SpringBoot整合SpringMVC, SpringBoot扩展SpringMVC

SpringBoot整合SpringMVC

把SpringMVC里面的一些内容整合到SpringBoot当中

中央转发器（DispatcherServlet）

中央转发器DispatcherServlet被springboot自动接管，不再需要我们在web.xml中配置，我们现在的项目也不是web项目，也不存在web.xml
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration

DispatcherServletAutoConfiguration类主要包含了两个内部类，分别是
1、DispatcherServletConfiguration
2、DispatcherServletRegistrationConfiguration
顾名思义，前者是配置DispatcherServlet，后者是配置DispatcherServlet的注册类。什么是注册类？我们知道Servlet实例是要被添加（注册）到如tomcat这样的ServletContext里的，这样才能够提供请求服务。所以，DispatcherServletRegistrationConfiguration将生成一个Bean，负责将DispatcherServlet给注册到ServletContext中。

package org.springframework.boot.autoconfigure.web.servlet;

@AutoConfigureOrder(Integer.MIN_VALUE)
@Configuration(
    proxyBeanMethods = false
)
@ConditionalOnWebApplication(
    type = Type.SERVLET
)
@ConditionalOnClass({
   DispatcherServlet.class})
@AutoConfigureAfter({
   ServletWebServerFactoryAutoConfiguration.class})
public class DispatcherServletAutoConfiguration {
   
    public static final String DEFAULT_DISPATCHER_SERVLET_BEAN_NAME = "dispatcherServlet";
    public static final String DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME = "dispatcherServletRegistration";

    public DispatcherServletAutoConfiguration() {
   
    }

    @Order(2147483637)
    private static class DispatcherServletRegistrationCondition extends SpringBootCondition {
   
        private DispatcherServletRegistrationCondition() {
   
        }

        public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) {
   
            ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
            ConditionOutcome outcome = this.checkDefaultDispatcherName(beanFactory);
            return !outcome.isMatch() ? outcome : this.checkServletRegistration(beanFactory);
        }

        private ConditionOutcome checkDefaultDispatcherName(ConfigurableListableBeanFactory beanFactory) {
   
            boolean containsDispatcherBean = beanFactory.containsBean("dispatcherServlet");
            if (!containsDispatcherBean) {
   
                return ConditionOutcome.match();
            } else {
   
                List<String> servlets = Arrays.asList(beanFactory.getBeanNamesForType(DispatcherServlet.class, false, false));
                return !servlets.contains("dispatcherServlet") ? ConditionOutcome.noMatch(this.startMessage().found("non dispatcher servlet").items(new Object[]{
   "dispatcherServlet"})) : ConditionOutcome.match();
            }
        }

        private ConditionOutcome checkServletRegistration(ConfigurableListableBeanFactory beanFactory) {
   
            ConditionMessage.Builder message = this.startMessage();
            List<String> registrations = Arrays.asList(beanFactory.getBeanNamesForType(ServletRegistrationBean.class, false, false));
            boolean containsDispatcherRegistrationBean = beanFactory.containsBean("dispatcherServletRegistration");
            if (registrations.isEmpty()) {
   
                return containsDispatcherRegistrationBean ? ConditionOutcome.noMatch(message.found("non servlet registration bean").items(new Object[]{
   "dispatcherServletRegistration"})) : ConditionOutcome.match(message.didNotFind("servlet registration bean").atAll());
            } else if (registrations.contains("dispatcherServletRegistration")) {
   
                return ConditionOutcome.noMatch(message.found("servlet registration bean").items(new Object[]{
   "dispatcherServletRegistration"}));
            } else {
   
                return containsDispatcherRegistrationBean