ServletContext

ServletContext

Web容器在启动的时候,它会为每个web程序创建一个对应的ServletContext对象,它代表了当前的web应用。 (由它进行一些其他操作，可以想象成中间商。拿着这个中间商去做一些事情)

– 共享数据 (创建一个访问数据的类)

我在这个Servlet中保存的数据，可以在另外一个Servlet中拿到；用的是（ServletContext）

创建一个Servlet的类，用来存储到ServletContext里面；

public class Servlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("Hello");


//        this.getInitParameter()    初始化参数
//        this.getServletConfig()    Servlet配置
//        this.getServletContext()   Servlet上下文

        ServletContext context = this.getServletContext();

        String username = "铁锤"; //数据

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


    }

2：创建一个getServlet的类，用来获取ServletContext,
读取它的类

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");
        resp.setCharacterEncoding("utf-8");
        resp.getWriter().print("名字:"+username);
        System.out.println(username);


    }

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

3：配置一个XML

<servlet>
    <servlet-name>hello</servlet-name>
    <servlet-class>com.kuang.servlet.Servlet</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>

测试访问结果
先向Context中放置一个数据，在去取出数据。从而实现我们的共享数据

– 获取初始化参数

public class ServletDemo03 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        ServletContext context = this.getServletContext();

        // this.getInitParameter()    初始化参

        String url = context.getInitParameter("url");
        resp.getWriter().print(url);
        
    }

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

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

配置Servlet
<servlet>
   <servlet-name>gp</servlet-name>
   <servlet-class>com.kuang.servlet.ServletDemo03</servlet-class>
</servlet>
<servlet-mapping>
   <servlet-name>gp</servlet-name>
   <url-pattern>/gp</url-pattern>
</servlet-mapping>

– 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("进入了ServletDemo04");

        //RequestDispatcher dispatcher = context.getRequestDispatcher("/gp"); //转发请求的路径
        //dispatcher.forward(req,resp); //调用forward方法，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);
    }

配置Servlet

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

– 读取配置文件

Properties

• 在Java 目录下新建properties
• 在Resource目录下新建properties

发现：都被打包在同一个路径下： classes ,我们俗称这个路径为类路径( classpath )

思路：需要一个文件流

在Servlet中写入一个 aa.properties

username=root
password=root

创建一个ServletDemo05的类；

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

        ServletContext context = this.getServletContext();

        InputStream is = context.getResourceAsStream("/WEB-INF/classes/com/kuang/servlet/aa.properties");

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

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


    }

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

配置Servlet

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

访问测试结果：