--webapps : Tomcat服务器的web目录
    -Root
    -xcwStudy ：网站的目录名
    	- WEB-INF
    		-classes ：java程序
    		-lib ：web应用程序所依赖的jar包
    		-web.xml ：网站配置文件
    	- index.html 默认的首页
    	- static
    		-css
    			-style.css
    		-js
    		-img
    	-...

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //this.getServletContext();    Servlet上下文

        ServletContext servletContext = this.getServletContext();
        String username = "行初雾"; //数据
        servletContext.setAttribute("username",username);  //将一个数据保存在了ServletContext中，名字为：username，值为username
    }
}

public class GetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String username = (String)context.getAttribute("username");

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

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

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    ServletContext context = this.getServletContext();
    String url = context.getInitParameter("url");
    resp.getWriter().print(url);
}

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    ServletContext context = this.getServletContext();
    System.out.println("进入了ServletDemo04");

    //RequestDispatcher requestDispatcher = context.getRequestDispatcher("/gp");    //转发的请求路径
    //requestDispatcher.forward(req,resp);    //调用forward实现请求转发
    context.getRequestDispatcher("/gp").forward(req,resp);

}

public class ServletDemo05 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");

        Properties prop = new Properties();
        prop.load(is);
        String user = prop.getProperty("username");
        String pwd = prop.getProperty("password");

        resp.getWriter().print(user+" : "+pwd);
    }

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

ServletOutputStream getOutputStream() throws IOException;

PrintWriter getWriter() throws IOException;

void setCharacterEncoding(String var1);

void setContentLength(int var1);

void setContentLengthLong(long var1);

void setContentType(String var1);

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;
int SC_SWITCHING_PROTOCOLS = 101;
int SC_OK = 200;
int SC_CREATED = 201;
int SC_ACCEPTED = 202;
int SC_NON_AUTHORITATIVE_INFORMATION = 203;
int SC_NO_CONTENT = 204;
int SC_RESET_CONTENT = 205;
int SC_PARTIAL_CONTENT = 206;
int SC_MULTIPLE_CHOICES = 300;
int SC_MOVED_PERMANENTLY = 301;
int SC_MOVED_TEMPORARILY = 302;
int SC_FOUND = 302;
int SC_SEE_OTHER = 303;
int SC_NOT_MODIFIED = 304;
int SC_USE_PROXY = 305;
int SC_TEMPORARY_REDIRECT = 307;
int SC_BAD_REQUEST = 400;
int SC_UNAUTHORIZED = 401;
int SC_PAYMENT_REQUIRED = 402;
int SC_FORBIDDEN = 403;
int SC_NOT_FOUND = 404;
int SC_METHOD_NOT_ALLOWED = 405;
int SC_NOT_ACCEPTABLE = 406;
int SC_PROXY_AUTHENTICATION_REQUIRED = 407;
int SC_REQUEST_TIMEOUT = 408;
int SC_CONFLICT = 409;
int SC_GONE = 410;
int SC_LENGTH_REQUIRED = 411;
int SC_PRECONDITION_FAILED = 412;
int SC_REQUEST_ENTITY_TOO_LARGE = 413;
int SC_REQUEST_URI_TOO_LONG = 414;
int SC_UNSUPPORTED_MEDIA_TYPE = 415;
int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;
int SC_EXPECTATION_FAILED = 417;
int SC_INTERNAL_SERVER_ERROR = 500;
int SC_NOT_IMPLEMENTED = 501;
int SC_BAD_GATEWAY = 502;
int SC_SERVICE_UNAVAILABLE = 503;
int SC_GATEWAY_TIMEOUT = 504;
int SC_HTTP_VERSION_NOT_SUPPORTED = 505;

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    //1. 要获取下载文件的路径
    String realPath = "E:\\javadProgram\\javaweb\\javaweb-02-maven\\response\\target\\response-1.0-SNAPSHOT\\WEB-INF\\classes\\1.png";
    System.out.println("下载文件路径："+realPath);
    //2. 下载的文件名是啥？
    String fileName = realPath.substring(realPath.lastIndexOf("\\")+1);
    //3. 设置想办法让浏览器能够支持下载我们需要的东西, 中文文件名URLEncoder.encode编码，否则有可能乱码
    resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(fileName,"UTF-8"));
    //4. 获取下载文件的输入流
    FileInputStream in = new FileInputStream(realPath);
    //5. 创建缓冲区
    int len = 0;
    byte[] buffer = new byte[1024];
    //6. 获取OutputStream
    ServletOutputStream out = resp.getOutputStream();
    //7. 讲FileOutputStream流写入到buffer缓冲区,使用OutputStream将缓冲区中的数据输出到客户端
    while((len = in.read(buffer))>0){
        out.write(buffer,0,len);
    }

    in.close();
    out.close();
}

public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //如何让浏览器3秒自动刷新一次
        resp.setHeader("refresh","3");
        //在内存中创建一个图片
        BufferedImage image = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);
        //得到图片
        Graphics2D g = (Graphics2D) image.getGraphics();  //笔
        //设置图片的背景颜色
        g.setColor(Color.WHITE);
        g.fillRect(0,0,80,20);
        //给图片写数据
        g.setColor(Color.BLUE);
        g.setFont(new Font(null,Font.BOLD,20));
        g.drawString(makeNum(),0,20);

