【SpringMVC】檔案上傳與下載、攔截器、異常處理器

gonghr發表於2021-09-06

檔案下載

使用ResponseEntity實現下載檔案的功能

index.html

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

控制器

@RequestMapping("/testDown")
public ResponseEntity<byte[]> testResponseEntity(HttpSession session) throws IOException {
    //獲取ServletContext物件
    ServletContext servletContext = session.getServletContext();
	
    //獲取伺服器中檔案的真實路徑
    String realPath = servletContext.getRealPath("/static/img/1.jpg");
	
    //建立輸入流
    InputStream is = new FileInputStream(realPath);
	
    //建立位元組陣列
    byte[] bytes = new byte[is.available()];
	
    //將流讀到位元組陣列中
    is.read(bytes);
	
    //建立HttpHeaders物件設定響應頭資訊
    MultiValueMap<String, String> headers = new HttpHeaders();
	
    //設定要下載方式以及下載檔案的名字
    headers.add("Content-Disposition", "attachment;filename=1.jpg");
	
    //設定響應狀態碼
    HttpStatus statusCode = HttpStatus.OK;
	
    //建立ResponseEntity物件
    ResponseEntity<byte[]> responseEntity = new ResponseEntity<>(bytes, headers, statusCode);
	
    //關閉輸入流
    is.close();
	
    return responseEntity;
}

注意:如果報500錯誤,可能是專案中無法找到靜態資原始檔,需要對專案重新打包。

檔案上傳

檔案上傳要求form表單的請求方式必須為post,並且新增屬性enctype="multipart/form-data"以二進位制方式上傳

SpringMVC中將上傳的檔案封裝到MultipartFile物件中,通過此物件可以獲取檔案相關資訊

上傳步驟:

  • 新增依賴
<!-- 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的配置檔案springMVC.xml中新增配置
<!--必須通過檔案解析器的解析才能將檔案轉換為MultipartFile物件-->
<!--必須設定id屬性,springMVC是根據id獲取,且id必須設定為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="上傳">
</form>
  • 控制器
@RequestMapping("/testUp")

//MultipartFile的形參名必須與index.html中的file標籤的name一致
public String testUp(MultipartFile photo, HttpSession session) throws IOException {
    //獲取上傳的檔案的檔名
    String fileName = photo.getOriginalFilename();
	
    //處理檔案重名問題
    String hzName = fileName.substring(fileName.lastIndexOf("."));
    fileName = UUID.randomUUID().toString() + hzName;
	
    //獲取伺服器中photo目錄的路徑
    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;
	
    //實現上傳功能
    photo.transferTo(new File(finalPath));
    return "success";
}

攔截器

攔截器的配置

SpringMVC中的攔截器用於攔截控制器方法的執行

SpringMVC中的攔截器需要實現HandlerInterceptor介面

HandlerInterceptor原始碼

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介面有三個預設方法

  • preHandle控制器方法執行之前執行preHandle(),其boolean型別的返回值表示是否攔截或放行,返回true為放行,即呼叫控制器方法;返回false表示攔截,即不呼叫控制器方法

  • postHandle控制器方法執行之後執行postHandle()

  • afterComplation:處理完檢視和模型資料,渲染檢視完畢之後執行afterComplation()

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的攔截器必須在SpringMVC的配置檔案中進行配置:

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

輸出:

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

注意提前開啟註解掃描,並把攔截器放入Ioc容器

輸出:

FirstInterceptor-->preHandle

注意:以上兩種配置方式都是對DispatcherServlet所處理的所有的請求進行攔截。

  • 方式三
    <mvc:interceptors>
        <mvc:interceptor>
            <mvc:mapping path="/**"/>  <!--攔截所有請求-->
            <mvc:exclude-mapping path="/"/>  <!--不攔截主頁-->
            <ref bean="firstInterceptor"></ref>
        </mvc:interceptor>
    </mvc:interceptors>

image
可以進入首頁

image
傳送任意請求都會被攔截

輸出:

FirstInterceptor-->preHandle

以上配置方式可以通過ref或bean標籤設定攔截器,通過mvc:mapping設定需要攔截的請求,通過mvc:exclude-mapping設定需要排除的請求,即不需要攔截的請求

/**:攔截所有請求
/*:攔截一級目錄的請求

多個攔截器的執行順序

第一個攔截器

@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");
    }
}

第二個攔截器

@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");
    }
}

兩個攔截器都設定為對任意請求放行。

輸出:

FirstInterceptor-->preHandle
SecondInterceptor-->preHandle
SecondInterceptor-->postHandle
FirstInterceptor-->postHandle
SecondInterceptor-->afterCompletion
FirstInterceptor-->afterCompletion
  • 若每個攔截器的preHandle()都返回true

此時多個攔截器的執行順序和攔截器在SpringMVC的配置檔案的配置順序有關:

preHandle()會按照配置的順序執行,而postHandle()afterComplation()會按照配置的反序執行

如果設定第一個攔截器對所有請求放行,第二個攔截器對所有請求攔截。

第一個攔截器

@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");
    }
}

第二個攔截器

@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");
    }
}

輸出:

FirstInterceptor-->preHandle
SecondInterceptor-->preHandle
FirstInterceptor-->afterCompletion
  • 若某個攔截器的preHandle()返回了false

preHandle()返回false和它之前的攔截器的preHandle()都會執行,postHandle()都不執行,返回false的攔截器之前的攔截器的afterComplation()會執行

異常處理器

基於配置的異常處理

SpringMVC提供了一個處理控制器方法執行過程中所出現的異常的介面:HandlerExceptionResolver

HandlerExceptionResolver介面的實現類有:DefaultHandlerExceptionResolverSimpleMappingExceptionResolver

SpringMVC提供了自定義的異常處理器SimpleMappingExceptionResolver,使用方式:

<bean class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver">
    <property name="exceptionMappings">
        <props>
        	<!--
        		properties的鍵表示處理器方法執行過程中出現的異常
        		properties的值表示若出現指定異常時,設定一個新的檢視名稱,跳轉到指定頁面
        	-->
            <prop key="java.lang.ArithmeticException">error</prop>
        </props>
    </property>
    <!--
    	exceptionAttribute屬性設定一個屬性名,將出現的異常資訊在請求域中進行共享
    -->
    <property name="exceptionAttribute" value="ex"></property>
</bean>

error.html

出現錯誤
<p th:text="${ex}"></p>

index.html

<a th:href="@{/testException}">測試異常處理</a>

image

基於註解的異常處理

//@ControllerAdvice將當前類標識為異常處理的元件
@ControllerAdvice
public class ExceptionController {

    //@ExceptionHandler用於設定所標識方法處理的異常
    @ExceptionHandler(value = {ArithmeticException.class,NullPointerException.class})
    //ex表示當前請求處理中出現的異常物件
    public String handleArithmeticException(Exception ex, Model model){
        model.addAttribute("ex", ex);
        return "error";
    }

}

image

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