SpringBoot接口如何对异常进行统一封装，并统一返回呢？以上文的参数校验为例，如何优雅的将参数校验的错误信息统一处理并封装返回呢？@pdai
为什么要优雅的处理异常
如果我们不统一的处理异常，经常会在controller层有大量的异常处理的代码， 比如：
@Slf4j
@Api(value = "User Interfaces", tags = "User Interfaces")
@RestController
@RequestMapping("/user")
public class UserController {
/**
* http://localhost:8080/user/add .
*
* @param userParam user param
* @return user
*/
@ApiOperation("Add User")
@ApiImplicitParam(name = "userParam", type = "body", dataTypeClass = UserParam.class, required = true)
@PostMapping("add")
public ResponseEntity<String> add(@Valid @RequestBody UserParam userParam) {
// 每个接口充斥着大量的异常处理
try {
// do something
} catch(Exception e) {
return ResponseEntity.fail("error");
}
return ResponseEntity.ok("success");
}
}
那怎么实现统一的异常处理，特别是结合参数校验等封装？
实现案例
简单展示通过@ControllerAdvice进行统一异常处理。
@ControllerAdvice异常统一处理
对于400参数错误异常
/**
* Global exception handler.
*
* @author pdai
*/
@Slf4j
@RestControllerAdvice
public class GlobalExceptionHandler {
/**
* exception handler for bad request.
*
* @param e
* exception
* @return ResponseResult
*/
@ResponseBody
@ResponseStatus(code = HttpStatus.BAD_REQUEST)
@ExceptionHandler(value = { BindException.class, ValidationException.class, MethodArgumentNotValidException.class })
public ResponseResult<ExceptionData> handleParameterVerificationException(@NonNull Exception e) {
ExceptionData.ExceptionDataBuilder exceptionDataBuilder = ExceptionData.builder();
log.warn("Exception: {}", e.getMessage());
if (e instanceof BindException) {
BindingResult bindingResult = ((MethodArgumentNotValidException) e).getBindingResult();
bindingResult.getAllErrors().stream().map(DefaultMessageSourceResolvable::getDefaultMessage)
.forEach(exceptionDataBuilder::error);
} else if (e instanceof ConstraintViolationException) {
if (e.getMessage() != null) {
exceptionDataBuilder.error(e.getMessage());
}
} else {
exceptionDataBuilder.error("invalid parameter");
}
return ResponseResultEntity.fail(exceptionDataBuilder.build(), "invalid parameter");
}
}
对于自定义异常
/**
* handle business exception.
*
* @param businessException
* business exception
* @return ResponseResult
*/
@ResponseBody
@ExceptionHandler(BusinessException.class)
public ResponseResult<BusinessException> processBusinessException(BusinessException businessException) {
log.error(businessException.getLocalizedMessage(), businessException);
// 这里可以屏蔽掉后台的异常栈信息，直接返回"business error"
return ResponseResultEntity.fail(businessException, businessException.getLocalizedMessage());
}
对于其它异常
/**
* handle other exception.
*
* @param exception
* exception
* @return ResponseResult
*/
@ResponseBody
@ExceptionHandler(Exception.class)
public ResponseResult<Exception> processException(Exception exception) {
log.error(exception.getLocalizedMessage(), exception);
// 这里可以屏蔽掉后台的异常栈信息，直接返回"server error"
return ResponseResultEntity.fail(exception, exception.getLocalizedMessage());
}
Controller接口
（接口中无需处理异常）
@Slf4j
@Api(value = "User Interfaces", tags = "User Interfaces")
@RestController
@RequestMapping("/user")
public class UserController {
/**
* http://localhost:8080/user/add .