        //告诉浏览器，这个请求用图片的方式打开
        resp.setContentType("image/jpeg");
        //网站存在缓存，不让浏览器缓存
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");

        //把图片写给浏览器
        ImageIO.write(image,"jpg",resp.getOutputStream());
    }
    //生产随机数
    private String makeNum(){
        Random random = new Random();
        String num = random.nextInt(9999999)+"";
        StringBuffer sb = new StringBuffer();
        for(int i = 0; i < 7-num.length(); i++)
            sb.append("0");
        num = sb.toString()+num;
        return num;
    }

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

void sendRedirect(String var1) throws IOException;

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    /*
            resp.setHeader("location","/r/img");
            resp.setStatus(302);
        */
    resp.sendRedirect("/r/img");//重定向
}

public class RequestTest extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //处理请求
        String username = req.getParameter("username");
        String password = req.getParameter("password");

        System.out.println(username+":"+password);

        //重定向的时候一定要注意，路径问题，否则404
        resp.sendRedirect("/r/success.jsp");
    }

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

public class LoginServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        String[] hobbys = req.getParameterValues("hobbys");
        System.out.println("===============");
        System.out.println(username);
        System.out.println(password);
        System.out.println(Arrays.toString(hobbys));
        System.out.println("===============");

        //通过请求转发
        //这里的/代表当前的web应用
        req.getRequestDispatcher("/success.jsp").forward(req,resp);

    }

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

Cookie[] cookies = req.getCookies();  //获得Cookie
cookie.getName()  //获得cookie中的key
cookie.getValue()  //获得cookie中的value
new Cookie("lastLoginTime",System.currentTimeMillis()+"")  //新建一个cookie
cookie.setMaxAge(24*60*60);  //设置cookie的有效期
resp.addCookie(cookie); //响应给客户端一个cookie

public class SessionDemo01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //解决乱码问题
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");

        //得到Session
        HttpSession session = req.getSession();
        //给Session中存东西
        session.setAttribute("name",new Person("行初雾",22));
        //获取Session的ID
        String sessionId = session.getId();
        //判断Session是不是新创建
        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了，ID："+sessionId);
        }
        //Session创建的时候做了什么事情：
        //Cookie cookie = new Cookie("JSESSIONID", sessionId);
        //resp.addCookie(cookie);
    }

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

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

Person person = (Person) session.getAttribute("name");
System.out.println(person.toString());

HttpSession session = req.getSession();
session.removeAttribute("name");
//手动注销
session.invalidate();

response.setContentType("text/html");    //设置相应的页面类型
pageContext = _jspxFactory.getPageContext(this, request, response,null, true, 8192, true);
_jspx_page_context = pageContext;
application = pageContext.getServletContext();
config = pageContext.getServletConfig();
session = pageContext.getSession();
out = pageContext.getOut();
_jspx_out = out;

pageContext.setAttribute("name1","行初雾1号"); //保存的数据只在一个页面中有效
request.setAttribute("name2","行初雾2号"); //保存的数据只在一次请求中有效，请求转发会携带这个数据
session.setAttribute("name3","行初雾3号"); //保存的数据只在一次会话中有效，从打开浏览器到关闭浏览器
application.setAttribute("name4","行初雾4号"); //保存的数据只在服务器中有效，从打开服务器到关闭服务器

class People{
    private int id;
    private String name;
    private int age;
    private String address;
}

class A{
    new People(1,"行初雾1号",18,"邯郸");
    new People(2,"行初雾2号",20,"西安");
    new People(3,"行初雾3号",23,"西安");
}

servlet--CRUD-->数据库
   弊端：程序十分臃肿，不利于维护
   servlet的代码中：处理请求、响应、视图跳转、处理JDBC、处理业务代码、处理逻辑代码

   架构：没有什么是加一层解决不了的！
   程序员调用
   |
   JDBC
   |
   Mysql Oracle SqlServer....

public class CharacterEncodingFilter implements Filter {

    //初始化：web服务器启动，就已经初始化了，随时等待过滤器对象出现
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("CharacterEncodingFilter初始化");
    }

