1.共享数据

ServletContext 对象

先调用对象，获取对象，往里面存数据

package com.kuang.servlet;import javax.servlet.ServletContext;
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 HelloServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//servletContext servlet上下文 相当于中间商ServletContext context = this.getServletContext();String name="鸡哥";context.setAttribute("name",name);}}

然后创建另一个servlet用来取数据

package com.kuang.servlet;import javax.servlet.ServletContext;
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 GetContext extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {ServletContext context = this.getServletContext();String name = (String)context.getAttribute("name");resp.setContentType("text/html");resp.setCharacterEncoding("utf-8");resp.getWriter().print("名字="+name);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

配置文件注册

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaeehttp://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"version="4.0"metadata-complete="true"><servlet><servlet-name>Hello</servlet-name><servlet-class>com.kuang.servlet.HelloServlet</servlet-class>
<!--        <init-param></init-param>--></servlet><!-- Servlet的请求路径   --><servlet-mapping><servlet-name>Hello</servlet-name><url-pattern>/hello</url-pattern></servlet-mapping><servlet><servlet-name>getc</servlet-name><servlet-class>com.kuang.servlet.GetContext</servlet-class><!--        <init-param></init-param>--></servlet><!-- Servlet的请求路径   --><servlet-mapping><servlet-name>getc</servlet-name><url-pattern>/getc</url-pattern></servlet-mapping></web-app>

运行tomcat

先/hello 获取数据

再/getc 输出数据

2.获取参数

     1.参数初始化

    <context-param><param-name>url</param-name><param-value>jdbc:mysql://localhost:3306/mybatis</param-value></context-param>

     2.获得参数

package com.kuang.servlet;import javax.servlet.ServletContext;
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 ServletDemo03 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {ServletContext context = this.getServletContext();String url = context.getInitParameter("url");resp.getWriter().print(url);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}}

 3.请求转发

记住这个请求转发，这是springmvc dispatchServlet的实现原理

package com.kuang.servlet;import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
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 ServletDemo04 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {ServletContext context = this.getServletContext();System.out.println("进入了Demo04");RequestDispatcher requestDispatcher = context.getRequestDispatcher("/geturl");//转发的请求路径requestDispatcher.forward(req,resp);//调用forward实现请求转发}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

转发是站内请求,重定向是站外请求

转发相当于是服务器请求到资源再转发给浏览器

重定向两次请求，转发一次请求

转发

 重定向

 4.读取资源文件

Properties

 要找的不是IDEA中的文件，而是导出的web应用的文件

package com.kuang.servlet;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;public class ServletDemo05 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");Properties properties = new Properties();properties.load(is);String username = properties.getProperty("username");String pwd = properties.getProperty("password");resp.getWriter().print(username+":"+pwd);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

<servlet><servlet-name>sd5</servlet-name><servlet-class>com.kuang.servlet.ServletDemo05</servlet-class><!--        <init-param></init-param>--></servlet><!-- Servlet的请求路径   --><servlet-mapping><servlet-name>sd5</servlet-name><url-pattern>/sd5</url-pattern></servlet-mapping>

package com.kuang.servlet;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;public class ServletDemo05 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");Properties properties = new Properties();properties.load(is);String username = properties.getProperty("username");String pwd = properties.getProperty("password");resp.getWriter().print(username+":"+pwd);is.close();}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

 <servlet><servlet-name>sd5</servlet-name><servlet-class>com.kuang.servlet.ServletDemo05</servlet-class><!--        <init-param></init-param>--></servlet><!-- Servlet的请求路径   --><servlet-mapping><servlet-name>sd5</servlet-name><url-pattern>/sd5</url-pattern></servlet-mapping>