第75节：Java的中的JSP，EL和JSTL

第75节：java中的jsp,el和jstl

哭吧看不完的!!!

cookie和`session

请求转发和重定向的区别:

1. 地址不一样
2. 请求次数也不一样
3. 数据无法传递
   4.跳转范围有限制
4. 效率

请求转发请求1次,只能对当前项目跳转,重定向请求2次.重定向是无法传递的,重定向对跳转范围没有限制.

cookie是服务器发送给客户端,存储在客户端的小数据.发送cookie:

cookie cookie = new cookie("key", value");
response.addcookie(cookie);

服务器返回cookie给客户端
// 响应头
set-cookie: a=b

接收cookie

cookie[] cookies =  request.getcookies();

客户端提交数据的cookie
// cookie: a=b;c=d;

cookie分会话cookie和持久cookie

关闭cookie,可以关闭浏览器.

持久的cookie,在一段时间内有效

cookie cookie = new cookie("a","b");
cookie.setmaxage(); // 秒
response.addcookie(cookie);

cookie.setdomain(".dashucoding.com");
// 只有带上这个域名的时候,才会有cookie
// 例如:www.dashucoding.com

cookie..setpath("/demo");
// 要进行访问上面的路径才会带cookie
http://localhost:8080/demo

移除cookie

cookie cookie = new cookie("a","b");
cookie.setmaxage(60*60*24);
response.addcookie(cookie);

// 获取以前cookie,设置有效期
cookie[] cookies = request.getcookies();
cookie cookie = cookieutil.findcookie(cookies,"a");
cookie.setmaxage(0);
reponse.addcookie(cookie);

cookie是存在客户端的.

可以创建一个新的cookie去替换

cookie cookie = new cookie("a","dashu");
cookie.setmaxage(0);
response.addcookie(cookie);

session是基于cookie的一种会话技术.cookie的安全隐患,是把数据存放在客户端,下次访问时,带上这个数据,服务端就知道客户端是谁.

session的数据是存放在服务端.

session对应sessionid传递给客户端,是通过cookie传递的.只要有sessiondi,就可以获取以前的数据.

httpsession session = request.getsession();
session.setattribute();
sesssion.getattribute();

package com.dashucoding.servlet;

import java.io.ioexception;
import javax.servlet.servletexception;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;
import javax.servlet.http.httpsession;

/**
 * servlet implementation class demo01
 */
public class demo01 extends httpservlet {
    
    protected void doget(httpservletrequest request, httpservletresponse response) throws servletexception, ioexception {
        // todo auto-generated method stub
        httpsession session = request.getsession();
        // 得到会话id
        session.getid();
        // 存值
        //session.setattribute(name, value);
        // 取值
        //session.getattribute(name);
        // 移植
        //session.removeattribute(name);
    }

    protected void dopost(httpservletrequest request, httpservletresponse response) throws servletexception, ioexception {
        // todo auto-generated method stub
        doget(request, response);
    }

}

session创建:

request.getsession

销毁

关闭服务器,或自动会话过期,默认时间为30分钟.

在进行访问浏览器时,再次重启是无法获取以前的数据的,因为sessionid是通过cookie来传递的,cookie没有设置有效期,关闭后,就cookie删除了,同时cookie带过来sessionid同样也没有了.

手动设置cookie

string id = request.getsession().getid();
cookie cookie = new cookie("jsessionid",id);
cookie.setmaxage(60*60*24*7);
response.addcookie(cookie);

jsp和el和jstl

什么是jsp

jsp就是一个网页而已,或者是一个java类,继承了servlet,所以jsp是一个servlet.

jsp设计目的是因为html是显示静态内容,有时网页要一些动态数据.html是不支持java代码,jsp支持java代码.

