SpringMVC 之拦截器和异常处理

1. 文件上传

• Spring 使用 Jakarta Commons FileUpload 技术实现了一个 MultipartResolver 实现类:
  CommonsMultipartResolver;
• SpringMVC 上下文中默认没有装配 MultipartResolver,因此默认情况下不能处理文件的上传;
  若要使用上传功能,需要在上下文中配置 MultipartResolver;

// 1. 导入 jar 包
      /* commons-fileupload;
       * commons-io;
       */

// 2. 配置 MultipartResolver(多媒体解析器)
<bean id="multipartResolver"
        class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
    <property name="defaultEncoding" value="UTF-8"></property>

    <!-- 文件大小 1M -->
    <property name="maxUploadSize" value="1048576"/>
</bean>

// index.jsp
<h2>文件上传</h2>
<form action="${pageContext.request.contextPath}/testUpload" method="post"
                                                    enctype="multipart/form-data">
    file1:<input type="file" name="upload"/><br/>
    file2:<input type="file" name="upload"/><br/>
    file3:<input type="file" name="upload"/><br/>
    <input type="submit" value="上传"/><br/>
</form>


// Demo.java
@RequestMapping(value="/testUpload",method=RequestMethod.POST)
public String testUpload(@RequestParam("upload") MultipartFile[] file)
                                     throws IllegalStateException, IOException {

    for(MultipartFile mf : file){
        if(!mf.isEmpty()){
            mf.transferTo(new File("/Users/用户名/Documents/上传/"+
                                                          mf.getOriginalFilename()));
        }
    }
    return "ok";
}

2. 自定义拦截器

1. 自定义的拦截器必须实现 HandlerInterceptor 接口:
   • preHandle():这个方法在业务处理器处理请求之前被调用,在该方法中对用户请求 request 进行
     处理;如果拦截处理后,还需要调用其他的拦截器,或者是业务处理器,则返回 true; 否则,返回false;
   • postHandle():这个方法在业务处理器处理完请求后,但是,DispatcherServlet 向客户端返回
     响应前被调用,处理用户的 request请求;
   • afterCompletion():这个方法在 DispatcherServlet 完全处理完请求后被调用,可以在该方
     法中进行一些资源清理的操作;

// FirstInterceptor.java
public class FirstInterceptor implements HandlerInterceptor{
    public boolean preHandle(HttpServletRequest req,HttpServletResponse resp,
                                                Object handler)throws Exception{
        System.out.println("FirstInterceptor.....preHandle");
        return true;                                                    
    }

    public void postHandle(HttpServletRequest req, HttpServletResponse resp,
                    Object handler, ModelAndView modelAndView)throws Exception{
        System.out.println("FirstInterceptor.....postHandle");         
    }

    public void afterCompletion(HttpServletRequest req,HttpServletResponse resp,
                                  Object handler,Exception ex) throws Exception{
        System.out.println("FirstInterceptor.....afterCompletion");                    
    }
}

// 注册该拦截器
<mvc:interceptors>
    <bean id="firstInterceptor"
                        class="cn.itcast.springmvc.interceptor.firstInterceptor"/>
</mvc:interceptors>

// index.jsp
示例:<a href="${pageContext.request.contextPath}/helloworld">点击这里</a>

// Demo.java
@Controller
public class Demo{
    @RequestMapping(value="/hellowrold",method=RequestMethod.GET)
    public String helloworld(){
        System.out.println("======helloworld");
        return "ok";
    }
}

运行结果:

2.1 拦截器配置

// 自定义两个拦截器
// FirstInterceptor.java(同上)
// SecondInterceptor.java
public class SecondInterceptor implements HandlerInterceptor{
    public boolean preHandle(HttpServletRequest req,HttpServletResponse resp,
                                                Object handler)throws Exception{
        System.out.println("SecondInterceptor.....preHandle");
        return true;                                                    
    }

    public void postHandle(HttpServletRequest req, HttpServletResponse resp,
                    Object handler, ModelAndView modelAndView)throws Exception{
        System.out.println("SecondInterceptor.....postHandle");         
    }

    public void afterCompletion(HttpServletRequest req,HttpServletResponse resp,
                                  Object handler,Exception ex) throws Exception{
        System.out.println("SecondInterceptor.....afterCompletion");                    
    }
}

// 注册拦截器
<mvc:interceptors>
    <bean id="firstInterceptor"
                        class="cn.itcast.springmvc.interceptor.FirstInterceptor"/>

    <mvc:interceptor>
        <mvc:mapping path="/emps"></mvc:mapping>
        <bean id="secondInterceptor"
                        class="cn.itcast.springmvc.interceptor.SecondInterceptor"/>
    </mvc:interceptor>
</mvc:interceptors>

// Demo.java
@Controller
public class Demo{
    @RequestMapping(value="/emps",method=RequestMethod.GET)
    public String list(Map<String,Object> map){

        System.out.println("emps .... 执行");
        map.put("employees",employeeService.getAll());
        return "list";
    }
}

// index.jsp
查询所有员工: <a href="${pageContext.request.contextPath}/emps">查询所有</a>

结果分析

• 第一个拦截器 preHandler 返回 true,第二个也为 true;

• 第一个拦截器返回 false,第二个为true或false;

• 第一个拦截器返回 true,第二个为 false;

3. 异常处理

1. SpringMVC 通过 HandlerExceptionResolver接口处理程序的异常,包括Handler映射,数据绑定以
   及目标方法执行时,发生的异常;
2. SpringMVC 提供的 HandlerExceptionResolver接口的实现类:
   • ExceptionHandlerExceptionResolver;
   • DefaultHandlerExceptionResolver;
   • ResponseStatusExdeptionResolver;
   • SimpleMappingExceptionResolver;