    //Chain：链
    /*
    1. 过滤中的所有代码，在过滤特定请求的时候都会执行
    2. 必须要让过滤器继续通行
        chain.doFilter(request,response);
    */
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=UTF-8");

        System.out.println("CharacterEncodingFilter执行前...");
        chain.doFilter(request,response);    //让我们的请求继续走，如果不写，程序大奥这里就被拦截停止
        System.out.println("CharacterEncodingFilter执行后...");
    }

    //销毁：web服务器关闭的时候，过滤会销毁
    public void destroy() {
        System.out.println("CharacterEncodingFilter销毁");
    }
}

//统计网站在线人数：统计session
public class OnlineCountListener implements HttpSessionListener {

    //创建session监听：看你的一举一动
    //一旦创建session就会触发一次这个事件
    public void sessionCreated(HttpSessionEvent httpSessionEvent) {
        ServletContext ctx = httpSessionEvent.getSession().getServletContext();

        System.out.println(httpSessionEvent.getSession().getId());

        Integer onlineCount = (Integer) ctx.getAttribute("OnlineCount");

        if(onlineCount == null){
            onlineCount = new Integer(1);
        } else {
            int count = onlineCount.intValue();
            onlineCount = new Integer(count+1);
        }

        ctx.setAttribute("OnlineCount",onlineCount);
    }

    //销毁session监听
    //一旦销毁session就会触发一次这个事件
    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
        ServletContext ctx = httpSessionEvent.getSession().getServletContext();

        System.out.println(httpSessionEvent.getSession().getId());

        Integer onlineCount = (Integer) ctx.getAttribute("OnlineCount");

        if(onlineCount == null){
            onlineCount = new Integer(0);
        } else {
            int count = onlineCount.intValue();
            onlineCount = new Integer(count-1);
        }

        ctx.setAttribute("OnlineCount",onlineCount);
    }

    /*
    Session销毁：
    1. 手动销毁 getSession().invalidate();
    2. 自动销毁
    */
}

HttpServletRequest request = (HttpServletRequest) servletRequest;
HttpServletResponse response = (HttpServletResponse) servletResponse;

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

public class TestJdbc {
    public static void main(String[] args) throws ClassNotFoundException, SQLException {
        //配置信息
        //useUnicode=true&characterEncoding=utf-8  解决中文乱码
        String url = "jdbc:mysql://localhost:3306/jdbc?useUnicode=true&characterEncoding=utf-8";
        String username = "root";
        String password = "cjy521213";

        //1.加载驱动
        Class.forName("com.mysql.jdbc.Driver");
        //2.连接数据库，代表数据库
        Connection connection = DriverManager.getConnection(url, username, password);
        //3.向数据库发送SQL的对象Statement ：CRUD
        Statement statement = connection.createStatement();
        //4.编写SQL
        String sql = "select * from users";
        //5.执行查询SQL，返回一个ResultSet ：结果集
        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"));
            System.out.println("--------------------------");
        }
        //6.关闭连接
        rs.close();
        statement.close();
        connection.close();
    }
}

public class TestJdbc2 {
    public static void main(String[] args) throws ClassNotFoundException, SQLException {
        //配置信息
        //useUnicode=true&characterEncoding=utf-8  解决中文乱码
        String url = "jdbc:mysql://localhost:3306/jdbc?useUnicode=true&characterEncoding=utf-8";
        String username = "root";
        String password = "cjy521213";

        //1.加载驱动
        Class.forName("com.mysql.jdbc.Driver");
        //2.连接数据库，代表数据库
        Connection connection = DriverManager.getConnection(url, username, password);
        //3.编写SQL
        String sql = "insert into users(id, name, password, email, birthday) value(?,?,?,?,?)";
        //4.预编译
        PreparedStatement preparedStatement = connection.prepareStatement(sql);

        preparedStatement.setInt(1,4);//给第一个占位符？的值赋值为 4
        preparedStatement.setString(2,"行初雾");//给第二个占位符？的值赋值为 行初雾
        preparedStatement.setString(3,"123456");//给第三个占位符？的值赋值为 123456
        preparedStatement.setString(4,"1092315259@qq.com");//给第四个占位符？的值赋值为 1092315259@qq.com
        preparedStatement.setDate(5,new Date(new java.util.Date().getTime()));//给第五个占位符？的值赋值为 new Date(new java.util.Date().getTime())


        //5.执行SQL
        int i = preparedStatement.executeUpdate();

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

        //6.关闭连接
        preparedStatement.close();
        connection.close();
    }
}

@Test
public void test(){
    System.out.println("hello");
}