ServletContext

2023-10-09 10:58:34

ServletContext

1、简介

web容器在启动时会为每个web程序创建一个ServletContext对象，它代表了当前的web应用

2、应用（以下方法现在几乎不用）

共享数据（setAttribute()，getAttribute()）

在一个Servlet中保存的数据，可以在另一个Servlet中拿到，例：

放置类

public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String userName = "张晟伟";
        context.setAttribute("userName",userName);//将userName放进content对象
    }
}

获取类

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().println("名字："+userName);
    }

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

xml

 <servlet>
        <servlet-name>hello</servlet-name>
        <servlet-class>com.zhang.servlet.HelloServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>
    <servlet>
        <servlet-name>getcontext</servlet-name>
        <servlet-class>com.zhang.servlet.GetServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>getcontext</servlet-name>
        <url-pattern>/getc</url-pattern>
    </servlet-mapping>

测试结果：

ServletContext

原理图：

ServletContext

获取初始化参数（getInitParameter()）

java代码

public class ServletDemo_01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String url = context.getInitParameter("url");
        resp.getWriter().println(url);
    }

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

xml

 <!--
    context-param标签为配置一些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>
    <servlet>
        <servlet-name>gp</servlet-name>
        <servlet-class>com.zhang.servlet.ServletDemo_01</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>gp</servlet-name>
        <url-pattern>/gp</url-pattern>
    </servlet-mapping>

请求转发（RequestDispatcher）

原理图：

ServletContext

java代码

public class ServletDemo_04 extends HelloServlet{
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
//        RequestDispatcher requestDispatcher = context.getRequestDispatcher("/gp");//请求参数对象，转发请求路径
//        requestDispatcher.forward(req,resp);//调用方法实现请求转发
        context.getRequestDispatcher("/gp").forward(req,resp);//将被注释的两行代码合并
    }

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

xml

<servlet>
        <servlet-name>respdispatcher</servlet-name>
        <servlet-class>com.zhang.servlet.ServletDemo_04</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>respdispatcher</servlet-name>
        <url-pattern>/rc</url-pattern>
    </servlet-mapping>

实现效果：

! ServletContext

读取资源文件（Properties）

新建Properties

在resources下新建properties文件

启动服务器propertis文件导出

在java目录下新建properties文件

注：由于在maven中约定大于配置，所以写在java目录下的propertis文件可能无法被导出或者生效

ServletContext

启动服务器发现在target文件相应路径下并没有aa.properties文件

ServletContext

解决方法

在pom.xml文件中配置resources

<!--在build中配置resources，来防止我们资源导出失败问题-->
    <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>

重启服务器，问题解决

ServletContext

发现properties文件都被打包到了同一个路径下：classes，我们俗称这个路径为 classpath（类路径）

读取Properties

需要一个流及properties中的内容

ServletContext

java代码

public class ServletDemo_05 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        InputStream i = context.getResourceAsStream("/WEB-INF/classes/db.properties");
        Properties prop = new Properties();
        prop.load(i);
        String user = prop.getProperty("username");
        String pwd = prop.getProperty("password");
        resp.getWriter().println(user+":"+pwd);
    }

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

xml

<servlet>
    <servlet-name>a_05</servlet-name>
    <servlet-class>com.zhang.servlet.ServletDemo_05</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>a_05</servlet-name>
    <url-pattern>/rp</url-pattern>
</servlet-mapping>

实现效果

ServletContext

码农公寓

ServletContext

1、简介

2、应用（以下方法现在几乎不用）

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