SpringMVC 之拦截器和异常处理

2022-02-20 11:08:27

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

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

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;
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

码农公寓

1. 文件上传

2. 自定义拦截器

运行结果:

2.1 拦截器配置

结果分析

3. 异常处理

3.1 HandlerExceptionResolver

3.2 @ControllerAdvice

3.3 ReponseStatusExceptionResolver

3.4 SimpleMappingExceptionResolver

相关文章

3.2 `@ControllerAdvice`