Servlet 3实现文件上传

UploadServlet.java

import java.io.File;
import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;

/**
 * Servlet 3 实现文件上传
 */
@WebServlet("/UploadServlet")
@MultipartConfig(fileSizeThreshold=1024*1024*2, // 2MB  当数据量大于该值时，内容将被写入文件
        maxFileSize=1024*1024*10,      // 10MB  允许上传的文件最大值。默认值为 -1，表示没有限制
        maxRequestSize=1024*1024*50)   // 50MB  针对该 multipart/form-data 请求的最大数量，默认值为 -1，表示没有限制
public class UploadServlet extends HttpServlet {

    /**
     * Name of the directory where uploaded files will be saved, relative to
     * the web application directory.
     */
    private static final String SAVE_DIR = "uploadFiles";

    /**
     * handles file upload
     */
    protected void doPost(HttpServletRequest request,
                          HttpServletResponse response) throws ServletException, IOException {
        // gets absolute path of the web application
        String appPath = request.getServletContext().getRealPath("");
        // constructs path of the directory to save uploaded file
        String savePath = appPath + File.separator + SAVE_DIR;

        // creates the save directory if it does not exists
        File fileSaveDir = new File(savePath);
        if (!fileSaveDir.exists()) {
            fileSaveDir.mkdir();
        }

        for (Part part : request.getParts()) {
            String fileName = extractFileName(part);
            part.write(savePath + File.separator + fileName);
        }

        request.setAttribute("message", "Upload has been done successfully!");
        getServletContext().getRequestDispatcher("/message.jsp").forward(
                request, response);
    }

    /**
     * 从 HTTP header content-disposition中获得文件名
     * content-disposition中内容：form-data; name="dataFile"; filename="PHOTO.JPG"
     */
    private String extractFileName(Part part) {
        String contentDisp = part.getHeader("content-disposition");
        String[] items = contentDisp.split(";");
        for (String s : items) {
            if (s.trim().startsWith("filename")) {
                return s.substring(s.indexOf("=") + 2, s.length()-1);
            }
        }
        return "";
    }
}