1. Spring boot默认使用Tomcat作为嵌入式的servlet容器，只要引入spring-boot-starter-web依赖，就会默认用Tomcat作为servlet容器。
2. Spring boot默认以jar包的方式启动嵌入式的servlet容器，来启动spring boot的web应用，没有web.xml
3. 以往要注册servlet组件都是在web.xml文件中配置，现在没有了web.xml，该如何注册。
4. spring boot提供ServletRegistrationBean，FilterRegistrationBean以及ServletListenerRegistrationBean类，供我们向嵌入式的servlet容器中注册Servlet、Filter、Listener组件，获取完全控制。
🆗回顾一下，以往的web应用程序中，是如何来向servlet容器中注册servlet组件
自定义servlet组件
import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.HttpServlet;import java.io.IOException;import java.io.PrintWriter;public class MyServlet extends HttpServlet {@Overridepublic void init() throws ServletException {System.out.println("配置自动加载后会自动执行init()方法");}@Overridepublic void service(ServletRequest request, ServletResponse response) throws ServletException, IOException {System.out.println("正在执行服务...");response.setCharacterEncoding("UTF-8");response.setContentType("text/html;charset=utf-8");PrintWriter out = response.getWriter();out.println("<a href=''>百度一下</a>");}}
在web.xml中注册servlet，并指定映射路径
<?xml version="1.0" encoding="UTF-8"?><web-app xmlns="/xml/ns/javaee"xmlns:xsi="/2001/XMLSchema-instance"xsi:schemaLocation="/xml/ns/javaee /xml/ns/javaee/web-app_4_0.xsd"version="4.0"><!--注册MyServlet--><servlet><servlet-name>myServlet</servlet-name><servlet-class>com.cd.servlet.MyServlet</servlet-class></servlet><!--指定MyServlet的映射路径--><servlet-mapping><servlet-name>myServlet</servlet-name><url-pattern>/baidu</url-pattern></servlet-mapping></web-app>
效果
/cd是项目的根路径(应用上下文路径)，/baidu是MyServlet这个servlet组件的映射路径
🆗接下来看看，spring boot是如何来向servlet容器中注册servlet组件
自定义servlet组件
import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.HttpServlet;import java.io.IOException;import java.io.PrintWriter;public class MyServlet extends HttpServlet {@Overridepublic void init() throws ServletException {System.out.println("配置自动加载后会自动执行init()方法");}@Overridepublic void service(ServletRequest request, ServletResponse response) throws ServletException, IOException {System.out.println("正在执行服务...");response.setCharacterEncoding("UTF-8");response.setContentType("text/html;charset=utf-8");PrintWriter out = response.getWriter();out.println("<a href=''>百度一下</a>");}}
通过ServletRegistrationBean类向servlet容器注册servlet，并指定映射路径
import org.springframework.boot.web.servlet.ServletRegistrationBean;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;@Configurationpublic class MyServletConfig {//注册servlet@Bean(name = "myServlet")public ServletRegistrationBean servletRegistrationBean(){//注册MyServlet类到servlet容器中，并指定映射路径ServletRegistrationBean servletRegistrationBean = new ServletRegistrationBean(new MyServlet(),"/baidu");return servletRegistrationBean;}}
效果
/cd是项目的根路径(应用上下文路径)，/baidu是MyServlet这个servlet组件的映射路径
Servlet容器有三大组件servlet、filter、listener。前面我们讲了spring boot注册servlet组件的方式，下面顺便介绍filter组件的注册
自定义一个编码过滤器
import javax.servlet.*;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;public class MyFilter implements Filter {@Overridepublic void init(FilterConfig filterConfig) throws ServletException {System.out.println("过滤器初始化. . .");}@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {HttpServletRequest request = (HttpServletRequest) servletRequest;HttpServletResponse response = (HttpServletResponse) servletResponse;request.setCharacterEncoding("utf-8");response.setCharacterEncoding("utf-8");//放行，继续执行过滤器链的下一个组件(下一个过滤器)filterChain.doFilter(request,response);}}
通过spring boot提供的FilterRegistrationBean类，向servlet容器注册filter组件
import org.springframework.boot.web.servlet.FilterRegistrationBean;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;import java.util.Arrays;@Configurationpublic class MyFilterConfig {//注册Filter@Bean(name = "myFilter")public FilterRegistrationBean filterRegistrationBean() {FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();//指定要注册的FilterfilterRegistrationBean.setFilter(new MyFilter());//指定映射路径filterRegistrationBean.setUrlPatterns(Arrays.asList("/*"));return filterRegistrationBean;}}
