Java Web，servlet，附件下载，学习笔记，记录，解决服务器启动不了问题【诗书画唱】
个人解决服务器启动不了的问题的方法
本地的拷贝
在同一台电脑上进行的操作。例如将一个文件从d盘拷贝到c盘。
一、附件上传
在两台电脑之间进行的拷贝，或者通过网页的方式进行的文件的拷贝。
附件上传的步骤：
1、导包（附件上传的包有很多种，我们今天使用的是这些包中的一种）
2、创建附件上传的jsp页面
3、创建附件上传的servlet
在附件上传中，除了type="file"的input标签以外，其他的input的isFormField都是true
地址：http://192.168.43.208:8888/j1908021/index.jsp
有时要实现的操作：
一、上传图片后显示图片
二、附件下载
将需要下载的文件放到服务器上，然后客户端就可以通过访问网页来下载响应的文件。
1、将需要下载的文件放到服务器上去
2、导包（附件上传的包一样）
3、创建附件下载的jsp页面download.jsp
4、创建一个servlet实现附件下载功能
作业
1、实现一个附件上传程序，为了避免上传的文件名重复，请在上传以后，给上传的文件名添加一个时间戳。
例如：上传的文件名叫2.png，为了避免跟其他人的文件名相同，将文件名改为2_2020-08-05-15-35-13-876.png进行保存
自己想出关键
再运行后：
2、将一些文件拷贝到服务器上，将这些文件名保存在一个数据库表中，要求打开一个download.jsp页面，要能够显示数据库表中的下载链接，要求能够下载这些文件。
fileinfo:id,filename
create table fileinfo(
id int primary key auto_increment,
filename varchar(100)
);
insert into fileinfo(filename) values ("20201012.txt"),('20201013.txt' );
--select * from fileinfo
--drop table fileinfo
自己想出的好方法：
package bean;
public class Fileinfo {
private Integer id;
private String filename;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getFilename() {
return filename;
}
public void setFilename(String filename) {
this.filename = filename;
}
}
package com.SSHC.controller;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
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;
/**
* Servlet implementation class DownloadServlet
*/
@WebServlet("/ds")
public class DownloadServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public DownloadServlet() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request,
* HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
this.doPost(request, response);
}
/**
* @see HttpServlet#doPost(HttpServletRequest
* request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws
ServletException, IOException {
// TODO Auto-generated method stub
//设置响应的字符集编码
response.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
//获取需要下载的附件的名字
String fileName = request.getParameter("fileName");
System.out.println("需要下载的附件名是：" + fileName);
//获取附件在服务器上的路径
String folder = "/doc/";
//通知浏览器以下载的形式打开一个界面
response.addHeader("Content-type", "appllication/octet-stream");
response.addHeader("Content-Disposition", "attachment;filename="
+ fileName);
//读取服务器上的文件
InputStream is = this.getServletContext()
.getResourceAsStream(folder + fileName);
//将流写到客户端去
OutputStream os = response.getOutputStream();
//每次缓存1024字节
byte[]buf = new byte[1024];
//每次读取的字节长度
int len = 0;
while((len = is.read(buf)) != -1) {
os.write(buf,0,len);
}
//清理资源
os.close();
is.close();
}
}
package com.SSHC.controller;
import java.io.IOException;
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 bean.Fileinfo;
import DAO.Dao;
/**
* Servlet implementation class ELServlet
*/
@WebServlet("/ELServlet")
public class ELDownloadServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public ELDownloadServlet() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest
* request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
this.doPost(request, response);
}
/**
* @see HttpServlet#doPost(HttpServletRequest
* request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest
request, HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
Dao gd = new Dao();
List<Fileinfo>list = gd.selectAll();
StringBuilder html = new StringBuilder();
html.append("<h1>诗书画唱提醒你！</h1>"
+ "<br>点击链接后可以下载对应的文件哦！");
for(Fileinfo g : list) {
Integer ID= g.getId();
String filename=g.getFilename();
System.out.println(filename);
html.append(" <ul><li><a href='ds?fileName="+filename
+"'>下载"+filename+"</a></li> </ul>");
}
request.setAttribute("html", html);
System.out.println(html);
request.getRequestDispatcher("SSHCdownload.jsp")
.forward(request, response);
}
}
package DAO;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import Utils.DBUtils;
import bean.Fileinfo;
public class Dao {
public List<Fileinfo>selectAll(){
String sql = "select * from fileinfo";
