目录
- 准备
- 源码跟踪
- ExceptionHandlerExceptionResolver初始化
- ExceptionHandlerExceptionResolver注入
- ExceptionHandlerExceptionResolver中exceptionHandlerAdviceCache初始化
- ExceptionHandlerMethodResolver中mappedMethods初始化
- 结尾
准备
- 准备一个controller类, 里面抛出一个异常
@RestController
@RequestMapping("/hello")
public class HelloController {
@GetMapping("/h")
public String hello(HttpServletResponse response) throws ArithmeticException {
try {
int a = 1 / 0;
} catch (Exception e) {
throw e;
}
return "hello";
}
}
- 配置一个全局异常处理类
/**
* 异常处理器
*/
@RestControllerAdvice
public class BDExceptionHandler {
/**
* 参数异常
* @param e 异常
* @return BaseResult
*/
@ExceptionHandler(ArithmeticException.class)
public R doBaseExceptionHandler(ArithmeticException e) {
return R.error(e.getMessage());
}
}
- 接下来访问url, 跟踪源码
源码跟踪
进入到mvc的入口类DispatcherServlet的 doDispatch方法, 可以发现整体逻辑被try catch包围, 当第3步抛出异常之后就会被捕获, dispatchException对象则不为空,最后进入processDispatchResult方法进行处理
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
//1.获取处理器链路
//2.执行拦截器前置方法
//3.调用controller方法, 返回结果集
//4.执行拦截器后置方法
}
catch (Exception ex) {
//
dispatchException = ex;
}
catch (Throwable err) {
dispatchException = new NestedServletException("Handler dispatch failed", err);
}
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Throwable err) {
triggerAfterCompletion(processedRequest, response, mappedHandler,
new NestedServletException("Handler processing failed", err));
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}
进入processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
@Nullable Exception exception) throws Exception {
boolean errorView = false;
//判断异常是否为空, 如果不是空则处理
if (exception != null) {
//处理ModelAndViewDefiningException异常
if (exception instanceof ModelAndViewDefiningException) {
logger.debug("ModelAndViewDefiningException encountered", exception);
mv = ((ModelAndViewDefiningException) exception).getModelAndView();
}
else {
//处理其他所有的异常
Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
mv = processHandlerException(request, response, handler, exception);
errorView = (mv != null);
}
}
//省略下面代码
进入mv = processHandlerException(request, response, handler, exception);
protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
@Nullable Object handler, Exception ex) throws Exception {
// Success and error responses may use different content types
request.removeAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);
// Check registered HandlerExceptionResolvers...
ModelAndView exMv = null;
if (this.handlerExceptionResolvers != null) {
//this.handlerExceptionResolvers里面默认有两个处理异常的类
for (HandlerExceptionResolver resolver : this.handlerExceptionResolvers) {
// 遍历,判断使用那个类来处理
exMv = resolver.resolveException(request, response, handler, ex);
if (exMv != null) {
break;
}
}
}
if (exMv != null) {
//省略代码
return exMv;
}
throw ex;
}
看一下上面for循环里面的this.handlerExceptionResolvers对象的结构 :
DefaultErrorAttributes : 没做任何处理, 只是将异常设置到request对象的属性当中;
HandlerExceptionResolverComposite : 里面有三个异常处理类, 分别的作用是 :
ExceptionHandlerExceptionResolver：基于 @ExceptionHandler 配置 HandlerMethod 的 HandlerExceptionResolver 实现类。例如通过 @ControllerAdvice 注解自定义异常处理器，加上@ExceptionHandler注解指定方法所需要处理的异常类型
ResponseStatusExceptionResolver：基于 @ResponseStatus 提供错误响应的 HandlerExceptionResolver 实现类。例如在方法上面添加 @ResponseStatus 注解，指定该方法发生异常时，需要设置的 code 响应码和 reason 错误信息
DefaultHandlerExceptionResolver：默认 HandlerExceptionResolver 实现类，针对各种异常，设置错误响应码。例如 HTTP Method 不支持，则在这个实现类中往响应中设置错误码和错误信息
原文链接：https://blog.csdn.net/Running666/article/details/130786561
进入HandlerExceptionResolverComposite类的resolveException(); 遍历上面的三种异常处理类, 判断应该使用哪个处理
public ModelAndView resolveException(
HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex) {
if (this.resolvers != null) {
//获取, 遍历
for (HandlerExceptionResolver handlerExceptionResolver : this.resolvers) {
ModelAndView mav = handlerExceptionResolver.resolveException(request, response, handler, ex);
if (mav != null) {
return mav;
}
}
}
return null;
}
由于只设置了第一种异常处理方式, 所以异常会由ExceptionHandlerExceptionResolver来处理, 进入handlerExceptionResolver.resolveException()
public ModelAndView resolveException(
HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex) {
if (shouldApplyTo(request, handler)) {
prepareResponse(ex, response);
//主要的异常处理逻辑
ModelAndView result = doResolveException(request, response, handler, ex);
if (result != null) {
// Print debug message when warn logger is not enabled.