写法

指令
<%@ %>
language
contenttype内容类型
content-type="text/html;charset=utf-8"
pageencoding jsp内容编码

extends="httpjspbase"
用于指定jsp翻译成java文件后,继承的父类是谁

import导包使用,一般不用手写
session
true or false

errorpage 错误的页面.
iserrorpage="true" 显示错误
errorpage="error.jsp" 呈现错误

errorpage 值需要给错误的页面路径

include
<%-- <%@ include file="other02.jsp"%> --%>
把另外一个页面的内容拿过来

<%--  <%@ taglib prefix=""  uri=""%>    --%>
url标签库的路径
prefix别名

include和forward

<%-- 
    <jsp:include page=""></jsp:include>
    <jsp:param value="" name=""/>
    <jsp:forward page=""></jsp:forward> --%>

    <%-- <jsp:include page="other02.jsp"></jsp:include> --%>
    
    <%-- <jsp:forward page="other02.jsp"></jsp:forward>
    等同于以下代码 --%>
    <% 
        //请求转发
        //request.getrequestdispatcher("other02.jsp").forward(request, response);
    %>  
    
    <jsp:forward page="other02.jsp">
        <jsp:param value="beijing" name="address"/>
    </jsp:forward>

jsp: param
<jsp:forward page="other02.jsp">
 <jsp:param value="beijing" name="address"/>
</jsp:forward>

<%= request.getparameter("address")%>

小结

什么是jsp
为什么会有jsp
三大指令集

page
有什么用,那么怎么用,有哪些常用的属性
include
有什么用,那么怎么用
taglib
有什么用,怎么用
jsp动作标签
jsp:forword
jsp:include
jsp:param

jsp的内置对象

四个作用域
pagecontext
request
session
appiication

jsp内置对象

内置对象是在jsp页面中使用的这些对象,不用创建

pagecontext
request
session
application

exception
out
page
config
response

application: servletcontext
config: servletconfig
out: jspwriter
page: object
pagecontext: pagecontext
request: httpservletrequest
session: httpsession

final javax.servlet.jsp.pagecontext pagecontext;
javax.servlet.http.httpsession session = null;
final javax.servlet.servletcontext application;
final javax.servlet.servletconfig config;
javax.servlet.jsp.jspwriter out = null;
final java.lang.object page = this;
javax.servlet.jsp.jspwriter _jspx_out = null;
javax.servlet.jsp.pagecontext _jspx_page_context = null;
request, response

四个作用域

pagecontext
request
session
application

作用域,就是这个对象可以在哪用,对象可以存值,取值范围限定.
作用的对象是不一样的

setattribute
getattribute

pagecontext:作用域只能在当前页面,pagecontext

request:作用域限于一次请求
只要服务器做出反应,域中的值就没有了httpservletrequest

session:限于一次会话,第二次会话就没了,httpsession

application:都有,都可以访问,只有服务器关闭后就不能访问了.->servletcontext
一个工程只能有一个

exception -> throwable
config -> servletconfig
page -> object -> 当前类的实例

response  -> httpservletresponse
out jsp -> jspwriter

out
response.getwriter

out对象输出的内容是放到response的缓冲区内的,先输出response本身的内容,然后才是out里面的内容.

exception -> throwable
page -> object -> 一般就是jsp翻译成java类的实例对象 -> this -> 当前实例类
config -> servletconfig

out -> jspwriter
response -> httpservletresponse

pagecontext -> pagecontext: 作用域当前页面

request -> httpservletreques: 作用域限于一次请求

session -> httpsession -> 作用域限于一次会话

application -> servletcontext

整个工程可以访问,服务器关闭后就不能进行访问了

pagecontext 也可以获取其他8个内置对象

el表达式:

是什么,怎么用,也有内置对象?

// 作用域
pagescope
requestscope
sessionscope
applicationscope

// 请求头
header
headervalues

参数
param
params

el表达式

简化jsp中java的代码.

