JavaWeb入门:ServletContext详解和应用

<!--1、获取web应用程序初始化参数-->

< context-param >

     < param-name >name</ param-name >

     < param-value >crush</ param-value >

</ context-param >

< context-param >

     < param-name >school</ param-name >

     < param-value >hngy</ param-value >

</ context-param >

/**

  * @Author: crush

  * @Date: 2021-05-09 16:32

  * version 1.0

  */

@WebServlet ( "/servlet" )

public class ServletContextTest extends HttpServlet {

     @Override

     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         //设置响应头

         resp.setContentType( "text/html;charset=utf-8" );

         PrintWriter writer = resp.getWriter();

         ServletContext servletContext = this .getServletContext();

         // 根据名称 获取单个初始化参数

         String parameter = servletContext.getInitParameter( "name" );

         writer.print(parameter);

         writer.print( "<br><hr>" );

         // 获取全部初始化参数

         Enumeration<String> initParameterNames = servletContext.getInitParameterNames();

         while (initParameterNames.hasMoreElements()){

             String name = initParameterNames.nextElement();

             String value = servletContext.getInitParameter(name);

             writer.print(name+ ":" +value);

             writer.print( "<hr>" );

         }

     }

     @Override

     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         doGet(req, resp);

     }

}

< servlet >

     < servlet-name >/servlet1</ servlet-name >

     < servlet-class >com.crush.servlet.ServletContextTest</ servlet-class >

</ servlet >

< servlet-mapping >

     < servlet-name >/servlet1</ servlet-name >

     < url-pattern >/servlet1</ url-pattern >

</ servlet-mapping >

/**

  * @Author: crush

  * @Date: 2021-05-09 16:59

  * version 1.0

  */

@WebServlet ( "/servlet1" )

public class ServletContextTest1 extends HttpServlet {

     @Override

     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         // 获取ServletContext对象

         ServletContext servletContext = this .getServletContext();

         //设置值  ServletContext 域属性 name 域属性名 obj是值

         // 往ServletContext 中放进 username=crush 这个键值对

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

         // 在控制台给出提示

         System.out.println( "值已经设置完成" );

         // 重定向

//        resp.sendRedirect("/servlet2");

         // 转发

         req.getRequestDispatcher( "servlet2" ).forward(req, resp);

     }

     @Override

     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         doGet(req, resp);

     }

}

/**

  * @Author: crush

  * @Date: 2021-05-09 16:59

  * version 1.0

  */

@WebServlet ( "/servlet2" )

public class ServletContextTest2 extends HttpServlet {

     @Override

     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         // 获取ServletContext对象

         ServletContext servletContext = this .getServletContext();

         // 通过之前的设置的名字 取出username 的值

         String username =(String) servletContext.getAttribute( "username" );

         PrintWriter writer = resp.getWriter();

         writer.print(username);

         //返回一个Enumeration其中包含该ServletContext中可用的属性名称

         // Enumeration<String> attributeNames = servletContext.getAttributeNames();

         //从此ServletContext中删除具有给定名称的属性。

//        servletContext.removeAttribute("");

     }

     @Override

     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         doGet(req, resp);

     }

}

user =root

password =123456

url=jdbc:mysql://localhost:3306/mysql

drive=com

/**

  * 读取资源内容

  * @Author: crush

  * @Date: 2021-05-09 16:59

  * version 1.0

  */

@WebServlet ( "/servlet3" )

public class ServletContextTest3 extends HttpServlet {

     @Override

     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         resp.setContentType( "text/html;charset=utf-8" );

         ServletContext servletContext = this .getServletContext();

         // 获取相对路径中的输入流对象  是要获取web应用程序的路径

         InputStream inputStream = servletContext.getResourceAsStream( "\\WEB-INF\\classes\\mysql.properties" );

         // 资源类对象

         Properties properties = new Properties();

         // load 从输入字节流中读取属性列表（键和元素对）

         properties.load(inputStream);

         PrintWriter writer = resp.getWriter();

         writer.print( "user" +properties.getProperty( "user" )+ "<br>" );

         writer.print( "password" +properties.getProperty( "password" )+ "<br>" );

         writer.print( "url" +properties.getProperty( "url" )+ "<br>" );

         writer.print( "drive" +properties.getProperty( "drive" )+ "<br>" );

     }

     @Override

     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         doGet(req, resp);

     }

}

/**

  * 请求转发

  * @Author: crush

  * @Date: 2021-05-09 16:59

  * version 1.0

  */

@WebServlet ( "/servlet5" )

public class ServletContextTest5 extends HttpServlet {

     @Override

     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         resp.setContentType( "text/html;charset=utf-8" );

         ServletContext servletContext = this .getServletContext();

         // RequestDispatcher对象可用于将请求转发到资源或将资源包括在响应中。 资源可以是动态的也可以是静态的。

         //路径名必须以/开头，并被解释为相对于当前上下文根。 使用getContext获取外部上下文中资源的RequestDispatcher

         servletContext.getRequestDispatcher( "/servlet" ).forward(req,resp);

         //forward:将请求从servlet转发到服务器上的另一个资源（servlet，JSP文件或HTML文件）

     }

     @Override

     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         doGet(req, resp);

     }

}

/**

  * 乱码问题

  * @Author: crush

  * @Date: 2021-05-09 16:59

  * version 1.0

  */

@WebServlet ( "/servlet6" )

public class ServletContextTest6 extends HttpServlet {

     @Override

     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         // 解决乱码 只是解决单独的响应乱码 如果有请求 还要设置请求的编码

         req.setCharacterEncoding( "utf-8" );

         resp.setContentType( "text/html;charset=utf-8" );

         PrintWriter writer = resp.getWriter();

         writer.print( "你好啊，JavaWeb" );

     }

     @Override

     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

         doGet(req, resp);

     }

}