if (logger.isDebugEnabled() && (this.warnLogger == null || !this.warnLogger.isWarnEnabled())) {
logger.debug("Resolved [" + ex + "]" + (result.isEmpty() ? "" : " to " + result));
}
logException(ex, request);
}
return result;
}
else {
return null;
}
}
进入doResolveException(request, response, handler, ex)方法;
@Override
@Nullable
protected ModelAndView doResolveHandlerMethodException(HttpServletRequest request,
HttpServletResponse response, @Nullable HandlerMethod handlerMethod, Exception exception) {
//根据controller类和异常来判断由哪个类来处理这个异常
ServletInvocableHandlerMethod exceptionHandlerMethod = getExceptionHandlerMethod(handlerMethod, exception);
if (exceptionHandlerMethod == null) {
return null;
}
//填充参数处理器
if (this.argumentResolvers != null) {
exceptionHandlerMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
}
//填充返回结果处理器
if (this.returnValueHandlers != null) {
exceptionHandlerMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
}
ServletWebRequest webRequest = new ServletWebRequest(request, response);
ModelAndViewContainer mavContainer = new ModelAndViewContainer();
ArrayList<Throwable> exceptions = new ArrayList<>();
try {
//省略代码
Object[] arguments = new Object[exceptions.size() + 1];
exceptions.toArray(arguments); // efficient arraycopy call in ArrayList
arguments[arguments.length - 1] = handlerMethod;
//反射调用异常处理类
exceptionHandlerMethod.invokeAndHandle(webRequest, mavContainer, arguments);
}
catch (Throwable invocationEx) {
// Any other than the original exception (or a cause) is unintended here,
// probably an accident (e.g. failed assertion or the like).
if (!exceptions.contains(invocationEx) && logger.isWarnEnabled()) {
logger.warn("Failure in @ExceptionHandler " + exceptionHandlerMethod, invocationEx);
}
// Continue with default processing of the original exception...
return null;
}
//省略
}
主要逻辑就是看如何找到处理对应异常的方法, 进入getExceptionHandlerMethod(handlerMethod, exception);
进入到了ExceptionHandlerExceptionResolver类中, 在这个类里面有两个关键的属性,exceptionHandlerCache和exceptionHandlerAdviceCache, 两个都是map, exceptionHandlerAdviceCache的初始化下面再说,exceptionHandlerCache的初始化想知道的自己去查一下吧
private final Map<Class<?>, ExceptionHandlerMethodResolver> exceptionHandlerCache =
new ConcurrentHashMap<>(64);
private final Map<ControllerAdviceBean, ExceptionHandlerMethodResolver> exceptionHandlerAdviceCache =
new LinkedHashMap<>();
exceptionHandlerCache里面存的就是在当前controller里面包含@ExceptionHandler注解的方法, key: controller类, value : 方法包装类
exceptionHandlerAdviceCache里面存的就是标注了@ControllerAdvice注解的类,里面带有@ExceptionHandler注解的方法, key:
@RestControllerAdvice注解标注的类, value: 方法包装类
@Nullable
protected ServletInvocableHandlerMethod getExceptionHandlerMethod(
@Nullable HandlerMethod handlerMethod, Exception exception) {
Class<?> handlerType = null;
//从exceptionHandlerCache获取异常对应的处理方法, 由于没有配置, 肯定获取不到
if (handlerMethod != null) {
handlerType = handlerMethod.getBeanType();
ExceptionHandlerMethodResolver resolver = this.exceptionHandlerCache.get(handlerType);
if (resolver == null) {
resolver = new ExceptionHandlerMethodResolver(handlerType);
this.exceptionHandlerCache.put(handlerType, resolver);
}
Method method = resolver.resolveMethod(exception);
if (method != null) {
return new ServletInvocableHandlerMethod(handlerMethod.getBean(), method);
}
if (Proxy.isProxyClass(handlerType)) {
handlerType = AopUtils.getTargetClass(handlerMethod.getBean());
}
}
//遍历全局的异常处理类, 看是否可以获取到对应的处理方法
for (Map.Entry<ControllerAdviceBean, ExceptionHandlerMethodResolver> entry : this.exceptionHandlerAdviceCache.entrySet()) {
ControllerAdviceBean advice = entry.getKey();
if (advice.isApplicableToBeanType(handlerType)) {
ExceptionHandlerMethodResolver resolver = entry.getValue();
Method method = resolver.resolveMethod(exception);