${ 表达式 }

取值方式:

<%
string [] a = {"aa","bb","cc","dd"};
pagecontext.setattribute("array", a);
%>

<%
 user user = new user {"zhangsan",18};
 session.setattribute("u", user);
%>

${u.name}, ${u.age}

<%@page import="com.dashucoding.domain.user"%>
<%@ page language="java" contenttype="text/html; charset=utf-8"
    pageencoding="utf-8"%>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>insert title here</title>
</head>
<body>
    从域中取值。  得先存值。
    <%
        //pagecontext.setattribute("name", "zhangsan");
        session.setattribute("name", "lisi...");
    %>
    
    <br>直接指定说了，到这个作用域里面去找这个name<br>
    ${ pagescope.name } 
    
    
    <br>//先从page里面找，没有去request找，去session，去application <br>
    ${ name }
    
    <br>指定从session中取值<br>
    ${ sessionscope.name } 

<br>---------------------------------------------<br>

    <%
        user user = new user("zhangsan",18);
        
        session.setattribute("u", user);
    %>
    
    
    ${ u.name }  , ${ u.age } 
    
    ${ a > b}
    
    ${ a gt b }
    
    ${ empty u }
</body>
</html>

package com.dashucoding.domain;

public class user {
    private string name;
    private int age;

    public user(string name, int age) {
        super();
        this.name = name;
        this.age = age;
    }

    public string getname() {
        return name;
    }

    public void setname(string name) {
        this.name = name;
    }

    public int getage() {
        return age;
    }

    public void setage(int age) {
        this.age = age;
    }

}

<%@page import="java.util.hashmap"%>
<%@page import="java.util.map"%>
<%@page import="java.util.arraylist"%>
<%@page import="java.util.list"%>
<%@ page language="java" contenttype="text/html; charset=utf-8"
    pageencoding="utf-8"%>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>insert title here</title>
</head>
<body>
    <%
        pagecontext.setattribute("name", "page");
        request.setattribute("name", "request");
        session.setattribute("name", "session");
        application.setattribute("name", "application");
    %>
    
    按普通手段取值<br>
    
    <%= pagecontext.getattribute("name")%>
    <%= request.getattribute("name")%>
    <%= session.getattribute("name")%>
    <%= application.getattribute("name")%>
    
    <br>使用el表达式取出作用域中的值<br>
    
    ${ pagescope.name }
    ${ requestscope.name }
    ${ sessionscope.name }
    ${ applicationscope.name }
    
    ${name }
    
    
    <br>-----------------------------<br>
    
    <%
        string [] a = {"aa","bb","cc","dd"};
        pagecontext.setattribute("array", a);
    %>
    
    使用el表达式取出作用域中数组的值<br>
    
    ${array[0] } , ${array[1] },${array[2] },${array[3] }
    
    
        <br>-------------集合数据----------------<br>
    
    <%
        list list = new arraylist();
        list.add("11");
        list.add("22");
        list.add("33");
        list.add("44");
        //pagecontext.setattribute("li", list);
        session.setattribute("li", list);
    %>
    
    使用el表达式取出作用域中集合的值<br>
    
    ${li[0] } , ${li[1] },${li[2] },${li[7] }
    
    <br>-------------map数据----------------<br>
    <%
        map map = new hashmap();
        map.put("name", "zhangsna");
        map.put("age",18);
        map.put("address","北京..");
        
        map.put("address.aa","深圳..");
        
    
        //pagecontext.setattribute("map", map);
        application.setattribute("m", map);
    %>
    使用el表达式取出作用域中map的值<br>
    
    ${applicationscope.m.name } , ${m.age } , ${m.address }  , ${m["address.aa"] } 


</body>
</html>

el表达式隐式对象

11个内置对象

${ }

pagecotext

pagescope
requestscope
sessionscope
applicationscope

请求参数
param
paramvalues
请求头
header
headervalues
cookie
initparam初始化参数

pagecontext是pagecontext实例,其他都是map类.

el内置对象

// 作用域
pagescope
requestscope
sessionscope
applicationscope
// 请求头
header
headervalues
// 请求参数
param
params

cookie
全局初始化参数
initparam
pagecontext

引入

<%@ page language="java" contenttype="text/html; charset=utf-8"
    pageencoding="utf-8"%>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>insert title here</title>
</head>
<body>
这是el03页面

<jsp:forward page="el04.jsp">
    <jsp:param value="beijing...." name="address"/>
</jsp:forward>
</body>
</html>

<%@ page language="java" contenttype="text/html; charset=utf-8"
    pageencoding="utf-8"%>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>insert title here</title>
</head>
<body>
这是el04页面<br>

