JavaWeb学习笔记20/10/20ServletContext

ServletContext

Web容器再启动的时候，会为每个Web程序创建一个对应的ServletContext对象，它代表了当前的Web应用；

共享数据

在这个Servlet中保存的数据可以在另外一个Servlet中拿到:

public class HelloServlet extends HttpServlet {
    
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    

        //this.getInitParameter() 初始化参数
        //this.getServletConfig() Servlet配置
        //this.getServletContext() Servlet上下文
        ServletContext context = this.getServletContext();

        String username = "顾家明";//数据
        context.setAttribute("username",username);//将一个数据保存在ServletContext中，名字为：username，值为username

        System.out.println("Hello");
    }

}

public class GetServlet extends HttpServlet {
    
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
        ServletContext context = this.getServletContext();
        String username = (String) context.getAttribute("username");

        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        resp.getWriter().print("名字"+username);
    }

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

<servlet>
  <servlet-name>hello</servlet-name>
  <servlet-class>com.weng.servlet.HelloServlet</servlet-class>

</servlet>
<servlet-mapping>
  <servlet-name>hello</servlet-name>
  <url-pattern>/hello</url-pattern>
</servlet-mapping>

<servlet>
  <servlet-name>getc</servlet-name>
  <servlet-class>com.weng.servlet.GetServlet</servlet-class>

</servlet>
<servlet-mapping>
  <servlet-name>getc</servlet-name>
  <url-pattern>/getc</url-pattern>
</servlet-mapping>

获取初始化参数

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

public class ServletDemo03 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);

    }

}

请求转发

public class ServletDemo04 extends HttpServlet {
    
    

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
        ServletContext context = this.getServletContext();
        System.out.println("进入了ServletDemo04");
        //RequestDispatcher requestDispatcher = context.getRequestDispatcher("/gp");//转发的请求路径
        //requestDispatcher.forward(req,resp);//调用forward实现请求转发
        context.getRequestDispatcher("/gp").forward(req,resp);//合并以上两句
    }

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

    }
}

读取资源文件

Properties

• 在java目录下新建properties
• 在resources目录下新建properties

发现:都被打包到了同一个路径下: classes，我们称这个路径为classpath:

思路:需要一个文件流

public class ServletDemo05 extends HttpServlet {
    
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
        InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
        Properties prop = new Properties();
        prop.load(is);
        String user = prop.getProperty("username");
        String pwd = prop.getProperty("password");
        resp.getWriter().print(user+":"+pwd);

    }

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

    }
}