if (method != null) {
return new ServletInvocableHandlerMethod(advice.resolveBean(), method);
}
}
}
return null;
}
进入Method method = resolver.resolveMethod(exception);, 最终进入到resolveMethodByExceptionType()方法, 在ExceptionHandlerMethodResolver类中
ExceptionHandlerMethodResolver中有两个关键属性mappedMethods,和exceptionLookupCache, 两个也都是map, 两个都是根据异常获取对应的异常处理方法, mappedMethods在程序启动时候初始化, exceptionLookupCache相当于一个缓存,为了提高查询速度
@Nullable
public Method resolveMethodByExceptionType(Class<? extends Throwable> exceptionType) {
//从缓存中获取处理方法, 如果获取不到,返回null(第一次执行此方法肯定获取不到)
Method method = this.exceptionLookupCache.get(exceptionType);
if (method == null) {
//如果获取不到, 则去mappedMethods获取
method = getMappedMethod(exceptionType);
//将获取的结果缓存到exceptionLookupCache中
this.exceptionLookupCache.put(exceptionType, method);
}
return (method != NO_MATCHING_EXCEPTION_HANDLER_METHOD ? method : null);
}
进入getMappedMethod(exceptionType);
private Method getMappedMethod(Class<? extends Throwable> exceptionType) {
List<Class<? extends Throwable>> matches = new ArrayList<>();
//遍历所有可以处理的异常, 判断与抛出的异常是否匹配
for (Class<? extends Throwable> mappedException : this.mappedMethods.keySet()) {
if (mappedException.isAssignableFrom(exceptionType)) {
matches.add(mappedException);
}
}
if (!matches.isEmpty()) {
//如果有多个方法可以匹配来处理异常,则进行排序
if (matches.size() > 1) {
matches.sort(new ExceptionDepthComparator(exceptionType));
}
//获取第一个方法来处理异常,返回方法
return this.mappedMethods.get(matches.get(0));
}
else {
return NO_MATCHING_EXCEPTION_HANDLER_METHOD;
}
}
到此为止, 已经获取到对应的处理异常的方法了, 在上面的doResolveHandlerMethodException方法中, 最后通过反射调用该方法, 处理异常
接下来讨论一下ExceptionHandlerExceptionResolver类里面的exceptionHandlerCache和exceptionHandlerAdviceCache初始化和
ExceptionHandlerMethodResolver类中的mappedMethods初始化
ExceptionHandlerExceptionResolver初始化
ExceptionHandlerExceptionResolver实现了InitializingBean接口, 猜测初始化肯定在afterPropertiesSet()方法中, 我们至于要查找ExceptionHandlerExceptionResolver是如何注入到springboot容器中的, 及afterPropertiesSet()方法逻辑即可
ExceptionHandlerExceptionResolver注入
实际上，ExceptionHandlerExceptionResolver并不会成为bean交给Spring容器管理。但是在WebMvcConfigurationSupport初始化过程中，会手动调用afterPropertiesSet()进行默认初始化
还记得上面HandlerExceptionResolverComposite类里面有三个异常处理类吗? 看一下他们是如何注入的
在WebMvcConfigurationSupport类里面的handlerExceptionResolver()方法:
@Bean
public HandlerExceptionResolver handlerExceptionResolver(
@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager) {
List<HandlerExceptionResolver> exceptionResolvers = new ArrayList<>();
configureHandlerExceptionResolvers(exceptionResolvers);
//如果是空, 在下面的if里面将三个异常处理类添加到集合中
if (exceptionResolvers.isEmpty()) {
addDefaultHandlerExceptionResolvers(exceptionResolvers, contentNegotiationManager);
}
extendHandlerExceptionResolvers(exceptionResolvers);
HandlerExceptionResolverComposite composite = new HandlerExceptionResolverComposite();
composite.setOrder(0);
//赋值属性, 最后返回
composite.setExceptionResolvers(exceptionResolvers);
return composite;
}
进入到addDefaultHandlerExceptionResolvers(exceptionResolvers, contentNegotiationManager);
protected final void addDefaultHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers,
ContentNegotiationManager mvcContentNegotiationManager) {
//创建ExceptionHandlerExceptionResolver 对象
ExceptionHandlerExceptionResolver exceptionHandlerResolver = createExceptionHandlerExceptionResolver();
exceptionHandlerResolver.setContentNegotiationManager(mvcContentNegotiationManager);
exceptionHandlerResolver.setMessageConverters(getMessageConverters());
exceptionHandlerResolver.setCustomArgumentResolvers(getArgumentResolvers());
exceptionHandlerResolver.setCustomReturnValueHandlers(getReturnValueHandlers());
if (jackson2Present) {
exceptionHandlerResolver.setResponseBodyAdvice(
Collections.singletonList(new JsonViewResponseBodyAdvice()));
