Spring通过Java配置集成Tomcat的方法

添加Tomcat依赖

    org.apache
    apache-tomcat-9.0.36-src
    1.0-SNAPSHOT

首先需要一个tomcat启动类

public class TomcatRun {

	private static final int PORT = 8080;
	private static final String CONTEXT_PATH = "/com/yu";

	public static void main(String[] args) {
		Tomcat tomcat = new Tomcat();
    // 设置监听端口
		tomcat.setPort(PORT);
		tomcat.getHost().setAppBase(".");
    // 这里 Connector 不存在，自动创建一个 Connector，并将 tomcat 的端口赋值给 Connector
		tomcat.getConnector();
		tomcat.addWebapp(CONTEXT_PATH, new File("src/main/webapp").getAbsolutePath());
		try {
			tomcat.start();
		} catch (LifecycleException e) {
			e.printStackTrace();
		}
		tomcat.getServer().await();
	}
}

也可以自己创建一个Connector指定端口

// 手动创建 connector
// Connector connector = new Connector();
// connector.setPort(PORT);
// tomcat.getService().addConnector(connector);

创建Spring配置

public class MyWebApplicationInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
	@Override
	protected Class[] getRootConfigClasses() {
		return new Class[]{RootConfig.class};
	}

	@Override
	protected Class[] getServletConfigClasses() {
		return new Class[]{AppConfig.class};
	}

	@Override
	protected String[] getServletMappings() {
		return new String[]{"/*"};
	}

	@Override
	protected Filter[] getServletFilters() {
		return new Filter[]{
				//
				new CharacterEncodingFilter(StandardCharsets.UTF_8.name())
		};
	}
}

这里就结束了。。。

---

问题来了Tomcat是怎么启动Sping的?

实现了Servlet3.0的容器（例如Tomcat）会扫描classpath*下面的META-INF/services/javax.servlet.ServletContainerInitializer文件，里面指定ServletContainerInitializer的实现，另外还有一个注解HandlesTypes表达对某个类感兴趣，在调用onStartup方法时会将HandlesTypes指定接口的实现类传递进来。

例如：Spring中的ServletContainerInitializer实现类SpringServletContainerInitializer会调用WebApplicationInitializer的onStartup方法，也就是上面定义的MyWebApplicationInitializer父类的onStartup，这里就会相继完成AnnotationConfigWebApplicationContext和DispatcherServlet的初始化

@HandlesTypes(WebApplicationInitializer.class)
public class SpringServletContainerInitializer implements ServletContainerInitializer {

	@Override
	public void onStartup(@Nullable Set> webAppInitializerClasses, ServletContext servletContext)
			throws ServletException {

		List initializers = new LinkedList<>();

		if (webAppInitializerClasses != null) {
			for (Class waiClass : webAppInitializerClasses) {
				// Be defensive: Some servlet containers provide us with invalid classes,
				// no matter what @HandlesTypes says...
				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) {
      // 调用WebApplicationInitializer实现类的onStartup方法
			initializer.onStartup(servletContext);
		}
	}

}

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