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javaWeb随笔(2)

前言

javaWeb基础学习

正文

Demo1

Demo1

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package com.c0okb.test2;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.xml.crypto.Data;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;

public class CookieDemo extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html");
        PrintWriter out = resp.getWriter();
        Cookie[] cookies = req.getCookies();//获取该请求的cookie

        if(cookies != null){
            out.write("你上一次访问的时间是:");
            for (int i = 0; i < cookies.length; i++) {//遍历cookie
                Cookie cookie = cookies[i];
                if(cookie.getName().equals("lastLoginTime")){
                    long LT = Long.parseLong(cookie.getValue());//读取cookie的值
                    Date date = new Date(LT);
                    out.write(date.toString());
                }
            }
        }else{
            out.write("这是第一次访问本站");
        }

        Cookie cookie = new Cookie("lastLoginTime", System.currentTimeMillis()+"");//设置cookie
        cookie.setMaxAge(24*60*60);//设置cookie的最大存活时间

        resp.addCookie(cookie);//添加cookie
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }
}

通过cookie获取上一次访问该网页的时间

Demo2

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package com.c0okb.test2;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class CookieDemo2 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        Cookie cookie1 = new Cookie("lastLoginTime", System.currentTimeMillis() + "");
        cookie1.setMaxAge(0);
        resp.addCookie(cookie1);

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

设置存活时间为0，可以用于刷新cookie

Demo3

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package com.c0okb.test2;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.URL;
import java.net.URLDecoder;
import java.net.URLEncoder;
import java.util.Date;

public class CookieDemo3 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("进入该方法");
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        Cookie cookie1 = new Cookie("name", URLEncoder.encode("饼干屑","utf-8"));
        cookie1.setMaxAge(24*60*60);
        resp.addCookie(cookie1);
        PrintWriter out = resp.getWriter();
        Cookie[] cookies = req.getCookies();
        for (int i = 0; i < cookies.length; i++) {
            Cookie cookie = cookies[i];
            System.out.println(cookie.getName());
            if(cookie.getName().equals("name")){
                out.write(URLDecoder.decode(cookie.getValue()));
            }
        }

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

当cookie的值为中文时，使用

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URLEncoder.encode("饼干屑","utf-8")
URLDecoder.decode(cookie.getValue())

进行合理编码

SESSION(重点)

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//Person类
package com.c0okb.test2;

public class Person {
    private String name;
    private int age;

    public Person(String name) {
        this.name = name;
        System.out.println(name);
    }

    public Person() {
    }

    public int getAge() {
        return age;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

对Session进行操作

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package com.c0okb.test2;

import javax.servlet.ServletException;
import javax.servlet.http.*;
import java.io.IOException;

public class SessionTest extends HttpServlet {


    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html");
        req.setCharacterEncoding("utf-8");

        //获取Session
        HttpSession session = req.getSession();

        //给Session存东西
        session.setAttribute("name",new Person("c0okb"));

        //获取Session的ID
        String sessionId = session.getId();

        //判断Session是否已经创建
        if(session.isNew()){
            resp.getWriter().write("session创建成功，ID:"+sessionId);
        }else{
            resp.getWriter().write("session已经在服务器中存在. ID:"+sessionId);
        }

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

删除Session

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package com.c0okb.test2;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

public class SessionDelete extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        HttpSession session = req.getSession();
        session.removeAttribute("name");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

JSP原理

image-20201222103702852

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1.JSP(Java Server Page): Java的服务页面,Java动态网页.
    JSP本质就是Servlet
    服务器会解析请求中是否含有.jsp文件
    如果有，则将其编译为java文件
    再将java文件编译为class文件，供浏览器访问

maven需要安装的依赖

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<!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>4.0.1</version>
    <scope>provided</scope>
</dependency>
<!-- https://mvnrepository.com/artifact/javax.servlet.jsp/javax.servlet.jsp-api -->
<dependency>
    <groupId>javax.servlet.jsp</groupId>
    <artifactId>javax.servlet.jsp-api</artifactId>
    <version>2.3.1</version>
    <scope>provided</scope>
</dependency>
<!-- https://mvnrepository.com/artifact/javax.servlet.jsp.jstl/jstl-api -->
<dependency>
    <groupId>javax.servlet.jsp.jstl</groupId>
    <artifactId>jstl-api</artifactId>
    <version>1.2</version>
</dependency>
<!-- https://mvnrepository.com/artifact/taglibs/standard -->
<dependency>
    <groupId>taglibs</groupId>
    <artifactId>standard</artifactId>
    <version>1.1.2</version>
</dependency>

