SpringBoot integration of the three established (Servlet, Listener, Filter)

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3.SpringBoot integration Servlet

3.1. A way

step:

• Write a class MyFirstServlet inherit HttpServlet, and override doGet method.
• In the above class with the specified name and Servlet @WebServlet identification and urlPatterns.
• Have identified based on the main @SpringBootApplication plus @ServletComponentScan.

FirstServlet.java

package com.example.servlet.myservlet;

import javax.servlet.http.HttpServlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 *SpringBoot整合Servlet方式一
 *@WebServlet(name="MyFirstServlet",urlPatterns="/myFirst")相当于如下:
 *
 *<servlet>
 * <servlet-name>MyFirstServlet</servlet-name>
 * <servlet-class>ah.szxy.servlet.FirstServlet</servlet-class>
 *</servlet>
 *<servlet-mapping>
 * <servlet-name>MyFirstServlet</servlet-name>
 * <url-pattern>/first</url-pattern>
 *</servlet-mapping>
 *
 */

@WebServlet(name="MyFirstServlet",urlPatterns="/myFirst")
public class FirstServlet extends HttpServlet {

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

ServletApplication.java

package com.example.servlet;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.ServletComponentScan;

@SpringBootApplication
@ServletComponentScan //在springBoot启动时会扫描@WebServlet，并将该类实例化
public class ServletApplication {

   public static void main(String[] args) {
      SpringApplication.run(ServletApplication.class, args);
   }

}

Then start the project

Finally, enter in your browser localhost: 8080 / myFirstServlet, blank page, print MyFirstServlet init in the console ............

3.2. Second way

step:

• Creating a class SecondServlet inherit HttpServlet, and override doGet method.
• In a method of the main class @SpringBootApplication identification of @Bean added.
  SecondServlet.java

package com.example.servlet.myservlet;

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

/**
 * 整合Servlet的第二种方式
 */
public class SecondServlet extends HttpServlet {

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

ServletApplication.java

package com.example.servlet;

import com.example.servlet.myservlet.SecondServlet;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.ServletComponentScan;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
//@ServletComponentScan //在springBoot启动时会扫描@WebServlet，并将该类实例化
public class ServletApplication {

   public static void main(String[] args) {
      SpringApplication.run(ServletApplication.class, args);
   }

  /**
 * 整合Servlet的第二种方式，创建ServletRegistrationBean并添加路径
 * @return
 */
@Bean
public ServletRegistrationBean getServletRegistrationBean(){
   ServletRegistrationBean bean = new ServletRegistrationBean(new SecondServlet());
   bean.addUrlMappings("/mySecond");
   return bean;
}

Then start the project, visit localhost in the browser: 8080 / mySecondServlet, the page is blank, the console will print MySecondServlet init ..........

project structure shown in Figure

in conclusion:

• The above two methods recommended for the first annotation-based integration.
• While it is almost less than servlet, but the servlet learning framework for understanding SpringBoot integrate insights into the learning, the better.

4.SpringBoot integrated Filter

4.1. A way

step:

• MyFirstFilter create a class that implements the Filter interface, and marked @WebFilter in the class above.
• 在@SpringBootApplication的主类上加上@ServletComponentScan注解。

MyFirstFilter.java

package com.example.servlet.myfilter;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;

/**
 * 基于@WebFilter注解整合Filter方式一
 */
@WebFilter(filterName = "MyFirstFilter",urlPatterns = "/myFirst")
public class MyFirstFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2) throws IOException, ServletException {
        System.out.println("进入Filter中了.....");
        arg2.doFilter(arg0,arg1);
        System.out.println("离开Filter了.......");
    }

    @Override
    public void destroy() {

    }
}

ServletApplication.java

package com.example.servlet;

import com.example.servlet.myservlet.SecondServlet;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.ServletComponentScan;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
@ServletComponentScan //在springBoot启动时会扫描@WebServlet，并将该类实例化
public class ServletApplication {

   public static void main(String[] args) {
      SpringApplication.run(ServletApplication.class, args);
   }

   /**
    * 整合Servlet的第二种方式，创建ServletRegistrationBean并添加路径
    * @return
    */
   @Bean
   public ServletRegistrationBean getServletRegistrationBean(){
      ServletRegistrationBean bean = new ServletRegistrationBean(new SecondServlet());
      bean.addUrlMappings("/mySecond");
      return bean;
   }
}

