java学习基础
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java 从零开始，学习笔记之基础入门<servlet_文件下载>（二十六）
分类： java基础学习 2013-12-02 10:13 249人阅读 评论(2) 收藏 举报
java从零开始入门基础学习笔记
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
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">
<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>ShowFileAction</servlet-name>
<servlet-class>com.ibm.action.ShowFileAction</servlet-class>
</servlet>
<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>
<!--配置pdf文件下载路径 -->
<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
Index.jsp
<%@ pagelanguage="java"import="java.util.*"pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPEHTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<basehref="<%=basePath%>">
<title>导航页面</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">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</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
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
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)
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
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
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");
%>
<!DOCTYPEHTML PUBLIC "-//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">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
文件列表
<hr>
<table>
<tr>
<td>文件名称</td>
<td>操作</td>
</tr>
<%for(UFile file:list){%>
<tr>
<td><%=file.getFiName()%></td>
<!--文件下载连接 -->
<td><ahref="download?filename=<%=file.getFiName()%>">下载</a></td>
</tr>
<% }%>
</table>
</body>
</html>
Download.java
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);
}
}
}
分类： java基础学习 2013-12-02 10:13 249人阅读 评论(2) 收藏 举报
java从零开始入门基础学习笔记
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
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">
<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>ShowFileAction</servlet-name>
<servlet-class>com.ibm.action.ShowFileAction</servlet-class>
</servlet>
<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>
<!--配置pdf文件下载路径 -->
<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
Index.jsp
<%@ pagelanguage="java"import="java.util.*"pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPEHTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<basehref="<%=basePath%>">
<title>导航页面</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">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</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
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
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)
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
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
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");
%>
<!DOCTYPEHTML PUBLIC "-//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">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
文件列表
<hr>
<table>
<tr>
<td>文件名称</td>
<td>操作</td>
</tr>
<%for(UFile file:list){%>
<tr>
<td><%=file.getFiName()%></td>
<!--文件下载连接 -->
<td><ahref="download?filename=<%=file.getFiName()%>">下载</a></td>
</tr>
<% }%>
</table>
</body>
</html>
Download.java
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);
}
}
}
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