在java项目中使用Demo如何实现一个文件上传功能

发布时间：2020-11-19 15:47:38 阅读：188 作者：Leah 栏目：编程语言

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在java项目中使用Demo如何实现一个文件上传功能？相信很多没有经验的人对此束手无策，为此本文总结了问题出现的原因和解决方法，通过这篇文章希望你能解决这个问题。

说到文件上传我们要做到：

1.引入两个包：commons-fileupload-1.2.1.jar和commons-io-1.3.2.jar

2.将form改为上传文件模式：enctype="multipart/form-data"

3.开始编写相关代码

这里会用到几个关键的类：磁盘文件工厂DiskFileItemFactory ；创建servlet文件上传类：ServletFileUpload

还有几个重要的方法：DiskFileItemFactory类用于将以临时文件形式保存在磁盘上的存放目录的方法setRepository；

ServletFileUpload类得到表单中所有的数据，得到form表单中所有的元素方法：parseRequest

下面看具体代码：

说明以这种方式上传文件是保存在服务器端的！

import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
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.FileUtils;
 
 
public class UploadServlet extends HttpServlet {
 
  /**
   * Constructor of the object.
   */
  public UploadServlet() {
    super();
  }
 
  /**
   * Destruction of the servlet. <br>
   */
  public void destroy() {
    super.destroy(); // Just puts "destroy" string in log
    // Put your code here
  }
 
  /**
   * The doGet method of the servlet. <br>
   *
   * This method is called when a form has its tag value method equals to get.
   *
   * @param request the request send by the client to the server
   * @param response the response send by the server to the client
   * @throws ServletException if an error occurred
   * @throws IOException if an error occurred
   */
  public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
 
    this.doPost(request, response);
  }
 
  /**
   * The doPost method of the servlet. <br>
   *
   * This method is called when a form has its tag value method equals to post.
   *
   * @param request the request send by the client to the server
   * @param response the response send by the server to the client
   * @throws ServletException if an error occurred
   * @throws IOException if an error occurred
   */
  public void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
 
    response.setContentType("text/html");
    PrintWriter out = response.getWriter();
    DiskFileItemFactory sf= new DiskFileItemFactory();//实例化磁盘被文件列表工厂
    String path = request.getRealPath("/upload");//得到上传文件的存放目录
    sf.setRepository(new File(path));//设置文件存放目录
    sf.setSizeThreshold(1024*1024);//设置文件上传小于1M放在内存中
    String rename = "";//文件新生成的文件名
    String fileName = "";//文件原名称
    String name = "";//普通field字段
    //从工厂得到servletupload文件上传类
    ServletFileUpload sfu = new ServletFileUpload(sf);
     
    try {
      List<FileItem> lst = sfu.parseRequest(request);//得到request中所有的元素
      for (FileItem fileItem : lst) {
        if(fileItem.isFormField()){
          if("name".equals(fileItem.getFieldName())){
            name = fileItem.getString("UTF-8");
          }
        }else{
          //获得文件名称
          fileName = fileItem.getName();
          fileName = fileName.substring(fileName.lastIndexOf("\\")+1);
          String houzhui = fileName.substring(fileName.lastIndexOf("."));
          rename = UUID.randomUUID()+houzhui;
          fileItem.write(new File(path, rename));
        }
      }
    } catch (Exception e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }
     
    System.out.println("普通字段"+name);
    System.out.println("文件名称"+fileName);
    System.out.println("修改后生成的文件名称"+rename);
    response.sendRedirect("ok.jsp");
    out.flush();
    out.close();
  }
 
  /**
   * Initialization of the servlet. <br>
   *
   * @throws ServletException if an error occurs
   */
  public void init() throws ServletException {
    // Put your code here
  }
 
}

index.jsp页面：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
 <head>  
  <title>文件测试界面</title>
  <meta http-equiv="pragma" content="no-cache">
  <meta http-equiv="cache-control" content="no-cache">
  <meta http-equiv="expires" content="0">  
  <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
  <meta http-equiv="description" content="This is my page">
 </head>
 <body>
  <div align="center">
  <form action="UploadServlet" enctype="multipart/form-data" method="post">
    名称：<input name="name" /> <br>
    图片：<input name="img" type="file"/><br>
    <input type="submit" value="提交" />  
    <input type="reset" value="重置" />
  </form>
  </div>
 </body>
</html>

ok.jsp页面：

<body>
  <h2 align="center">上传文件成功!</h2>
 </body>

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