java 从零开始，学习笔记之基础入门<servlet_文件下载>（二十七）

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servlet_文件下载

文件下载

1. 利用BufferedInputStream读取服务器上的文件

2. 利用ServletOutputStream将读取到的字节内容传递到客户端

3. 注意在进行文件下载时，指定被下载文件的类型

文件下载步骤：

1. 下载页面。在页面上提供出下载的列表，如果和数据库连接，则动态从数据库中读取文件列表

2. 构建下载的Servlet，来处理下载的请求

两个servlet

1. 一个servlet处理显示文件列表

2. 一个servlet负责单独处理下载的事件

一个页面

一个页面显示所有文件列表信息

Action:视图所对应的活动会话

Dao:数据访问对象

Dto：数据持久(传输)对象

Factory:各种类型的工厂。在slesson2中表示的是连接工厂

Util：工具辅助类，开发中将经常抽象的重复的方法可以汇总之后存放到此包中，以供复用

文件下载代码:

Web.html

<?xmlversion="1.0"encoding="UTF-8"?>

<web-appversion="2.5"

xmlns="http://java.sun.com/xml/ns/javaee"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://java.sun.com/xml/ns/javaee

http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

<description>This is the description of my J2EE component</description>

<display-name>This is the display name of my J2EE component</display-name>

<servlet-name>ShowFileAction</servlet-name>

<servlet-class>com.ibm.action.ShowFileAction</servlet-class>

</servlet>

<description>This is the description of my J2EE component</description>

<display-name>This is the display name of my J2EE component</display-name>

<servlet-name>download</servlet-name>

<servlet-class>com.ibm.action.download</servlet-class>

<init-param>

<param-name>pdfdir</param-name>

<param-value>pdf</param-value>

</init-param>

</servlet>

<servlet-mapping>

<servlet-name>ShowFileAction</servlet-name>

<url-pattern>/showfile</url-pattern>

</servlet-mapping>

<servlet-mapping>

<servlet-name>download</servlet-name>

<url-pattern>/download</url-pattern>

</servlet-mapping>

<welcome-file-list>

<welcome-file>index.jsp</welcome-file>

</welcome-file-list>

</web-app>

Index.jsp

<%@ pagelanguage="java"import="java.util.*"pageEncoding="UTF-8"%>

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

<!DOCTYPEHTMLPUBLIC"-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

<head>

<basehref="<%=basePath%>">

<metahttp-equiv="pragma"content="no-cache">

<metahttp-equiv="cache-control"content="no-cache">

<metahttp-equiv="expires"content="0">

<metahttp-equiv="keywords"content="keyword1,keyword2,keyword3">

<metahttp-equiv="description"content="This is my page">

<!--

-->

</head>

<body>

导航

<br>

<ahref="showfile">跳转到下载页面</a>

</body>

</html>

UFile.java

package com.ibm.dto;

/**

*用户文件类

*@author123

public class UFile {

privateint fileId;

private StringfiName;

public int getFileId() {

returnfileId;

}

public void setFileId(int fileId) {

this.fileId = fileId;

}

public String getFiName() {

returnfiName;

}

public void setFiName(String fiName) {

this.fiName = fiName;

}

IFileDAO.java

package com.ibm.dao;

import java.util.List;

import com.ibm.dto.UFile;

/**

*文件操作接口

*@author123

public interface IFileDAO {

//ctrl+shift+o批量导包快捷键

//获得所有文件信息

public List<UFile> getAllFile();

}

FileDAOImp.java

package com.ibm.dao.imp;

import java.sql.Connection;

import java.sql.ResultSet;

import java.sql.SQLException;

import java.sql.Statement;

import java.util.ArrayList;

import java.util.List;

import com.ibm.dao.IFileDAO;

import com.ibm.dto.UFile;

public class FileDAOImpimplements IFileDAO {

//申明连接对象

private Connectionconn;

//通过构造函数为对连接对象赋值

public FileDAOImp(Connection conn){

this.conn=conn;

}

public List<UFile> getAllFile() {

//文件列表

List<UFile> list=null;

Statement stmt=null;

ResultSet rs=null;

try {

list=new ArrayList<UFile>();

String sql="select * from filetb";

//获取命令执行对象

stmt=conn.createStatement();

//执行sql语句获得结果集

rs=stmt.executeQuery(sql);

//边循环边取出文件信息并存到list中

while(rs.next()){

UFile ufile=new UFile();

ufile.setFileId(rs.getInt(1));

ufile.setFiName(rs.getString(2));

list.add(ufile);

}

} catch (Exception e) {

//TODO: handle exception

e.printStackTrace();

}finally{

//关闭是由小到大关闭

try {

if(rs!=null){

rs.close();

}

if(stmt!=null){

stmt.close();

}

if(conn!=null){

conn.close();

}

} catch (SQLException e) {

//TODO Auto-generated catch block

e.printStackTrace();

}

return list;

