SpringMVC 异常处理 - HandlerExceptionResolver
2018-01-23 21:49
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ref: http://blog.csdn.net/u012420654/article/details/52141807
基本概念
在 SpringMVC 中 HandlerExceptionResolver 接口负责统一异常处理。
内部构造
下面来看它的源码:public interface HandlerExceptionResolver { ModelAndView resolveException( HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex); }1
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再来看它的继承关系:
AbstractHandlerMethodExceptionResolver
该类是实现了 HandlerExceptionResolver 接口的抽象实现类。关键来看 resolveException 方法:public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) { // 1.判断是否支持该处理器 if (shouldApplyTo(request, handler)) { // 省略部分源码... // 2.预处理响应消息,让请求头取消缓存 prepareResponse(ex, response); // 3.异常处理,空方法 ModelAndView mav = doResolveException(request, response, handler, ex); if (mav != null) { logException(ex, request); } return mav; } else { return null; } }1
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接着来看 shouldApplyTo 方法:
protected boolean shouldApplyTo(HttpServletRequest request, Object handler) { if (handler != null) { // 分别比对 mappedHandlers 、mappedHandlerClasses if (this.mappedHandlers != null && this.mappedHandlers.contains(handler)) { return true; } if (this.mappedHandlerClasses != null) { for (Class<?> handlerClass : this.mappedHandlerClasses) { if (handlerClass.isInstance(handler)) { return true; } } } } return (this.mappedHandlers == null && this.mappedHandlerClasses == null); }1
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SimpleMappingExceptionResolver
它继承了 AbstractHandlerMethodExceptionResolver 。实现了真正的异常处理。来看该类的 doResolveException 方法:
protected ModelAndView doResolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) { // 1.决定的视图 String viewName = determineViewName(ex, request); if (viewName != null) { // 2.决定错误状态码 Integer statusCode = determineStatusCode(request, viewName); if (statusCode != null) { 3.设置错误状态码 applyStatusCodeIfPossible(request, response, statusCode); } // 4.返回错误页面 return getModelAndView(viewName, ex, request); } else { return null; } }1
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1.决定视图
// 被过滤的异常集合 private Class<?>[] excludedExceptions; // 被处理的异常集合 private Properties exceptionMappings; // 默认的错误显示页面 private String defaultErrorView; protected String determineViewName(Exception ex, HttpServletRequest request) { String viewName = null; // 1.判断属于被过滤的异常? if (this.excludedExceptions != null) { for (Class<?> excludedEx : this.excludedExceptions) { if (excludedEx.equals(ex.getClass())) { return null; } } } // 2.判断属于被处理的异常? if (this.exceptionMappings != null) { // 找到匹配的页面 viewName = findMatchingViewName(this.exceptionMappings, ex); } // 3.为空则使用默认的错误页面 if (viewName == null && this.defaultErrorView != null) { viewName = this.defaultErrorView; } return viewName; }1
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接着来看 findMatchingViewName 方法:
protected String findMatchingViewName(Properties exceptionMappings, Exception ex) { String viewName = null; String dominantMapping = null; int deepest = Integer.MAX_VALUE; // 遍历 exceptionMappings for (Enumeration<?> names = exceptionMappings.propertyNames(); names.hasMoreElements();) { String exceptionMapping = (String) names.nextElement(); // 关键 -> 匹配异常 int depth = getDepth(exceptionMapping, ex); if (depth >= 0 && ( depth < deepest || (depth == deepest && dominantMapping != null && exceptionMapping.length() > dominantMapping.length() ) )) { deepest = depth; dominantMapping = exceptionMapping; viewName = exceptionMappings.getProperty(exceptionMapping); } } // 省略代码... return viewName; }1
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继续来看 getDepth 方法:
protected int getDepth(String exceptionMapping, Exception ex) { // 匹配返回 0,不匹配返回 -1 ,depth 越低的好 return getDepth(exceptionMapping, ex.getClass(), 0); } private int getDepth(String exceptionMapping, Class<?> exceptionClass, int depth) { if (exceptionClass.getName().contains(exceptionMapping)) { return depth; } if (exceptionClass == Throwable.class) { return -1; } return getDepth(exceptionMapping, exceptionClass.getSuperclass(), depth + 1); }1
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2.决定错误状态码
// 在配置文件中定义 private Map<String, Integer> statusCodes = new HashMap<String, Integer>(); protected Integer determineStatusCode(HttpServletRequest request, String viewName) { if (this.statusCodes.containsKey(viewName)) { return this.statusCodes.get(viewName); } return this.defaultStatusCode; }1
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3.设置错误状态码
