一upload原理：

　　　　　　1.表单的method必须是post方法

　　　　　　2.enctype属性必须是“mutipatr/form-data”类型

　　　　　　　enctype默认的属性是“application/x-www-form-urlencoded”

　　　　　　　enctype的作用是：告知服务器请求正文的MIME类型

　　　　　　application/x-www-form-urlencoded:username=aaa&password=123

　　　　　　ServletRequest.getParameter(String name)，该方法是专门用来读取enctype是“application/x-www-form-urlencoded”时的方法

　　　　　　3.在Servlet里面通过request.getInputStream()方法就可以获得文件输入流

　　　　　　　　byte[] b= new byte[1024];

　　　　　　　　int len=0;

　　　　　　　　InputStream is = request.getInputStream();

　　　　　　　　while((len=is.read(b)) != -1){

　　　　　　　　System.out.println(new String(b,0 ,len));

　　　　　　　　}

代码示例

1 <%@ page language="java" contentType="text/html; charset=UTF-8" 2     pageEncoding="UTF-8"%> 3  4  5  6 
       7  8  9 10 
      
       11     请输入FileName
       12                 
       13                 
       14                 ${pageContext.request.contextPath}15                 16                 17     18     19 
      
20 21 22 

1 package jcbc.ds.test1; 2  3 import java.io.IOException; 4 import java.io.InputStream; 5 import java.util.List; 6  7 import javax.servlet.ServletException; 8 import javax.servlet.http.HttpServlet; 9 import javax.servlet.http.HttpServletRequest;10 import javax.servlet.http.HttpServletResponse;11 12 import org.apache.commons.fileupload.FileItem;13 import org.apache.commons.fileupload.FileUploadException;14 import org.apache.commons.fileupload.disk.DiskFileItemFactory;15 import org.apache.commons.fileupload.servlet.ServletFileUpload;16 17 /**18  * Servlet implementation class UploadServlet19  */20 public class UploadServlet extends HttpServlet {21     private static final long serialVersionUID = 1L;22        23     /**24      * @see HttpServlet#HttpServlet()25      */26     public UploadServlet() {27         super();28         29     }30 31     /**32      * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)33      */34     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {35         36         //创建DiskFileItemFactory对象37         //DiskFileItemFactory dis = new DiskFileItemFactory();38         //创建ServletFileUpload对象39         /*ServletFileUpload servletupload = new ServletFileUpload(dis);*/40         byte[] b= new byte[1024];41         int len=0;42         InputStream is = request.getInputStream();43         while((len=is.read(b)) != -1){44             System.out.println(new String(b,0 ,len));45         }46         /*try {47             List
      
           fileItem = servletupload.parseRequest(request);48             for(FileItem items : fileItem) {49                 System.out.println(items.getName());50                 //进行解析传过来的数据进行封装51             }52             is.close();53             54         } catch (FileUploadException e) {55             // TODO Auto-generated catch block56             e.printStackTrace();57         }*/58         59     }60 61 }
      

二借助第三方组件实现文件上传：

　　步骤：

　　1.拷贝jar包commons-fileupload.jar  commons-io.jar

　　　　具体参考　　

　　2.//创建DiskFileItemFactory对象

　　  DiskFileItemFactory disfileitemfactory = new DiskFileItemFactory();

　　  //创建ServletFileUpload对象

　　  ServletFileUpload servletupload = new ServletFileUpload(disfileitemfactory);

　　3.获取封装信息

　　　　List<FileItem> fileItem = servletupload.parseRequest(request);//这里会抛异常

　　具体步骤代码如下：

1 package jcbc.ds.test1; 2  3 import java.io.File; 4 import java.io.IOException; 5 import java.io.InputStream; 6 import java.io.OutputStream; 7 import java.util.List; 8  9 import javax.servlet.ServletException;10 import javax.servlet.http.HttpServlet;11 import javax.servlet.http.HttpServletRequest;12 import javax.servlet.http.HttpServletResponse;13 14 import org.apache.commons.fileupload.FileItem;15 import org.apache.commons.fileupload.FileUploadException;16 import org.apache.commons.fileupload.disk.DiskFileItemFactory;17 import org.apache.commons.fileupload.servlet.ServletFileUpload;18 import org.apache.commons.io.FileUtils;19 20 /**21  * Servlet implementation class UploadServlet22  */23 public class UploadServlet extends HttpServlet {24     private static final long serialVersionUID = 1L;25        26     /**27      * @see HttpServlet#HttpServlet()28      */29     public UploadServlet() {30         super();31         32     }33 34     /**35      * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)36      */37     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {38         response.setContentType("text/html; charset=gbk");39         //创建DiskFileItemFactory对象40         DiskFileItemFactory disfileitemfactory = new DiskFileItemFactory();41         //创建ServletFileUpload对象42         ServletFileUpload servletupload = new ServletFileUpload(disfileitemfactory);43         44         try {45             //封装46             List
      
           fileItem = servletupload.parseRequest(request);47             for(FileItem files : fileItem ){48                 if(files.isFormField()){49                     System.out.println(files.getFieldName());50                 }51                 else{52                     InputStream is = files.getInputStream();53                     String name = files.getName();54                     //截取文件名55                     String fileName = name.substring(name.lastIndexOf("\\")+1);56                     System.out.println(fileName);//打印结果为huxuebing.txt57                     58                     System.out.println(request.getServletContext().getRealPath("/fileName"));59                     //创建File类对象60                     File file = new File(request.getServletContext().getRealPath("/")+fileName);61                     //判断该文件是否存在如果不存在就创建，存在就不创建62                     if(file.exists()==false){63                         System.out.println("==================");64                         file.createNewFile();65                         System.out.println("==================");66                     }67                     try {68                         //向创建的文件写入69                         files.write(file);70                     } catch (Exception e) {71                         // TODO Auto-generated catch block72                         e.printStackTrace();73                     }74                     75                 }76                         77             }78             79         } catch (FileUploadException e) {80             // TODO Auto-generated catch block81             e.printStackTrace();82         }83         84     }85 86 }
      

FileNamehuxuebing.txtD:\workSpace\web2\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\day18\fileName====================================