在SpringBoot項目啟動過程中，當一些配置或者其他錯誤信息會有一些的規范的提示信息

***************************APPLICATION FAILED TO START***************************

Description:

Web server failed to start. Port 8080 was already in use.

Action:

Identify and stop the process that’s listening on port 8080 or configure this application to listen on another port.

在SpringBoot 中其實現原理是什么，我們該如何自定義異常信息呢

在springboot啟動的核心方法run中會加載所有的SpringBootExceptionReporter

exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[] { ConfigurableApplicationContext.class }, context);

調用了getSpringFactoriesInstances方法

private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) { ClassLoader classLoader = getClassLoader(); // Use names and ensure unique to protect against duplicates Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader)); List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names); AnnotationAwareOrderComparator.sort(instances); return instances; }

其主要通過Spring的Factories機制來加載

public ConfigurableApplicationContext run(String... args) { StopWatch stopWatch = new StopWatch(); stopWatch.start(); ConfigurableApplicationContext context = null; Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>(); configureHeadlessProperty(); SpringApplicationRunListeners listeners = getRunListeners(args); listeners.starting(); try { ApplicationArguments applicationArguments = new DefaultApplicationArguments(args); ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments); configureIgnoreBeanInfo(environment); Banner printedBanner = printBanner(environment); context = createApplicationContext(); exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[] { ConfigurableApplicationContext.class }, context); prepareContext(context, environment, listeners, applicationArguments, printedBanner); refreshContext(context); afterRefresh(context, applicationArguments); stopWatch.stop(); if (this.logStartupInfo) { new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch); } listeners.started(context); callRunners(context, applicationArguments); } catch (Throwable ex) { //異常捕獲中，向用戶打印異常信息 handleRunFailure(context, ex, exceptionReporters, listeners); throw new IllegalStateException(ex); } try { listeners.running(context); } catch (Throwable ex) { handleRunFailure(context, ex, exceptionReporters, null); throw new IllegalStateException(ex); } return context; }

在try catch中，catch會打印異常信息

private void handleRunFailure(ConfigurableApplicationContext context, Throwable exception, Collection<SpringBootExceptionReporter> exceptionReporters, SpringApplicationRunListeners listeners) { try { try { handleExitCode(context, exception); if (listeners != null) { listeners.failed(context, exception); } } finally { reportFailure(exceptionReporters, exception); if (context != null) { context.close(); } } } catch (Exception ex) { logger.warn('Unable to close ApplicationContext', ex); } ReflectionUtils.rethrowRuntimeException(exception); }

private void reportFailure(Collection<SpringBootExceptionReporter> exceptionReporters, Throwable failure) { try { for (SpringBootExceptionReporter reporter : exceptionReporters) { if (reporter.reportException(failure)) { registerLoggedException(failure); return; } } } catch (Throwable ex) { // Continue with normal handling of the original failure } if (logger.isErrorEnabled()) { logger.error('Application run failed', failure); registerLoggedException(failure); } }

遍歷exceptionReporters，打印日常信息

SpringBootExceptionReporter是一個回調接口，用于支持對SpringApplication啟動錯誤的自定義報告。里面就一個報告啟動失敗的方法。

其實現類：org.springframework.boot.diagnostics.FailureAnalyzers

用于觸發從spring.factories加載的FailureAnalyzer和FailureAnalysisReporter實例。

/** * <p> * * <p> * * @author: xuwd * @time: 2020/11/16 10:52 */public class WannaStopException extends RuntimeException {}

自定義異常信息打印

public class StopFailureAnalyzerextends AbstractFailureAnalyzer<WannaStopException> { @Override protected FailureAnalysis analyze(Throwable rootFailure, WannaStopException cause) {for (StackTraceElement stackTraceElement : cause.getStackTrace()) { if (stackTraceElement.getClassName().equals('com.pigx.demo.Config21')) {return new FailureAnalysis('A想停止', '別要A了', cause); }}return null; }}

接下來令他生效，通過上面分析可以可看出需要通過AutoConfigurationImportSelector，類似于自定義SpringBoot Starter AutoConfiguration的形式，我們需要在META-INF/spring.factories文件內進行定義，如下所示：

接著在合適的地方拋出WannaStopException 異常

在springboot 啟動過程中會先對異常信息進行補捕獲，對進行日志格式處理的日志進行處理；其核心是通過SpringBootExceptionReporter回調及sping-spi bean的管理。

以上為個人經驗，希望能給大家一個參考，也希望大家多多支持好吧啦網。