SpringBoot介面如何對異常進行統一封裝，並統一返回呢？以上文的引數校驗為例，如何優雅的將引數校驗的錯誤資訊統一處理並封裝返回呢？@pdai
為什麼要優雅的處理異常
如果我們不統一的處理異常，經常會在controller層有大量的異常處理的程式碼， 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) {
// 每個介面充斥著大量的異常處理
try {
// do something
} catch(Exception e) {
return ResponseEntity.fail("error");
}
return ResponseEntity.ok("success");
}
}
那怎麼實現統一的異常處理，特別是結合引數校驗等封裝？
實現案例
簡單展示通過@ControllerAdvice進行統一異常處理。
@ControllerAdvice異常統一處理
對於400引數錯誤異常
/**
* 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");
}
}
對於自定義異常
/**
* handle business exception.
*
* @param businessException
* business exception
* @return ResponseResult
*/
@ResponseBody
@ExceptionHandler(BusinessException.class)
public ResponseResult<BusinessException> processBusinessException(BusinessException businessException) {
log.error(businessException.getLocalizedMessage(), businessException);
// 這裡可以遮蔽掉後臺的異常棧資訊，直接返回"business error"
return ResponseResultEntity.fail(businessException, businessException.getLocalizedMessage());
}
對於其它異常
/**
* handle other exception.
*
* @param exception
* exception
* @return ResponseResult
*/
@ResponseBody
@ExceptionHandler(Exception.class)
public ResponseResult<Exception> processException(Exception exception) {
log.error(exception.getLocalizedMessage(), exception);
// 這裡可以遮蔽掉後臺的異常棧資訊，直接返回"server error"
return ResponseResultEntity.fail(exception, exception.getLocalizedMessage());
}
Controller介面
（介面中無需處理異常）
@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);
}
}
執行測試
這裡用postman測試下
進一步理解
我們再通過一些問題來幫助你更深入理解@ControllerAdvice。@pdai
@ControllerAdvice還可以怎麼用？
除了通過@ExceptionHandler註解用於全域性異常的處理之外，@ControllerAdvice還有兩個用法：
- @InitBinder註解
用於請求中註冊自定義引數的解析，從而達到自定義請求引數格式的目的；
比如，在@ControllerAdvice註解的類中新增如下方法，來統一處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中傳入引數（string型別）自動轉化為Date型別
@GetMapping("testDate")
public Date processApi(Date date) {
return date;
}
- @ModelAttribute註解
用來預設全域性引數，比如最典型的使用Spring Security時將新增當前登入的使用者資訊（UserDetails)作為引數。
@ModelAttribute("currentUser")
public UserDetails modelAttribute() {
return (UserDetails) SecurityContextHolder.getContext().getAuthentication().getPrincipal();
}
所有controller類中requestMapping方法都可以直接獲取並使用currentUser
@PostMapping("saveSomething")
public ResponseEntity<String> saveSomeObj(@ModelAttribute("currentUser") UserDetails operator) {
// 儲存操作，並設定當前操作人員的ID（從UserDetails中獲得）
return ResponseEntity.success("ok");
}
@ControllerAdvice是如何起作用的（原理）？
我們在Spring基礎 - SpringMVC案例和機制的基礎上來看@ControllerAdvice的原始碼實現。
DispatcherServlet中onRefresh方法是初始化ApplicationContext後的回撥方法，它會呼叫initStrategies方法，主要更新一些servlet需要使用的物件，包括國際化處理，requestMapping，檢視解析等等。
/**
* 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); // 檔案上傳
initLocaleResolver(context); // i18n國際化
initThemeResolver(context); // 主題
initHandlerMappings(context); // requestMapping
initHandlerAdapters(context); // adapters
initHandlerExceptionResolvers(context); // 異常處理
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}
從上述程式碼看，如果要提供@ControllerAdvice提供的三種註解功能，從設計和實現的角度肯定是實現的程式碼需要放在initStrategies方法中。
- @ModelAttribute和@InitBinder處理
具體來看，如果你是設計者，很顯然容易想到：對於@ModelAttribute提供的引數預置和@InitBinder註解提供的預處理方法應該是放在一個方法中的，因為它們都是在進入requestMapping方法前做的操作。
如下方法是獲取所有的HandlerAdapter，無非就是從BeanFactory中獲取（BeanFactory相關知識請參考 Spring進階- Spring IOC實現原理詳解之IOC體系結構設計)
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");
}
}
}
我們要處理的是requestMapping的handlerResolver，作為設計者，就很容易出如下的結構
在RequestMappingHandlerAdapter中的afterPropertiesSet去處理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);
}
// 快取所有modelAttribute註解方法
Set<Method> attrMethods = MethodIntrospector.selectMethods(beanType, MODEL_ATTRIBUTE_METHODS);
if (!attrMethods.isEmpty()) {
this.modelAttributeAdviceCache.put(adviceBean, attrMethods);
}
// 快取所有initBinder註解方法
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處理
@ExceptionHandler顯然是在上述initHandlerExceptionResolvers(context)方法中。
同樣的，從BeanFactory中獲取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");
}
}
}
我們很容易找到ExceptionHandlerExceptionResolver
同樣的在afterPropertiesSet去處理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);
}
}
}
示例原始碼
https://github.com/realpdai/tech-pdai-spring-demos
更多內容
告別碎片化學習，無套路一站式體系化學習後端開發: Java 全棧知識體系(https://pdai.tech)