本Spring Boot版本是2.2.2

1、流程

1.1、初始化流程

在run 方法中，将所有的方法都放在了try块中，而在catch 块中处理所有的异常和错误（Throwable ）

（1）创建 SpringBootExceptionReporter 实例
从spring.factories中获取 SpringBootExceptionReporter 类型的类的全类名，实例化这些类

（2）创建 FailureAnlyzer 实例
从从spring.factories中获取 FailureAnlyzer 类型的类的全类名，实例化这些类并放入 SpringBootExceptionReporter 实例的List实例变量中

1.2、调用流程

2、源码

public ConfigurableApplicationContext run(String... args) {...Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();...try {...// 从spring.factories 文件中获取并创建所有 SpringBootExceptionReporter 类型实例exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,new Class[] { ConfigurableApplicationContext.class }, context);...}catch (Throwable ex) {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;}

2.1、创建 SpringBootExceptionReporter 实例

1、从spring.factories 中解析出全类名（SpringBootExceptionReporter类型的类的）

之前分析过，这里略…

2、创建这些类的实例，其中有FailureAnalyzers（目前SpringBoot中SpringBootExceptionReporter接口只有这个一个实现类），FailureAnalyzers构造方法如下：

FailureAnalyzers(ConfigurableApplicationContext context, ClassLoader classLoader) {Assert.notNull(context, "Context must not be null");this.classLoader = (classLoader != null) ? classLoader : context.getClassLoader();this.analyzers = loadFailureAnalyzers(this.classLoader);prepareFailureAnalyzers(this.analyzers, context);
}

FailureAnalyzers 构造方法做了两件事情

（2.1）解析，创建，排序，即从spring.factories中解析所有 FailureAnalyzer 类型的类全名，并创建这些类的实例

private List<FailureAnalyzer> loadFailureAnalyzers(ClassLoader classLoader) {List<String> analyzerNames = SpringFactoriesLoader.loadFactoryNames(FailureAnalyzer.class, classLoader);List<FailureAnalyzer> analyzers = new ArrayList<>();for (String analyzerName : analyzerNames) {try {Constructor<?> constructor = ClassUtils.forName(analyzerName, classLoader).getDeclaredConstructor();ReflectionUtils.makeAccessible(constructor);analyzers.add((FailureAnalyzer) constructor.newInstance());}catch (Throwable ex) {logger.trace(LogMessage.format("Failed to load %s", analyzerName), ex);}}AnnotationAwareOrderComparator.sort(analyzers);return analyzers;
}

笔者环境解析结果

analyzers = {ArrayList@3363}  size = 180 = {BeanCurrentlyInCreationFailureAnalyzer@2918} 1 = {BeanDefinitionOverrideFailureAnalyzer@3402} 2 = {BeanNotOfRequiredTypeFailureAnalyzer@3403} 3 = {BindFailureAnalyzer@3404} 4 = {BindValidationFailureAnalyzer@3405} 5 = {UnboundConfigurationPropertyFailureAnalyzer@3406} 6 = {ConnectorStartFailureAnalyzer@3407} 7 = {NoSuchMethodFailureAnalyzer@3408} 8 = {NoUniqueBeanDefinitionFailureAnalyzer@3398} 9 = {PortInUseFailureAnalyzer@3409} 10 = {ValidationExceptionFailureAnalyzer@3410} 11 = {InvalidConfigurationPropertyNameFailureAnalyzer@3411} 12 = {InvalidConfigurationPropertyValueFailureAnalyzer@3412} 13 = {NoSuchBeanDefinitionFailureAnalyzer@3413} 14 = {FlywayMigrationScriptMissingFailureAnalyzer@3414} 15 = {DataSourceBeanCreationFailureAnalyzer@3415} 16 = {HikariDriverConfigurationFailureAnalyzer@3416} 17 = {NonUniqueSessionRepositoryFailureAnalyzer@3417}

这些类都是 FailureAnalyzer 接口的实现类，我们来看看 FailureAnalyzer 接口

public interface FailureAnalyzer {/*** Returns an analysis of the given {@code failure}, or {@code null} if no analysis* was possible.* @param failure the failure* @return the analysis or {@code null}*/
FailureAnalysis analyze(Throwable failure);
}

我们发现接口中只有 analyze 方法，方法返回类型是 FailureAnalysis ，FailureAnalysis 用来封装失败信息的，下面是FailureAnalysis 类的定义：

public class FailureAnalysis {private final String description;// 错误描述private final String action;// 处理失败的操作private final Throwable cause;// 失败原因
}

下面是使用同一端口第二次启动应用的报错信息，大家看看 Description 和 Action 的描述感受一下

Description:Web server failed to start. Port 8008 was already in use.
Action:Identify and stop the process that's listening on port 8008 or configure this application to listen on another port.

