【SpringMVC】文件上传与下载、拦截器、异常处理器

2021年9月7日 4点热度 0条评论 来源: gonghr

文件下载

使用ResponseEntity实现下载文件的功能

index.html

<!DOCTYPE html>
<html lang="en" xmlns:th="http:www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>首页</title>
</head>
<body>
<a th:href="@{/testDown}">点击下载</a>
</body>
</html>

控制器

@RequestMapping("/testDown")
public ResponseEntity<byte[]> testResponseEntity(HttpSession session) throws IOException {
    //获取ServletContext对象
    ServletContext servletContext = session.getServletContext();
	
    //获取服务器中文件的真实路径
    String realPath = servletContext.getRealPath("/static/img/1.jpg");
	
    //创建输入流
    InputStream is = new FileInputStream(realPath);
	
    //创建字节数组
    byte[] bytes = new byte[is.available()];
	
    //将流读到字节数组中
    is.read(bytes);
	
    //创建HttpHeaders对象设置响应头信息
    MultiValueMap<String, String> headers = new HttpHeaders();
	
    //设置要下载方式以及下载文件的名字
    headers.add("Content-Disposition", "attachment;filename=1.jpg");
	
    //设置响应状态码
    HttpStatus statusCode = HttpStatus.OK;
	
    //创建ResponseEntity对象
    ResponseEntity<byte[]> responseEntity = new ResponseEntity<>(bytes, headers, statusCode);
	
    //关闭输入流
    is.close();
	
    return responseEntity;
}

注意:如果报500错误,可能是项目中无法找到静态资源文件,需要对项目重新打包。

文件上传

文件上传要求form表单的请求方式必须为post,并且添加属性enctype="multipart/form-data"以二进制方式上传

SpringMVC中将上传的文件封装到MultipartFile对象中,通过此对象可以获取文件相关信息

上传步骤:

  • 添加依赖
<!-- https://mvnrepository.com/artifact/commons-fileupload/commons-fileupload -->
<dependency>
    <groupId>commons-fileupload</groupId>
    <artifactId>commons-fileupload</artifactId>
    <version>1.3.1</version>
</dependency>
  • 在SpringMVC的配置文件springMVC.xml中添加配置
<!--必须通过文件解析器的解析才能将文件转换为MultipartFile对象-->
<!--必须设置id属性,springMVC是根据id获取,且id必须设置为multipartResolver-->
<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver"></bean>

index.html

<form method="post" th:action="@{/testUp}" enctype="multipart/form-data">
    <input type="file" name="photo">
    <input type="submit" value="上传">
</form>
  • 控制器
@RequestMapping("/testUp")

//MultipartFile的形参名必须与index.html中的file标签的name一致
public String testUp(MultipartFile photo, HttpSession session) throws IOException {
    //获取上传的文件的文件名
    String fileName = photo.getOriginalFilename();
	
    //处理文件重名问题
    String hzName = fileName.substring(fileName.lastIndexOf("."));
    fileName = UUID.randomUUID().toString() + hzName;
	
    //获取服务器中photo目录的路径
    ServletContext servletContext = session.getServletContext();
    String photoPath = servletContext.getRealPath("photo");
    File file = new File(photoPath);
    if(!file.exists()){
        file.mkdir();
    }
    String finalPath = photoPath + File.separator + fileName;
	
    //实现上传功能
    photo.transferTo(new File(finalPath));
    return "success";
}

拦截器

拦截器的配置

SpringMVC中的拦截器用于拦截控制器方法的执行

SpringMVC中的拦截器需要实现HandlerInterceptor接口

HandlerInterceptor源码

public interface HandlerInterceptor {
    default boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        return true;
    }

    default void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable ModelAndView modelAndView) throws Exception {
    }

    default void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable Exception ex) throws Exception {
    }
}

HandlerInterceptor接口有三个默认方法

  • preHandle控制器方法执行之前执行preHandle(),其boolean类型的返回值表示是否拦截或放行,返回true为放行,即调用控制器方法;返回false表示拦截,即不调用控制器方法

  • postHandle控制器方法执行之后执行postHandle()

  • afterCompletion:处理完视图和模型数据,渲染视图完毕之后执行afterCompletion()

控制器

FirstInterceptor.java

public class FirstInterceptor implements HandlerInterceptor {
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("FirstInterceptor-->preHandle");
        return false;
    }

    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("FirstInterceptor-->postHandle");
    }

    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("FirstInterceptor-->afterCompletion");
    }
}

SpringMVC的拦截器必须在SpringMVC的配置文件中进行配置:

  • 方式一
    <mvc:interceptors>
        <bean class="com.gonghr.springmvc.interceptors.FirstInterceptor"></bean>
    </mvc:interceptors>

输出:

FirstInterceptor-->preHandle
  • 方式二
    <mvc:interceptors>
        <ref bean="firstInterceptor"></ref>
    </mvc:interceptors>

注意提前开启注解扫描,并把拦截器放入Ioc容器

输出:

FirstInterceptor-->preHandle

注意:以上两种配置方式都是对DispatcherServlet所处理的所有的请求进行拦截。

  • 方式三
    <mvc:interceptors>
        <mvc:interceptor>
            <mvc:mapping path="/**"/>  <!--拦截所有请求-->
            <mvc:exclude-mapping path="/"/>  <!--不拦截主页-->
            <ref bean="firstInterceptor"></ref>
        </mvc:interceptor>
    </mvc:interceptors>


可以进入首页


发送任意请求都会被拦截

输出:

FirstInterceptor-->preHandle

以上配置方式可以通过ref或bean标签设置拦截器,通过mvc:mapping设置需要拦截的请求,通过mvc:exclude-mapping设置需要排除的请求,即不需要拦截的请求

/**:拦截所有请求
/*:拦截一级目录的请求

多个拦截器的执行顺序

第一个拦截器

@Component
public class FirstInterceptor implements HandlerInterceptor {
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("FirstInterceptor-->preHandle");
        return true;
    }

    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("FirstInterceptor-->postHandle");
    }

    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("FirstInterceptor-->afterCompletion");
    }
}

第二个拦截器

@Component
public class SecondInterceptor implements HandlerInterceptor {
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("SecondInterceptor-->preHandle");
        return true;
    }

    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("SecondInterceptor-->postHandle");
    }

    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("SecondInterceptor-->afterCompletion");
    }
}

两个拦截器都设置为对任意请求放行。

输出:

FirstInterceptor-->preHandle
SecondInterceptor-->preHandle
SecondInterceptor-->postHandle
FirstInterceptor-->postHandle
SecondInterceptor-->afterCompletion
FirstInterceptor-->afterCompletion
  • 若每个拦截器的preHandle()都返回true

此时多个拦截器的执行顺序和拦截器在SpringMVC的配置文件的配置顺序有关:

preHandle()会按照配置的顺序执行,而postHandle()afterCompletion()会按照配置的反序执行

如果设置第一个拦截器对所有请求放行,第二个拦截器对所有请求拦截。

第一个拦截器

@Component
public class FirstInterceptor implements HandlerInterceptor {
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("FirstInterceptor-->preHandle");
        return true;
    }

    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("FirstInterceptor-->postHandle");
    }

    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("FirstInterceptor-->afterCompletion");
    }
}

第二个拦截器

@Component
public class SecondInterceptor implements HandlerInterceptor {
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("SecondInterceptor-->preHandle");
        return false;
    }

    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("SecondInterceptor-->postHandle");
    }

    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("SecondInterceptor-->afterCompletion");
    }
}

输出:

FirstInterceptor-->preHandle
SecondInterceptor-->preHandle
FirstInterceptor-->afterCompletion
  • 若某个拦截器的preHandle()返回了false

preHandle()返回false和它之前的拦截器的preHandle()都会执行,postHandle()都不执行,返回false的拦截器之前的拦截器的afterCompletion()会执行

异常处理器

基于配置的异常处理

SpringMVC提供了一个处理控制器方法执行过程中所出现的异常的接口:HandlerExceptionResolver

HandlerExceptionResolver接口的实现类有:DefaultHandlerExceptionResolverSimpleMappingExceptionResolver

SpringMVC提供了自定义的异常处理器SimpleMappingExceptionResolver,使用方式:

<bean class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver">
    <property name="exceptionMappings">
        <props>
        	<!--
        		properties的键表示处理器方法执行过程中出现的异常
        		properties的值表示若出现指定异常时,设置一个新的视图名称,跳转到指定页面
        	-->
            <prop key="java.lang.ArithmeticException">error</prop>
        </props>
    </property>
    <!--
    	exceptionAttribute属性设置一个属性名,将出现的异常信息在请求域中进行共享
    -->
    <property name="exceptionAttribute" value="ex"></property>
</bean>

error.html

出现错误
<p th:text="${ex}"></p>

index.html

<a th:href="@{/testException}">测试异常处理</a>

基于注解的异常处理

//@ControllerAdvice将当前类标识为异常处理的组件
@ControllerAdvice
public class ExceptionController {

    //@ExceptionHandler用于设置所标识方法处理的异常
    @ExceptionHandler(value = {ArithmeticException.class,NullPointerException.class})
    //ex表示当前请求处理中出现的异常对象
    public String handleArithmeticException(Exception ex, Model model){
        model.addAttribute("ex", ex);
        return "error";
    }

}

    原文作者:gonghr
    原文地址: https://www.cnblogs.com/gonghr/p/15235253.html
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