GET在浏览器回退时是无害的，而POST会再次提交请求。
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GET产生的URL地址可以被Bookmark，而POST不可以。
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GET请求会被浏览器主动cache，而POST不会，除非手动设置。
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GET请求只能进行url编码，而POST支持多种编码方式。
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GET请求参数会被完整保留在浏览器历史记录里，而POST中的参数不会被保留。
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GET请求在URL中传送的参数是有长度限制的，而POST么有。
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对参数的数据类型，GET只接受ASCII字符，而POST没有限制。
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GET比POST更不安全，因为参数直接暴露在URL上，所以不能用来传递敏感信息。
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GET参数通过URL传递，POST放在Request body中。

Accept: 告诉浏览器，它所支持的数据类型
Accept-Encoding: 支持那种编码格式
Accept-Language: 指定客户端期望服务器返回哪个国家语言文档
Host:指定资源所在的主机名和端口号
Referer:常被网站管理人员用来查看网站的访问者是如何导航进入网站的。也可以用于网站的防盗链
Authorization:Proxy-Authorization:if-Match:if-Modified-Since:Range:if-RangeMax-Forward:User-Agent:

<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">
  <!-- localRepository
   | The path to the local repository maven will use to store artifacts.
   | Default: ${user.home}/.m2/repository  localRepository 指定包下载的位置
  -->
  <!-- 本地仓库位置 -->
  <localRepository>D:\java\m2</localRepository>
  ...
  <!-- 远程仓库位置 -->
   <mirror>  
      <id>alimaven</id>  
      <mirrorOf>central</mirrorOf>  
      <name>aliyun maven</name>  
      <url>http://maven.aliyun.com/nexus/content/groups/public/</url>  
   </mirror>

mvn clean   # 清理编译项目
mvn compile # 编译项目
mvn test    # 测试项目
mvn package # 项目打包
mvn install # 安装到仓库中

ServletContext servletContext = this.getServletContext();
String username = "loh";
servletContext.setAttribute("username",username);

ServletContext servletContext = this.getServletContext();
String username = (String) servletContext.getAttribute("username");

resp.setContentType("text/html");
resp.setCharacterEncoding("utf-8");
resp.getWriter().print(username);

ServletContext context = this.getServletContext();
String url = context.getInitParameter("url");

PrintWriter printWriter = resp.getWriter();
printWriter.print(url);

ServletContext servletContext = this.getServletContext();
//        简短代码
//        servletContext.getRequestDispatcher("/hello").forward(req,resp);
RequestDispatcher requestDispatcher = servletContext.getRequestDispatcher("/hello");//转发的请求路径
requestDispatcher.forward(req,resp);//调用forward实现请求转发

//        获取Servletcontext读取资源转换为输入流
InputStream inputStream = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");

        
Properties prop = new Properties();
prop.load(inputStream);
//        properties对象从输入流中读取并输出
String user =prop.getProperty("username");
String pwd =prop.getProperty("password");
resp.getWriter().print(user+":"+pwd);

ServletOutputStream getOutputStream() throws IOException;  //写流用这个
 
PrintWriter getWriter() throws IOException;  //写中文用这个，如果用这个写一些东西的时候，会造成字符串损坏或者丢失

void setCharacterEncoding(String var1); //设置响应的编码
void setContentLength(int var1);   //设置响应的字符串长度
void setContentLengthLong(long var1);   //设置长度
void setContentType(String var1);   //设置类型

void setDateHeader(String var1, long var2);

void addDateHeader(String var1, long var2);

void setHeader(String var1, String var2);

void addHeader(String var1, String var2);

void setIntHeader(String var1, int var2);

void addIntHeader(String var1, int var2);

int SC_CONTINUE = 100;  //100是服务器接收到客户端发来的请求的初始部分，并且请客户端继续发送
int SC_OK = 200;   //状态ok
int SC_NOT_FOUND = 404;   //没有找到
int SC_INTERNAL_SERVER_ERROR = 500;  //服务器端错误
int SC_BAD_GATEWAY = 502;   //网关出现了问题

//        获取下载文件路径
        String resourcePath = "G:\\Loh\\Code\\javaweb-maven\\ServletResponse\\src\\main\\resources\\2.png";
        System.out.println("下载文件路径："+resourcePath);
//        下载的文件名是什么
        String fileName = resourcePath.substring(resourcePath.lastIndexOf("\\")+1);
//        头部声明，通知浏览器在下载文件,中文文件名使用URLEncoder.encode编码防止乱码
        resp.setHeader("Content-Disposition","attachment;fileName="+fileName);
//        获取下载文件的输入流
        FileInputStream in = new FileInputStream(resourcePath);
//       创建缓冲区
        int len =0;
        byte[] buffer = new byte[1024];
//        获取输出流对象
        ServletOutputStream out = resp.getOutputStream();
//        写入缓冲
        while ((len = in.read(buffer))!= -1){
            out.write(buffer,0,len);
        }
//        关闭流
        in.close();
        out.close();

@Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //浏览器5秒刷新一次
        resp.setHeader("refresh","5");

        //在内存中创建图片
        BufferedImage Image = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);
        //获取画笔
        Graphics2D g = Image.createGraphics();
        //设置画笔颜色
        g.setColor(Color.WHITE);
        //填充背景颜色
        g.fillRect(0,0,80,20);

        //设置画笔颜色
        g.setColor(Color.black);

        //设置画笔字体、粗细、字号
        g.setFont(new Font("宋体",Font.BOLD,20));

        //画笔绘制，绘制坐标
        g.drawString(makeNum(),0,20);

        //浏览器响应类型参数设置
        resp.setContentType("image/jpeg");
        //浏览器响应的过期时间,立即过期
        resp.setDateHeader("expires",-1);
        //响应，缓存控制为不缓存
        resp.setHeader("Cache-Control","no-cache");
        //不缓存
        resp.setHeader("Pragma","no-cache");

        //IO写图,格式化类型,从响应对象中输出
        boolean jpg_out = ImageIO.write(Image, "jpg", resp.getOutputStream());
    }
    
        //随机数生成
        private String makeNum(){
            Random random = new Random();
            String num = random.nextInt(9999999)+"";
            StringBuffer stringBuffer = new StringBuffer();
            //随机数不足7位时for循环遍历补足
            for (int i = 0; i < 7-num.length(); i++) {
                stringBuffer.append("0");
            }
            String s = stringBuffer.toString() + num;
            //返回
            return  num;
        }

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

<body>
<h1>login</h1>
<div>
   <%--   当前项目路径获取--%>
    <form action="${pageContext.request.contextPath}login" method="post">
        name:<input type="text" name="username"><br>
        password:<input type="password" name="password"><br>
        hobby:
        <input type="checkbox" name="hobby" value="code">code
        <input type="checkbox" name="hobby" value="sing">sing
        <input type="checkbox" name="hobby" value="watch movie">movie
        <br>
        <input type="submit">
        <input type="reset">
    </form>
</div>
</body>

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    String name =req.getParameter("username");
    String pwd =req.getParameter("password");
    System.out.println(name);
    System.out.println(pwd);

}

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

//        设置响应和查询编码
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");

//        获取响应输出流
        PrintWriter out = resp.getWriter();
//        获取cookie
        Cookie[] cookies = req.getCookies();
//        从cookie中获取参数
        if (cookies != null){
            out.print("上次访问时间");
            for (int i = 0; i < cookies.length; i++) {
                Cookie cookie = cookies[i];

                if (cookie.getName().equals("lastLoginTime")){

                    long lastLoginTime = Long.parseLong(cookie.getValue());
                    Date date = new Date(lastLoginTime);
                    out.write(date.toLocaleString());
                }
            }
        }else {
            out.write("首次访问");
        }
        
//        创建一个Cookie
        Cookie cookie = new Cookie("lastLoginTime", System.currentTimeMillis() + "");
//        设置有效期
        cookie.setMaxAge(24*60*60);
//        响应给浏览器一个cookie
        resp.addCookie(cookie);

package com.loh.listener;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import java.net.http.WebSocket;
//实现session监听
public class OnlineCountListener implements HttpSessionListener {
//    创建session时监听
    @Override
    public void sessionCreated(HttpSessionEvent se) {
//        获取ServletContext
        ServletContext sct = se.getSession().getServletContext();
//        从ServletContext中获取字段值
        Integer onlineCount = (Integer) sct.getAttribute("OnlineCount");

        if(onlineCount==null){
            onlineCount =Integer.valueOf(1);
        }else {
            int count = onlineCount.intValue();
            onlineCount=Integer.valueOf(count+1);
        }
        sct.setAttribute("OnlineCount",onlineCount);
    }
//销毁session时监听

    @Override
    public void sessionDestroyed(HttpSessionEvent se) {
        //        获取ServletContext
        ServletContext sct = se.getSession().getServletContext();
//        从ServletContext中获取字段值
        Integer onlineCount = (Integer) sct.getAttribute("OnlineCount");

        if(onlineCount==null){
            onlineCount =Integer.valueOf(0);
        }else {
            int count = onlineCount.intValue();
            onlineCount=Integer.valueOf(count-1);
        }
        sct.setAttribute("OnlineCount",onlineCount);
    }
}

package com.loh.listener;

import javax.swing.*;
import java.awt.*;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;

public class TestPanel {
    public static void main(String[] args) {
//        窗口
        Frame frame = new Frame("lets go");
//        面板
        Panel panel = new Panel();
//        窗口设置布局tr
        frame.setLayout(null);
//        窗口大小
        frame.setBounds(300,300,500,500);
//        窗口背景色
        frame.setBackground(new Color(0,0,255));
//        面板大小
        panel.setBounds(50,50,300,300);
        
        panel.setBackground(new Color(0,255,0));
        frame.add(panel);
        frame.setVisible(true);

        
        frame.addWindowListener(new WindowListener() {
            @Override
            public void windowOpened(WindowEvent e) {
                