<%=request.getparameter("address") %>

<br>

使用el表达式获取这个参数

<%-- response.addcookie(new cookie("name","value"));

${cookie.name } --%>
${param.address }
</body>
</html>

小结案例

<%@ page language="java" contenttype="text/html; charset=utf-8"
    pageencoding="utf-8" %>
<%-- <%@ include file="other02.jsp"%> --%>

<%--  <%@ taglib prefix=""  uri=""%>    --%>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>insert title here</title>
</head>
<body>
<%-- <jsp:include page="other02.jsp"></jsp:include> --%>

    这是other页面的内容.
</body>
</body>
</html>

<%@ page language="java" contenttype="text/html; charset=utf-8"
    pageencoding="utf-8" iserrorpage="true"%>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>insert title here</title>
</head>
<body>

    <h3>这是other022222的内容</h3>
    
    <br>收到的参数是：<br>
    
    <%= request.getparameter("address")%>
    
    <%
        
    %>
</body>
</html>

<%@ page language="java" contenttype="text/html; charset=utf-8"
    pageencoding="utf-8"%>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>insert title here</title>
</head>
<body>
这是other03的页面
<br>使用作用域来存储数据<br>

<%
    pagecontext.setattribute("name", "page");
    request.setattribute("name", "request");
    session.setattribute("name", "session");
    application.setattribute("name", "application");
%>

取出四个作用域中的值<br>

<%=pagecontext.getattribute("name")%>
<%=request.getattribute("name")%>
<%=session.getattribute("name")%>
<%=application.getattribute("name")%>

<!-- //跳转到下一个界面去了 -->

<%
    //请求转发. 一次请求
    //request.getrequestdispatcher("other04.jsp").forward(request, response);

    //重定向 2次请求
    response.sendredirect("other04.jsp");
    
%>
</body>
</html>

<%@ page language="java" contenttype="text/html; charset=utf-8"
    pageencoding="utf-8"%>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>insert title here</title>
</head>
<body>
    <h3>这是04的页面</h3><br>
    
    取出四个作用域中的值<br>

    <%=pagecontext.getattribute("name")%>
    <%=request.getattribute("name")%>
    <%=session.getattribute("name")%>
    <%=application.getattribute("name")%>
</body>
</html>

<%@ page language="java" contenttype="text/html; charset=utf-8"
    pageencoding="utf-8"%>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>insert title here</title>
</head>
<body>
这是other05的页面<br>

<%
    out.write("这是使用out对象输出的内容");
%>

<br>
<%
    response.getwriter().write("这是使用response对象输出的内容");
%>
</body>
</html>

<%@ page language="java" contenttype="text/html; charset=utf-8"
    pageencoding="utf-8"%>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>insert title here</title>
</head>
<body>
<%-- 
    <jsp:include page=""></jsp:include>
    <jsp:param value="" name=""/>
    <jsp:forward page=""></jsp:forward> --%>
        这是jsp_action的页面.
    <%-- <jsp:include page="other02.jsp"></jsp:include> --%>
    
    <%-- <jsp:forward page="other02.jsp"></jsp:forward>
    等同于以下代码 --%>
    <% 
        //请求转发
        //request.getrequestdispatcher("other02.jsp").forward(request, response);
    %>  
    
    <jsp:forward page="other02.jsp">
        <jsp:param value="beijing" name="address"/>
    </jsp:forward>
</body>
</html>

<%@ page language="java" contenttype="text/html; charset=utf-8"
    pageencoding="utf-8" iserrorpage="true"%>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>insert title here</title>
</head>
<body>
服务器正在维护，请稍后访问..
<%-- <%=exception.tostring() %> --%>
</body>
</html>

<%@page import="java.util.hashmap"%>
<%@page import="java.util.map"%>
<%@page import="java.util.arraylist"%>
<%@page import="java.util.list"%>
<%@ page language="java" contenttype="text/html; charset=utf-8"
    pageencoding="utf-8"%>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>insert title here</title>
</head>
<body>
    <%
        pagecontext.setattribute("name", "page");
        request.setattribute("name", "request");
        session.setattribute("name", "session");
        application.setattribute("name", "application");
    %>
    