}
if (this.applicationContext != null) {
exceptionHandlerResolver.setApplicationContext(this.applicationContext);
}
//手动调用afterPropertiesSet()给属性初始化
exceptionHandlerResolver.afterPropertiesSet();
//添加第一个
exceptionResolvers.add(exceptionHandlerResolver);
ResponseStatusExceptionResolver responseStatusResolver = new ResponseStatusExceptionResolver();
responseStatusResolver.setMessageSource(this.applicationContext);
//添加第二个
exceptionResolvers.add(responseStatusResolver);
//添加第三个
exceptionResolvers.add(new DefaultHandlerExceptionResolver());
}
所以我们只需要看WebMvcConfigurationSupport是如何注入的就可以了, 实际上他是通过WebMvcAutoConfiguration类来间接注入的
而WebMvcAutoConfiguration类的注入是通过自动装配来注册的
ExceptionHandlerExceptionResolver中exceptionHandlerAdviceCache初始化
@Override
public void afterPropertiesSet() {
// Do this first, it may add ResponseBodyAdvice beans
initExceptionHandlerAdviceCache();
if (this.argumentResolvers == null) {
List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.returnValueHandlers == null) {
List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
}
}
进入initExceptionHandlerAdviceCache()方法
private void initExceptionHandlerAdviceCache() {
if (getApplicationContext() == null) {
return;
}
//获取带有ControllerAdvice注解的类
List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());
for (ControllerAdviceBean adviceBean : adviceBeans) {
Class<?> beanType = adviceBean.getBeanType();
if (beanType == null) {
throw new IllegalStateException("Unresolvable type for ControllerAdviceBean: " + adviceBean);
}
//构建value对象, 存入到exceptionHandlerAdviceCache中
//ExceptionHandlerMethodResolver中mappedMethods初始化逻辑也在其中
ExceptionHandlerMethodResolver resolver = new ExceptionHandlerMethodResolver(beanType);
if (resolver.hasExceptionMappings()) {
this.exceptionHandlerAdviceCache.put(adviceBean, resolver);
}
if (ResponseBodyAdvice.class.isAssignableFrom(beanType)) {
this.responseBodyAdvice.add(adviceBean);
}
}
}
ExceptionHandlerMethodResolver中mappedMethods初始化
mappedMethods的初始化逻辑很简单, 在上面的initExceptionHandlerAdviceCache()方法中我们已经找到了带有ControllerAdvice的所有类, 将类的类型作为参数创建了ExceptionHandlerMethodResolver对象, mappedMethods的初始化就在构造方法中
进入ExceptionHandlerMethodResolver resolver = new ExceptionHandlerMethodResolver(beanType) 方法
public ExceptionHandlerMethodResolver(Class<?> handlerType) {
//获取到handlerType类中所有的带有ExceptionHandler注解的方法,
for (Method method : MethodIntrospector.selectMethods(handlerType, EXCEPTION_HANDLER_METHODS)) {
//解析ExceptionHandler注解中的属性, 因为可以配置多个异常类型, 所有返回的是集合, 进行遍历
for (Class<? extends Throwable> exceptionType : detectExceptionMappings(method)) {
//将异常类型作为key, 方法作为value, 存入到mappedMethods中
addExceptionMapping(exceptionType, method);
}
}
}
private List<Class<? extends Throwable>> detectExceptionMappings(Method method) {
List<Class<? extends Throwable>> result = new ArrayList<>();
//获取method上的ExceptionHandler注解的所有的异常类型,存入到result中, 返回
detectAnnotationExceptionMappings(method, result);
if (result.isEmpty()) {
for (Class<?> paramType : method.getParameterTypes()) {
if (Throwable.class.isAssignableFrom(paramType)) {
result.add((Class<? extends Throwable>) paramType);
}
}
}
if (result.isEmpty()) {
throw new IllegalStateException("No exception types mapped to " + method);
}
return result;
}
private void addExceptionMapping(Class<? extends Throwable> exceptionType, Method method) {
Method oldMethod = this.mappedMethods.put(exceptionType, method);
if (oldMethod != null && !oldMethod.equals(method)) {
throw new IllegalStateException("Ambiguous @ExceptionHandler method mapped for [" +
exceptionType + "]: {" + oldMethod + ", " + method + "}");
}
}
结尾
上面已经说了到逻辑代码发生异常之后, 我们自定义的异常处理类如何加载处理这些异常(同时包括系统启动时的一些系统异常), 但是如果抛出一种没有处理类的异常会怎么样呢? 下篇文章在讨论一下
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