*
* @param userParam user param
* @return user
*/
@ApiOperation("Add User")
@ApiImplicitParam(name = "userParam", type = "body", dataTypeClass = UserParam.class, required = true)
@PostMapping("add")
public ResponseEntity<UserParam> add(@Valid @RequestBody UserParam userParam) {
return ResponseEntity.ok(userParam);
}
}
运行测试
这里用postman测试下
进一步理解
我们再通过一些问题来帮助你更深入理解@ControllerAdvice。@pdai
@ControllerAdvice还可以怎么用？
除了通过@ExceptionHandler注解用于全局异常的处理之外，@ControllerAdvice还有两个用法：
- @InitBinder注解
用于请求中注册自定义参数的解析，从而达到自定义请求参数格式的目的；
比如，在@ControllerAdvice注解的类中添加如下方法，来统一处理日期格式的格式化
@InitBinder
public void handleInitBinder(WebDataBinder dataBinder){
dataBinder.registerCustomEditor(Date.class,
new CustomDateEditor(new SimpleDateFormat("yyyy-MM-dd"), false));
}
Controller中传入参数（string类型）自动转化为Date类型
@GetMapping("testDate")
public Date processApi(Date date) {
return date;
}
- @ModelAttribute注解
用来预设全局参数，比如最典型的使用Spring Security时将添加当前登录的用户信息（UserDetails)作为参数。
@ModelAttribute("currentUser")
public UserDetails modelAttribute() {
return (UserDetails) SecurityContextHolder.getContext().getAuthentication().getPrincipal();
}
所有controller类中requestMapping方法都可以直接获取并使用currentUser
@PostMapping("saveSomething")
public ResponseEntity<String> saveSomeObj(@ModelAttribute("currentUser") UserDetails operator) {
// 保存操作，并设置当前操作人员的ID（从UserDetails中获得）
return ResponseEntity.success("ok");
}
@ControllerAdvice是如何起作用的（原理）？
我们在Spring基础 - SpringMVC案例和机制的基础上来看@ControllerAdvice的源码实现。
DispatcherServlet中onRefresh方法是初始化ApplicationContext后的回调方法，它会调用initStrategies方法，主要更新一些servlet需要使用的对象，包括国际化处理，requestMapping，视图解析等等。
/**
* This implementation calls {@link #initStrategies}.
*/
@Override
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}
/**
* Initialize the strategy objects that this servlet uses.
* <p>May be overridden in subclasses in order to initialize further strategy objects.
*/
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context); // 文件上传
initLocaleResolver(context); // i18n国际化
initThemeResolver(context); // 主题
initHandlerMappings(context); // requestMapping
initHandlerAdapters(context); // adapters
initHandlerExceptionResolvers(context); // 异常处理
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}
从上述代码看，如果要提供@ControllerAdvice提供的三种注解功能，从设计和实现的角度肯定是实现的代码需要放在initStrategies方法中。
- @ModelAttribute和@InitBinder处理
具体来看，如果你是设计者，很显然容易想到：对于@ModelAttribute提供的参数预置和@InitBinder注解提供的预处理方法应该是放在一个方法中的，因为它们都是在进入requestMapping方法前做的操作。
如下方法是获取所有的HandlerAdapter，无非就是从BeanFactory中获取（BeanFactory相关知识请参考 Spring进阶- Spring IOC实现原理详解之IOC体系结构设计)
private void initHandlerAdapters(ApplicationContext context) {
this.handlerAdapters = null;
if (this.detectAllHandlerAdapters) {
// Find all HandlerAdapters in the ApplicationContext, including ancestor contexts.
Map<String, HandlerAdapter> matchingBeans =
BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerAdapters = new ArrayList<>(matchingBeans.values());
// We keep HandlerAdapters in sorted order.
AnnotationAwareOrderComparator.sort(this.handlerAdapters);
}
}
else {
try {
HandlerAdapter ha = context.getBean(HANDLER_ADAPTER_BEAN_NAME, HandlerAdapter.class);
this.handlerAdapters = Collections.singletonList(ha);
}
catch (NoSuchBeanDefinitionException ex) {
// Ignore, we'll add a default HandlerAdapter later.
}
}
// Ensure we have at least some HandlerAdapters, by registering
// default HandlerAdapters if no other adapters are found.
