Spring中的@ExceptionHandler注解统一异常处理详解
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1，基本使用方法
Spring的@ExceptionHandler可以用来统一处理方法抛出的异常，比如这样：
@ExceptionHandler()
public String handleExeption2(Exception ex) {
System.out.println("抛异常了:" + ex);
ex.printStackTrace();
String resultStr = "异常：默认";
return resultStr;
}当我们使用这个@ExceptionHandler注解时，我们需要定义一个异常的处理方法，比如上面的handleExeption2()方法，给这个方法加上@ExceptionHandler注解，这个方法就会处理类中其他方法（被@RequestMapping注解）抛出的异常。
2，注解的参数
@ExceptionHandler注解中可以添加参数，参数是某个异常类的class，代表这个方法专门处理该类异常，比如这样：
@ExceptionHandler(NumberFormatException.class)
public String handleExeption(Exception ex) {
System.out.println("抛异常了:" + ex);
ex.printStackTrace();
String resultStr = "异常：NumberFormatException";
return resultStr;
}此时注解的参数是NumberFormatException.class，表示只有方法抛出NumberFormatException时，才会调用该方法。
3，就近原则
当异常发生时，Spring会选择最接近抛出异常的处理方法。
比如之前提到的NumberFormatException，这个异常有父类RuntimeException，RuntimeException还有父类Exception，如果我们分别定义异常处理方法，@ExceptionHandler分别使用这三个异常作为参数，比如这样：
@ExceptionHandler(NumberFormatException.class)
public String handleExeption(Exception ex) {
System.out.println("抛异常了:" + ex);
ex.printStackTrace();
String resultStr = "异常：NumberFormatException";
return resultStr;
}
@ExceptionHandler()
public String handleExeption2(Exception ex) {
System.out.println("抛异常了:" + ex);
ex.printStackTrace();
String resultStr = "异常：默认";
return resultStr;
}
@ExceptionHandler(RuntimeException.class)
public String handleExeption3(Exception ex) {
System.out.println("抛异常了:" + ex);
ex.printStackTrace();
String resultStr = "异常：RuntimeException";
return resultStr;
}那么，当代码抛出NumberFormatException时，调用的方法将是注解参数NumberFormatException.class的方法，也就是handleExeption()，而当代码抛出IndexOutOfBoundsException时，调用的方法将是注解参数RuntimeException的方法，也就是handleExeption3()。
4，注解方法的返回值
标识了@ExceptionHandler注解的方法，返回值类型和标识了@RequestMapping的方法是统一的，可参见@RequestMapping的说明，比如默认返回Spring的ModelAndView对象，也可以返回String，这时的String是ModelAndView的路径，而不是字符串本身。
有些情况下我们会给标识了@RequestMapping的方法添加@ResponseBody，比如使用Ajax的场景，直接返回字符串，异常处理类也可以如此操作，添加@ResponseBody注解后，可以直接返回字符串，比如这样：
@ExceptionHandler(NumberFormatException.class)
@ResponseBody
public String handleExeption(Exception ex) {
System.out.println("抛异常了:" + ex);
ex.printStackTrace();
String resultStr = "异常：NumberFormatException";
return resultStr;
}这样的操作可以在执行完方法后直接返回字符串本身。
5，错误的操作
使用@ExceptionHandler时尽量不要使用相同的注解参数。
如果我们定义两个处理相同异常的处理方法：
@ExceptionHandler(NumberFormatException.class)
@ResponseBody
public String handleExeption(Exception ex) {
System.out.println("抛异常了:" + ex);
ex.printStackTrace();
String resultStr = "异常：NumberFormatException";
return resultStr;
}
@ExceptionHandler(NumberFormatException.class)
@ResponseBody
public String handleExeption2(Exception ex) {
System.out.println("抛异常了:" + ex);
ex.printStackTrace();
String resultStr = "异常：默认";
return resultStr;
}两个方法都处理NumberFormatException，这种定义方式编译可以通过，而当NumberFormatException真正被抛出时，Spring会给我们报错：
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]
我在工作当中的使用：
做统一异常处理，如下
1.在app-auth服务我抛出了一个一异常
2.该异常是在common下面定义的一个基础异常
3.然后在common的另一个模块中用这个方法来统一处理BaseException异常
AjaxResult 是一个通用的返回前端的对象，所以只要在需要的地方抛出这个基础异常，就可以直接统一处理，返回需要的数据到前端。
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