javaweb - leileigwl

1.编写Servlet#

重要补充：request是从服务器获取数据，response是从服务器向浏览器返回数据
通过配置的maven新建webapp模板工程并且配置pom.xml文件(是mvn的核心文件)来导入Servlet的依赖

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<dependency>
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    <groupId>javax.servlet</groupId>
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    <artifactId>javax.servlet-api</artifactId>
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    <version>3.1.0</version>
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</dependency>

创建一个类继承HttpServlet，并重写Service方法

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public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
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    res.getWriter().write("Hello servlet");//通过浏览器窗口输出Hello servlet
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}

在web.xml里编写映射

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<?xml version="1.0" encoding="UTF-8"?>
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<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
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         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
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                      http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
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         version="3.1"
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         metadata-complete="true">
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</web-app>

2.ServletContext#

解释：每一个web应用都有且仅有一个ServletContext对象，又称Application对象，从名称中可知，该对象是与应用程序相关的。在WEB容器启动的时候，会为每一个WEB应用程序创个对应的ServletContext对象。
作用：共享数据，可以通过一方来保存，另一方可以读取
两个小方法：

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getServletContext//设置储存的信息，以键值对的形式
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getAttribute//获取储存的信息，需要键的名为对象

3.请求转发#

不改变原来的地址，但是能够改变跳转的位置

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ServletContext context = this.getServletContext();//先获取context对象
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context.getRequestDispatcher("/cf").forward(req,resp);//调用getRequestDispatcher方法输入请求转发的地址

4.通过Servletcontext读取配置文件#

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protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
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    ServletContext context = this.getServletContext();
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    Properties prop = new Properties();
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    InputStream ras = context.getResourceAsStream("/WEB-INF/classes/db.properties");
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    prop.load(ras);
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    String username = prop.getProperty("username");
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    String pwd = prop.getProperty("password");
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    resp.getWriter().write(username+":"+pwd);
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}

5.Response#

5.1 下载#

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protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
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    String realPath = "D:\\project\\java\\execrise\\project02\\src\\main\\resources\\a.jpg";
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    String fileName = realPath.substring(realPath.lastIndexOf("\\") + 1);
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    resp.setHeader("Content-Disposition", "attachment;filename=" +fileName );//最重要的设置头，表明下载
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    FileInputStream fis = new FileInputStream(realPath);
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    ServletOutputStream os = resp.getOutputStream();//获取流去读写
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    byte[] buffer = new byte[1024];
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    int len ;
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    while((len = fis.read(buffer))!=-1){
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        os.write(len);
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    }
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    os.close();
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    fis.close();
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}

5.2 重定向#

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public class Demo02 extends HttpServlet {
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    @Override
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    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
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        resp.sendRedirect("/cf/demo03");//重定向的地址
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    }
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}

6.Request#

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public class Demo06 extends HttpServlet {
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    @Override
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    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
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        System.out.println("进入了这个服务");
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        String username = req.getParameter("username");//获取username信息
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        String password = req.getParameter("password");//获取password信息
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        System.out.println(username+":"+password);
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    }
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}

7.Cookies#

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protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
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    resp.setContentType("text/html;charset = utf-8");//设置服务器返回编码
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    Cookie[] cookies = req.getCookies();//先获取cookies
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    PrintWriter writer = resp.getWriter();//浏览器输出
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    boolean flag =false;
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    for (Cookie cookie : cookies) {
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        if (cookie.getName().equals("lastTime")){
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            Long timer = Long.valueOf(cookie.getValue());//还原原来的日期格式
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            Date date = new Date(timer);
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            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");//设置日期格式
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            String currentTime = sdf.format(date);
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            writer.write("你上一次访问本站的时间是:"+currentTime);
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            flag =true;
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        }
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    }
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    if (!flag)   writer.write("这是你第一次访问,我们为您创建了cookie，方便下次访问");
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    Cookie lastTime = new Cookie("lastTime", System.currentTimeMillis() + "");//Cookie都是以键值对的形式存在
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    resp.addCookie(lastTime);
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}

8.Session#

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protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
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    req.setCharacterEncoding("utf-8");
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    resp.setContentType("text/html;charset = utf-8");
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    HttpSession session = req.getSession();
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    session.setAttribute("username", new Person("借口",18));
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}

9.JSP#

9.1 Jsp语法#

整个JSP的内容实际上是一个HTML，但是稍有不同：

包含在<%--和--%>之间的是JSP的注释；
包含在<%和%>之间的是Java代码，可以编写任意Java代码；
如果使用<%= xxx %>则可以快捷输出一个变量的值。
<%! %>可以写java代码（作用域更高的，相当于全局），称之为声明

9.2 内置9大对象#

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PageContext        //存东西，级别最次
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Request            //存东西，级别次
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Response
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Session            //存东西，级别中
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Application->SerlvetContext  //存东西，级别高
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config->SerlvetConfig
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out
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page
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exception

10.Filter过滤器#

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public class FilterDemo01 implements Filter {
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    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
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        servletRequest.setCharacterEncoding("utf-8");//请求编码
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        servletResponse.setContentType("text/html;charset = utf-8");//响应编码
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        System.out.println("doFilter进入前面");
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        filterChain.doFilter(servletRequest,servletResponse);//主要方法，看成一条链，传递原来的req和resp对象
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        System.out.println("doFilter进入后面");
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    }
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}

11.Listener#

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public void sessionCreated(HttpSessionEvent se) {//创建方法
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    ServletContext context = se.getSession().getServletContext();
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    Integer onlineCnt = (Integer) context.getAttribute("onlineCnt");//获取onlineCnt的字段
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    if (onlineCnt==null){
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        onlineCnt= 1;
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    }else {
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        onlineCnt = onlineCnt+1;
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    }
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    context.setAttribute("onlineCnt",onlineCnt);//每次添加这字段
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}

12.JDBC#

12.1 配置信息#

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String url = "jdbc:mysql://localhost:3306/test01?useUnicode=true&characterEncoding=UTF-8&serverTimezone=UTC";
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String username = "root";
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String password = "root";

12.2 加载驱动#

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Class.forName("com.mysql.cj.jdbc.Driver") ;

12.3 连接数据库#

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Connection connection = DriverManager.getConnection(url, username, password);

12.4 向数据库发送statement请求，CRUD#

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Statement statement = connection.createStatement();

12.5 写sql#

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String sql ="select *from person";

12.6 执行sql#

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ResultSet res = statement.executeQuery(sql);
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while (res.next()){
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    System.out.println("id："+ res.getObject("id"));
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    System.out.println("name："+ res.getObject("name"));
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    System.out.println("password："+ res.getObject("password"));
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    System.out.println("email："+ res.getObject("email"));
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    System.out.println("birthday："+ res.getObject("birthday"));
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}

12.7 关闭连接#

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res.close();
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statement.close();
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connection.close();