springboot系列教程（九）——Servlet、Filter、Listener

方式一

新建servlet

/**
 * @author :小虎
 * @date :2017/12/27
 */

@WebServlet(name = "IndexServlet",urlPatterns = "/hello")
public class IndexServlet extends HttpServlet{
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().print("hello word");
        resp.getWriter().flush();
        resp.getWriter().close();
    }

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

新建IndexFilter

package com.example.demo.filter;

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

/**
 * @author :小虎
 * @date :2017/12/27
 */


@WebFilter(urlPatterns = "/*", filterName = "indexFilter")
public class IndexFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("init IndexFilter");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("doFilter IndexFilter");
        filterChain.doFilter(servletRequest,servletResponse);

    }

    @Override
    public void destroy() {

    }
}

新建IndexListener

package com.example.demo.filter;

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

/**
 * @author :小虎
 * @date :2017/12/27
 */


@WebListener
public class IndexListener implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        System.out.println("IndexListener contextInitialized");
    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {

    }
}

上面配置完了，需要配置一个核心的注解@ServletComponentScan,具体配置项如下，可以配置扫描的路径

方式二

新建IndexFilter1

package com.example.demo.config;

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

/**
 * @author :小虎
 * @date :2017/12/27
 */


public class IndexFilter1 implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("init IndexFilter111");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("doFilter IndexFilter111");
        filterChain.doFilter(servletRequest,servletResponse);

    }

    @Override
    public void destroy() {

    }
}

新建IndexListener1

package com.example.demo.config;

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

/**
 * @author :小虎
 * @date :2017/12/27
 */


public class IndexListener1 implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        System.out.println("IndexListener1111 contextInitialized");
    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {

    }
}

新建IndexServlet1

package com.example.demo.config;

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

/**
 * @author :小虎
 * @date :2017/12/27
 */

public class IndexServlet1 extends HttpServlet{
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().print("hello word11111");
        resp.getWriter().flush();
        resp.getWriter().close();
    }

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

新建WebConfig

package com.example.demo.config;

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 org.springframework.context.annotation.Configuration;

/**
 * @author :小虎
 * @date :2017/12/27
 */

@Configuration
public class WebConfig {
    @Bean
    public ServletRegistrationBean indexServletRegistration() {
        ServletRegistrationBean registration = new ServletRegistrationBean(new IndexServlet1());
        registration.addUrlMappings("/hello1");
        return registration;
    }

    @Bean
    public FilterRegistrationBean indexFilterRegistration() {
        FilterRegistrationBean registration = new FilterRegistrationBean(new IndexFilter1());
        registration.addUrlPatterns("/");
        return registration;
    }
    @Bean
    public ServletListenerRegistrationBean servletListenerRegistrationBean(){
        ServletListenerRegistrationBean servletListenerRegistrationBean = new ServletListenerRegistrationBean();
        servletListenerRegistrationBean.setListener(new IndexListener1());
        return servletListenerRegistrationBean;
    }
}

总结

两种方案在使用上有差别，但是在内部SpringBoot的实现上是无差别的，即使使用的是Servlet3.0注解，也是通过扫描注解
转换成这三种bean的FilterRegistrationBean、ServletRegistrationBean、ServletListenerRegistrationBean

扩展

大家在使用的时候有没有发觉，其实SpringBoot在使用SpringMvc的时候不需要配置DispatcherServlet的，因为已经自动配置了， 但是如果想要加一些初始配置参数如何解决，方案如下：

    @Bean
    public ServletRegistrationBean dispatcherRegistration(DispatcherServlet dispatcherServlet) {
        ServletRegistrationBean registration = new ServletRegistrationBean(dispatcherServlet);
        registration.addUrlMappings("*.do");
        registration.addUrlMappings("*.json");
        return registration;
    }

可以通过注入DispatcherServlet 然后用ServletRegistrationBean包裹一层 动态的加上一些初始参数