServletRequest request)方法。分别进行处理。（只会匹配其中一个，Spring MVC会尝试匹配与请求路径最匹配的RequestMapping）

• 1.部分源码：

@Controller
@RequestMapping("${server.error.path:${error.path:/error}}")
public class BasicErrorController extends AbstractErrorController {private final ErrorProperties errorProperties;/*** Create a new {@link BasicErrorController} instance.* @param errorAttributes the error attributes* @param errorProperties configuration properties*/public BasicErrorController(ErrorAttributes errorAttributes, ErrorProperties errorProperties) {this(errorAttributes, errorProperties, Collections.emptyList());}/*** Create a new {@link BasicErrorController} instance.* @param errorAttributes the error attributes* @param errorProperties configuration properties* @param errorViewResolvers error view resolvers*/public BasicErrorController(ErrorAttributes errorAttributes, ErrorProperties errorProperties,List<ErrorViewResolver> errorViewResolvers) {super(errorAttributes, errorViewResolvers);Assert.notNull(errorProperties, "ErrorProperties must not be null");this.errorProperties = errorProperties;}@RequestMapping(produces = MediaType.TEXT_HTML_VALUE)   //请求类型为HTML 文本public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response) {HttpStatus status = getStatus(request);Map<String, Object> model = Collections.unmodifiableMap(getErrorAttributes(request, getErrorAttributeOptions(request, MediaType.TEXT_HTML)));response.setStatus(status.value());ModelAndView modelAndView = resolveErrorView(request, response, status, model);return (modelAndView != null) ? modelAndView : new ModelAndView("error", model);}@RequestMappingpublic 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, getErrorAttributeOptions(request, MediaType.ALL));return new ResponseEntity<>(body, status);}...
}

• 2.匹配成功之后，错误页面解析的核心代码

  //1、解析错误的自定义视图地址
  ModelAndView modelAndView = resolveErrorView(request, response, status, model);
  //2、如果解析不到错误页面的地址，默认的错误页就是 error
  return (modelAndView != null) ? modelAndView : new ModelAndView("error", model);
  

• 3.在ErrorMvcAutoConfiguration自动装配类中，SpringBoot在底层写好一个 ==DefaultErrorViewResolver==的组件，注入到了容器中

  	@Configuration(proxyBeanMethods = false)@EnableConfigurationProperties({ WebProperties.class, WebMvcProperties.class })static class DefaultErrorViewResolverConfiguration {private final ApplicationContext applicationContext;private final Resources resources;DefaultErrorViewResolverConfiguration(ApplicationContext applicationContext, WebProperties webProperties) {this.applicationContext = applicationContext;this.resources = webProperties.getResources();}@Bean@ConditionalOnBean(DispatcherServlet.class)@ConditionalOnMissingBean(ErrorViewResolver.class)DefaultErrorViewResolver conventionErrorViewResolver() {return new DefaultErrorViewResolver(this.applicationContext, this.resources);}}
  

• 4.在DefaultErrorViewResolver中定义了错误页的默认规则，功能如下：

  • 如果在类路径下，查看是否存在 error/错误码 的页面，存在就返回该视图；
  • 否则，去4个CLASSPATH_RESOURCE_LOCATIONS路径下，查看是否写了 error/错误码.html 的页面，存在则返回该视图；
  • 都不存在，则modelAndView=null;则判断是否有 error/4xx 或者 error/5xx 的页面，存在则返回该视图
  • 否则，去4个CLASSPATH_RESOURCE_LOCATIONS路径下，查看是否写了 error/4xx.html 或者 error/5xx.html 的页面，存在则返回该视图；

  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);}// 查看是否存在 error/错误码 的页面，存在就返回该视图// 不存在，则判断是否有  error/4xx  或者  error/5xx  的页面，存在则返回该视图@Overridepublic ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status, Map<String, Object> model) {ModelAndView modelAndView = resolve(String.valueOf(status.value()), model);if (modelAndView == null && SERIES_VIEWS.containsKey(status.series())) {modelAndView = resolve(SERIES_VIEWS.get(status.series()), model);}return modelAndView;}// 在类路径下，查看是否存在 error/错误码 的模板引擎，存在就返回该视图；// 否则去下面的4个CLASSPATH_RESOURCE_LOCATIONS路径下，查看是否写了  error/错误码.html 的页面，存在则返回该视图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);}//去下面的4个CLASSPATH_RESOURCE_LOCATIONS路径下，查看是否写了  error/错误码.html  的页面，存在则返回该视图//this.resources.getStaticLocations()//private static final String[] CLASSPATH_RESOURCE_LOCATIONS = { "classpath:/META-INF/resources/",//			"classpath:/resources/", "classpath:/static/", "classpath:/public/" };private ModelAndView resolveResource(String viewName, Map<String, Object> model) {for (String location : this.resources.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;}...
  }
  