JSP的基础语法与指令

JSP的基本语法

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JSP语法:
    1.JSP的注释：注释Java脚本代码
        <%--注释--%>
    2.JSP的Java脚本表达式：输出数据到页面上
        <%=代买%> (实际上就是调用输出流打印到页面上) out.print(表达式);
    3.JSP中的Java脚本片段：(实际开发中，应做到JSP中不能出现一行Java脚本片段):书写Java代码逻辑
        <%代码%>
        原理：其中的语句会原封不动的被服务器翻译到对应的Servlet的_jspService方法中。
    4.JSP的声明：：定义类的成员
        <%!代码%>

JSP三大指令

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1.特点
    1.并不向客户端产生任何输出，
    2.指令在JSP整个文件范围内有效
    3.为翻译阶段提供了全局信息
2.指令语法格式: <%指令名称 属性名='属性值' 属性名='属性值'....%>
3.page指令:表示JSP的相关配置
    <%page contentType='text/html' charset='UTF-8' language='java'%>
        contentType:表示文件的MIME类型
        charset:表示文档的字符集
        language:表示JSP文档编写的脚本语言
        import:用于导入JSP脚本中使用到的类,等价于Java代码中的: import 类的全限定名;
        errorPage:如果服务器发生错误，会自动跳转到指定页面
        isErrorPage:判断页面是否为错误页面，
            true:是，则可以判断内置对象为Exception
            false:不是,默认值，不可以使用
        
4.include指令：
    1.静态包含：使用JSP的include指令
        <%@include file='被包含的文件'%>
        特点：
            在编译阶段就将多个JSP文件，合并成一个java类
    2.动态包含：使用JSP的动作指令    
        <%jsp: include='被包含的文件'%>
        特点:
            把每一个JSP编译成Servlet类，在编译过程中，动态的合并在一起，最终得到多个java类(动态包含会包含多个java类)

    3.动态包含和静态包含的选择:
        如果在包含的时候,需要传递数据,此时只能使用动态包含.(
        如果被包含的页面如果是静态页面,那么使用静态包含
        如果被包含的如果是动态页面,那么使用动态包含
    4.注意:在实际开始中通常将被包含的jsp页面的后缀名设置为jspf

JSP九大内置对象

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PageContext //保存东西
Request //保存东西
Response
Session //保存东西
Application [ServletContext] //保存东西
config [ServletConfig]
out
page
exception

image-20201223210220838

Filter 过滤器

原理图：

image-20201226210439851

PS:导包的时候一定不能导错包 java.servelt.Filter

编写一个过滤器用于解决中文乱码问题

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package com.c0okb.filter;

import javax.servlet.*;
import java.io.IOException;

public class Encoding implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("过滤器启动中..............");
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");
        response.setContentType("text/html");

        System.out.println("过滤器运行中.....");
        chain.doFilter(request,response);//链
        System.out.println("过滤器结束运行");

    }

    @Override
    public void destroy() {
        System.out.println("过滤器销毁中..............");
    }
}

其中很重要的代码

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chain.doFilter(request,response);//链

image-20201226215332953

编写一个测试类

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package com.c0okb.show;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class show extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().write("我是小吴");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

注册Servlet

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<filter>
    <filter-name>Encoding</filter-name>
    <filter-class>com.c0okb.filter.Encoding</filter-class>
</filter>
<filter-mapping>
    <filter-name>Encoding</filter-name>
    <url-pattern>/ServletShow/*</url-pattern>
</filter-mapping>