Connection conn = null;
PreparedStatement pstm = null;
ResultSet rs = null;
List<Fileinfo>list = new ArrayList<Fileinfo>();
try {
conn = DBUtils.getConn();
pstm = conn.prepareStatement(sql);
rs = pstm.executeQuery();
while(rs.next()) {
Integer id = rs.getInt("id");
String Filename= rs.getString("filename");
Fileinfo edu = new Fileinfo();
edu.setId(id);
edu.setFilename(Filename);
list.add(edu);
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return list;
}
}
package Utils;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.Properties;
public class DBUtils {
private static String driverName;
private static String url;
private static String user;
private static String pwd;
static {
//读取properties文件
Properties prop = new Properties();
//将db.properties文件读取到内存中去
InputStream is = DBUtils.class.getClassLoader()
.getResourceAsStream("db.properties");
//加载内容
try {
prop.load(is);
//读取内容
driverName = prop.getProperty("dn");
//System.out.println(driverName);
url = prop.getProperty("url");
user = prop.getProperty("un");
pwd = prop.getProperty("up");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
//获取数据库连接对象的方法
public static Connection getConn(){
Connection conn = null;
try {
Class.forName(driverName);
conn = DriverManager
.getConnection(url,user,pwd);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return conn;
}
public static void close(ResultSet
rs,PreparedStatement pstm
,Connection conn){
try {
if(rs != null) {
rs.close();
}
if(pstm != null) {
pstm.close();
}
if(conn != null) {
conn.close();
}
} catch(Exception e) {
e.printStackTrace();
}
}
}
dn=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/firstjsp?useUnicode=true&characterEncoding=UTF-8
un=root
up=root
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+
request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base hreff="<%=basePath%>">
<title></title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<style type="text/css">
* {
font-size: 50px;
}
</style>
</head>
<body>
${html }
</body>
</html>
————————————————————————————
附件下载的例子：
package com.jy.controller;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class DownloadServlet
*/
@WebServlet("/ds")
public class DownloadServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public DownloadServlet() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
this.doPost(request, response);
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
//设置响应的字符集编码
response.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
//获取需要下载的附件的名字
String fileName = request.getParameter("fileName");
System.out.println("需要下载的附件名是：" + fileName);
//获取附件在服务器上的路径
String folder = "/doc/";
//通知浏览器以下载的形式打开一个界面
response.addHeader("Content-type", "appllication/octet-stream");
response.addHeader("Content-Disposition", "attachment;filename="
+ fileName);
//读取服务器上的文件
InputStream is = this.getServletContext()
.getResourceAsStream(folder + fileName);
//将流写到客户端去
OutputStream os = response.getOutputStream();
//每次缓存1024字节
byte[]buf = new byte[1024];
//每次读取的字节长度
int len = 0;
while((len = is.read(buf)) != -1) {
os.write(buf,0,len);
}
//清理资源
os.close();
is.close();
}
}
1、实现附件上传功能。尝试对上传文件的类型进行限制，只能传图片(png,jpg)文件。
2、在两台电脑之间进行附件上传的操作。
3、学会使用cmd命令：ipconfig查看服务器的ip地址，ping检查跟指定的ip地址的电脑是否连接在同一个网内的
ping 192.168.42.133就是检查你的电脑跟这个ip地址的电脑是否连接在一起了。
abc.txt.png
1、实现一个附件上传程序，为了避免上传的文件名重复，请在上传以后，给上传的文件名添加一个时间戳。
例如：上传的文件名叫2.png，为了避免跟其他人的文件名相同，将文件名改为2_2020-08-05-15-35-13-876.png进行保存
2、将一些文件拷贝到服务器上，将这些文件名保存在一个数据库表中，要求打开一个download.jsp页面，要能够显示数据库表中的下载链接，要求能够下载这些文件。
fileinfo:id,filename
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base hreff="<%=basePath%>">
<title></title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<style type="text/css">
* {
font-size: 50px;
}
</style>
</head>
<body>
<ul>
<li><a href="ds?fileName=20201012.txt">20201012作业</a></li>
<li><a href="ds?fileName=20201013.txt">20201013作业</a></li>
</ul>
</body>
</html>