• 5.在ErrorMvcAutoConfiguration自动装配类中，向容器中放入了一个默认名为error的视图，提供了默认的白页功能，如果上述都无法处理

  	@Configuration(proxyBeanMethods = false)@ConditionalOnProperty(prefix = "server.error.whitelabel", name = "enabled", matchIfMissing = true)@Conditional(ErrorTemplateMissingCondition.class)protected static class WhitelabelErrorViewConfiguration {private final StaticView defaultErrorView = new StaticView();//   注入了error视图@Bean(name = "error")@ConditionalOnMissingBean(name = "error")public View defaultErrorView() {return this.defaultErrorView;}// If the user adds @EnableWebMvc then the bean name view resolver from// WebMvcAutoConfiguration disappears, so add it back in to avoid disappointment.@Bean@ConditionalOnMissingBeanpublic BeanNameViewResolver beanNameViewResolver() {BeanNameViewResolver resolver = new BeanNameViewResolver();resolver.setOrder(Ordered.LOWEST_PRECEDENCE - 10);return resolver;}}
  

  默认的白页源码，就在类ErrorMvcAutoConfiguration中定义的

  private static class StaticView implements View {private static final MediaType TEXT_HTML_UTF8 = new MediaType("text", "html", StandardCharsets.UTF_8);private static final Log logger = LogFactory.getLog(StaticView.class);@Overridepublic void render(Map<String, ?> model, HttpServletRequest request, HttpServletResponse response)throws Exception {if (response.isCommitted()) {String message = getMessage(model);logger.error(message);return;}response.setContentType(TEXT_HTML_UTF8.toString());StringBuilder builder = new StringBuilder();Object timestamp = model.get("timestamp");Object message = model.get("message");Object trace = model.get("trace");if (response.getContentType() == null) {response.setContentType(getContentType());}builder.append("<html><body><h1>Whitelabel Error Page</h1>").append("<p>This application has no explicit mapping for /error, so you are seeing this as a fallback.</p>").append("<div id='created'>").append(timestamp).append("</div>").append("<div>There was an unexpected error (type=").append(htmlEscape(model.get("error"))).append(", status=").append(htmlEscape(model.get("status"))).append(").</div>");if (message != null) {builder.append("<div>").append(htmlEscape(message)).append("</div>");}if (trace != null) {builder.append("<div style='white-space:pre-wrap;'>").append(htmlEscape(trace)).append("</div>");}builder.append("</body></html>");response.getWriter().append(builder.toString());}private String htmlEscape(Object input) {return (input != null) ? HtmlUtils.htmlEscape(input.toString()) : null;}private String getMessage(Map<String, ?> model) {Object path = model.get("path");String message = "Cannot render error page for request [" + path + "]";if (model.get("message") != null) {message += " and exception [" + model.get("message") + "]";}message += " as the response has already been committed.";message += " As a result, the response may have the wrong status code.";return message;}@Overridepublic String getContentType() {return "text/html";}}
  

• 6.在ErrorMvcAutoConfiguration自动装配类中，封装了JSON格式的错误信息(初始化了错误的类型、错误的状态码、路径、栈信息、时间戳等信息)

  @Bean
  @ConditionalOnMissingBean(value = ErrorAttributes.class, search = SearchStrategy.CURRENT)
  public DefaultErrorAttributes errorAttributes() {return new DefaultErrorAttributes();
  }
  

规则如下：

• 1.解析一个错误页：

  • 如果发生了500、404、503、403 这些错误
    • 1. 如果有模板引擎，默认在 classpath:/templates/error/精确码.html
    • 2. 如果没有模板引擎，在静态资源文件夹下找 精确码.html
  • 如果匹配不到精确码.html这些精确的错误页，就去找5xx.html，4xx.html模糊匹配
    • 1. 如果有模板引擎，默认在 classpath:/templates/error/5xx.html
    • 2. 如果没有模板引擎，在静态资源文件夹下找 5xx.html

• 2.如果模板引擎路径templates下有 error.html页面，就直接渲染

5、自定义错误响应

​ 1) 自定义json响应：使用文章第2和第3部分介绍的，使用注解进行统一的异常处理

​ 2）自定义页面响应：根据第4部分介绍的规则，在对应的项目路径"classpath:/METAINF/resources/","classpath:/resources/","classpath:/static/", "classpath:/public/"或者模板引擎目录下，定义错误页面即可。

6、测试

1、在项目的resources/templates/目录下创建一个error文件夹，放入4xx.html、5xx.html

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>Title</title>
</head>
<body>4xx.html
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>Title</title>
</head>
<body>
5xx.html
</body>
</html>

2、在项目的resources/templates/error文件夹中，再放入404.html、500.html

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>Title</title>
</head>
<body>
404.html
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>Title</title>
</head>
<body>
500.html
</body>
</html>

3、浏览器先后测试上述情况

• 1.访问一个不存在的路径；
• 2.制造除0错误。