简单总结：
- Servlet3.0 onStartup()中初始化ApplictaionContext去web.xml
- 全注解，@Configuration去spring配置文件
- yaml 配置替换属性文件配置
1. 全注解: 去ApplicationContext.xml
使用configuration注解替换替换applicationContext.xml中的<beans>标签
@Configuration //注解配置 - 相当于xml的<beans>标签
@ComponentScan({ "com.cengel.cglab" })//启用组件扫描 - 不写将默认仅扫描此类所在包及其子包
@Import({ HibernateConfig.class, RedisConfig.class, SpringRmiConfig.class })
public class RootConfig {
@Bean
public Student student(){
return new Student();
}
}
2. 内置web容器
SpringBoot除了高度集成封装了Spring一系列框架之外，还封装了web容器.
SpringBoot支持嵌入tomcat jetty undertow三种web容器,查看EmbeddedServletContainerAutoConfiguration 类源码可知.
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
@ConditionalOnWebApplication
@Import(BeanPostProcessorsRegistrar.class)
public class EmbeddedServletContainerAutoConfiguration {
@Configuration
@ConditionalOnClass({ Servlet.class, Tomcat.class })
@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
public static class EmbeddedTomcat {
@Bean
public TomcatEmbeddedServletContainerFactory tomcatEmbeddedServletContainerFactory() {
return new TomcatEmbeddedServletContainerFactory();
}
}
@Configuration
@ConditionalOnClass({ Servlet.class, Server.class, Loader.class,
WebAppContext.class })
@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
public static class EmbeddedJetty {
@Bean
public JettyEmbeddedServletContainerFactory jettyEmbeddedServletContainerFactory() {
return new JettyEmbeddedServletContainerFactory();
}
}
@Configuration
@ConditionalOnClass({ Servlet.class, Undertow.class, SslClientAuthMode.class })
@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
public static class EmbeddedUndertow {
@Bean
public UndertowEmbeddedServletContainerFactory undertowEmbeddedServletContainerFactory() {
return new UndertowEmbeddedServletContainerFactory();
}
}
// .. . 其他省略
}
在spring-boot-starter-web的pom中可以看到,springweb application默认使用的是tomcat容器.
3.Servlet3.0去web.xml
在Servlet3.0环境中,Web容器会在类路径(META-INF/services)目录下查找javax.servlet.ServletContainerInitilalizer文件(文件配置其实现类)，web容器加载时，会执行该接口实现类的onStart方法
1. 为什么在web项目代码中继承AbstractAnnotationConfigDispatcherServletInitializer该类，不需要配置web.xml,spring环境就能运行？
1.实现javax.servlet.ServletContainerInitializer
@HandlesTypes({WebApplicationInitializer.class})
public class SpringServletContainerInitializer implements ServletContainerInitializer {
public SpringServletContainerInitializer() {
}
public void onStartup(Set<Class<?>> webAppInitializerClasses, ServletContext servletContext) throws ServletException {
//todo tomcat容器加载时，会执行，spring容器初始化在这里执行
//存放spring-web项目的WebApplicationInitializer接口的所有实现类
List<WebApplicationInitializer> initializers = new LinkedList<>();
if (webAppInitializerClasses != null) {
for (Class<?> waiClass : webAppInitializerClasses) {
// 查找spring-web项目的WebApplicationInitializer接口的所有实现类
if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
try {
initializers.add((WebApplicationInitializer)
ReflectionUtils.accessibleConstructor(waiClass).newInstance());
}
catch (Throwable ex) {
throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);
}
}
}
}
if (initializers.isEmpty()) {
servletContext.log("No Spring WebApplicationInitializer types detected on classpath");
return;
}
servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath");
AnnotationAwareOrderComparator.sort(initializers);
for (WebApplicationInitializer initializer : initializers) {
//逐一执行这些实现类的onStartUp方法
//一般Spring的ApplicationContext Configure Servlet Filter等都包含在这些实现类的中,调用onStart方法时,执行这些初始化
initializer.onStartup(servletContext);
}
}
}
-
在Spring-Web的jar包META-INF下配置该接口
配置webServletContainerInitailizer实现类 - AbstractAnnotationConfigDispatcherServletInitializer 这个抽象类继承了WebApplicationInitializer
也就是说,此类的onStart方法会在web容器加载时被执行
而逐一向上查看此类的父类,onStart方法包含了Servlet Config Filter等的初始化
public abstract class AbstractAnnotationConfigDispatcherServletInitializer extends AbstractDispatcherServletInitializer {
public AbstractAnnotationConfigDispatcherServletInitializer() {
}
protected WebApplicationContext createRootApplicationContext() {
Class<?>[] configClasses = this.getRootConfigClasses();
if (!ObjectUtils.isEmpty(configClasses)) {
AnnotationConfigWebApplicationContext rootAppContext = new AnnotationConfigWebApplicationContext();
rootAppContext.register(configClasses);
return rootAppContext;
} else {
return null;
}
}
protected WebApplicationContext createServletApplicationContext() {
AnnotationConfigWebApplicationContext servletAppContext = new AnnotationConfigWebApplicationContext();
Class<?>[] configClasses = this.getServletConfigClasses();
if (!ObjectUtils.isEmpty(configClasses)) {
servletAppContext.register(configClasses);
}
return servletAppContext;
}
//基于注解的bean配置类
protected abstract Class<?>[] getRootConfigClasses();
//基于注解的servlet配置类(webmvc viewResoler)
protected abstract Class<?>[] getServletConfigClasses();
}
就这样,springbootApplication执行main方法时启动tomcat容器,tomcat容器初始化加载时,会执行ServletContainerInitializer的onStartup方法,Spring通过对该接口的实现,完成spring上下文,配置,servlet等的初始化装载.
