java實現文件的上傳和下載

本文轉載自查看原文 2019-08-05 09:21 873

【文件上傳和下載】是很多系統必備功能，比如PM\OA\ERP等；系統中常見的開發模式有B/S和C/S，而前者主要是通過瀏覽器來訪問web服務器，一般采用七層協議中的【應用層http】進行數據傳輸，后者主要通過編程語言開發的app作為客戶端來訪問服務端，一般采用七層協議中的【傳輸層tcp】進行數據傳輸。
文章主要完成簡單java web涉及的文件上傳和下載功能。

正文

1. java原生servlet實現：

pom.xml配置：

<dependency>
	  <groupId>javax</groupId>
	  <artifactId>javaee-api</artifactId>
	  <version>8.0</version>
	  <scope>provided</scope>
</dependency>
<dependency>
	  <groupId>javax</groupId>
	  <artifactId>javaee-web-api</artifactId>
	  <version>8.0</version>
	  <scope>provided</scope>
</dependency>
<dependency>
	  <groupId>javax.servlet</groupId>
	  <artifactId>jstl</artifactId>
	  <version>1.</version>
	  <scope>runtime</scope>
</dependency>

web.xml配置：

<welcome-file-list>  
	<welcome-file>/WEB-INF/view/jsp/upload/upload.jsp</welcome-file>
</welcome-file-list>
<!-- 聲明Servlet對象 -->
<servlet>
	<!-- 指定Servlet對象的名稱 -->
	<servlet-name>UploadServlet</servlet-name>
	<!-- 指定Servlet對象的完整位置，包含包名和類名 -->
	<servlet-class>pers.chaffee.servlet.UploadServlet</servlet-class>
</servlet>
<!-- 映射Servlet -->
<servlet-mapping>
	<!--<servlet-name>與上面<Servlet>標簽的<servlet-name>元素相對應，不可以隨便起名 -->
	<servlet-name>UploadServlet</servlet-name>
	<!-- 用於映射訪問URL -->
	<url-pattern>/UploadFileServlet</url-pattern>
</servlet-mapping>

servlet實現：

@WebServlet("/UploadServlet")
public class UploadServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) {

        //根據文件擴展名設置文件MIME類型
        resp.setContentType(getServletContext().getMimeType("hello.txt"));

        //設置下載消息響應,提示文件保存attachment
        resp.setHeader("Content-Disposition", "attachment;filename=" + "hello");

        /* * 設置緩沖區 * is.read(b)當文件讀完時返回-1 */
        try {
            //輸入流為項目文件，輸出流指向瀏覽器
            InputStream is = new FileInputStream("E:\\hello.txt");

            // 提供了將二進制數據寫入響應的流
            ServletOutputStream os = resp.getOutputStream();

            int len = -1;
            byte[] b = new byte[1024];
            while ((len = is.read(b)) != -1) {
                os.write(b, 0, len);
            }
            //關閉流
            is.close();
            os.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) {
        // 文件上傳到本地磁盤工廠類
        DiskFileItemFactory factory = new DiskFileItemFactory();
        //設置內存緩沖區的大小
        factory.setSizeThreshold(20480);
        //設置臨時文件目錄,供上傳文件過大時臨時存儲
        factory.setRepository(new File("F:\\f"));

        //文件上傳操作核心類
        ServletFileUpload upload = new ServletFileUpload(factory);
        //設置限制單個上傳文件的大小
        upload.setFileSizeMax(50480);
        //設置限制總上傳文件大小
        upload.setSizeMax(80480);
        // 這個路徑相對當前應用的目錄
        try {
            List<FileItem> formItems = upload.parseRequest(req);
            if (formItems != null && formItems.size() > 0) {
                // 迭代表單數據
                for (FileItem item : formItems) {
                    // 處理不在表單中的字段
                    if (!item.isFormField()) {
                        File storeFile = new File("F:\\fromweb_" + item.getName());
                        // 保存文件到硬盤
                        item.write(storeFile);
                    }
                }
            }
        } catch (FileUploadException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

upload.jsp:

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>文件上傳實例</h1>
<!--請求編碼類型必須為"multipart/form-data"-->
<form method="post" action="/UploadFileServlet" enctype="multipart/form-data">
    選擇一個文件:
    <input type="file" name="uploadFile"/>
    <input type="file" name="uploadFile2"/>
    <br/><br/>
    <input type="submit" value="上傳"/>
</form>
<a href="/UploadFileServlet" rel="nofollow">下載</a>
</body>
</html>

