1.1 ServletConfig的概述

  Servlet容器初始化一个servlet对象时，会为这个servlet对象创建一个servletConfig对象。在servletConfig对象中包含了servlet的初始化参数信息。此外，servletConfig对象还与servletContext对象关联。Servlet容器在调用servlet对象的init(ServletConfig config)方法时，会把servletConfig对象当做参数传递给servlet对象。Init(ServletConfig config)方法会使得当前servlet对象与servletConfig对象建立关联关系。

  简单的说就是：servlet 容器使用的 servlet 配置对象，该对象在初始化期间将信息传递给 servlet。

1.1.1 ServletConfig的方法

1.1.2 ServletConfig的入门案例

xml文件加入的内容

<servlet>
    <description></description>
    <display-name>Demo5Servlet</display-name>
    <servlet-name>Demo5Servlet</servlet-name>
    <servlet-class>com.itheima.servlet.Demo5Servlet</servlet-class>
    <init-param>
      <param-name>username</param-name>
      <param-value>zhangsan</param-value>
    </init-param>
    <init-param>
      <param-name>password</param-name>
      <param-value>123456</param-value>
    </init-param>
  </servlet>

注意 <init-param> 标签是 <servlet>的子标签 同时 里面的子标签是的内容类似于键值对的

程序代码

public class Demo5Servlet extends HttpServlet {
    
    /*private ServletConfig config;
    
    @Override
    public void init(ServletConfig config) throws ServletException {
        this.config = config;
    }*/
    
    
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletConfig config = getServletConfig();
        //根据初始化参数的name来获取value
        String username = config.getInitParameter("username");
        String password = config.getInitParameter("password");
        
        
        System.out.println(username);
        System.out.println(password);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

• 在实际的作用有
  • 获取字符集编码 UTF-8
  • 获取数据库连接信息 用户名 密码 url
  • 获取配置文件

1.2 ServletContext的概述

  ServletContext是servlet与servlet容器之间的直接通信的接口。Servlet容器在启动一个Web应用时，会为它创建一个servletContext对象。每个web应用有唯一的servletContext对象。同一个web应用的所有servlet对象共享一个serveltContext,servlet对象可以通过它来访问容器中的各种资源。

  上下文对象, 他是在服务器启动的时候,会为每个web项目创建一个单独的servletContext对象,他代表了当前的WEB应用

1.2.1 ServletContext的部分方法

1.2.2 ServletContext代码功能演示

• 获取Context对象

public class ContextDemo extends HttpServlet {
   
   protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       //获取ServletContext对象
       //通过ServletConfig对象来获取
       //ServletContext context = getServletConfig().getServletContext();
       
       //同过Servlet的方法来获取
       ServletContext context = getServletContext();
       
       //根据name来获取value
       String username = context.getInitParameter("username");
       String password = context.getInitParameter("password");
       
       System.out.println(username);
       System.out.println(password);
   }

   
   protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       // TODO Auto-generated method stub
       doGet(request, response);
   }

}

• 获取属性值

public class ContextDemo2 extends HttpServlet {
   
   protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       //获取ServletContext对象
       ServletContext context = getServletContext();
       //设置数据
       context.setAttribute("username", "zhangsan");
       context.setAttribute("username", "lisi");
       //获取数据
       Object obj = context.getAttribute("username");
       
       response.getWriter().println(obj);
   }

   
   protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       // TODO Auto-generated method stub
       doGet(request, response);
   }

}

• 获取路径

public class ContextDemo4 extends HttpServlet {
    
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.getWriter().println("itcast");
        
        //获取ServletContext对象
        ServletContext context = getServletContext();
        //获取当前WEB应用的绝对路径
        //String path = context.getRealPath("/WEB-INF");
        //System.out.println(path);
        
        RequestDispatcher rd = context.getRequestDispatcher("/ContextDemo2");
        //转发
        //rd.forward(request, response);
        
        //包含
        rd.include(request, response);
        
        response.getWriter().println("itheima");
    }

    
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

1.3 ServletConfig与ServletContext的区别

这里推荐其他程序员的一篇博客 写的很棒

跳转地址 《ServletConfig和ServletContext的区别及应用》