if (this.handlerAdapters == null) {
this.handlerAdapters = getDefaultStrategies(context, HandlerAdapter.class);
if (logger.isTraceEnabled()) {
logger.trace("No HandlerAdapters declared for servlet '" + getServletName() +
"': using default strategies from DispatcherServlet.properties");
}
}
}
我们要处理的是requestMapping的handlerResolver，作为设计者，就很容易出如下的结构
在RequestMappingHandlerAdapter中的afterPropertiesSet去处理advice
@Override
public void afterPropertiesSet() {
// Do this first, it may add ResponseBody advice beans
initControllerAdviceCache();
if (this.argumentResolvers == null) {
List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.initBinderArgumentResolvers == null) {
List<HandlerMethodArgumentResolver> resolvers = getDefaultInitBinderArgumentResolvers();
this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.returnValueHandlers == null) {
List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
}
}
private void initControllerAdviceCache() {
if (getApplicationContext() == null) {
return;
}
List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());
List<Object> requestResponseBodyAdviceBeans = new ArrayList<>();
for (ControllerAdviceBean adviceBean : adviceBeans) {
Class<?> beanType = adviceBean.getBeanType();
if (beanType == null) {
throw new IllegalStateException("Unresolvable type for ControllerAdviceBean: " + adviceBean);
}
// 缓存所有modelAttribute注解方法
Set<Method> attrMethods = MethodIntrospector.selectMethods(beanType, MODEL_ATTRIBUTE_METHODS);
if (!attrMethods.isEmpty()) {
this.modelAttributeAdviceCache.put(adviceBean, attrMethods);
}
// 缓存所有initBinder注解方法
Set<Method> binderMethods = MethodIntrospector.selectMethods(beanType, INIT_BINDER_METHODS);
if (!binderMethods.isEmpty()) {
this.initBinderAdviceCache.put(adviceBean, binderMethods);
}
if (RequestBodyAdvice.class.isAssignableFrom(beanType) || ResponseBodyAdvice.class.isAssignableFrom(beanType)) {
requestResponseBodyAdviceBeans.add(adviceBean);
}
}
if (!requestResponseBodyAdviceBeans.isEmpty()) {
this.requestResponseBodyAdvice.addAll(0, requestResponseBodyAdviceBeans);
}
}
- @ExceptionHandler处理
@ExceptionHandler显然是在上述initHandlerExceptionResolvers(context)方法中。
同样的，从BeanFactory中获取HandlerExceptionResolver
/**
* Initialize the HandlerExceptionResolver used by this class.
* <p>If no bean is defined with the given name in the BeanFactory for this namespace,
* we default to no exception resolver.
*/
private void initHandlerExceptionResolvers(ApplicationContext context) {
this.handlerExceptionResolvers = null;
if (this.detectAllHandlerExceptionResolvers) {
// Find all HandlerExceptionResolvers in the ApplicationContext, including ancestor contexts.
Map<String, HandlerExceptionResolver> matchingBeans = BeanFactoryUtils
.beansOfTypeIncludingAncestors(context, HandlerExceptionResolver.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerExceptionResolvers = new ArrayList<>(matchingBeans.values());
// We keep HandlerExceptionResolvers in sorted order.
AnnotationAwareOrderComparator.sort(this.handlerExceptionResolvers);
}
}
else {
try {
HandlerExceptionResolver her =
context.getBean(HANDLER_EXCEPTION_RESOLVER_BEAN_NAME, HandlerExceptionResolver.class);
this.handlerExceptionResolvers = Collections.singletonList(her);
}
catch (NoSuchBeanDefinitionException ex) {
// Ignore, no HandlerExceptionResolver is fine too.
}
}
// Ensure we have at least some HandlerExceptionResolvers, by registering
// default HandlerExceptionResolvers if no other resolvers are found.
if (this.handlerExceptionResolvers == null) {
this.handlerExceptionResolvers = getDefaultStrategies(context, HandlerExceptionResolver.class);
if (logger.isTraceEnabled()) {
logger.trace("No HandlerExceptionResolvers declared in servlet '" + getServletName() +
"': using default strategies from DispatcherServlet.properties");
}
}
}
我们很容易找到ExceptionHandlerExceptionResolver
同样的在afterPropertiesSet去处理advice
@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);
}
}
private void initExceptionHandlerAdviceCache() {
if (getApplicationContext() == null) {
return;
}
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);
}
ExceptionHandlerMethodResolver resolver = new ExceptionHandlerMethodResolver(beanType);
if (resolver.hasExceptionMappings()) {
this.exceptionHandlerAdviceCache.put(adviceBean, resolver);
}
if (ResponseBodyAdvice.class.isAssignableFrom(beanType)) {
this.responseBodyAdvice.add(adviceBean);
}
}
}
示例源码
https://github.com/realpdai/tech-pdai-spring-demos
更多内容
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