jsp+servlet实现上传文件功能解析

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package Servlet.bookServlet;

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 javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.List;


@WebServlet(name = "UploadImageServlet")
public class UploadImageServlet extends HttpServlet {
  @Override
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    this.doPost(request,response);
  }
  @Override
  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //1、判断请求是不是multipart请求
    if(!ServletFileUpload.isMultipartContent(request)){
      throw new RuntimeException("当前请求不支持文件上传");
    }
    System.out.println("开始上传文件");
    //2、创建FileItem工厂==>文件写入硬盘的作用
    try {
      DiskFileItemFactory factory = new DiskFileItemFactory();
      //3、创建temp临时文件夹
      String tempPath ="D:\tomcat\apache-tomcat-9.0.35-windows-x64\apache-tomcat-9.0.35\webapps\librarySystem\web\net\temp";
      File tempFile = new File(tempPath);
      factory.setRepository(tempFile);
      //4、设置使用临时文件的边界值,大于该值，上传文件先保存在临时文件中，小于该值，则直接写入内存
      //单位是字节
      factory.setSizeThreshold(1024*1024*1);

      //5、创建文件上传核心组件
      // 调用ServletFileUpload.parseRequest方法解析request对象，得到一个保存了所有上传内容的List对象。
      ServletFileUpload upload = new ServletFileUpload(factory);
      upload.setHeaderEncoding("utf-8");//可以解决文件名中文乱码
      upload.setFileSizeMax(1024*1024*2);

      String bNo="defaultBNo",bName="defaultBName";
      //6、解析请求
      List items =upload.parseRequest(request);
      //7、遍历请求
      for(FileItem item:items){
        //普通表单项，上传名字，编号等普通信息的上i传
        if(item.isFormField()){
          String fileName = item.getFieldName();// name属性值
          String fileValue = item.getString("utf-8");// name对应的value值
          System.out.println(fileName + " -- " + fileValue);
          if(fileName.equalsIgnoreCase("BNO")){
            bNo = fileValue;
          }
          if(fileName.equalsIgnoreCase("BNAME")){
            bName = fileValue;
          }
         }
        else{//上传图片等
          String fileName = item.getName();
          System.out.println("上传文件名字:"+fileName);
          String suffix = fileName.substring(fileName.lastIndexOf('.'));//获取文件类型
          String newFileName = bNo+"_"+bName+suffix;
          System.out.println(newFileName);
          //获取输入流，其中有上传文件的内容
          InputStream is = item.getInputStream();
          //String path = this.getServletContext().getRealPath("/net/bookImage");//获得当前项目保存服务器地址，也就是web文件夹下
          String path ="D:\tomcat\apache-tomcat-9.0.35-windows-x64\apache-tomcat-9.0.35\webapps\librarySystem\web\net\bookImage";
          //文件夹内文件数目有上限，但是可以创建子目录
            //获取当前系统时间
            Calendar now = Calendar.getInstance();
            int year = now.get(Calendar.YEAR);
            int month = now.get(Calendar.MONTH)+1;
            int day = now.get(Calendar.DAY_OF_MONTH);
            path = path+"/"+year+"/"+month+"/"+day;
            //若该目录不存在，直接创建新目录
            File dirFile = new File(path);
            if(!dirFile.exists()){
              dirFile.mkdirs();
            }
          //创建目标文件，用来保存上传文件
          File desFile = new File(path,newFileName);
          //创建文件输出流
          OutputStream os = new FileOutputStream(desFile);
          //将输入流数据写入到输出流中
          int len=-1;
          byte[]buf = new byte[1024];
          while((len=is.read(buf))!=-1){
            os.write(buf,0,len);
          }
          //desFile.delete();//删除临时文件
          os.close();//输出流
          is.close();//输入流
          //删除临时文件
          item.delete();
        }
      }
    } catch (FileUploadException e) {
      e.printStackTrace();
    }
  }
}