Spring Boot - 使用Servlet，Filter和L

在Spring Boot应用中，Servlet，Filter和Listener可以通过两种方式注册：一是使用Spring的@Bean，二是使用内置容器通过扫描@WebServlet，@WebFilter和@WebListener注解类。

本文介绍如何使用@Bean的方式注册Servlet，Filter和Listener。

可以使用ServletRegistrationBean，FilterRegistrationBean和ServletListenerRegistrationBean分别注册Servlet，Filter和Listener。

依赖jar包

编辑pom.xml文件，添加spring-boot-starter-web依赖。

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.boraji.tutorial.springboot</groupId>
  <artifactId>spring-boot-servlet-filter-example</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <name>Spring Boot - Servlet, Filter and  Listener example</name>
  <packaging>war</packaging>
  <properties>
    <java.version>1.8</java.version>
  </properties>
  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>1.5.9.RELEASE</version>
  </parent>
  <dependencies>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
  </dependencies>
  <build>
    <plugins>
      <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>
      </plugin>
    </plugins>
  </build>
</project>

创建Servlet，Filter和Listener

Servlet

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class MyServlet extends HttpServlet {

  private static final long serialVersionUID = 1L;

  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp)
      throws ServletException, IOException {
    System.out.println("MyServlet's doGet() method is invoked.");
    doAction(req, resp);
  }
  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp)
      throws ServletException, IOException {
    System.out.println("MyServlet's doPost() method is invoked.");
    doAction(req, resp);
  }
  
  private void doAction(HttpServletRequest req, HttpServletResponse resp)
      throws ServletException, IOException {
    String name = req.getParameter("name");
    resp.setContentType("text/plain");
    resp.getWriter().write("Hello " + name + "!");
  }
  
}

Filter

import java.io.IOException;
import java.util.Enumeration;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class MyFilter implements Filter {

  @Override
  public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
      throws IOException, ServletException {
    
    System.out.println("MyFilter doFilter() is invoked.");
    Enumeration<String> params = req.getParameterNames();
    while (params.hasMoreElements()) {
      String param=params.nextElement();
      System.out.println("Parameter:"+param+"\tValue:"+req.getParameter(param));
    }
    chain.doFilter(req, res);
  }

  @Override
  public void init(FilterConfig config) throws ServletException {
    
  }

  @Override
  public void destroy() {

  }

}

Listener

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

public class MyServletContextListener implements ServletContextListener {
  @Override
  public void contextInitialized(ServletContextEvent e) {
    System.out.println("MyServletContextListener Context Initialized");
  }

  @Override
  public void contextDestroyed(ServletContextEvent e) {
    System.out.println("MyServletContextListener Context Destroyed");
  }

}

注册Servlet，Filter和Listener

如上所述，可以使用ServletRegistrationBean，FilterRegistrationBean和ServletListenerRegistrationBean注册Servlet，Filter和Listener。

创建SpringBootApp类并如下声明ServletRegistrationBean，FilterRegistrationBean和ServletListenerRegistrationBean的bean方法。

import javax.servlet.ServletContextListener;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.boot.web.servlet.ServletListenerRegistrationBean;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;

import com.boraji.tutorial.springboot.filter.MyFilter;
import com.boraji.tutorial.springboot.listener.MyServletContextListener;
import com.boraji.tutorial.springboot.servlet.MyServlet;

@SpringBootApplication
public class SpringBootApp {

  // Register Servlet
  @Bean
  public ServletRegistrationBean servletRegistrationBean() {
    ServletRegistrationBean bean = new ServletRegistrationBean(
        new MyServlet(), "/myServlet");
    return bean;
  }

  // Register Filter
  @Bean
  public FilterRegistrationBean filterRegistrationBean() {
    FilterRegistrationBean bean = new FilterRegistrationBean(new MyFilter());
    // Mapping filter to a Servlet
    bean.addServletRegistrationBeans(new ServletRegistrationBean[] {
          servletRegistrationBean() 
       });
    return bean;
  }

  // Register ServletContextListener
  @Bean
  public ServletListenerRegistrationBean<ServletContextListener> listenerRegistrationBean() {
    ServletListenerRegistrationBean<ServletContextListener> bean = 
        new ServletListenerRegistrationBean<>();
    bean.setListener(new MyServletContextListener());
    return bean;

  }

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

}

运行

运行SpringBootApp.java类。可以通过Run -> Run as -> Java Application或者使用mvn spring-boot：run命令运行spring boot应用。

启动成功后，在浏览器输入http://localhost:8080/myServlet?name=Sunil%20Singh%20Bora。

浏览器显示
控制台输出如下：
控制台输出