    按普通手段取值<br>
    
    <%= pagecontext.getattribute("name")%>
    <%= request.getattribute("name")%>
    <%= session.getattribute("name")%>
    <%= application.getattribute("name")%>
    
    <br>使用el表达式取出作用域中的值<br>
    
    ${ pagescope.name }
    ${ requestscope.name }
    ${ sessionscope.name }
    ${ applicationscope.name }
    
    ${name }
    
    
    <br>-----------------------------<br>
    
    <%
        string [] a = {"aa","bb","cc","dd"};
        pagecontext.setattribute("array", a);
    %>
    
    使用el表达式取出作用域中数组的值<br>
    
    ${array[0] } , ${array[1] },${array[2] },${array[3] }
    
    
        <br>-------------集合数据----------------<br>
    
    <%
        list list = new arraylist();
        list.add("11");
        list.add("22");
        list.add("33");
        list.add("44");
        //pagecontext.setattribute("li", list);
        session.setattribute("li", list);
    %>
    
    使用el表达式取出作用域中集合的值<br>
    
    ${li[0] } , ${li[1] },${li[2] },${li[7] }
    
    <br>-------------map数据----------------<br>
    <%
        map map = new hashmap();
        map.put("name", "zhangsna");
        map.put("age",18);
        map.put("address","北京..");
        
        map.put("address.aa","深圳..");
        
    
        //pagecontext.setattribute("map", map);
        application.setattribute("m", map);
    %>
    使用el表达式取出作用域中map的值<br>
    
    ${applicationscope.m.name } , ${m.age } , ${m.address }  , ${m["address.aa"] } 


</body>
</html>

jstl介绍

jstl是什么,用来做什么.
el只能取值操作
jstl遍历的效果

jstl. jsp standard tag library jsp标签库
简化jsp,与el表达式配合

// 使用jstl
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<c:set var = "name" value="dashu"></c:set>
${name}
<c:set var = "name" value="dashu" scope="session"></c:set>
${sessionscope.name}
默认存储的是page

<c:set var = "age" value="12" ></c:set>
<c:if text="${age>10}">
 age大于10
</c:if>

<c:foreach begin="1" end="10" var="i" step="2">
 ${i}
</c:foreach>

学生信息管理系统

login.jsp -> 一个页面
login_servlet -> 一个页面
基本操作页面 -> 查看学生列表
stu_list.jsp
获取信息
查询数据库
判断账号信息
正确前往下一页
错误,登录失败

案例:

package com.dashucoding.dao;

import java.util.list;

import com.dashucoding.domain.student;

public interface studao {
    /**
     * 查询出来所有的学生信息
     * @return list集合
     */
    list<student> findall();
}

package com.dashucoding.dao;
/*
 * 定义
 * 该dao定义了对用户表的访问规则
 * */
public interface userdao {

    /**
     * 这里简单就返回一个boolean类型， 成功或者失败即可。
     * 
     * 但是开发的时候，登录的方法，一旦成功。这里应该返回该用户的个人信息
     * @param username 
     * @param password
     * 
     * @return true : 登录成功， false : 登录失败。
     */
    boolean login(string username , string password);
}

package com.dashucoding.dao.impl;

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 com.dashucoding.dao.studao;
import com.dashucoding.domain.student;
import com.dashucoding.util.jdbcutil;

public class studaoimpl implements studao{

    @override
    public list<student> findall() {
        
        list<student> list = new arraylist<student>();
        
        connection conn = null;
        preparedstatement ps = null;
        resultset rs   = null;
        
        try {
            //1. 得到连接对象
            conn = jdbcutil.getconn();
            
            string sql = "select * from t_stu";
            
            ps = conn.preparestatement(sql);
            
            rs = ps.executequery();
            
            
            
            //数据多了，用对象装， 对象也多了呢？ 用集合装。 
            while(rs.next()){ //10 次 ，10个学生
                
                student stu = new student();
                
                stu.setid(rs.getint("id"));
                stu.setage(rs.getint("age"));
                stu.setname(rs.getstring("name"));
                stu.setgender(rs.getstring("gender"));
                stu.setaddress(rs.getstring("address"));
                
                list.add(stu);
                
