Springboot默認(rèn)的錯(cuò)誤頁(yè)是如何工作及工作原理你肯定不知道？
作者：Springboot實(shí)戰(zhàn)案例錦集
到此你就知道了一個(gè)錯(cuò)誤的頁(yè)是如何在Springboot中被注冊(cè)的。到目前為止我們看到的注冊(cè)到tomcat容器中的錯(cuò)誤頁(yè)都是個(gè)地址，比如：默認(rèn)是/error。那這個(gè)默認(rèn)的/error又是怎么提供的接口呢？
環(huán)境：Springboot2.4.12
環(huán)境配置
接下來的演示都是基于如下接口進(jìn)行。
@RestController
@RequestMapping("/exceptions")
public class ExceptionsController {
@GetMapping("/index")
public Object index(int a) {
if (a == 0) {
throw new BusinessException() ;
}
return "exception" ;
}
}默認(rèn)錯(cuò)誤輸出
默認(rèn)情況下，當(dāng)請(qǐng)求一個(gè)接口發(fā)生異常時(shí)會(huì)有如下兩種情況的錯(cuò)誤信息提示
- 基于HTML
圖片
- 基于JSON
圖片
上面兩個(gè)示例通過請(qǐng)求的Accept請(qǐng)求頭設(shè)置希望接受的數(shù)據(jù)類型，得到不同的響應(yīng)數(shù)據(jù)類型。
標(biāo)準(zhǔn)web錯(cuò)誤頁(yè)配置
在標(biāo)準(zhǔn)的java web項(xiàng)目中我們一般是在web.xml文件中進(jìn)行錯(cuò)誤頁(yè)的配置，如下：
<error-page>
<location>/error</location>
</error-page>如上配置后，如發(fā)生了異常以后容器會(huì)自動(dòng)地跳轉(zhuǎn)到錯(cuò)誤頁(yè)面。
Spring實(shí)現(xiàn)原理
在Springboot中沒有web.xml，并且Servlet API也沒有提供相應(yīng)的API進(jìn)行錯(cuò)誤頁(yè)的配置。那么在Springboot中又是如何實(shí)現(xiàn)錯(cuò)誤頁(yè)的配置呢？
Springboot內(nèi)置了應(yīng)用服務(wù)，如Tomcat，Undertow，Jetty，默認(rèn)是Tomcat。那接下來看下基于默認(rèn)的Tomcat容器錯(cuò)誤頁(yè)是如何進(jìn)行配置的。
- Servlet Web服務(wù)自動(dòng)配置
@EnableConfigurationProperties(ServerProperties.class)
@Import({ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class,
ServletWebServerFactoryConfiguration.EmbeddedTomcat.class,...})
public class ServletWebServerFactoryAutoConfiguration {
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass({ Servlet.class, Tomcat.class, UpgradeProtocol.class })
@ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
static class EmbeddedTomcat {
// 這里主要就是配置Web 容器服務(wù)，如這里使用的Tomcat
// 注意該類實(shí)現(xiàn)了ErrorPageRegistry ，那么也就是說該類可以用來注冊(cè)錯(cuò)誤頁(yè)的
@Bean
TomcatServletWebServerFactory tomcatServletWebServerFactory(
ObjectProvider<TomcatConnectorCustomizer> connectorCustomizers,
ObjectProvider<TomcatContextCustomizer> contextCustomizers,
ObjectProvider<TomcatProtocolHandlerCustomizer<?>> protocolHandlerCustomizers) {
TomcatServletWebServerFactory factory = new TomcatServletWebServerFactory();
factory.getTomcatConnectorCustomizers().addAll(connectorCustomizers.orderedStream().collect(Collectors.toList()));
factory.getTomcatContextCustomizers().addAll(contextCustomizers.orderedStream().collect(Collectors.toList()));
factory.getTomcatProtocolHandlerCustomizers().addAll(protocolHandlerCustomizers.orderedStream().collect(Collectors.toList()));
return factory;
}
}
}在@Import中只列出了兩個(gè)比較重要的BeanPostProcessorsRegistrar與EmbeddedTomcat
BeanPostProcessorsRegistrar注冊(cè)了兩個(gè)BeanPostProcessor處理器
public static class BeanPostProcessorsRegistrar implements ImportBeanDefinitionRegistrar, BeanFactoryAware {
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
if (this.beanFactory == null) {
return;
}
registerSyntheticBeanIfMissing(registry, "webServerFactoryCustomizerBeanPostProcessor", WebServerFactoryCustomizerBeanPostProcessor.class, WebServerFactoryCustomizerBeanPostProcessor::new);
registerSyntheticBeanIfMissing(registry, "errorPageRegistrarBeanPostProcessor", ErrorPageRegistrarBeanPostProcessor.class, ErrorPageRegistrarBeanPostProcessor::new);
