使用fileupload包进行文件上传

• 文件上传的必要前提：
  1. 提供form表单，method必须是post
  2. form表单的enctype必须是multipart/form-data（默认是application/x-www-form-urlencoded）
  3. 提供input type="file"类的上传输入域
• 下面是实现文件上传的示例代码：
• 需要导入的包如下：

WEB-INF/lib/commons-fileupload-1.2.2.jar
WEB-INF/lib/commons-io-2.2.jar

package Upload;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.util.List;
import java.util.UUID;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.apache.commons.io.FilenameUtils;

public class UploadServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        // 要执行文件上传的操作
        // 判断表单是否支持文件上传。即：enctype="multipart/form-data"
        boolean isMultipartContent = ServletFileUpload.isMultipartContent(request);
        if (!isMultipartContent) {
            throw new RuntimeException("your form is not multipart/form-data");
        }

        // 创建一个DiskFileItemfactory工厂类
        DiskFileItemFactory factory = new DiskFileItemFactory();
        factory.setRepository(new File("d:\\"));// 指定临时文件的存储目录
        // 创建一个ServletFileUpload核心对象
        ServletFileUpload sfu = new ServletFileUpload(factory);
        // 解决上传文件名乱码问题
        sfu.setHeaderEncoding("UTF-8");

        // 解析request对象，并得到一个表单项的集合
        try {
            List<FileItem> fileItems = sfu.parseRequest(request);

            // 遍历表单项数据
            for (FileItem fileitem : fileItems) {
                if (fileitem.isFormField()) {
                    // 普通表单项
                    processFormField(fileitem);
                } else {
                    // 上传表单项
                    processUploadField(fileitem);
                }
            }
        } catch (FileUploadException e) {
            e.printStackTrace();
        }
    }

    // 上传表单项
    private void processUploadField(FileItem fileitem) {
        try {
            // 得到文件输入流
            InputStream is = fileitem.getInputStream();

            // 创建一个文件存盘的目录
            String directoryRealPath = this.getServletContext().getRealPath("/WEB-INF/upload");
            File storeDirectory = new File(directoryRealPath);
            if (!storeDirectory.exists()) {
                storeDirectory.mkdirs();// 创建一个指定的目录
            }
            // 得到上传的文件名称
            String filename = fileitem.getName();
            //下面的操作只是为了防止上面的上传文件名包含路径名
            if (filename != null) {
                filename = FilenameUtils.getName(filename);
            }

            // 解决文件同名的问题
            filename = UUID.randomUUID() + "_" + filename;

            // 目录打散
            String childDirectory = makeChildDirectory(storeDirectory, filename);

            // 在storeDirectory下，创建完整目录下的文件
            File file = new File(storeDirectory, childDirectory + File.separator + filename); // 绝对目录/生成的子目录/文件名
            // 通过文件输出流将上传的文件保存到磁盘
            FileOutputStream fos = new FileOutputStream(file);

            int len = 0;
            byte[] b = new byte[1024];
            while ((len = is.read(b)) != -1) {
                fos.write(b, 0, len);
            }
            fos.close();
            is.close();
            //删除临时文件
            fileitem.delete();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    // 目录打散
    private String makeChildDirectory(File storeDirectory, String filename) {
        int hashcode = filename.hashCode();// 返回字符转换的32位hashcode码
        System.out.println(hashcode);//1417749484
        String code = Integer.toHexString(hashcode); // 把hashcode转换为16进制的字符
        System.out.println(code);//548123ec
        String childDirectory = code.charAt(0) + File.separator + code.charAt(1); // 5/4
        // 创建指定目录
        File file = new File(storeDirectory, childDirectory);
        if (!file.exists()) {
            file.mkdirs();
        }
        return childDirectory;
    }

    // 普通表单项
    private void processFormField(FileItem fileitem) {
        try {
            String fieldname = fileitem.getFieldName();// 字段名
            String fieldvalue = fileitem.getString("UTF-8");// 字段值
            System.out.println(fieldname + "=" + fieldvalue);
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }

}