作为一名Java开发者，相信大家都会遇到文件上传的需求。Java提供了多种方式实现文件上传，下面我就来介绍一下Java实现文件上传的三种方式，希望对大家有所帮助。

1.使用Servlet实现文件上传

Servlet是Java Web开发的重要组成部分，下面我们利用Servlet来实现文件上传：

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  try {
    // Create a factory for disk-based file items
    DiskFileItemFactory factory = new DiskFileItemFactory();
    // Configure a repository (to ensure a secure temp location is used)
    ServletContext servletContext = this.getServletConfig().getServletContext();
    File repository = (File) servletContext.getAttribute("javax.servlet.context.tempdir");
    factory.setRepository(repository);
    // Create a new file upload handler
    ServletFileUpload upload = new ServletFileUpload(factory);
    // Parse the request
    List
  items = upload.parseRequest(request);
 
    for (FileItem item : items) {
      // Process uploaded item
      if (!item.isFormField()) {
        String fileName = item.getName();
        InputStream inputStream = item.getInputStream();
        // ... Save the file to a temporary location
      }
    }
  } catch (FileUploadException e) {
    throw new ServletException("Cannot parse multipart request.", e);
  }
}

2.使用Apache Commons Fileupload实现文件上传

Apache Commons Fileupload是Apache开源组织提供的一个文件上传组件，可以方便地实现文件上传功能。下面我们利用Apache Commons Fileupload来实现文件上传：

// Import required libraries
import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
import org.apache.commons.fileupload.*;
import org.apache.commons.fileupload.disk.*;
import org.apache.commons.fileupload.servlet.*;
import javax.servlet.*;
import javax.servlet.http.*;
// Set the encoding type
String encoding = "utf-8";
if (ServletFileUpload.isMultipartContent(request)) {
  // Create a factory for disk-based file items
  DiskFileItemFactory factory = new DiskFileItemFactory();
  // Configure a repository (to ensure a secure temp location is used)
  ServletContext servletContext = this.getServletConfig().getServletContext();
  File repository = (File) servletContext.getAttribute("javax.servlet.context.tempdir");
  factory.setRepository(repository);
  // Create a new file upload handler
  ServletFileUpload upload = new ServletFileUpload(factory);
  // Set the encoding type
  upload.setHeaderEncoding(encoding);
  // Parse the request
  List
  items = upload.parseRequest(request);
 
  // Process the uploaded file items
  Iterator
  iter = items.iterator();
 
  while (iter.hasNext()) {
    FileItem item = iter.next();
    if (!item.isFormField()) {
      String fileName = item.getName();
      // Write the file
      File uploadedFile = new File("D:\\" + fileName);
      item.write(uploadedFile);
    }
  }
}

3.使用SpringMVC实现文件上传

SpringMVC是一种轻量级的MVC框架，相信大家都比较熟悉。下面我们利用SpringMVC来实现文件上传：

@RequestMapping(value = "/fileupload", method = RequestMethod.POST)
public String handleFileUpload(@RequestParam("file") MultipartFile file) {
  if (!file.isEmpty()) {
    try {
      byte[] bytes = file.getBytes();
      // store the bytes somewhere
      return "redirect:add_entry.html";
    } catch (Exception e) {
      return "You failed to upload " + file.getOriginalFilename() + " => " + e.getMessage();
    }
  } else {
    return "You failed to upload " + file.getOriginalFilename() + " because the file was empty.";
  }
}

以上就是我介绍的Java实现文件上传的三种方式，希望对大家有所帮助。

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