3.1 HandlerExceptionResolver

• @ExceptionHandler只处理当前 handler 方法中抛出的异常

// index.jsp
异常示例:<a href="{pageContext.request.contextPath}/testHandler?age=5">异常处理1</a>

// Demo.java
@Controller
public class Demo{

    @RequestMapping(value="/testHandler",method=RequestMethod.GET)
    public String testHandler(@RequestParam("age") Integer age){
        int result = 10 / age;
        System.out.println(result);
        return "ok";
    }

    // 如果请求参数 age=0, 会报异常

    // error.jsp
    <body>
    抱歉,系统繁忙,请稍候在试....
    </body>

    // 第一种方式: 返回到错误页面,不带异常信息
    @ExceptionHandler(value={ArithmeticException.class})
    public String dealHandlerExceptionResolver(Exception e){

        System.out.println("111111"+e.getMessage());
        return "error";
    }

    // 第二种方式: 将异常信息返回到错误页面, 需要使用 ModelAndView, 不能使用 Map
    @ExceptionHandler(value={ArithmeticException.class})
    public ModelAndView dealHandlerExceptionResolver(Excetption e){

        System.out.println("22222"+e.getMessage());
        ModelAndView mv = new ModelAndView();
        mv.addObject("myexception",e.getMessage());
        mv.setViewName("error");
        return mv;
    }

    // error.jsp
    <body>
    抱歉,系统繁忙,请稍候在试....<br/>
    异常信息:${requestScope.myexception}
    </body>

    // 异常优先级问题
    // ArithmeticExcetion 继承了 RuntimeException
    // 如果一个类中既有ArithmeticException, 也有 RuntimeException
    // 如果出现 ArithmeticException, 会执行ArithmeticException
    @ExceptionHandler(value={RuntimeException.class})
    public ModelAndView dealHandlerExceptionResolver2(Excetption e){

        System.out.println("33333"+e.getMessage());
        ModelAndView mv = new ModelAndView();
        mv.addObject("myexception",e.getMessage());
        mv.setViewName("error");
        return mv;
    }
}

3.2 @ControllerAdvice

• 将所有异常存放在 exception 包下,将业务方法和处理异常的方法分离;
• @ExceptionHandler中找不到的话,就去@ControllerAdvice标记的类里面查找标记了
  @ExceptionHandler的方法;

// cn.itcast.springmvc.exception.CommonHelperException 类

@ControllerAdvice
public class CommonHelperException{
    @ExceptionHandler(value={ArithmeticException.class})
    public ModelAndView dealHandlerExceptionResolver(Excetption e){

        System.out.println("44444"+e.getMessage());
        ModelAndView mv = new ModelAndView();
        mv.addObject("myexception",e.getMessage());
        mv.setViewName("error");
        return mv;
    }
}

3.3 ReponseStatusExceptionResolver

// 模拟账户锁定,自定义一个 MyUserLockException 继承了 RuntimeException 的异常类

// index.jsp
账户锁定异常:
<a href="${pageContext.request.contextPath}/testResponse?username=lisi">异常示例</a>


// cn.itcast.springmvc.exception.MyUserLockException 类
@ResponseStatus(value=HttpStatus.LOCKED,reason="账户被锁定,请拨打10086")
public class MyUserLockException extends RuntimeException{
    private static final long serialVersionUID = 1L;
}

// Demo.java
@Controller
public class Demo{
    @RequestMapping(value="/testResponse",method=RequestMethod.GET)
    public String testResponse(@RequestParam("username") String username){

        // username=zhangsan, 抛出异常
        if("zhangsan".equalsIgnoreCase(username)){
            throw new MyUserLockException();
        }
        return "ok";
    }

    //第二种用法,@ResponseStatus 用在方法上
    // 如果 name=zhangsan, 报 MyUserLockException,
    // 如果 name 为其他,报 Not Found
    @RequestMapping(value="/testResponse",method=RequestMethod.GET)
    @ResponseStatus(value=HttpStatus.NOT_FOUND,reason="测试...")
    public String testResponse(@RequestParam("username") String username){

        // username=zhangsan, 抛出异常
        if("zhangsan".equalsIgnoreCase(username)){
            throw new MyUserLockException();
        }
        return "ok";
    }
}

3.4 SimpleMappingExceptionResolver

// 示例: 数组下标越界异常

// springDispatcherServlet-servlet.xml 配置
<bean id="simpleMappingExceptionResolver"
    class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver">

    <!-- 可以自定义 requestScope.异常名称 --
    <property name="exceptionAttribute" value="自定义异常名称"/>

    <property name="exceptionMappings">
    <props>
        <prop key="java.lang.ArrayIndexOutOfBoundsException">error</prop>
    </props>
    </property>
</bean>

// index.jsp
异常示例:<a href="${pageContext.request.contextPath}/testSimple?id=3">数组下标越界</a>

// error.jsp
<body>
抱歉,系统繁忙,请稍候在试!<br/>
数组下标越界:${requestScope.exception}<br/>
</body>

// Demo.java
@Controller
public class Demo{
    @RequestMapping(value="/testSimple",method=RequestMethod.GET)
    public String testSimple(@RequestParam("id") Integer id){

        int[] arr = new int[10];
        System.out.println(arr[id]);
        return "ok";
    }
}

参考资料

• SpringMVC 基础