（2.2）为BeanFactoryAware 或 EnvironmentAware类型的 FailureAnalyzer 实例，注入BeanFactory 或 Environment

private void prepareFailureAnalyzers(List<FailureAnalyzer> analyzers, ConfigurableApplicationContext context) {for (FailureAnalyzer analyzer : analyzers) {prepareAnalyzer(context, analyzer);}
}private void prepareAnalyzer(ConfigurableApplicationContext context, FailureAnalyzer analyzer) {if (analyzer instanceof BeanFactoryAware) {((BeanFactoryAware) analyzer).setBeanFactory(context.getBeanFactory());}if (analyzer instanceof EnvironmentAware) {((EnvironmentAware) analyzer).setEnvironment(context.getEnvironment());}
}

FailureAnalyzer 类型的实例有：

1、BeanFactoryAwareNoUniqueBeanDefinitionFailureAnalyzerNoSuchBeanDefinitionFailureAnalyzer
2、EnvironmentAwareInvalidConfigurationPropertyValueFailureAnalyzerDataSourceBeanCreationFailureAnalyzer

2.2、处理异常

当程序发生异常时，在 catch 块中处理这个异常

private void handleRunFailure(ConfigurableApplicationContext context, Throwable exception,Collection<SpringBootExceptionReporter> exceptionReporters, SpringApplicationRunListeners listeners) {try {try {// 1、handleExitCode(context, exception);if (listeners != null) {// 2、listeners.failed(context, exception);}}finally {// 3、reportFailure(exceptionReporters, exception);if (context != null) {// 4、context.close();}}}catch (Exception ex) {logger.warn("Unable to close ApplicationContext", ex);}ReflectionUtils.rethrowRuntimeException(exception);
}

发生端口占用异常时：

exception = {PortInUseException@5268} "org.springframework.boot.web.server.PortInUseException: Port 8008 is already in use"$assertionsDisabled = truecause = nullCAUSE_CAPTION = "Caused by: "detailMessage = "Port 8008 is already in use"EMPTY_THROWABLE_ARRAY = {Throwable[0]@5295} Exception.serialVersionUID = -3387516993124229948NULL_CAUSE_MESSAGE = "Cannot suppress a null exception."port = 8008SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted"serialVersionUID = -7034897190745766939stackTrace = {StackTraceElement[10]@5300} SUPPRESSED_CAPTION = "Suppressed: "SUPPRESSED_SENTINEL = {Collections$UnmodifiableRandomAccessList@5302}  size = 0suppressedExceptions = {Collections$UnmodifiableRandomAccessList@5302}  size = 0Throwable.serialVersionUID = -3042686055658047285UNASSIGNED_STACK = {StackTraceElement[0]@5298}

（1）、


/********** org.springframework.boot.SpringApplication ******************/
private void handleExitCode(ConfigurableApplicationContext context, Throwable exception) {int exitCode = getExitCodeFromException(context, exception);if (exitCode != 0) {if (context != null) {context.publishEvent(new ExitCodeEvent(context, exitCode));}SpringBootExceptionHandler handler = getSpringBootExceptionHandler();if (handler != null) {handler.registerExitCode(exitCode);}}
}
private int getExitCodeFromException(ConfigurableApplicationContext context, Throwable exception) {int exitCode = getExitCodeFromMappedException(context, exception);if (exitCode == 0) {exitCode = getExitCodeFromExitCodeGeneratorException(exception);}return exitCode;
}
private int getExitCodeFromMappedException(ConfigurableApplicationContext context, Throwable exception) {if (context == null || !context.isActive()) {return 0;}ExitCodeGenerators generators = new ExitCodeGenerators();Collection<ExitCodeExceptionMapper> beans // 空的= context.getBeansOfType(ExitCodeExceptionMapper.class).values();generators.addAll(exception, beans);// exception 就是 PortInUseException实例return generators.getExitCode();
}
private int getExitCodeFromExitCodeGeneratorException(Throwable exception) {if (exception == null) {return 0;}if (exception instanceof ExitCodeGenerator) {return ((ExitCodeGenerator) exception).getExitCode();}return getExitCodeFromExitCodeGeneratorException(exception.getCause());
}/********** org.springframework.boot.ExitCodeGenerators ******************/
void addAll(Throwable exception, Iterable<? extends ExitCodeExceptionMapper> mappers) {Assert.notNull(exception, "Exception must not be null");Assert.notNull(mappers, "Mappers must not be null");for (ExitCodeExceptionMapper mapper : mappers) {add(exception, mapper);}
}
void add(Throwable exception, ExitCodeExceptionMapper mapper) {Assert.notNull(exception, "Exception must not be null");Assert.notNull(mapper, "Mapper must not be null");add(new MappedExitCodeGenerator(exception, mapper));
}
void add(ExitCodeGenerator generator) {Assert.notNull(generator, "Generator must not be null");this.generators.add(generator);
}int getExitCode() {int exitCode = 0;for (ExitCodeGenerator generator : this.generators) {try {int value = generator.getExitCode();if (value > 0 && value > exitCode || value < 0 && value < exitCode) {exitCode = value;}}catch (Exception ex) {exitCode = (exitCode != 0) ? exitCode : 1;ex.printStackTrace();}}return exitCode;
}

（2）、

（3）、报告异常

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);}
}
private FailureAnalysis analyze(Throwable failure, List<FailureAnalyzer> analyzers) {for (FailureAnalyzer analyzer : analyzers) {try {FailureAnalysis analysis = analyzer.analyze(failure);if (analysis != null) {return analysis;}}catch (Throwable ex) {logger.debug(LogMessage.format("FailureAnalyzer %s failed", analyzer), ex);}}return null;
}
protected Class<? extends T> getCauseType() {return (Class<? extends T>) ResolvableType.forClass(AbstractFailureAnalyzer.class, getClass()).resolveGeneric();
}

（4）、

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2.7、Spring Boot 异常处理体系

1、流程

1.1、初始化流程

1.2、调用流程

2、源码

2.1、创建 SpringBootExceptionReporter 实例

2.2、处理异常

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2.7、Spring Boot 异常处理体系

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1.2、调用流程

2、源码

2.1、创建 SpringBootExceptionReporter 实例

2.2、处理异常

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1.1、初始化流程