ServletContext

web容器在启动的时候，它会为每个web程序都创建对应的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，可以在另外一个Servlet中拿到；

创建放置数据的类

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
        ServletContext context = this.getServletContext();//Servlet上下文

        String username = "小红";//数据
        context.setAttribute("username",username);//将一个数据保存在ServletContext中，名字为username，值 username


    }


}

读取数据的类

public class GetServlet extends HttpServlet {
    @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;charset=utf-8");
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        resp.getWriter().print("名字:" + username);

    }

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

配置web.xml

   <servlet>
        <servlet-name>hello</servlet-name>
        <servlet-class>com.uestc.servlet.HelloServlet</servlet-class>
<!--        <init-param>-->
<!--            <param-name></param-name>-->
<!--            <param-value></param-value>-->
<!--        </init-param>-->
    </servlet>
    <servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>getc</servlet-name>
        <servlet-class>com.uestc.servlet.GetServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>getc</servlet-name>
        <url-pattern>/getc</url-pattern>
    </servlet-mapping>

测试访问结果；名字:小红

2.获取初始化参数

<!--   配置一些web应用的初始化参数 -->
    <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

java类

   @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        System.out.println("进入了ServletDemo04");
//        RequestDispatcher requestDispatcher = context.getRequestDispatcher("/gp");//转发的请求路径
//        requestDispatcher.forward(req,resp);//调用forward实现请求转发；
        context.getRequestDispatcher("/gp").forward(req,resp);

    }

web.xml

<servlet>
    <servlet-name>sd4</servlet-name>
    <servlet-class>com.uestc.servlet.ServletDemo04</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>sd4</servlet-name>
    <url-pattern>/sd4</url-pattern>
</servlet-mapping>

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：都被打包到了同一个路径下：classes路径，我们俗称这个路径为classpath；

思路：需要一个文件流：

Java类

public class ServletDemo05 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/com/uestc/servlet/aa.properties");

        Properties prop = new Properties();
        prop.load(is);
        String user = prop.getProperty("username");
        String pwd = prop.getProperty("password");

        resp.getWriter().print(user+":"+pwd);

    }

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

db.properties在resources下创建

username=root
password=123456

aa.properties在Java下面创建j

username=root123123
password=root12356

配置web.xml文件

<servlet>
    <servlet-name>sd5</servlet-name>
    <servlet-class>com.uestc.servlet.ServletDemo05</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>sd5</servlet-name>
    <url-pattern>/sd5</url-pattern>
</servlet-mapping>