两种java文件上传实例讲解

下面是详细讲解“两种java文件上传实例讲解”的攻略：

一、基于Spring MVC框架的文件上传实例

1. 在Maven项目配置中添加以下依赖：

<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-webmvc</artifactId>
  <version>4.3.1.RELEASE</version>
</dependency>

<dependency>
  <groupId>commons-fileupload</groupId>
  <artifactId>commons-fileupload</artifactId>
  <version>1.3.1</version>
</dependency>

<dependency>
  <groupId>commons-io</groupId>
  <artifactId>commons-io</artifactId>
  <version>2.5</version>
</dependency>

2. 配置Spring MVC配置文件

在spring配置文件中，添加multipartResolver Bean，用来处理文件上传的请求。

<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
  <property name="maxUploadSize" value="50000000"/>
</bean>

3. 编写Controller类

@Controller
public class UploadFileController {
  @RequestMapping(value="/uploadFile", method=RequestMethod.POST)
  public String uploadFileHandler(@RequestParam("file") MultipartFile file) {

    if (!file.isEmpty()) {
      try {
          byte[] bytes = file.getBytes();

          // 创建文件保存路径
          String path = "/tmp/" + file.getOriginalFilename();
          File serverFile = new File(path);
          BufferedOutputStream stream = new BufferedOutputStream(
                  new FileOutputStream(serverFile));
          stream.write(bytes);
          stream.close();

          System.out.println("You have successfully uploaded " + file.getOriginalFilename());
      } catch (Exception e) {
          System.out.println("You failed to upload " + file.getOriginalFilename() + " => " + e.getMessage());
      }
    } else {
        System.out.println("You failed to upload " + file.getOriginalFilename() + " because the file was empty.");
    }
    return "uploadFileSuccessView";
  }
}

4. 编写前端页面

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

二、不依赖框架的文件上传实例

1. 前端页面

<form enctype="multipart/form-data" method="post" action="UploadServlet">
  <input type="file" name="fileToUpload" id="fileToUpload">
  <br>
  <input type="submit" value="Upload">
</form>

2. 服务器端Java代码

@WebServlet("/UploadServlet")
@MultipartConfig(fileSizeThreshold = 1024 * 1024 * 2, // 2MB
                 maxFileSize = 1024 * 1024 * 10, // 10MB
                 maxRequestSize = 1024 * 1024 * 50) // 50MB
public class UploadServlet extends HttpServlet {
  private static final long serialVersionUID = 1L;

  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    InputStream inputStream = null;
    OutputStream outputStream = null;
    PrintWriter out = response.getWriter();

    try {
      Part filePart = request.getPart("file");
      inputStream = filePart.getInputStream();

      File file = new File("C:/uploads/" + filePart.getSubmittedFileName());
      outputStream = new FileOutputStream(file);

      int read = 0;
      final byte[] bytes = new byte[1024];

      while ((read = inputStream.read(bytes)) != -1) {
        outputStream.write(bytes, 0, read);
      }
      System.out.println("New file " + file.getName() + " created at " + file.getAbsolutePath());
      out.println("Received file=" + file.getName());
    } catch (Exception e) {
      out.println("Error=" + e.getMessage());
    } finally {
      if (inputStream != null) inputStream.close();
      if (outputStream != null) outputStream.close();
      if (out != null) out.close();
    }
  }
}

这是两种Java文件上传的实例，总体来说，使用Spring MVC框架上传文件更为简便，而不依赖框架的上传方式更为灵活，可以在任何Java Web项目中使用。我们可以根据实际需求，选择合适的文件上传方式。