}

Test.java(测试)

package com.ibm.test;

import java.util.List;

import com.ibm.dao.IFileDAO;

import com.ibm.dto.UFile;

import com.ibm.factory.DAOFactory;

import com.ibm.factory.SqlDAOFactory;

public class Test {

public staticvoid main(String[] args) {

//根据选择的产品获得DAO工厂

SqlDAOFactory daoFactory=(SqlDAOFactory)DAOFactory.getDaoFactory(1);

//获得具体的DAO

IFileDAO dao=daoFactory.getFileDAO();

//调用getAllFile方法获得文件信息列表

List<UFile> list=dao.getAllFile();

//循环输出获得的信息

for(UFile file:list){

System.out.println("文件名是:"+file.getFiName());

}

ShowFileAction.java

package com.ibm.action;

import java.io.IOException;

import java.io.PrintWriter;

import java.util.List;

import javax.servlet.RequestDispatcher;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import com.ibm.dao.IFileDAO;

import com.ibm.dto.UFile;

import com.ibm.factory.DAOFactory;

import com.ibm.factory.SqlDAOFactory;

public class ShowFileActionextends HttpServlet {

/**

*Constructoroftheobject.

public ShowFileAction() {

super();

}

/**

*Destructionoftheservlet.<br>

publicvoid destroy() {

super.destroy();// Just puts "destroy" string in log

// Put your code here

}

public void doGet(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

SqlDAOFactory daoFactory=(SqlDAOFactory)DAOFactory.getDaoFactory(1);

//获得具体的DAO

IFileDAO dao=daoFactory.getFileDAO();

//调用getAllFile方法获得文件信息列表

List<UFile> list=dao.getAllFile();

request.setAttribute("filelist", list);

//服务器内部转发对象将文件信息列表传递到filelist.jsp页面中

RequestDispatcher rd=request.getRequestDispatcher("filelist.jsp");

rd.forward(request,response);

}

public void doPost(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

response.setContentType("text/html");

PrintWriter out = response.getWriter();

out

.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");

out.println("<HTML>");

out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");

out.println(" <BODY>");

out.print(" This is ");

out.print(this.getClass());

out.println(", using the POST method");

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

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

out.flush();

out.close();

}

/**

*Initializationoftheservlet.<br>

*@throwsServletExceptionifanerroroccurs

public void init()throws ServletException {

// Put your code here

}

Filelist.java

<%@ pagelanguage="java"import="java.util.*"pageEncoding="UTF-8"%>

<%@pageimport="com.ibm.dto.UFile"%>

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

//从request对象中获得文件列表信息

List<UFile> list=(ArrayList<UFile>)request.getAttribute("filelist");

<!DOCTYPEHTMLPUBLIC"-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

<head>

<basehref="<%=basePath%>">

<title>My JSP 'filelist.jsp' starting page</title>

<metahttp-equiv="pragma"content="no-cache">

<metahttp-equiv="cache-control"content="no-cache">

<metahttp-equiv="expires"content="0">

<metahttp-equiv="keywords"content="keyword1,keyword2,keyword3">

<metahttp-equiv="description"content="This is my page">

<!--

-->

</head>

<body>

文件列表

<hr>

<table>

<tr>

</tr>

<%for(UFile file:list){%>

<tr>

</tr>

<% }%>

</table>

</body>

</html>

Download.java

package com.ibm.action;

import java.io.BufferedInputStream;

import java.io.File;

import java.io.FileInputStream;

import java.io.IOException;

import java.io.PrintWriter;

import javax.servlet.ServletException;

import javax.servlet.ServletOutputStream;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

public class downloadextends HttpServlet {

//pdf文件在web应用存放的文件夹名称

private StringpdfDir;

/**

*Constructoroftheobject.

public download() {

super();

}

/**

*Destructionoftheservlet.<br>

publicvoid destroy() {

super.destroy();// Just puts "destroy" string in log

// Put your code here

}

/**

*ThedoGetmethodoftheservlet.<br>

*Thismethodiscalledwhenaformhasitstagvaluemethodequalstoget.

*@paramrequesttherequestsendbytheclienttotheserver

*@paramresponsetheresponsesendbytheservertotheclient

*@throwsServletExceptionifanerroroccurred

*@throwsIOExceptionifanerroroccurred

publicvoid doGet(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

//默认的连接方式的请求都是用doGet方式来处理的

//获得用户需要下载的文件名称

String fileName=request.getParameter("filename");

System.out.println("用户需要下载的文件是:"+fileName);

//getServletContext获得当前servlet在容器中的上下文信息

String appPath=this.getServletContext().getRealPath("/");

System.out.println("服务器中应用所在的根目录是:"+appPath);

//第一步:拼装需要下载的文件的完整路径

String filePath=appPath+File.separator+"pdf"+File.separator+fileName;

System.out.println("下载的文件所在的完整路径是:"+filePath);

//第二步指定文件下载的类型，并将相关文件信息写出到客户端浏览器的头部

response.setContentType("application/pdf");

//以附件的形式传递到客户端附件名称由"attachment;filename="中的filename指定

response.addHeader("Content-Disposition","attachment;filename="+fileName);

//第三步：边读取服务器上的文件边以字节流的形式向客户端输出

BufferedInputStream br=new BufferedInputStream(new FileInputStream(filePath));

//读取的大小

byte[] buffer=newbyte[1024];

int len=0;

//获取网络传递流对象

ServletOutputStream os=response.getOutputStream();

while((len=br.read(buffer))!=-1){

os.write(buffer,0,len);

}

//都写完后关闭流

os.flush();

os.close();

br.close();

}

/**

*ThedoPostmethodoftheservlet.<br>

*Thismethodiscalledwhenaformhasitstagvaluemethodequalstopost.

