SpringMVC实现文件上传与下载、拦截器、异常处理器等功能
目录
- 文件下载
- 文件上传
- 拦截器
- 拦截器的配置
- 多个拦截器的执行顺序
- 异常处理器
- 基于配置的异常处理
- 基于注解的异常处理
- 总结
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}" rel="external nofollow" >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()和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:DefaultHandlerExceptionResolver和SimpleMappingExceptionResolver
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"; } }
总结
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