            }
        } catch (sqlexception e) {
            e.printstacktrace();
        }finally {
            jdbcutil.release(conn, ps, rs);
        }
        
        return list;
    }

}

package com.dashucoding.dao.impl;

import java.sql.connection;
import java.sql.preparedstatement;
import java.sql.resultset;
import java.sql.sqlexception;

import com.dashucoding.dao.userdao;
import com.dashucoding.util.jdbcutil;

public class userdaoimpl implements userdao {

    @override
    public boolean login(string username , string password) {
        
        connection conn = null;
        preparedstatement ps = null;
        resultset rs   = null;
        try {
            //1. 得到连接对象
            conn = jdbcutil.getconn();
            
            string sql = "select * from t_user where username=? and password=?";
            
            //2. 创建ps对象
            ps = conn.preparestatement(sql);
            ps.setstring(1, username);
            ps.setstring(2, password);
            
            
            //3. 开始执行。
            rs = ps.executequery();
            
            //如果能够成功移到下一条记录，那么表明有这个用户。 
            return rs.next();
            
        } catch (sqlexception e) {
            e.printstacktrace();
        }finally {
            jdbcutil.release(conn, ps, rs);
        }
        return false;
    }

}

package com.dashucoding.domain;

public class student {
    private int id ; 
    private string name;
    private int age ;
    private string gender;
    private string address;
    
    public int getid() {
        return id;
    }
    public void setid(int id) {
        this.id = id;
    }
    public string getname() {
        return name;
    }
    public void setname(string name) {
        this.name = name;
    }
    public int getage() {
        return age;
    }
    public void setage(int age) {
        this.age = age;
    }
    public string getgender() {
        return gender;
    }
    public void setgender(string gender) {
        this.gender = gender;
    }
    public string getaddress() {
        return address;
    }
    public void setaddress(string address) {
        this.address = address;
    }
    
}

package com.dashucoding.servlet;

import java.io.ioexception;
import java.util.list;

import javax.servlet.servletexception;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;

import com.dashucoding.dao.studao;
import com.dashucoding.dao.userdao;
import com.dashucoding.dao.impl.studaoimpl;
import com.dashucoding.dao.impl.userdaoimpl;
import com.dashucoding.domain.student;

/**
 * servlet implementation class loginservlet
 */
public class loginservlet extends httpservlet {

    protected void doget(httpservletrequest request, httpservletresponse response)
            throws servletexception, ioexception {
        // todo auto-generated method stub
        // 提交的数据有可能有中文
        request.setcharacterencoding("utf-8");
        response.setcontenttype("text/html;charset=utf-8");
        // 获取客户端提交的信息
        string username = request.getparameter("username");
        string password = request.getparameter("password");

        // 去访问dao ， 看看是否满足登录
        userdao dao = new userdaoimpl();
        boolean issuccess = dao.login(username, password);

        if (issuccess) {
//          response.getwriter().write("登录成功.");
            // 请求转发
            // 查询所有的学生信息
            studao studao = new studaoimpl();
            list<student> list = studao.findall();
            
            // 先把这个集合存到作用域
            request.getsession().setattribute("list", list);
            
            
            
            
            
            // 重定向
            response.sendredirect("stu_list.jsp");
        } else {
            response.getwriter().write("用户名或者密码错误！");
        }
    }

    protected void dopost(httpservletrequest request, httpservletresponse response)
            throws servletexception, ioexception {
        // todo auto-generated method stub
        doget(request, response);
    }

}

package com.dashucoding.util;

import java.io.fileinputstream;
import java.io.inputstream;
import java.sql.connection;
import java.sql.drivermanager;
import java.sql.resultset;
import java.sql.sqlexception;
import java.sql.statement;
import java.util.properties;

public class jdbcutil {
    
    static string driverclass = null;
    static string url = null;
    static string name = null;
    static string password= null;
    
    static{
        try {
            //1. 创建一个属性配置对象
            properties properties = new properties();
//          inputstream is = new fileinputstream("jdbc.properties");
            