这时注册的Servlet说明该过滤器适用于/ServletShow下的文件

image-20201226213838017

对比测试

image-20201226214710714

Listener 监听器

编写监听器-用于记录网站在线人数

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package com.c0okb.filter;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.*;
import java.io.IOException;

public class OnlineAccount extends HttpServlet implements HttpSessionListener {

    @Override
    public void sessionCreated(HttpSessionEvent se) {
        ServletContext servletContext = se.getSession().getServletContext();
        Integer onlineAccount = (Integer) servletContext.getAttribute("OnlineAccount");
        if(onlineAccount == null){
            onlineAccount = new Integer(1);
        }else {
            int account = onlineAccount.intValue();
            onlineAccount = new Integer(account+1);
        }
        servletContext.setAttribute("OnlineAccount",onlineAccount);
    }



    @Override
    public void sessionDestroyed(HttpSessionEvent se) {
        ServletContext servletContext = se.getSession().getServletContext();
        Integer onlineAccount = (Integer) servletContext.getAttribute("OnlineAccount");
        if(onlineAccount == null){
            onlineAccount = new Integer(0);
        }else {
            int account = onlineAccount.intValue();
            onlineAccount = new Integer(account-1);
        }
        servletContext.setAttribute("OnlineAccount",onlineAccount);
    }
}

在index.jsp

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<%--
  Created by IntelliJ IDEA.
  User: cookie
  Date: 2020/12/26
  Time: 21:09
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
  <head>
    <title>$Title$</title>
  </head>
  <body>
  <h1>
    当前在线的人数是:<%=this.getServletConfig().getServletContext().getAttribute("OnlineAccount")%>
  </h1>
  </body>
</html>

注册servlet

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<listener>
    <listener-class>com.c0okb.filter.OnlineAccount</listener-class>
</listener>

image-20201226225635587

用户登陆与用户注销-Filter拦截判断

用户登录后才能进入主页，用户注销后就不能进入主页

JDBC事务

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package com.Sql.Demo;

import java.sql.*;



public class JDBCTest {

    public static void main(String[] args) throws ClassNotFoundException, SQLException {
        String url = "jdbc:mysql://localhost:3306/security?useUnicode=true&characterEncoding=UTF8";
        String username = "root";
        String password = "root";

        //1.加载驱动
        Class.forName("com.mysql.jdbc.Driver");
        Connection connection = DriverManager.getConnection(url, username, password);

        String sql = "SELECT username\n" +
                "FROM\n" +
                "users\n" +
                "where id=?";
        PreparedStatement preparedStatement = connection.prepareStatement(sql);

        preparedStatement.setString(1,"1");

        ResultSet rs = preparedStatement.executeQuery();


        while (rs.next()){
            System.out.println(rs.getString("username"));
        }

        //关闭数据库池，先开后关
        rs.close();
        preparedStatement.close();
        connection.close();
    }

}

InnoDB的存储引擎才支持JDBC事务

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package com.Sql.Demo;

import java.sql.*;


public class Test {

@org.junit.Test
    public void test() throws SQLException, ClassNotFoundException {
    String url = "jdbc:mysql://localhost:3306/security?useUnicode=true&characterEncoding=UTF8";
    String username = "root";
    String password = "root";
    Class.forName("com.mysql.jdbc.Driver");
    Connection connection = DriverManager.getConnection(url, username, password);

    //1.加载驱动
    try {

        //2.连接数据库

        //3.通知数据开启事务
        connection.setAutoCommit(false);

        String sql1 = "update account set money=money+10 where name='A'";

        connection.prepareStatement(sql1).executeUpdate();

        //int i = 1/0;

        String sql2 = "update account set money=money-10 where name='B'";
        connection.prepareStatement(sql2).executeUpdate();

        //结束事务
        connection.commit();
        System.out.println("SUCCESS");
    } catch (Exception e) {
        try {
            connection.rollback();
        } catch (SQLException e1) {
            e1.printStackTrace();
        }
        e.printStackTrace();
    }finally {
        connection.close();
    }

}

}
Author: 我是小吴啦
Link: http://yoursite.com/2020/12/20/javaWeb%E9%9A%8F%E7%AC%94-2/
Copyright Notice: All articles in this blog are licensed under CC BY-NC-SA 4.0 unless stating additionally.
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