java实现文件的下载

*本例主要是实现从服务器中取到指定的文件保存到本地

页面

 

<table>  
	<tr>  
	     <td>下载模版：</td>  
	     <td><a href="${pageContext.request.contextPath}/servlet/DownLoadServlet" id="downloadTemplate" >下载模板文件</a></td>  
	</tr>  
</table>

 

DownLoadServlet.java类

 

 

 

package icss.cjpl.action;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.URLEncoder;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * 
 * @ClassName: DownLoadServlet
 * @Description: DownLoadServlet，
 * @author: huayi
 * @date: 2017-10-28 下午11:40:24
 *
 */
@SuppressWarnings("serial")
public class DownLoadServlet extends HttpServlet {

    
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //得到要下载的文件名
//        String fileName = request.getParameter("");  //模板
    	String fileName = "价格情况模板.xls";
//        fileName = new String(fileName.getBytes("iso8859-1"),"UTF-8");
//如果this.getServletContext().getRealPath有问题可以用request.getSession().getServletContext().getRealPath("/")
        //上传的文件都是保存在/WEB-INF/upload目录下的子目录当中
        String fileSaveRootPath=this.getServletContext().getRealPath("/WEB-INF/upload");
        //通过文件名找出文件的所在目录
//        String path = findFileSavePathByFileName(fileName,fileSaveRootPath);
        //得到要下载的文件
        File file = new File(fileSaveRootPath + "\\" + fileName);
        //如果文件不存在
        if(!file.exists()){
            request.setAttribute("message", "您要下载的资源已被删除！！");
            request.getRequestDispatcher("/page/cjwj/proprichange/message.jsp").forward(request, response);
            return;
        }
        //处理文件名
        String realname = fileName.substring(fileName.indexOf("_")+1);
        //设置响应头，控制浏览器下载该文件
        response.setHeader("content-disposition", "attachment;filename=" + URLEncoder.encode(realname, "UTF-8"));
        //读取要下载的文件，保存到文件输入流
        FileInputStream in = new FileInputStream(fileSaveRootPath + "\\" + fileName);
        //创建输出流
        OutputStream out = response.getOutputStream();
        //创建缓冲区
        byte buffer[] = new byte[1024];
        int len = 0;
        //循环将输入流中的内容读取到缓冲区当中
        while((len=in.read(buffer))>0){
            //输出缓冲区的内容到浏览器，实现文件下载
            out.write(buffer, 0, len);
        }
        //关闭文件输入流
        in.close();
        //关闭输出流
        out.close();
    }
    
    /**
    * @Method: findFileSavePathByFileName
    * @Description: 通过文件名和存储上传文件根目录找出要下载的文件的所在路径
    * @Anthor:huayi
    * @param filename 要下载的文件名
    * @param saveRootPath 上传文件保存的根目录，也就是/WEB-INF/upload目录
    * @return 要下载的文件的存储目录
    */ 
    public String findFileSavePathByFileName(String filename,String saveRootPath){
        int hashcode = filename.hashCode();
        int dir1 = hashcode&0xf;  //0--15
        int dir2 = (hashcode&0xf0)>>4;  //0-15
        String dir = saveRootPath + "\\" + dir1 + "\\" + dir2;  //upload\2\3  upload\3\5
        File file = new File(dir);
        if(!file.exists()){
            //创建目录
            file.mkdirs();
        }
        return dir;
    }
    
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }
}

web.xml

<!-- 上传 -->
     <servlet>
	    <servlet-name>UploadHandleServlet</servlet-name>
	    <servlet-class>icss.cjpl.action.UploadHandleServlet</servlet-class>
	</servlet>
	
	<servlet-mapping>
	    <servlet-name>UploadHandleServlet</servlet-name>
	    <url-pattern>/servlet/UploadHandleServlet</url-pattern>
	</servlet-mapping>
	<!-- 下载 -->
	<servlet>
      <servlet-name>DownLoadServlet</servlet-name>
      <servlet-class>icss.cjpl.action.DownLoadServlet</servlet-class>
	</servlet>
	 
	<servlet-mapping>
	      <servlet-name>DownLoadServlet</servlet-name>
	      <url-pattern>/servlet/DownLoadServlet</url-pattern>
	</servlet-mapping>

 

/*如有借鉴代码，在此感谢作者*/