4.2.方式二

步骤：

• 创建一个类MySecondFilter实现Filter接口，重写方法。
• 在@SpringBootApplication标识的主类中加@Bean的一个方法，将MySecondFilter对象注入容器中。

MySecondFilter.java

package com.example.servlet.myfilter;

import javax.servlet.*;
import java.io.IOException;

/**
 * 整合Filter的第二种方式
 */
public class MySecondFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2) throws IOException, ServletException {
        System.out.println("进入MySecondFilter了......");
        arg2.doFilter(arg0, arg1);
        System.out.println("离开MySecondFilter了......");
    }

    @Override
    public void destroy() {

    }
}

ServletApplication.java

package com.example.servlet;

import com.example.servlet.myfilter.MySecondFilter;
import com.example.servlet.myservlet.SecondServlet;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.boot.web.servlet.ServletComponentScan;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
//@ServletComponentScan //在springBoot启动时会扫描@WebServlet，并将该类实例化
public class ServletApplication {

   public static void main(String[] args) {
      SpringApplication.run(ServletApplication.class, args);
   }

   /**
    * 整合Filter的第二种方式
    * 注册Filter
    */
   @Bean
   public FilterRegistrationBean getFilterRegistrationBean() {
      FilterRegistrationBean bean = new FilterRegistrationBean(new MySecondFilter());
      // bean.addUrlPatterns(new String[]{"*.do","*.jsp"});//拦截多个时
      bean.addUrlPatterns("/mySecond");
      return bean;
   }
}

然后在浏览器访问localhost:8080/mySecond,就可以看到控制台打印如下

5.SpringBoot整合Listener

5.1.方式一

步骤：

• 创建一个类MyFirstListener实现ServletContextListener接口，重写方法
• 在该类上加上@WebListener注解

package com.example.servlet.mylistener;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

/**
 * springBoot 整合Listener第一种方式
 * 创建一个Servlet上下文的监听器
 * @WebListener 自动注册，相当于在web.xml中添加如下代码
 *
 *<listener>
 * <listener-class>ah.szxy.listener.FirstListener</listener-class>
 *</listener>
 */
@WebListener
public class MyFirstListener implements ServletContextListener {

    @Override
    public void contextDestroyed(ServletContextEvent arg0) {
        // TODO Auto-generated method stub
        System.out.println("MyFirstListener执行销毁了。。。");
    }

    @Override
    public void contextInitialized(ServletContextEvent arg0) {
        // TODO Auto-generated method stub
        System.out.println("MyFirstListener执行初始化了。。。");
    }
}

执行项目会打印如下，因为用了@ServletComponentScan注解，在项目启动的时候就会扫描包中是否含有servlet，若有就初始化。由于FirstServlet是基于注解初始化的，所以在项目启动的时候，就会执行初始化servlet，被Listener监听到

5.1.方式二

步骤：

• 创建一个类MySecondListener实现ServletContextListener接口，重写方法。
• 在@SpringBootApplication标识的主类中加@Bean的一个方法，将MySecondListener对象注入容器中。

package com.example.servlet.mylistener;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

/**
 * 整合Listener的第二种方式
 */
public class MySecondListener implements ServletContextListener {

    @Override
    public void contextDestroyed(ServletContextEvent arg0) {
        // TODO Auto-generated method stub
        System.out.println("MySecondListener执行销毁了。。。");
    }

    @Override
    public void contextInitialized(ServletContextEvent arg0) {
        // TODO Auto-generated method stub
        System.out.println("MySecondListener执行初始化了。。。");
    }

}

package com.example.servlet;

import com.example.servlet.myfilter.MySecondFilter;
import com.example.servlet.mylistener.MySecondListener;
import com.example.servlet.myservlet.SecondServlet;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.boot.web.servlet.ServletComponentScan;
import org.springframework.boot.web.servlet.ServletListenerRegistrationBean;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
@ServletComponentScan //在springBoot启动时会扫描@WebServlet，并将该类实例化
public class ServletApplication {

   public static void main(String[] args) {
      SpringApplication.run(ServletApplication.class, args);
   }

   /**
    * 注册listener
    */
   @Bean
   public ServletListenerRegistrationBean<MySecondListener> getServletListenerRegistrationBean() {
      ServletListenerRegistrationBean<MySecondListener> bean = new ServletListenerRegistrationBean<MySecondListener>(
            new MySecondListener());
      return bean;
   }

}

执行项目，在控制台可以看到输出如下，两个Servlet监听器都执行了

总的项目目录包结构如下：

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