spring4 文件下载功能

需要准备的工具和框架

• Spring 4.2.0.RELEASE
• Bootstrap v3.3.2
• Maven 3
• JDK 1.7
• Tomcat 8.0.21
• Eclipse JUNO Service Release 2

文件结构如下

设置依赖包

 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
   <modelVersion>4.0.0</modelVersion>
   <groupId>com.gome.springmvc</groupId>
   <artifactId>Spring4MVCFileDownloadExample</artifactId>
   <packaging>war</packaging>
   <version>1.0.0</version>
   <name>Spring4MVCFileDownloadExample Maven Webapp</name>

      <properties>
         <springframework.version>4.2.0.RELEASE</springframework.version>
     </properties>

     <dependencies>
         <dependency>
             <groupId>org.springframework</groupId>
             <artifactId>spring-webmvc</artifactId>
             <version>${springframework.version}</version>
         </dependency>

         <dependency>
             <groupId>javax.servlet</groupId>
             <artifactId>javax.servlet-api</artifactId>
             <version>3.1.0</version>
         </dependency>
         <dependency>
             <groupId>javax.servlet</groupId>
             <artifactId>jstl</artifactId>
             <version>1.2</version>
         </dependency>
     </dependencies>

     <build>
         <pluginManagement>
             <plugins>
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-compiler-plugin</artifactId>
                     <version>3.2</version>
                     <configuration>
                         <source>1.7</source>
                         <target>1.7</target>
                     </configuration>
                 </plugin>
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-war-plugin</artifactId>
                     <version>2.4</version>
                     <configuration>
                         <warSourceDirectory>src/main/webapp</warSourceDirectory>
                         <warName>Spring4MVCFileDownloadExample</warName>
                         <failOnMissingWebXml>false</failOnMissingWebXml>
                     </configuration>
                 </plugin>
             </plugins>
         </pluginManagement>

         <finalName>Spring4MVCFileDownloadExample</finalName>
     </build>
 </project>

controller实现

package com.gome.springmvc.controller;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URLConnection;
import java.nio.charset.Charset;

import javax.servlet.http.HttpServletResponse;

import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.util.FileCopyUtils;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@Controller
public class FileDownloadController {

    private static final String INTERNAL_FILE="irregular-verbs-list.pdf";
    private static final String EXTERNAL_FILE_PATH="C:/mytemp/SpringMVCHibernateManyToManyCRUDExample.zip";

    @RequestMapping(value={"/","/welcome"}, method = RequestMethod.GET)
    public String getHomePage(ModelMap model) {
        return "welcome";
    }

    /*
     * Download a file from
     *   - inside project, located in resources folder.
     *   - outside project, located in File system somewhere.
     */
    @RequestMapping(value="/download/{type}", method = RequestMethod.GET)
    public void downloadFile(HttpServletResponse response, @PathVariable("type") String type) throws IOException {

        File file = null;

        if(type.equalsIgnoreCase("internal")){
            ClassLoader classloader = Thread.currentThread().getContextClassLoader();
            file = new File(classloader.getResource(INTERNAL_FILE).getFile());
        }else{
            file = new File(EXTERNAL_FILE_PATH);
        }

        if(!file.exists()){
            String errorMessage = "Sorry. The file you are looking for does not exist";
            System.out.println(errorMessage);
            OutputStream outputStream = response.getOutputStream();
            outputStream.write(errorMessage.getBytes(Charset.forName("UTF-8")));
            outputStream.close();
            return;
        }

        String mimeType= URLConnection.guessContentTypeFromName(file.getName());
        if(mimeType==null){
            System.out.println("mimetype is not detectable, will take default");
            mimeType = "application/octet-stream";
        }

        System.out.println("mimetype : "+mimeType);

        response.setContentType(mimeType);

        /* "Content-Disposition : inline" will show viewable types [like images/text/pdf/anything viewable by browser] right on browser
            while others(zip e.g) will be directly downloaded [may provide save as popup, based on your browser setting.]*/
        response.setHeader("Content-Disposition", String.format("inline; filename=\"" + file.getName() +"\""));

        /* "Content-Disposition : attachment" will be directly download, may provide save as popup, based on your browser setting*/
        //response.setHeader("Content-Disposition", String.format("attachment; filename=\"%s\"", file.getName()));

        response.setContentLength((int)file.length());

        InputStream inputStream = new BufferedInputStream(new FileInputStream(file));

        //Copy bytes from source to destination(outputstream in this example), closes both streams.
        FileCopyUtils.copy(inputStream, response.getOutputStream());
    }

}

文件下载中需要注意的几个问题

1. 文件存储路径应该做混淆，防止从过猜测url等参数尝试获得其他文件

2. 除了对参数校验，还要对将下载的文件绝对路径、类型校验。

3. 白名单策略，只有规定路径下，规定类型、拥有规定权限的人才可以下载。