Servlet(三)ServletContext

Servlet(三)ServletContext

ServletContextd对象:

web容器在启动的时候,它会为每个web程序都创建一个对象的ServletContext对象,它代表了当前的web应用;

  • 共享数据

    我在一个Servlet中保存的数据,可以在另一个Servlet中拿到

    实际开发时,少用servletContext,用session

    //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
    //        this.getServletContext(); Servlet上下文
            ServletContext servletContext = this.getServletContext();
            String username = "困了就睡";
            servletContext.setAttribute("username",username);//将一个数据保存到ServletContext中,名字:username,值:username,看成键值对的形式
        }
    }
    
    //读取数据的类
    public class GetServlet extends HttpServlet{
    
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            ServletContext servletContext = this.getServletContext();
            String username = (String) servletContext.getAttribute("username");
    
            resp.setCharacterEncoding("utf-8");
            resp.setContentType("text/html");
            resp.getWriter().print(username);
        }
    
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            doGet(req, resp);
        }
    }
    
    //配置xml
    <servlet>
            <servlet-name>hello</servlet-name>
            <servlet-class>com.godwin.servlet.HelloServlet</servlet-class>
        </servlet>
    
        <servlet-mapping>
            <servlet-name>hello</servlet-name>
            <url-pattern>/hello</url-pattern>
        </servlet-mapping>
        
        <servlet>
            <servlet-name>get</servlet-name>
            <servlet-class>com.godwin.servlet.GetServlet</servlet-class>
        </servlet>
        <servlet-mapping>
            <servlet-name>get</servlet-name>
            <url-pattern>/get</url-pattern>
        </servlet-mapping>
    

    测试访问时,

    注意:读取数据的类,记得解决乱码问题

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

    第一次访问http://localhost:8080/s2/get,页面显示为null,

    接着访问http://localhost:8080/s2/hello,页面为空,但是拿了数据

    在访问http://localhost:8080/s2/get,拿到数据,并且页面显示“困了就睡”,即设置好的数据

ServletContextd应用

获取初始化参数

实际开发中,几乎不用这么做

web.xml

<context-param>
        <param-name>url</param-name>
        <param-value>jdbc:mysql://localhost:3306/mybatis</param-value>
    </context-param>

<servlet>
        <servlet-name>gp</servlet-name>
        <servlet-class>com.godwin.servlet.ServletDemo01</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>gp</servlet-name>
        <url-pattern>/gp</url-pattern>
    </servlet-mapping>
public class ServletDemo01 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String url = context.getInitParameter("url");
        resp.getWriter().print(url);

    }

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

请求转发

实际开发中,我们用Request去做

请求转发时,路径不会变

web.xml

<servlet>
        <servlet-name>tp</servlet-name>
        <servlet-class>com.godwin.servlet.ServletDemo02</servlet-class>
    </servlet>
    
    <servlet-mapping>
        <servlet-name>tp</servlet-name>
        <url-pattern>/tp</url-pattern>
    </servlet-mapping>
public class ServletDemo02 extends HttpServlet{

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
//        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);
    }

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

Servlet(三)ServletContext

读取资源文件

实际开发中,用类加载或者反射等去做,几乎不用这个方式去做

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路径下:classes,俗称:类路径 。

思路:需要一个文件流

解决资源导出问题:

<!--在build中配置resources,来防止我们资源导出失败的问题-->
    <build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>
public class ServletDemo03 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/dp.properties");
        Properties prop = new Properties();
        prop.load(is);
        String username = prop.getProperty("username");
        String password = prop.getProperty("password");
        resp.getWriter().print(username + ":" + password);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}
<servlet>
        <servlet-name>sd3</servlet-name>
        <servlet-class>com.godwin.servlet.ServletDemo03</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>sd3</servlet-name>
        <url-pattern>/sd3</url-pattern>
    </servlet-mapping>
username=root
password=root

复习笔记资料参考B站UP主狂神说

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