从 01 开始
2023-08-22
目录

错误处理-底层组件源码分析

# 420.错误处理-底层组件源码分析

本文讲讲原理，掌握原理后，就能更方便地定制化。

‍

# 异常处理-自动配置原理

之前我们讲了 SpringBoot 的默认处理，那么这些处理肯定也是配置在源码的；

我们可以在 IDEA 中打开 spring-boot-autoconfigure-2.3.4.RELEASE.jar，

然后打开该目录：org\springframework\boot\autoconfigure\web\servlet\error：

‍

其中 ErrorMvcAutoConfiguration，就是自动配置异常处理规则的；

# BasicErrorController

在 ErrorMvcAutoConfiguration 类中，还配置了一个 ErrorController：

@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().collect(Collectors.toList()));
}
1
2
3
4
5
6
7

该类的源码如下：

@Controller
@RequestMapping("${server.error.path:${error.path:/error}}")
public class BasicErrorController extends AbstractErrorController {
1
2
3

‍ 可以看到，首先是一个 Controller，然后定义了访问路径：先取出我们定义的配置文件中的 server.error.path，如果没有，则取出 error.path；还是没有，则会取值 /error，也就是我们之前说的默认值。 ‍ 既然是 Controller，那么就会响应内容，例如下面第一个方法是响应 HTML，第二个方法是响应 JSON：

@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, getErrorAttributeOptions(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, getErrorAttributeOptions(request, MediaType.ALL));
	return new ResponseEntity<>(body, status);
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23

如果是响应 HTML，则是响应 error（第 8 行）：

return (modelAndView != null) ? modelAndView : new ModelAndView("error", model);
1

‍ 如果是响应 JSON，则直接封装 JSON：

Map<String, Object> body = getErrorAttributes(request, getErrorAttributeOptions(request, MediaType.ALL));
return new ResponseEntity<>(body, status);
1
2

# Error-View

ErrorMvcAutoConfiguration 就定义了一个叫做 error 的组件，其是一个 View 类型：

@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();

	@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
	@ConditionalOnMissingBean
	public BeanNameViewResolver beanNameViewResolver() {
		BeanNameViewResolver resolver = new BeanNameViewResolver();
		resolver.setOrder(Ordered.LOWEST_PRECEDENCE - 10);
		return resolver;
	}

}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

‍ 可以看到还定义了 BeanNameViewResolver 组件，这个就是通过 Bean 的名字，来寻找视图的一种视图解析器。

而 StaticView，里面的 render 方法是这样的：

@Override
public void render(Map<String, ?> model, HttpServletRequest request, HttpServletResponse response) throws Exception {
    //......
    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>");
    //.....
1
2
3
4
5
6
7
8
9

所以这就是我们之前看到的默认错误页面。 ‍

# DefaultErrorViewResolver

还配置了一个 id 叫做 conventionErrorViewResolver 的组件，其类型是 DefaultErrorViewResolver：

@Configuration(proxyBeanMethods = false)
static class DefaultErrorViewResolverConfiguration {

    private final ApplicationContext applicationContext;

    private final ResourceProperties resourceProperties;

    DefaultErrorViewResolverConfiguration(ApplicationContext applicationContext,
			ResourceProperties resourceProperties) {
	this.applicationContext = applicationContext;
	this.resourceProperties = resourceProperties;
    }

    @Bean
    @ConditionalOnBean(DispatcherServlet.class)
    @ConditionalOnMissingBean(ErrorViewResolver.class)
    DefaultErrorViewResolver conventionErrorViewResolver() {
	   return new DefaultErrorViewResolver(this.applicationContext, this.resourceProperties);
    }

}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21

‍ 该类部分源码如下：

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);
	}
1
2
3
4
5
6
7
8
9
10

可以看到，定义了客户端错误就是 4xx，服务端错误是 5xx ‍ 既然是视图解析器，那么就会解析请求返回内容，例如 resolveErrorView 方法，就回调用 resolve 方法，得到 modelAndView 对象并返回：

@Override
public 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;
}
1
2
3
4
5
6
7
8

会传参 status，也就是 HTTP 状态码；

然后 resolve 方法，就会拼接错误路径 + HTTP 状态码，来拼接视图的名字：

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);
}
1
2
3
4
5
6
7
8
9

‍ 所以，如果发生了 404 错误，那么 resolve 方法收到的参数 viewName 就是 404，然后会拼接成 /error/404.html 页面； ‍

# DefaultErrorAttributes

SpringBoot 还自动配置了 DefaultErrorAttributes 这个组件；

@Bean
@ConditionalOnMissingBean(value = ErrorAttributes.class, search = SearchStrategy.CURRENT)
public DefaultErrorAttributes errorAttributes() {
	return new DefaultErrorAttributes();
}
1
2
3
4
5

‍ DefaultErrorAttributes 类，主要就是定义了错误信息应该包含什么，例如 message，trace 等属性，例如这是其 getErrorAttributes 方法：

@Override
public Map<String, Object> getErrorAttributes(WebRequest webRequest, ErrorAttributeOptions options) {
	Map<String, Object> errorAttributes = getErrorAttributes(webRequest, options.isIncluded(Include.STACK_TRACE));
	if (Boolean.TRUE.equals(this.includeException)) {
		options = options.including(Include.EXCEPTION);
	}
	if (!options.isIncluded(Include.EXCEPTION)) {
		errorAttributes.remove("exception");
	}
	if (!options.isIncluded(Include.STACK_TRACE)) {
		errorAttributes.remove("trace");
	}
	if (!options.isIncluded(Include.MESSAGE) && errorAttributes.get("message") != null) {
		errorAttributes.put("message", "");
	}
	if (!options.isIncluded(Include.BINDING_ERRORS)) {
		errorAttributes.remove("errors");
	}
	return errorAttributes;
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

默认会包含很多属性，if 判断里主要是看是否要包含，来决定是否移除。

该类实现了 ErrorAttributes 和 HandlerExceptionResolver 接口：

public class DefaultErrorAttributes implements ErrorAttributes, HandlerExceptionResolver, Ordered {
1

这两个接口是什么，我们后续再说

# 最后

‍ 我们说了很多自动配置的东西

  • 想要修改返回的错误信息，就修改 DefaultErrorAttributes
  • 想要修改默认的错误路径（/error），就修改 BasicErrorController
  • 想要修改默认的错误页面路径，就修改 DefaultErrorViewResolver ‍ 至于他们是怎么串起来的，下节课再说 ‍
上次更新: 2025/6/3 09:31:54
错误处理机制
异常处理流程

← 异常处理流程→

最近更新
01
学点统计学：轻松识破一本正经的胡说八道
06-05
02
2025 年 5 月记
05-31
03
《贫穷的本质》很棒，但可能不适合你
05-27
更多文章>
Theme by Vdoing | Copyright © 2022-2025 | 粤 ICP 备 2022067627 号 -1 | 粤公网安备 44011302003646 号 | 点击查看十年之约