}
}通過名稱也能知道WebServerFactoryCustomizerBeanPostProcessor用來處理Tomcat相關(guān)的自定義信息；ErrorPageRegistrarBeanPostProcessor 這個(gè)就是重點(diǎn)了，這個(gè)就是用來配置我們的自定義錯(cuò)誤頁(yè)面的。
public class ErrorPageRegistrarBeanPostProcessor implements BeanPostProcessor, BeanFactoryAware {
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
// 這里判斷了當(dāng)前的bean對(duì)象是否是ErrorPageRegistry的實(shí)例
// 當(dāng)前類既然是BeanPostProcessor實(shí)例，同時(shí)上面注冊(cè)了一個(gè)TomcatServletWebServerFactory Bean實(shí)例
// 那么在實(shí)例化TomcatServletWebServerFactory時(shí)一定是會(huì)調(diào)用該BeanPostProcessor處理器的
if (bean instanceof ErrorPageRegistry) {
postProcessBeforeInitialization((ErrorPageRegistry) bean);
}
return bean;
}
// 注冊(cè)錯(cuò)誤頁(yè)面
private void postProcessBeforeInitialization(ErrorPageRegistry registry) {
for (ErrorPageRegistrar registrar : getRegistrars()) {
registrar.registerErrorPages(registry);
}
}
private Collection<ErrorPageRegistrar> getRegistrars() {
if (this.registrars == null) {
// Look up does not include the parent context
// 從當(dāng)前上下文中（比包括父上下文）查找ErrorPageRegistrar Bean對(duì)象
this.registrars = new ArrayList<>(this.beanFactory.getBeansOfType(ErrorPageRegistrar.class, false, false).values());
this.registrars.sort(AnnotationAwareOrderComparator.INSTANCE);
this.registrars = Collections.unmodifiableList(this.registrars);
}
return this.registrars;
}
}注冊(cè)錯(cuò)誤頁(yè)面
在上一步中知道了錯(cuò)誤頁(yè)的注冊(cè)入口是在一個(gè)ErrorPageRegistrarBeanPostProcessor Bean后處理器中進(jìn)行注冊(cè)的，接下來繼續(xù)深入查看這個(gè)錯(cuò)誤頁(yè)是如何被注冊(cè)的。
接著上一步在ErrorPageRegistrarBeanPostProcessor中查找ErrorPageRegistrar類型的Bean對(duì)象。在另外一個(gè)自動(dòng)配置中（ErrorMvcAutoConfiguration）有注冊(cè)ErrorPageRegistrar Bean對(duì)象
@AutoConfigureBefore(WebMvcAutoConfiguration.class)
@EnableConfigurationProperties({ ServerProperties.class, WebMvcProperties.class })
public class ErrorMvcAutoConfiguration {
// 該類是ErrorPageRegistrar子類，那么在注冊(cè)錯(cuò)誤頁(yè)的時(shí)候注冊(cè)的就是該類中生成的錯(cuò)誤頁(yè)信息
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;
}
@Override
public void registerErrorPages(ErrorPageRegistry errorPageRegistry) {
// 錯(cuò)誤頁(yè)的地址可以在配置文件中自定義server.error.path進(jìn)行配置，默認(rèn)：/error
ErrorPage errorPage = new ErrorPage(this.dispatcherServletPath.getRelativePath(this.properties.getError().getPath()));
errorPageRegistry.addErrorPages(errorPage);
}
@Override
public int getOrder() {
return 0;
}
}
}關(guān)鍵代碼
// errorPageRegistry對(duì)象的實(shí)例是TomcatServletWebServerFactory
errorPageRegistry.addErrorPages(errorPage);TomcatServletWebServerFactory中注冊(cè)錯(cuò)誤頁(yè)信息，該類的父類（AbstractConfigurableWebServerFactory）方法中有添加錯(cuò)誤也的方法
public abstract class AbstractConfigurableWebServerFactory {
private Set<ErrorPage> errorPages = new LinkedHashSet<>();
public void addErrorPages(ErrorPage... errorPages) {
this.errorPages.addAll(Arrays.asList(errorPages));
}
}這個(gè)錯(cuò)誤頁(yè)的注冊(cè)到Tomcat容器中又是如何實(shí)現(xiàn)的呢？
Tomcat中注冊(cè)錯(cuò)誤頁(yè)
接下來看看這個(gè)錯(cuò)誤頁(yè)是如何與Tomcat關(guān)聯(lián)在一起的。
Spring容器最核心的方法是refresh方法
public abstract class AbstractApplicationContext {
public void refresh() {
// ...