2. java web主流框架【ssm】實現：

pom.xml配置

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-core</artifactId>
    <version>${spring.version}</version>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-webmvc</artifactId>
    <version>${spring.version}</version>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-web</artifactId>
    <version>${spring.version}</version>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-context</artifactId>
    <version>${spring.version}</version>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-context-support</artifactId>
    <version>${spring.version}</version>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-aop</artifactId>
    <version>${spring.version}</version>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-aspects</artifactId>
    <version>${spring.version}</version>
</dependency>

web.xml配置

<context-param>
    <param-name>contextConfigLocation</param-name>
    <!--<param-value>classpath*:applicationContext-*.xml</param-value>-->
    <param-value>classpath*:*.xml</param-value>
</context-param>
<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<listener>
    <listener-class>org.springframework.web.util.IntrospectorCleanupListener</listener-class>
</listener>
<servlet>
    <servlet-name>dispatcherServlet</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:spring-mvc.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
    <servlet-name>dispatcherServlet</servlet-name>
    <url-pattern>/service/*</url-pattern>
</servlet-mapping>

spring-mvc.xml:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:p="http://www.springframework.org/schema/p" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xmlns:mvc="http://www.springframework.org/schema/mvc" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd">

    <!-- 啟動SpringMVC的注解功能 -->
    <mvc:annotation-driven/>

    <!-- 掃描controller（controller層注入） -->
    <context:component-scan base-package="pers.chaffee.controller"/>

    <!-- 對模型視圖添加前后綴 -->
    <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver" p:prefix="/WEB-INF/view/jsp/" p:suffix=".jsp"/>

    <!-- 靜態資源不走controller -->
    <mvc:resources mapping="/resources/**" location="/resources/"/>
</beans>

servlet實現:

	@RequestMapping(value = "/upload2", method = RequestMethod.POST, consumes = {"multipart/form-data"})
	public ModelAndView postUpload(HttpServletRequest request, HttpServletResponse response) {
		
		//文件上傳核心類
		CommonsMultipartResolver multipartResolver = new CommonsMultipartResolver(request.getSession().getServletContext());
		
		//判斷request是否有文件上傳
		if (multipartResolver.isMultipart(request)) {
		    //通過MultipartHttpServletRequest解析上傳請求中的文件
		    MultipartHttpServletRequest multiRequest = (MultipartHttpServletRequest) request;
		    //獲取上傳請求中的所有文件
		    Iterator<String> iter = multiRequest.getFileNames();
		    while (iter.hasNext()) {
		        //轉換成spring支持的文件類型MultipartFile
		        MultipartFile file = multiRequest.getFile(iter.next());
		        if (file != null) {
		            File localFile = new File("F:\\f\\" + file.getOriginalFilename());
		            try {
		                //將上傳文件寫到指定位置,此處是本地文件夾
		                file.transferTo(localFile);
		            } catch (IllegalStateException e) {
		                e.printStackTrace();
		            } catch (IOException e) {
		                e.printStackTrace();
		            }
		        }
		    }
		}
		
		ModelAndView modelAndView = new ModelAndView();
		modelAndView.setViewName("upload/upload2");
		return modelAndView;
		}
	
	@RequestMapping(value = "/download", method = RequestMethod.GET)
	public ResponseEntity<byte[]> downLoad() throws IOException {
		byte[] responseBody;
		//獲取文件
		File file = new File("E:\\hello.txt");
		InputStream is = new FileInputStream(file);
		responseBody = new byte[is.available()];
		is.read(responseBody);
		HttpHeaders headers = new HttpHeaders();
		
		//設置文件類型
		headers.add("Content-Disposition", "attachment;filename=" + file.getName());
		
		//設置Http狀態碼
		HttpStatus stateCode = HttpStatus.OK;
		
		//返回數據
		ResponseEntity<byte[]> entity = new ResponseEntity<>(responseBody, headers, stateCode);
		return entity;
	}

小結

截至目前，只初步完成B/S方式的上傳和下載，且文件存儲方式僅限本地磁盤。而C/S方式的文件傳輸可以考慮thrift框架，thrift是一種跨平台跨語言的RPC框架，使用過程中發現在數據量不是很大的情況下thrift應用是一種比較合適的C/S解決方案；另外，文件存儲方式可以根據具體情況選用文件服務器、數據庫等。

功能介紹

在頁面中選擇好相應的上傳目錄，點擊粘貼上傳按鈕，數據即可快速開始上傳

說明: http://bbsres2.ncmem.com/731fda07.png