上传文件的Servlet在写入文件的那部分有点不懂

qvcqjzdgq 2015-11-18 12:55:53

以下代码的两个fileName.substring的作用请讲一下。



// 导入必需的 java 库

import java.io.*;

import java.util.*;

 

import javax.servlet.ServletConfig;

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.output.*;



public class UploadServlet extends HttpServlet {

   

   private boolean isMultipart;

   private String filePath;

   private int maxFileSize = 50 * 1024;

   private int maxMemSize = 4 * 1024;

   private File file ;



   public void init( ){

      // 获取文件将被存储的位置

      filePath = 

             getServletContext().getInitParameter("file-upload"); 

   }

   public void doPost(HttpServletRequest request, 

               HttpServletResponse response)

              throws ServletException, java.io.IOException {

      // 检查我们有一个文件上传请求

      isMultipart = ServletFileUpload.isMultipartContent(request);

      response.setContentType("text/html");

      java.io.PrintWriter out = response.getWriter( );

      if( !isMultipart ){

         out.println("<html>");

         out.println("<head>");

         out.println("<title>Servlet upload</title>");  

         out.println("</head>");

         out.println("<body>");

         out.println("<p>No file uploaded</p>"); 

         out.println("</body>");

         out.println("</html>");

         return;

      }

      DiskFileItemFactory factory = new DiskFileItemFactory();

      // 文件大小的最大值将被存储在内存中

      factory.setSizeThreshold(maxMemSize);

      // Location to save data that is larger than maxMemSize.

      factory.setRepository(new File("c:\\temp"));



      // 创建一个新的文件上传处理程序

      ServletFileUpload upload = new ServletFileUpload(factory);

      // 允许上传的文件大小的最大值

      upload.setSizeMax( maxFileSize );



      try{ 

      // 解析请求，获取文件项

      List fileItems = upload.parseRequest(request);

	

      // 处理上传的文件项

      Iterator i = fileItems.iterator();



      out.println("<html>");

      out.println("<head>");

      out.println("<title>Servlet upload</title>");  

      out.println("</head>");

      out.println("<body>");

      while ( i.hasNext () ) 

      {

         FileItem fi = (FileItem)i.next();

         if ( !fi.isFormField () )	

         {

            // 获取上传文件的参数

            String fieldName = fi.getFieldName();

            String fileName = fi.getName();

            String contentType = fi.getContentType();

            boolean isInMemory = fi.isInMemory();

            long sizeInBytes = fi.getSize();

            // 写入文件

            if( fileName.lastIndexOf("\\") >= 0 ){

               file = new File( filePath + 

               fileName.substring( fileName.lastIndexOf("\\"))) ;

            }else{

               file = new File( filePath + 

               fileName.substring(fileName.lastIndexOf("\\")+1)) ;

            }

            fi.write( file ) ;

            out.println("Uploaded Filename: " + fileName + "<br>");

         }

      }

      out.println("</body>");

      out.println("</html>");

   }catch(Exception ex) {

       System.out.println(ex);

   }

   }

   public void doGet(HttpServletRequest request, 

                       HttpServletResponse response)

        throws ServletException, java.io.IOException {

        

        throw new ServletException("GET method used with " +

                getClass( ).getName( )+": POST method required.");

   } 

}