（JavaWeb）ServletContext对象

文章目录

• ServletContext
• • 1.共享数据
  • 2.获取初始化参数
  • 3.请求转发
  • 4.读取资源文件

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；

1.共享数据

Servlet1可以将数据存放在ServletContext中，Servlet2和Servlet3可以在ServletContext中取得Servlet1在ServletContext中存放的数据。

在HelloServlet中存放String数据 伊泽瑞尔。

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取servletContext对象
        ServletContext servletContext = this.getServletContext();
        String name = "伊泽瑞尔";
        //以键值对的形式将数据放入servletContext对象中
        servletContext.setAttribute("name",name);
    }

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

在GetNameServlet中取得数据并显示在网站上

public class GetNameServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取ServletContext对象
        ServletContext servletContext = this.getServletContext();
        //获取HelloServlet中在获取ServletContext对象中存放的数据
        String name = (String) servletContext.getAttribute("name");
        //设置响应信息为中文
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        resp.getWriter().write(name);
    }

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

           

先访问HelloServlet页面将数据存放在ServletContext中，再访问GetNameServlet拿出数据并显示在网页。

2.获取初始化参数

<!--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>
           

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    ServletContext context = this.getServletContext();
    String url = context.getInitParameter("url");
    resp.getWriter().print(url);
}
           

3.请求转发

public class ServletDemo01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //创建servletContext对象
        ServletContext servletContext = this.getServletContext();
        //请求转发
        servletContext.getRequestDispatcher("/getName").
        	forward(req,resp);
    }

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

运行，显示的是GetNameServlet的页面，这里null是由于没有访问hello的缘故。

显示的是GetNameServlet的页面，但是路径却还是自己的。

如图，A向B请求资源，B向C请求资源，B将C返回的资源再返回给A，A自始至终没有接触C，所以显示的还是B的路径。

4.读取资源文件

Properties

• 在resources目录下新建db.properties文件

username=ez
password=123456
           

public class ServletDemo02 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //创建servletContext对象
        ServletContext servletContext = this.getServletContext();
        //获取properties文件的字节输入流对象
        InputStream is = servletContext.getResourceAsStream("/WEB-INF/classes/db.properties");
        //创建properies对象
        Properties prop = new Properties();
        //加载流
        prop.load(is);
        String user = prop.getProperty("username");
        String pwd = prop.getProperty("password");
        //显示
        resp.getWriter().write(user+":"+pwd);
    }

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