            
            //使用类加载器，去读取src底下的资源文件。 后面在servlet
            inputstream is = jdbcutil.class.getclassloader().getresourceasstream("jdbc.properties");
            //导入输入流。
            properties.load(is);
            
            //读取属性
            driverclass = properties.getproperty("driverclass");
            url = properties.getproperty("url");
            name = properties.getproperty("name");
            password = properties.getproperty("password");
            
        } catch (exception e) {
            e.printstacktrace();
        }
    }
    
    /**
     * 获取连接对象
     * @return
     */
    public static connection getconn(){
        connection conn = null;
        try {
            class.forname(driverclass);
            //静态代码块 ---> 类加载了，就执行。 java.sql.drivermanager.registerdriver(new driver());
            //drivermanager.registerdriver(new com.mysql.jdbc.driver());
            //drivermanager.getconnection("jdbc:mysql://localhost/test?user=monty&password=greatsqldb");
            //2. 建立连接 参数一： 协议 + 访问的数据库 ， 参数二： 用户名 ， 参数三： 密码。
            conn = drivermanager.getconnection(url, name, password);
        } catch (exception e) {
            e.printstacktrace();
        }
        return conn;
    }
    
    /**
     * 释放资源
     * @param conn
     * @param st
     * @param rs
     */
    public static void release(connection conn , statement st , resultset rs){
        closers(rs);
        closest(st);
        closeconn(conn);
    }
    public static void release(connection conn , statement st){
        closest(st);
        closeconn(conn);
    }

    
    private static void closers(resultset rs){
        try {
            if(rs != null){
                rs.close();
            }
        } catch (sqlexception e) {
            e.printstacktrace();
        }finally{
            rs = null;
        }
    }
    
    private static void closest(statement st){
        try {
            if(st != null){
                st.close();
            }
        } catch (sqlexception e) {
            e.printstacktrace();
        }finally{
            st = null;
        }
    }
    
    private static void closeconn(connection conn){
        try {
            if(conn != null){
                conn.close();
            }
        } catch (sqlexception e) {
            e.printstacktrace();
        }finally{
            conn = null;
        }
    }
}

<%@ page language="java" contenttype="text/html; charset=utf-8"
    pageencoding="utf-8"%>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>insert title here</title>
</head>
<body>
    <h2>欢迎学生管理系统</h2>
    
    <form action="loginservlet" method="post">
        账号: <input type="text" name="username" /><br>
        密码: <input type="password" name="password" /><br>
        <input type="submit" value="登录">
    </form>
</body>
</html>

<%@ page language="java" contenttype="text/html; charset=utf-8"
    pageencoding="utf-8"%>

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>学生信息管理系统</title>
</head>
<body>
<br>学生列表<br>
    <table border="1" width="700">
        <tr align="center">
            <td>编号</td>
            <td>姓名</td>
            <td>年龄</td>
            <td>性别</td>
            <td>住址</td>
            <td>操作</td>
        </tr>
        
        <c:foreach items="${list}" var="stu">
        
            <c:if test=""></c:if>
            
            <tr align="center">
                <td>${stu.id }</td>
                <td>${stu.name }</td>
                <td>${stu.age }</td>
                <td>${stu.gender }</td>
                <td>${stu.address }</td>
                <td><a href="#">更新</a>   <a href="#">删除</a></td>
            </tr>
        </c:foreach>
        
    </table>
</body>
</html>

分析

login.jsp -> loginservlet -> 获取登录信息
创建用户表, 
创建userdao
创建userdaoimple
loginservlet里面访问userdao,判断登录,
创建stu_list.jsp,让登录进入
创建学生表
定义dao,studao
studao, studaoimpl

数据库

小结

jsp

jsp -> 九个内置对象
page
include
taglib
<jsp:include>
<jsp:forward>
<jsp:param>


el -> 11个内置对象

${ 表达式 }
取4个作用域中的值
    pagecontext

    pagescope
    requestscope
    sessionscope
    applicationscope
    
    header
    headervalues
    
    param
    paramvalues
    
    cookie
    initparam

jstl

<c:set>
<c:if>
<c:foreach>

如果看了觉得不错

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