java-web中几种注册方式

第一种：Servlet

建WEB项目

1606290940431

增加web.xml

<servlet>
        <servlet-name>partServlet</servlet-name>
        <servlet-class>servlet.asyn.PartServlet</servlet-class>
        <load-on-startup>0</load-on-startup>
        <init-param>
            <param-name>db</param-name>
            <param-value>mysql</param-value>
        </init-param>
    </servlet>
    <servlet-mapping>
        <servlet-name>partServlet</servlet-name>
        <url-pattern>/test11</url-pattern>
    </servlet-mapping>

1606290972612

其中

1	<load-on-startup>0</load-on-startup>

表示servlet在何时初始化，Web容器启动时初始化，还是用户请求某个Servlet时对其初始化。

设置为0时，表示容器在应用启动时就加载并初始化这个servlet

写个servlet实现类

package servlet.asyn;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Collection;

public class PartServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request,response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        OutputStream os = response.getOutputStream();
        os.write("test".getBytes());
    }
}

访问

1606291144253

第二种：使用Filter

web.xml配置

<filter>
        <filter-name>EncodingFilter</filter-name>
        <filter-class>filter.EncodingFilter</filter-class>
        <async-supported>false</async-supported>
        <init-param>
            <param-name>encoding</param-name>
            <param-value>utf-8</param-value>
        </init-param>
    </filter>
    <filter-mapping>
        <filter-name>EncodingFilter</filter-name>
        <url-pattern>/*</url-pattern>
        <dispatcher>REQUEST</dispatcher>
    </filter-mapping>

1606291364233

类实现注意使用javax.servlet的接口：

1606291289806

第三种：使用Listener

1
2
3

<listener>
        <listener-class>listener.CustomServletContextListener</listener-class>
</listener>

实现ServletContextListener接口

1606291578999

第四种：注解注册（Servlet3.0+）