Servlet 03 ----【javaweb-06】

SERVLET

ServletContext

  web容器在启动的时候,它会为每个web程序都创建一个对应的ServletContext对象,它代表了当前的web应用。

接下来,让我们来看看ServletContext对象有什么用处吧。

 

1. 数据传输

  我们可以在保存一个类中的servlet的同时,在另一个类获取该servlet数据。

代码展示:

类1:

package com.charels.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 {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
     //this.getServletContext()  Servlet上下文 ServletContext context
= this.getServletContext(); String name = "小明"; context.setAttribute("name",name); } }

 

类2.

package com.charels.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 GetServlet extends HttpServlet {
        @Override
        protected 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("GBK");
            resp.getWriter().print("名字"+name);
        }

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

 

在web.xml注册,两个servlet。

  <!--  注册servlet-->
  <servlet>
    <servlet-name>hello</servlet-name>
    <servlet-class>com.charels.servlet.HelloServlet</servlet-class>
  </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.charels.servlet.GetServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>getc</servlet-name>
    <url-pattern>/getc</url-pattern>
  </servlet-mapping>

 

接下来,让我们康康运行Tomcat后的展示结果:

在这里要注意,根据代码的意思,要获取上下文数据,则需要先访问第一个类的servlet,再访问第二个才能获取数据。

 

第一个类的网页:

第二个类的网页:

2. 获取初始化参数

代码展示:

 

首先在web.xml中配置初始化数据:

 

    <!--配置一些web应用初始化参数-->
    <context-param>
        <param-name>url</param-name>
        <param-value>jdbc:mysql://localhost:3306/mybatis</param-value>
    </context-param>

 

 

 

接下来编写获取初始化数据的代码:

 

package com.charels.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 GetUrl extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String url = context.getInitParameter("url");

        resp.getWriter().print(url);
    }

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

 

 

 

编写完毕后,注册servlet,然后运行Tomcat:

 

3. 请求与转发

  我们可以通过一个servlet的类来实现页面的转发。

代码展示:

 

package com.charels.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class Dri extends GetUrl{
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("进入Dri");

        ServletContext context = this.getServletContext();
        context.getRequestDispatcher("/g1").forward(req,resp);
    }

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

 

 

 

结果展示:

  控制台:

    

  页面展示:

    

 

4. 读取资源文件

  首先,在properties的包中创建一个db.properties并编写数据

  

  在servlet类中编写读取资源的代码:

package com.charels.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 GetPro extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setCharacterEncoding("gbk");

        InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");

        Properties pro = new Properties();
        pro.load(is);
        String username = pro.getProperty("username");
        String passsword= pro.getProperty("password");

        resp.getWriter().print(username + ':' + passsword);
    }

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

 

 

编写完毕后,运行Tomcat,展示结果:

 

 

posted @ 2020-08-02 16:19  Charles_H  阅读(122)  评论(0编辑  收藏  举报