ServletContext

6.5 ServletContext

web容器启动的时候，会为每个web程序创建一个ServletContext对象，仅代表了当前web应用(所有当前web页面共享，servlet共享数据)

1.贡献数据

我在这里servlet保存的数据，可以在另一个servlet中共享

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        super.doGet(req, resp);
        System.out.println("hello");
        resp.setCharacterEncoding("uft-8");

        ServletContext servletContext = getServletContext();
        String username = "秦疆";

        servletContext.setAttribute("username",username);
    }

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

public class GetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        super.doGet(req, resp);
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        ServletContext servletContext = this.getServletContext();
        String username = (String) servletContext.getAttribute("username");
        PrintWriter writer = resp.getWriter();
        writer.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.kuang.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.kuang.servlet.GetServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>getc</servlet-name>
        <url-pattern>/getc</url-pattern>
    </servlet-mapping>

测试访问：

2.获取初始化参数

• 1-在web.xml中配置参数

    <context-param>
        <param-name>url</param-name>
        <param-value>jdbc:mysql://localhost3306/mybatis</param-value>
    </context-param>

• 2-使用servlet拿到参数

public class ServletDemo03 extends HttpServlet {
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        super.doGet(req, resp);
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        ServletContext servletContext = this.getServletContext();
        String url = servletContext.getInitParameter("url");
        resp.getWriter().print(url);

    }

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

3.请求转发：重要！

public class ServletDemo04 extends HttpServlet {
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        ServletContext servletContext = this.getServletContext();
        RequestDispatcher requestDispatcher = servletContext.getRequestDispatcher("/gp");//转发请求路径
        requestDispatcher.forward(req,resp);//调用forward实现请求转发
    }

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

4.读取资源文件

• 在java目录下新建aa.properties
• 在sources目录下新建db.properties
  发现都被打包一个目录下：classes,这个路径成为classpath。有可能在Java目录下的打包失败。

username=qingjiang
password=123456

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

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

访问测试OK即可。