            }

            @Override
            public void windowClosing(WindowEvent e) {
            
//                退出
                System.exit(1);
            }

            @Override
            public void windowClosed(WindowEvent e) {

            }

            @Override
            public void windowIconified(WindowEvent e) {

            }

            @Override
            public void windowDeiconified(WindowEvent e) {

            }

            @Override
            public void windowActivated(WindowEvent e) {

            }

            @Override
            public void windowDeactivated(WindowEvent e) {

            }
        });
    }
}

package com.loh.filter_admin;

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 LoginMethod extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        获取前端参数
        String username = req.getParameter("username");
        if (username.equals("admin")){//登录成功
//             设置session字段值给常量USER_SESSION
            req.getSession().setAttribute("USER_SESSION",req.getSession().getId());
//            重定向
            resp.sendRedirect("/sys/success.jsp");
        }else {//登录失败
            resp.sendRedirect("/error.jsp");
        }

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

package com.loh.filter_admin;

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 LogoutMethod extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Object userSession = req.getSession().getAttribute("USER_SESSION");
        if (userSession != null){
            req.getSession().removeAttribute("USER_SESSION");
            resp.sendRedirect("/Login.jsp");
        }
    }

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

package com.loh.filter_admin;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class FilterDo implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }

    @Override
    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) resp;

        if (request.getSession().getAttribute("USER_SESSION")==null){
            response.sendRedirect("/error.jsp");
        }

//        执行过滤
        chain.doFilter(req,resp);
    }

    @Override
    public void destroy() {

    }
}

package com.loh.test;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

public class TestJdbc01_Statement {
    public static void main(String[] args) throws Exception {
        //  配置jdbc信息
        String url = "jdbc:mysql://localhost:3306/JDBC_WEB?useUnicode=true&characterEncoding=utf-8";
        String username = "root";
        String password = "123456";

//        加载驱动
        Class.forName("com.mysql.cj.jdbc.Driver");
//        连接数据库
        Connection connection = DriverManager.getConnection(url, username, password);
//         statement对象：CRUD
        Statement statement = connection.createStatement();
//        编写sql
        String sql = "select * from users";
//        执行查询sql
        ResultSet rs = statement.executeQuery(sql);

        while (rs.next()){
            System.out.println("id=" + rs.getObject("id"));
            System.out.println("name=" + rs.getObject("name"));
            System.out.println("password=" + rs.getObject("password"));
            System.out.println("email=" + rs.getObject("email"));
            System.out.println("birthday=" + rs.getObject("birthday"));
        }
//        关闭连接释放
        rs.close();
        statement.close();
        connection.close();
    }
}

//        注释：增删改		
//        增删改使用update
        sql ="insert into jdbc_web.users(ID, NAME, PASSWORD, EMAIL, BIRTHDAY) 	VALUES(4,'DA','12234','21423@QQ.COM','2021-10-28')";
//        statement使用update处理sql，该方法返回一个int类型的数（表中受影响的行数）
        int i = statement.executeUpdate(sql);
        System.out.println("有"+i+"行受影响");

package com.loh.test;

import java.sql.*;

//使用preparedStatement处理sql
public class TestJdbc02_PrepareStatement {
    public static void main(String[] args) throws ClassNotFoundException, SQLException {
//  配置jdbc信息
        String url = "jdbc:mysql://localhost:3306/JDBC_WEB?useUnicode=true&characterEncoding=utf-8";
        String username = "root";
        String password = "123456";

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

//        编写sql和占位符
        String sql = "insert into jdbc_web.users(id, name, password, email, birthday) VALUES (?,?,?,?,?);";

//        安全sql查询,预编译
        PreparedStatement preparedStatement = connection.prepareStatement(sql);

//        对占位符进行赋值
        preparedStatement.setInt(1,5);
        preparedStatement.setString(2,"xaxa");
        preparedStatement.setString(3,"54321");
        preparedStatement.setString(4,"dasda@qq.com");
        preparedStatement.setDate(5,new java.sql.Date(new java.util.Date().getTime()));

        int rs = preparedStatement.executeUpdate();

        if (rs > 0){
            System.out.println("插入成功");
        }else {
            System.out.println("错误");
        }

//        关闭连接释放
        preparedStatement.close();
        connection.close();
    }
}