ServletContext

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

• 共享数据:在Servlet-1中设置保存的数据，可以在Servlet-02中拿到

  • 用于设置参数的Servlet类-HelloServlet

    @WebServlet("/hello")
    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 servletContext = this.getServletContext();
            servletContext.setAttribute("name","saxon");
            System.out.println("hello :HelloServlet");
        }
    }
    

  • 用于获取参数的Servlet类-GetServlet

    @WebServlet("/get")
    public class GetServlet extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            //解决中文乱码
            resp.setContentType("text/html");
            resp.setCharacterEncoding("utf-8");
            ServletContext servletContext = this.getServletContext();
            String username = (String) servletContext.getAttribute("name");
            resp.getWriter().write(username);
            System.out.println("hello GetServlet");
        }
    }
    

    必须先访问hello接口，然后访问get接口，才能获取name的值。

获取初始化参数

• web.xml中配置

      <!--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/test</param-value>
      </context-param>
  

@WebServlet("/demo01")
public class ServletDemo01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
        String url = servletContext.getInitParameter("url");
        resp.getWriter().print(url);
    }
}

请求转发:

• 该类实现了请求的转发，转发至了/url这个映射路径

• @WebServlet("/demo02")
  public class DemoServlet02 extends HttpServlet {
      @Override
      protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          ServletContext servletContext = getServletContext();
          //请求转发
          servletContext.getRequestDispatcher("/demo1").forward(req, resp);
  //        RequestDispatcher requestDispatcher = req.getRequestDispatcher("/demo1");
  //        requestDispatcher.forward(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：都被打包到同一个路径下：classes，俗称为classpath：

思路：需要一个文件流

• 获取properties文件的Servlet类-PropertiesServlet

@WebServlet("/propertiesServlet")
public class PropertiesServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        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("psw");
        resp.getWriter().write("username="+username);
        resp.getWriter().write("psw="+password);
    }
}

• properties文件（此处放置在resources目录下）

  username = root
  psw = 123456
  

  然后测试访问即可。http://localhost:8080/servlet02_war/propertiesServlet

原文：https://www.cnblogs.com/saxonsong/p/14805147.html