public static final String ERROR_STATUS_CODE_ATTRIBUTE = "javax.servlet.error.status_code"; protected void applyStatusCodeIfPossible(HttpServletRequest request, HttpServletResponse response, int statusCode) { if (!WebUtils.isIncludeRequest(request)) { // 省略代码... // 设置错误状态码,并添加到 request 的属性 response.setStatus(statusCode); request.setAttribute(WebUtils.ERROR_STATUS_CODE_ATTRIBUTE, statusCode); } }1
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4.返回错误页面
protected ModelAndView getModelAndView(String viewName, Exception ex, HttpServletRequest request) { return getModelAndView(viewName, ex); } protected ModelAndView getModelAndView(String viewName, Exception ex) { ModelAndView mv = new ModelAndView(viewName); if (this.exceptionAttribute != null) { // 省略代码... mv.addObject(this.exceptionAttribute, ex); } return mv; }1
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实例探究
下面来看 springmvc 中常见的统一异常处理方法。
1.实现 HandlerExceptionResolver 接口
首先需要实现 HandlerExceptionResolver 接口。public class MyExceptionResolver implements HandlerExceptionResolver { @Override public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) { // 异常处理... // 视图显示专门的错误页 ModelAndView modelAndView = new ModelAndView("error"); return modelAndView; } }1
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配置到 Spring 配置文件中,或者加上@Component 注解。
<bean class="com.resolver.MyExceptionResolver"/>1
2.添加 @ExceptionHandler 注解
首先来看它的注解定义:// 只能作用在方法上,运行时有效 Target(ElementType.METHOD) Retention(RetentionPolicy.RUNTIME) @Documented public @interface ExceptionHandler { // 这里可以定义异常类型,为空表示匹配任何异常 Class<? extends Throwable>[] value() default {}; }1
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在控制器中使用,可以定义不同方法来处理不同类型的异常。
public abstract class BaseController { // 处理 IO 异常 @ExceptionHandler(IOException.class) public ModelAndView handleIOException(HttpServletRequest request, HttpServletResponse response, Exception e) { // 视图显示专门的错误页 ModelAndView modelAndView = new ModelAndView("error"); return modelAndView; } // 处理空指针异常 @ExceptionHandler(NullPointerException.class) public ModelAndView handleException(HttpServletRequest request, HttpServletResponse response, Exception e) { // 视图显示专门的错误页 ModelAndView modelAndView = new ModelAndView("error"); return modelAndView; } }1
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使用 @ExceptionHandler 注解实现异常处理有个缺陷就是只对该注解所在的控制器有效。
想要让所有的所有的控制器都生效,就要通过继承来实现。
如上所示(定义了一个抽象的基类控制器) ,可以让其他控制器继承它实现异常处理。
public class HelloController extends BaseController1
3.利用 SimpleMappingExceptionResolver 类
该类实现了 HandlerExceptionResolver 接口,是 springmvc 默认实现的类,通过它可以实现灵活的异常处理。只需要在 xml 文件中进行如下配置:
<bean class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver"> <property name="exceptionMappings"> <props> <prop key="NullPointerException">nullpointpage</prop> <prop key="IOException">iopage</prop> <prop key="NumberFormatException">numberpage</prop> </props> </property> <property name="statusCodes"> <props> <prop key="nullpointpage">400</prop> <prop key="iopage">500</prop> </props> </property> <property name="defaultErrorView" value="errorpage"/> <property name="defaultStatusCode" value="404"/> </bean>1
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exceptionMappings:定义 springmvc 要处理的异常类型和对应的错误页面;
statusCodes:定义错误页面和response 中要返回的错误状态码
defaultErrorView:定义默认错误显示页面,表示处理不了的异常都显示该页面。在这里表示 springmvc 处理不了的异常都跳转到 errorpage页面。
defaultStatusCode:定义 response 默认返回的错误状态码,表示错误页面未定义对应的错误状态码时返回该值;在这里表示跳转到 errorpage、numberpage 页面的 reponse 状态码为 404。
4.ajax 异常处理
对于页面 ajax 的请求产生的异常不就适合跳转到错误页面,而是应该是将异常信息显示在请求回应的结果中。实现方式也很简单,需要继承了 SimpleMappingExceptionResolver ,重写它的异常处理流程(下面会详细分析)。
public class CustomSimpleMappingExceptionResolver extends SimpleMappingExceptionResolver { @Override protected ModelAndView doResolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) { // 判断是否 Ajax 请求 if ((request.getHeader("accept").indexOf("application/json") > -1 || (request.getHeader("X-Requested-With") != null && request.getHeader("X-Requested-With").indexOf("XMLHttpRequest") > -1))){ try { response.setContentType("text/html;charset=UTF-8"); response.setCharacterEncoding("UTF-8"); PrintWriter writer = response.getWriter(); writer.write(ex.getMessage()); writer.flush(); writer.close(); } catch (Exception e) { LogHelper.info(e); } return null; } return super.doResolveException(request, response, handler, ex); } }1
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配置文件如上,只是将注入的 Bean 替换成我们自己的定义的 CustomSimpleMappingExceptionResolver 。
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