// Initialize other special beans in specific context subclasses.
onRefresh();
// ...
}
}執(zhí)行onRefresh方法
public class ServletWebServerApplicationContext extends GenericWebApplicationContext {
protected void onRefresh() {
super.onRefresh();
try {
// 創(chuàng)建Tomcat服務(wù)
createWebServer();
} catch (Throwable ex) {
throw new ApplicationContextException("Unable to start web server", ex);
}
}
private void createWebServer() {
// ...
// 返回應(yīng)用于創(chuàng)建嵌入的Web服務(wù)器的ServletWebServerFactory。默認(rèn)情況下，此方法在上下文本身中搜索合適的bean。
// 在上面ServletWebServerFactoryAutoConfiguration自動(dòng)配置中，已經(jīng)自動(dòng)的根據(jù)當(dāng)前的環(huán)境創(chuàng)建了TomcatServletWebServerFactory對(duì)象
ServletWebServerFactory factory = getWebServerFactory();
// 獲取WebServer實(shí)例， factory = TomcatServletWebServerFactory
this.webServer = factory.getWebServer(getSelfInitializer());
// ...
}
}調(diào)用TomcatServletWebServerFactory#getWebServer方法
public class TomcatServletWebServerFactory extends AbstractServletWebServerFactory {
public WebServer getWebServer(ServletContextInitializer... initializers) {
// ...
Tomcat tomcat = new Tomcat();
// ...
// 預(yù)處理上下文
prepareContext(tomcat.getHost(), initializers);
return getTomcatWebServer(tomcat);
}
protected void prepareContext(Host host, ServletContextInitializer[] initializers) {
// ...
// 配置上下文
configureContext(context, initializersToUse);
}
protected void configureContext(Context context, ServletContextInitializer[] initializers) {
TomcatStarter starter = new TomcatStarter(initializers);
// ...
// 在這里就將錯(cuò)誤的頁(yè)面注冊(cè)到了tomcat容器中
for (ErrorPage errorPage : getErrorPages()) {
org.apache.tomcat.util.descriptor.web.ErrorPage tomcatErrorPage = new org.apache.tomcat.util.descriptor.web.ErrorPage();
tomcatErrorPage.setLocation(errorPage.getPath());
tomcatErrorPage.setErrorCode(errorPage.getStatusCode());
tomcatErrorPage.setExceptionType(errorPage.getExceptionName());
context.addErrorPage(tomcatErrorPage);
}
// ...
}
}到此你就知道了一個(gè)錯(cuò)誤的頁(yè)是如何在Springboot中被注冊(cè)的。到目前為止我們看到的注冊(cè)到tomcat容器中的錯(cuò)誤頁(yè)都是個(gè)地址，比如：默認(rèn)是/error。那這個(gè)默認(rèn)的/error又是怎么提供的接口呢？
默認(rèn)錯(cuò)誤頁(yè)
在Springboot中默認(rèn)有個(gè)自動(dòng)配置的錯(cuò)誤頁(yè)，在上面有一個(gè)代碼片段你應(yīng)該注意到了
@AutoConfigureBefore(WebMvcAutoConfiguration.class)
@EnableConfigurationProperties({ ServerProperties.class, WebMvcProperties.class })
public class ErrorMvcAutoConfiguration {
@Bean
@ConditionalOnMissingBean(value = ErrorAttributes.class, search = SearchStrategy.CURRENT)
public DefaultErrorAttributes errorAttributes() {
return new DefaultErrorAttributes();
}
@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()));
}
}查看這個(gè)Controller
// 默認(rèn)的錯(cuò)誤頁(yè)地址是/error
@Controller
@RequestMapping("${server.error.path:${error.path:/error}}")
public class BasicErrorController extends AbstractErrorController {
@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);
}
}這里有兩個(gè)方法，分別處理了不同的Accept請(qǐng)求頭。到此你是否真正地明白了Springboot中的錯(cuò)誤處理的工作原理呢？
責(zé)任編輯：武曉燕
來源：
Spring全家桶實(shí)戰(zhàn)案例源碼
