Springmvc文件上传实现流程解析

<dependency>
  <groupId>commons-fileupload</groupId>
  <artifactId>commons-fileupload</artifactId>
  <version>1.4</version>
</dependency>

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

@Controller
public class FileUploadController {
  SimpleDateFormat sdf = new SimpleDateFormat("/yyyy/MM/dd/");
    @RequestMapping("/upload")
  @ResponseBody
  public String upload(MultipartFile file, HttpServletRequest req) {
    String format = sdf.format(new Date());
    String realPath = req.getServletContext().getRealPath("/img") + format;
    File folder = new File(realPath);
    if (!folder.exists()) {
      folder.mkdirs();
    }
    String oldName = file.getOriginalFilename();
    String newName = UUID.randomUUID().toString() + oldName.substring(oldName.lastIndexOf("."));
    try {
      file.transferTo(new File(folder, newName));
      String url = req.getScheme() + "://" + req.getServerName() + ":" + req.getServerPort() + "/img" + format + newName;
      return url;
    } catch (IOException e) {
      e.printStackTrace();
    }
    return "failed";
  }
}

<bean class="org.springframework.web.multipart.commons.CommonsMultipartResolver" id="multipartResolver">
  <!--默认的编码-->
  <property name="defaultEncoding" value="UTF-8"/>
  <!--上传的总文件大小-->
  <property name="maxUploadSize" value="1048576"/>
  <!--上传的单个文件大小-->
  <property name="maxUploadSizePerFile" value="1048576"/>
  <!--内存中最大的数据量，超过这个数据量，数据就要开始往硬盘中写了-->
  <property name="maxInMemorySize" value="4096"/>
  <!--临时目录，超过 maxInMemorySize 配置的大小后，数据开始往临时目录写，等全部上传完成后，再将数据合并到正式的文件上传目录-->
  <property name="uploadTempDir" value="file:///E:\\tmp"/>
</bean>

<servlet>
  <servlet-name>springmvc</servlet-name>
  <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
  <init-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath:spring-servlet.xml</param-value>
  </init-param>
  <multipart-config>
    <!--文件保存的临时目录，这个目录系统不会主动创建-->
    <location>E:\\temp</location>
    <!--上传的单个文件大小-->
    <max-file-size>1048576</max-file-size>
    <!--上传的总文件大小-->
    <max-request-size>1048576</max-request-size>
    <!--这个就是内存中保存的文件最大大小-->
    <file-size-threshold>4096</file-size-threshold>
  </multipart-config>
</servlet>
<servlet-mapping>
  <servlet-name>springmvc</servlet-name>
  <url-pattern>/</url-pattern>
</servlet-mapping>

<form action="/upload2" method="post" enctype="multipart/form-data">
  <input type="file" name="files" multiple>
  <input type="submit" value="上传">
</form>

@RequestMapping("/upload2")
@ResponseBody
public void upload2(MultipartFile[] files, HttpServletRequest req) {
  String format = sdf.format(new Date());
  String realPath = req.getServletContext().getRealPath("/img") + format;
  File folder = new File(realPath);
  if (!folder.exists()) {
    folder.mkdirs();
  }
  try {
    for (MultipartFile file : files) {
      String oldName = file.getOriginalFilename();
      String newName = UUID.randomUUID().toString() + oldName.substring(oldName.lastIndexOf("."));
      file.transferTo(new File(folder, newName));
      String url = req.getScheme() + "://" + req.getServerName() + ":" + req.getServerPort() + "/img" + format + newName;
      System.out.println(url);
    }
  } catch (IOException e) {
    e.printStackTrace();
  }
}

<form action="/upload3" method="post" enctype="multipart/form-data">
  <input type="file" name="file1">
  <input type="file" name="file2">
  <input type="submit" value="上传">
</form>

@RequestMapping("/upload3")
@ResponseBody
public void upload3(MultipartFile file1, MultipartFile file2, HttpServletRequest req) {
  String format = sdf.format(new Date());
  String realPath = req.getServletContext().getRealPath("/img") + format;
  File folder = new File(realPath);
  if (!folder.exists()) {
    folder.mkdirs();
  }
  try {
    String oldName = file1.getOriginalFilename();
    String newName = UUID.randomUUID().toString() + oldName.substring(oldName.lastIndexOf("."));
    file1.transferTo(new File(folder, newName));
    String url1 = req.getScheme() + "://" + req.getServerName() + ":" + req.getServerPort() + "/img" + format + newName;
    System.out.println(url1);
    String oldName2 = file2.getOriginalFilename();
    String newName2 = UUID.randomUUID().toString() + oldName2.substring(oldName2.lastIndexOf("."));
    file2.transferTo(new File(folder, newName2));
    String url2 = req.getScheme() + "://" + req.getServerName() + ":" + req.getServerPort() + "/img" + format + newName2;
    System.out.println(url2);
  } catch (IOException e) {
    e.printStackTrace();
  }
}