实现文件上传的完整java代码

在Java中实现文件上传通常涉及到Servlet、MultipartHttpServletRequest以及File类型的处理。以下是一个简单的示例，展示了一个基于Apache Commons FileUpload库的文件上传过程：

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import org.apache.commons.fileupload.FileItem;

public class FileUploadServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private File uploadDirectory = new File("path/to/upload/directory");

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 创建一个临时目录用于处理上传文件
        DiskFileItemFactory factory = new DiskFileItemFactory();
        ServletFileUpload upload = new ServletFileUpload(factory);
        
        try {
            List<FileItem> fileItems = upload.parseRequest(request);

            for (FileItem item : fileItems) {
                if (!item.isFormField()) { // 检查是否为表单字段，如果是，则忽略
                    String fileName = FilenameUtils.getName(item.getName());
                    InputStream inputStream = item.getInputStream();

                    // 将文件保存到指定目录
                    File uploadedFile = new File(uploadDirectory, fileName);
                    OutputStream outputStream = new FileOutputStream(uploadedFile);
                    byte[] bytes = new byte[4096];
                    int length;
                    while ((length = inputStream.read(bytes)) != -1) {
                        outputStream.write(bytes, 0, length);
                    }
                    outputStream.close();
                    inputStream.close();
                    System.out.println("File " + fileName + " uploaded successfully.");
                } else {
                    System.out.println("This is a form field.");
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
            response.sendError(HttpServletResponse.SC_BAD_REQUEST, "File upload failed.");
        }
    }
}