java实现文件上传下载

<form method= "post" action= "fileupload" enctype= "multipart/form-data" >

　　<input type= "file" name= "uploadfile" />

　　<br/>

　　<input type= "submit" value= "上传" />

</form>

import java.io.file;

import java.io.ioexception;

import java.io.printwriter;

import java.util.list;

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 org.apache.commons.fileupload.fileitem;

import org.apache.commons.fileupload.disk.diskfileitemfactory;

import org.apache.commons.fileupload.servlet.servletfileupload;

import dao.filedao;

@webservlet ( "/fileupload" )

public class fileupload extends httpservlet {

   private static final long serialversionuid = 1l;

   // 上传配置

   private static final int memory_threshold  = 1024 * 1024 * 3 ; // 3mb

   private static final int max_file_size   = 1024 * 1024 * 40 ; // 40mb

   private static final int max_request_size  = 1024 * 1024 * 50 ; // 50mb

   public fileupload() {

     super ();

   }

   protected void doget(httpservletrequest request, httpservletresponse response) throws servletexception, ioexception {

     request.setcharacterencoding( "utf-8" );

     response.setcharacterencoding( "utf-8" );

     response.setcontenttype( "text/html;charset=utf-8" );

     printwriter out = response.getwriter();

       if (!servletfileupload.ismultipartcontent(request)) {

       // 如果不是则停止

       out.println( "error: 表单必须包含 enctype=multipart/form-data" );

       out.flush();

       return ;

     }

     // 配置上传参数

     diskfileitemfactory factory = new diskfileitemfactory();

     // 设置内存临界值 - 超过后将产生临时文件并存储于临时目录中

     factory.setsizethreshold(memory_threshold);

     // 设置临时存储目录

     factory.setrepository( new file(system.getproperty( "java.io.tmpdir" )));

     servletfileupload upload = new servletfileupload(factory);

     // 设置最大文件上传值

     upload.setfilesizemax(max_file_size);

     // 设置最大请求值 (包含文件和表单数据)

     upload.setsizemax(max_request_size);

     // 中文处理

     upload.setheaderencoding( "utf-8" );

     string uploadpath = request.getservletcontext().getrealpath( "/files" );

     file uploaddir = new file(uploadpath);

     if (!uploaddir.exists()) {

       uploaddir.mkdir();

     }

     try {

       // 解析请求的内容提取文件数据

       list<fileitem> formitems = upload.parserequest(request);

       if (formitems != null && formitems.size() > 0 ) {

         // 迭代表单数据

         for (fileitem item : formitems) {

           // 处理不在表单中的字段

           if (!item.isformfield()) {

             string filename = new file(item.getname()).getname();

             string filepath = uploadpath + file.separator + filename;

             file storefile = new file(filepath);

             // 在控制台输出文件的上传路径

//            system.out.println(filepath);

             // 保存文件到硬盘

             if (storefile.exists()) {

               out.println( "上传失败，文件已存在！" );

             } else {

               item.write(storefile);

               out.println( "文件上传成功!" );

             } 

           }

         }

       }

     } catch (exception ex) {

       response.getwriter().println( "文件上传成功!" );

     }

   }

   protected void dopost(httpservletrequest request, httpservletresponse response) throws servletexception, ioexception {

     doget(request, response);

   }

}

import java.io.file;

import java.io.fileinputstream;

import java.io.ioexception;

import java.io.printwriter;

import java.net.urlencoder;

import javax.servlet.servletexception;

import javax.servlet.annotation.webservlet;

import javax.servlet.http.httpservlet;

import javax.servlet.http.httpservletrequest;

import javax.servlet.http.httpservletresponse;

@webservlet ( "/filedownload" )

public class filedownload extends httpservlet {

   private static final long serialversionuid = 1l;

   public filedownload() {

     super ();

   }

   protected void doget(httpservletrequest request, httpservletresponse response) throws servletexception, ioexception {

     request.setcharacterencoding( "utf-8" );

     response.setcharacterencoding( "utf-8" );

     printwriter out = response.getwriter();

     string dirpath = request.getservletcontext().getrealpath( "/files" );

     string filename = urlencoder.encode(request.getparameter( "filename" ), "utf-8" );  //需要对url中的中文参数进行编码，否则出现乱码

     response.getwriter().println(filename);

     string filepath = dirpath + file.separator + filename;

     response.setcontenttype( "application/octet-stream" );

     response.setheader( "content-disposition" , "attachment; filename=\"" + filename + "\"" );

     fileinputstream fileinputstream = new fileinputstream(filepath);

     int i = 0 ;

     while ((i = fileinputstream.read()) != - 1 ) {

       out.write(i);

     }

     fileinputstream.close();

     out.close();

   }

   protected void dopost(httpservletrequest request, httpservletresponse response) throws servletexception, ioexception {

     doget(request, response);

   }

}