SpringMVC文件上传和文件下载

一.文件上传

文件上传是项目开发中最常见的功能之一 ,springMVC 可以很好的支持文件上传，但是SpringMVC上下文中默认没有装配MultipartResolver，因此默认情况下其不能处理文件上传工作。如果想使用Spring的文件上传功能，则需要在上下文中配置MultipartResolver

1.前端

为了能上传文件，必须将表单的method设置为POST，并将enctype设置为multipart/form-data。只有在这样的情况下，浏览器才会把用户选择的文件以二进制数据发送给服务器；

<form action="" method="post" enctype="multipart/form-data">
    <input type="file" name="file">
    <input type="submit" value="upload">
form>

设置了enctype为multipart/form-data，浏览器即会采用二进制流的方式来处理表单数据，之前使用的commons-fileupload是Servlet/JSP程序员上传文件的最佳选择，Servlet3.0规范已经提供方法来处理文件上传，但这种上传需要在Servlet中完成。而Spring MVC则提供了更简单的封装，即直接用multipartResolver实现。

2.导包

        <dependency>
            <groupId>commons-fileuploadgroupId>
            <artifactId>commons-fileuploadartifactId>
            <version>1.3.3version>
        dependency>

        <dependency>
            <groupId>javax.servletgroupId>
            <artifactId>javax.servlet-apiartifactId>
            <version>4.0.1version>
        dependency>

3. springmvc-servlet.xml配置

bena的id必须为：multipartResolver ， 否则上传文件会报400的错误

<beans xmlns="http://www.springframework.org/schema/beans"
       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.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd">
    <context:component-scan base-package="org.westos.controller"/>
    <mvc:default-servlet-handler/>
    <mvc:annotation-driven/>
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver" id="internalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/"/>
        <property name="suffix" value=".jsp"/>
    bean>
    
    <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        
        <property name="defaultEncoding" value="utf-8"/>
        
        <property name="maxUploadSize" value="1048576"/>
        <property name="maxInMemorySize" value="40960"/>
    bean>
beans>

4.采用流的方式上传文件

Tip：@RequestParam(“file”) 将name=file控件得到的文件封装成CommonsMultipartFile 对象，我们在上面的前端配置的地方将input类型为file的标签的name设置为了file，所以这里注解内也为file

实现思路：

1.首先获取上传文件的文件名
2.设置上传文件的保存路径
3.使用字节输入流和字节输出流实现文件上传
4.关闭流

@Controller
public class FileController {
    //采用流的方式上传文件
    @RequestMapping("/upload")
    @ResponseBody
    public String upload(@RequestParam("file")CommonsMultipartFile file, HttpServletRequest request) throws IOException {
        //获得文件名
        String filename = file.getOriginalFilename();
        if ("".equals(filename)){
            return "文件不存在";
        }
        //上传文件保存路径
        String path = request.getServletContext().getRealPath("/upload");
        File realPath = new File(path);
        if (!realPath.exists()){
            realPath.mkdir();
        }
        //文件上传
        InputStream inputStream = file.getInputStream();
        FileOutputStream outputStream = new FileOutputStream(new File(realPath, filename));
        int len = 0;
        byte[] bytes = new byte[1024];
        while ((len=inputStream.read(bytes))!=-1){
            outputStream.write(bytes,0,len);
            outputStream.flush();
        }
        //关闭流
        outputStream.close();
        inputStream.close();
        return "上传完毕";
    }
}

5.使用file.Transto上传文件

除了使用流的方式上传文件，我们还可以使用Transto方法上传文件

@Controller
public class FileController {
    //采用file.Transto上传文件
    @RequestMapping("/upload2")
    @ResponseBody
    public String upload2(@RequestParam("file") CommonsMultipartFile file,HttpServletRequest request) throws IOException {
        //上传文件保存路径
        String path = request.getServletContext().getRealPath("/upload");
        File realPath = new File(path);
        if (!realPath.exists()){
            realPath.mkdir();
        }
        //transferTo将文件写入磁盘，参数传入一个文件
        file.transferTo(new File(realPath+"/"+file.getOriginalFilename()));
        return "上传完毕";
    }
}

二、SpringMVC实现文件下载

package org.westos.controller;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
@Controller
public class DownloadController {
    @RequestMapping("/download2")
    public String download(HttpServletRequest request, HttpServletResponse response) {
        String fileName = "1.png";
        System.out.println(fileName);
        response.setContentType("text/html;charset=utf-8");
        try {
            request.setCharacterEncoding("UTF-8");//设定请求字符编码
        } catch (UnsupportedEncodingException e1) {
            e1.printStackTrace();
        }
        BufferedInputStream bis = null;//创建输入输出流
        BufferedOutputStream bos = null;
        String realPath = request.getSession().getServletContext().getRealPath("/") + "upload/";//获取文件真实路径
        System.out.println(realPath);
        String downLoadPath = realPath + fileName;
        System.out.println(downLoadPath);
        try {
            long fileLength = new File(downLoadPath).length();//获取文件长度
            //设置响应头信息；【固定的不用记，保存即可】
            response.setContentType("application/x-msdownload;");
            response.setHeader("Content-disposition", "attachment; filename=" + new String(fileName.getBytes("utf-8"), "ISO8859-1"));
            response.setHeader("Content-Length", String.valueOf(fileLength));
            bis = new BufferedInputStream(new FileInputStream(downLoadPath));//创建输入输出流实例
            bos = new BufferedOutputStream(response.getOutputStream());
            byte[] buff = new byte[2048];//创建字节缓冲大小
            int bytesRead;
            while (-1 != (bytesRead = bis.read(buff, 0, buff.length))) {
                bos.write(buff, 0, bytesRead);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (bis != null)
                try {
                    bis.close();//关闭输入流
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            if (bos != null)
                try {
                    bos.close();//关闭输出流
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
        }
        return null;
    }
}