8.6、ServletContext 对象

8.6、ServletContext 对象

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

我在这个servlet中保存的数据，可以再另外一个servlet中拿到

1.新建一个module

2.HelloServlet

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 = "高壮壮";
        context.setAttribute("username",username);  //将一个数据保存在ServletContext中，名字为username，值为高壮壮
        System.out.println("Hello");
    }

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

3.GetServlet

public class GetServlet extends HelloServlet{

    @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");
        PrintWriter writer = resp.getWriter();
        writer.print("名字："+username);
    }

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

4.web.xml

    
    
        hello
        com.kuang.servlet.HelloServlet
    
    
        hello
        /hello
    

    
    
        getContext
        com.kuang.servlet.GetServlet
    
    
        getContext
        /getContext
    

5.测试

5.1 先调用localhost:8080/s2/getContext

5.2 再调用localhost:8080/s2/hello

5.3 重启，再调用localhost:8080/s2/hello

5.4 再调用localhost:8080/s2/getContext

2、获取初始化参数

 
    
        url
        jdbc:mysql://localhost:3306/mybatis
    
     
        gp
        com.kuang.servlet.ServletDemo03
    
    
        gp
        /gp
    

public class ServletDemo03 extends HelloServlet{

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

    }

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

3、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");
//        RequestDispatcher requestDispatcher = context.getRequestDispatcher("/gp"); //请求的转发路径
//        requestDispatcher.forward(req,resp);  //调用forward实现请求转发
        context.getRequestDispatcher("/gp").forward(req,resp);
    }

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

        dis
        com.kuang.servlet.ServletDemo04
    
    
        dis
        /dis
    

4、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：都被打包到同一个路径下：classes 我们俗称这个路径为classpath

思路：需要一个文件流

username=root
password=123456

    
        sd5
        com.kuang.servlet.ServletDemo05
    
    
        sd5
        /sd5
    

public class ServletDemo05 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        InputStream inputStream = req.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");

        Properties properties = new Properties();
        properties.load(inputStream);

        String username = properties.getProperty("username");
        String password = properties.getProperty("password");

        resp.getWriter().print(username+":"+password);
    }

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