*@paramrequesttherequestsendbytheclienttotheserver

*@paramresponsetheresponsesendbytheservertotheclient

*@throwsServletExceptionifanerroroccurred

*@throwsIOExceptionifanerroroccurred

publicvoid doPost(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

response.setContentType("text/html");

PrintWriter out = response.getWriter();

out

.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");

out.println("<HTML>");

out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");

out.println(" <BODY>");

out.print(" This is ");

out.print(this.getClass());

out.println(", using the POST method");

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

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

out.flush();

out.close();

}

/**

*Initializationoftheservlet.<br>

*@throwsServletExceptionifanerroroccurs

public void init()throws ServletException {

// Put your code here

//pdfdir来自于web.xml中servlet节点中配置的param-name

this.getInitParameter("pdfdir");

System.out.println("pdf所存放的路径名是:"+pdfDir);

}

数据库加工厂

ConnectionFactory.java

package com.ibm.factory;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.SQLException;

/**

*单子模式

*@authoryxx

*作业:模仿DAOfactory的构建方式创建ConnectionFactory

public class ConnectionFactory {

//驱动字符串

private static final StringdriverCls="com.microsoft.sqlserver.jdbc.SQLServerDriver";

//连接字符串

privatestatic final Stringurl="jdbc:sqlserver://localhost:1433;databasename=j1201";

//用户名

private static final Stringusername="sa";

//用户密码

privatestaticfinal Stringuserpwd="123";

//连接对象

private static Connectionconn;

private ConnectionFactory() {

//TODO Auto-generated constructor stub

}

/**

*获得数据库连接对象

*@returnConnection

publicstatic Connection getInstance(){

try {

if(conn==null){

Class.forName(driverCls);

conn=DriverManager.getConnection(url,username,userpwd);

}

} catch (ClassNotFoundException e) {

//TODO Auto-generated catch block

e.printStackTrace();

} catch (SQLException e) {

//TODO Auto-generated catch block

e.printStackTrace();

}

return conn;

}

DAOFactory.java

package com.ibm.factory;

import javax.sql.rowset.CachedRowSet;

/**

*根据不同的数据库产品，获取不同的数据连接对象，

*从而生成不同类型的DAO

*@authoryxx

public abstract class DAOFactory {

//默认选择的值1是Sql类型的数据库

publicstatic final intnum=1;

/**

*返回数据库DAO工厂

*@paramchoose选择的数据库产品

*@returnDAOFactory

public static DAOFactory getDaoFactory(int choose){

//com.sun.rowset.

DAOFactory df=null;

switch (choose==0?num:choose) {

//返回Sql工厂

case 1:

df= new SqlDAOFactory(ConnectionFactory.getInstance());

break;

//返回Mysql工厂

case 2:

df= new MysqlDAOFactory(ConnectionFactory.getInstance());

break;

default:

break;

}

return df;

}

MysqlDAOFactory.java

package com.ibm.factory;

import java.sql.Connection;

import com.ibm.dao.UserDAO;

import com.ibm.dao.imp.UserDAOImp;

public class MysqlDAOFactoryextends DAOFactory {

//com.sun.rowset.CachedRowSetImpl

private Connectionconn =null;

public MysqlDAOFactory(Connection conn) {

//TODO Auto-generated constructor stub

this.conn = conn;

}

/**

*获得UserDAO

*@paramconn

* 连接对象

*@returnUserDAO

public UserDAO getUserDAO(Connection conn) {

// CachedRowSetImpl cri=new CachedRowSetImpl();

returnnew UserDAOImp(conn);

}

SqlDAOFactory.java

package com.ibm.factory;

import java.sql.Connection;

import com.ibm.dao.IFileDAO;

import com.ibm.dao.UserDAO;

import com.ibm.dao.imp.FileDAOImp;

import com.ibm.dao.imp.UserDAOImp;

public class SqlDAOFactoryextends DAOFactory{

private Connectionconn=null;

public SqlDAOFactory(Connection conn) {

//TODO Auto-generated constructor stub

this.conn=conn;

}

/**

*获得UserDAO

*@paramconn连接对象

*@returnUserDAO

public UserDAO getUserDAO(){

return new UserDAOImp(conn);

}

/**

*获得文件操作DAO

*@return

public IFileDAO getFileDAO(){

return new FileDAOImp(conn);

}