@ExceptionHandler異常攔截器

1，基本使用方法

Spring的@ExceptionHandler可以用來統(tǒng)一處理方法拋出的異常，比如這樣：

@ExceptionHandler()
public String handleExeption2(Exception ex) {
    System.out.println("拋異常了:" + ex);
    ex.printStackTrace();
    String resultStr = "異常：默認(rèn)";
    return resultStr;
}

當(dāng)我們使用這個@ExceptionHandler注解時，我們需要定義一個異常的處理方法，比如上面的handleExeption2()方法，給這個方法加上@ExceptionHandler注解，這個方法就會處理類中其他方法（被@RequestMapping注解）拋出的異常。

2，注解的參數(shù)

@ExceptionHandler注解中可以添加參數(shù)，參數(shù)是某個異常類的class，代表這個方法專門處理該類異常，比如這樣：

@ExceptionHandler(NumberFormatException.class)
public String handleExeption(Exception ex) {
    System.out.println("拋異常了:" + ex);
    ex.printStackTrace();
    String resultStr = "異常：NumberFormatException";
    return resultStr;
}

此時注解的參數(shù)是NumberFormatException.class，表示只有方法拋出NumberFormatException時，才會調(diào)用該方法。

3，就近原則

當(dāng)異常發(fā)生時，Spring會選擇最接近拋出異常的處理方法。

比如之前提到的NumberFormatException，這個異常有父類RuntimeException，RuntimeException還有父類Exception，如果我們分別定義異常處理方法，@ExceptionHandler分別使用這三個異常作為參數(shù)，比如這樣：  

@ExceptionHandler(NumberFormatException.class)
public String handleExeption(Exception ex) {
    System.out.println("拋異常了:" + ex);
    ex.printStackTrace();
    String resultStr = "異常：NumberFormatException";
    return resultStr;
}
@ExceptionHandler()
public String handleExeption2(Exception ex) {
    System.out.println("拋異常了:" + ex);
    ex.printStackTrace();
    String resultStr = "異常：默認(rèn)";
    return resultStr;
}
@ExceptionHandler(RuntimeException.class)
public String handleExeption3(Exception ex) {
    System.out.println("拋異常了:" + ex);
    ex.printStackTrace();
    String resultStr = "異常：RuntimeException";
    return resultStr;
}

那么，當(dāng)代碼拋出NumberFormatException時，調(diào)用的方法將是注解參數(shù)NumberFormatException.class的方法，也就是handleExeption()，而當(dāng)代碼拋出IndexOutOfBoundsException時，調(diào)用的方法將是注解參數(shù)RuntimeException的方法，也就是handleExeption3()。

4，注解方法的返回值

標(biāo)識了@ExceptionHandler注解的方法，返回值類型和標(biāo)識了@RequestMapping的方法是統(tǒng)一的，可參見@RequestMapping的說明，比如默認(rèn)返回Spring的ModelAndView對象，也可以返回String，這時的String是ModelAndView的路徑，而不是字符串本身。

有些情況下我們會給標(biāo)識了@RequestMapping的方法添加@ResponseBody，比如使用Ajax的場景，直接返回字符串，異常處理類也可以如此操作，添加@ResponseBody注解后，可以直接返回字符串，比如這樣：

@ExceptionHandler(NumberFormatException.class)
@ResponseBody
public String handleExeption(Exception ex) {
    System.out.println("拋異常了:" + ex);
    ex.printStackTrace();
    String resultStr = "異常：NumberFormatException";
    return resultStr;
}

這樣的操作可以在執(zhí)行完方法后直接返回字符串本身。

5，錯誤的操作

使用@ExceptionHandler時盡量不要使用相同的注解參數(shù)。

如果我們定義兩個處理相同異常的處理方法：

@ExceptionHandler(NumberFormatException.class)
@ResponseBody
public String handleExeption(Exception ex) {
    System.out.println("拋異常了:" + ex);
    ex.printStackTrace();
    String resultStr = "異常：NumberFormatException";
    return resultStr;
}
@ExceptionHandler(NumberFormatException.class)
@ResponseBody
public String handleExeption2(Exception ex) {
    System.out.println("拋異常了:" + ex);
    ex.printStackTrace();
    String resultStr = "異常：默認(rèn)";
    return resultStr;
}

兩個方法都處理NumberFormatException，這種定義方式編譯可以通過，而當(dāng)NumberFormatException真正被拋出時，Spring會給我們報錯：

java.lang.IllegalStateException: Ambiguous @ExceptionHandler method mapped for [class java.lang.NumberFormatException]: {public java.lang.String TestController.handleExeption(java.lang.Exception), public java.lang.String TestController.handleExeption2(java.lang.Exception)}
    at org.springframework.web.method.annotation.ExceptionHandlerMethodResolver.addExceptionMapping(ExceptionHandlerMethodResolver.java:102) ~[spring-web-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.web.method.annotation.ExceptionHandlerMethodResolver.<init>(ExceptionHandlerMethodResolver.java:66) ~[spring-web-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver.getExceptionHandlerMethod(ExceptionHandlerExceptionResolver.java:458) ~[spring-webmvc-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver.doResolveHandlerMethodException(ExceptionHandlerExceptionResolver.java:378) ~[spring-webmvc-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.web.servlet.handler.AbstractHandlerMethodExceptionResolver.doResolveException(AbstractHandlerMethodExceptionResolver.java:61) ~[spring-webmvc-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.web.servlet.handler.AbstractHandlerExceptionResolver.resolveException(AbstractHandlerExceptionResolver.java:140) ~[spring-webmvc-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.web.servlet.handler.HandlerExceptionResolverComposite.resolveException(HandlerExceptionResolverComposite.java:78) ~[spring-webmvc-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.processHandlerException(DispatcherServlet.java:1255) ~[spring-webmvc-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1062) ~[spring-webmvc-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1008) ~[spring-webmvc-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925) ~[spring-webmvc-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:974) ~[spring-webmvc-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:877) ~[spring-webmvc-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:707) ~[javax.servlet-api-3.1.0.jar:3.1.0]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:851) ~[spring-webmvc-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) ~[javax.servlet-api-3.1.0.jar:3.1.0]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) ~[tomcat-embed-websocket-8.5.29.jar:8.5.29]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:109) ~[spring-web-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:81) ~[spring-web-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) ~[spring-web-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) ~[tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:496) [tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) [tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) [tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803) [tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790) [tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459) [tomcat-embed-core-8.5.29.jar:8.5.29]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.29.jar:8.5.29]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_172]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_172]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.29.jar:8.5.29]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_172]

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