Java-Servlet技术入门笔记-2

@WebServlet("/getcontext")
public class GetContextServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //通过HttpServlet获取
        ServletContext servletContext1 = this.getServletContext();
        //通过HttpServletRequest req对象获取
        ServletContext servletContext2 = req.getServletContext();
        //通过servletConfig对象获取
        ServletContext servletContext3 = this.getServletConfig().getServletContext();
        System.out.println(servletContext1);
        System.out.println(servletContext2);
        System.out.println(servletContext3);
    }
}

<?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/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
    <!--新增部分-->
    <!--context-param是上下文参数（它属于整个web工程），可以配置多组-->
    <context-param>
        <param-name>username</param-name>
        <param-value>context</param-value>
    </context-param>
    <context-param>
        <param-name>password</param-name>
        <param-value>root</param-value>
    </context-param>
    <!--新增部分-->
    <servlet>
        <servlet-name>HelloServlet</servlet-name>
        <servlet-class>com.first.cyh.HelloServlet</servlet-class>
        <init-param>
            <param-name>username</param-name>
            <param-value>root</param-value>
        </init-param>
        <init-param>
            <param-name>url</param-name>
            <param-value>jdbc:mysql//localhost/test</param-value>
        </init-param>
    </servlet>
    <servlet-mapping>
        <servlet-name>HelloServlet</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>
</web-app>

public class ContextServlet1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //GenericServlet获取获取ServletContext对象的方式，等同于getServletConfig().getServletContext()
        ServletContext servletContext = getServletContext();
        System.out.println("保存之前Context1中获取域数据key1的值是：" + servletContext.getAttribute("key1"));
 public class ContextServlet2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext servletContext = getServletContext();
        System.out.println("Context2中获取域数据key1的值是：" + servletContext.getAttribute("key1"));
    }
}
       //存数据
        servletContext.setAttribute("key1","value1");
        //取数据
        System.out.println("Context1中获取域数据key1的值是：" + servletContext.getAttribute("key1"));
    }
}
public class ContextServlet2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext servletContext = getServletContext();
        System.out.println("Context2中获取域数据key1的值是：" + servletContext.getAttribute("key1"));
    }
}

@WebServlet("/getmime")
public class GetMime extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
        //定义文件名
        String filename = "a.jpg";
        //通过文件名的后缀获取对应MIME类型
        String mimeType = servletContext.getMimeType(filename);
        System.out.println(mimeType);
    }
}

public class RequestAPIServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("URI-->" + req.getRequestURI());//URI-->/myfirst/req
        System.out.println("URL-->" + req.getRequestURL());//URL-->http://localhost:8080/myfirst/req
        //如果以localhost访问，则返回0:0:0:0:0:0:0:10:0:0:0:0:0:0:1
        //以127.0.0.1访问，则返回127.0.0.1
        //以真实ip访问，则返回真实ip
        System.out.println("HOST-->" + req.getRemoteHost());
        //HEADER-->Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/95.0.4638.54 Safari/537.36 Edg/95.0.1020.30
        System.out.println("METHOD-->" + req.getMethod());//GET
        System.out.println("HEADER-->" + req.getHeader("User-Agent"));
    }
}

public class Servlet1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //查看请求的带来的数据
        String username = req.getParameter("username");
        System.out.println("servlet1中请求带来的数据:" + username);
        //处理业务
        //doSth
        username += "ahahha";
        System.out.println("业务1完成，username=" + username);
        //处理完业务，在request域中存储数据
        req.setAttribute("username",username);
        //询问servlet2的路径
        //请求转发必须以斜杆开始，表示http://ip:8080/工程名/
        RequestDispatcher requestDispatcher = req.getRequestDispatcher("/servlet2");
        //带着请求走向servlet
        requestDispatcher.forward(req,resp);
    }
}