Spring5.1源码解析（二）spring整合springmvc去配置化的原理

springmvc与spring整合去除xml方式

我们用xml方式整合spring与springMVC，通常用xml方式进行配置

<web-app>

    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>

    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:applicationContext.xml</param-value>
    </context-param>

    <servlet>
        <servlet-name>app</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value></param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>app</servlet-name>
        <url-pattern>/app/*</url-pattern>
    </servlet-mapping>

</web-app>

上述xml主要完成的事情

• 初始化spring的上下文
• 注册一个servlet给容器，并且这个servlet会拦截所有请求

ContextLoaderListener的作用就是启动web容器时，自动装配ApplicationContext的配置信息，因为它实现了ServletContextListener这个接口，容器启动时会执行ServletContextListener的实现方法

public class ContextLoaderListener extends ContextLoader implements ServletContextListener {

	/**
	 * Create a new {@code ContextLoaderListener} that will create a web application
	 * context based on the "contextClass" and "contextConfigLocation" servlet
	 * context-params. See {@link ContextLoader} superclass documentation for details on
	 * default values for each.
	 * <p>This constructor is typically used when declaring {@code ContextLoaderListener}
	 * as a {@code <listener>} within {@code web.xml}, where a no-arg constructor is
	 * required.
	 * <p>The created application context will be registered into the ServletContext under
	 * the attribute name {@link WebApplicationContext#ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE}
	 * and the Spring application context will be closed when the {@link #contextDestroyed}
	 * lifecycle method is invoked on this listener.
	 * @see ContextLoader
	 * @see #ContextLoaderListener(WebApplicationContext)
	 * @see #contextInitialized(ServletContextEvent)
	 * @see #contextDestroyed(ServletContextEvent)
	 */
	public ContextLoaderListener() {
	}

	/**
	 * Create a new {@code ContextLoaderListener} with the given application context. This
	 * constructor is useful in Servlet 3.0+ environments where instance-based
	 * registration of listeners is possible through the {@link javax.servlet.ServletContext#addListener}
	 * API.
	 * <p>The context may or may not yet be {@linkplain
	 * org.springframework.context.ConfigurableApplicationContext#refresh() refreshed}. If it
	 * (a) is an implementation of {@link ConfigurableWebApplicationContext} and
	 * (b) has <strong>not</strong> already been refreshed (the recommended approach),
	 * then the following will occur:
	 * <ul>
	 * <li>If the given context has not already been assigned an {@linkplain
	 * org.springframework.context.ConfigurableApplicationContext#setId id}, one will be assigned to it</li>
	 * <li>{@code ServletContext} and {@code ServletConfig} objects will be delegated to
	 * the application context</li>
	 * <li>{@link #customizeContext} will be called</li>
	 * <li>Any {@link org.springframework.context.ApplicationContextInitializer ApplicationContextInitializer org.springframework.context.ApplicationContextInitializer ApplicationContextInitializers}
	 * specified through the "contextInitializerClasses" init-param will be applied.</li>
	 * <li>{@link org.springframework.context.ConfigurableApplicationContext#refresh refresh()} will be called</li>
	 * </ul>
	 * If the context has already been refreshed or does not implement
	 * {@code ConfigurableWebApplicationContext}, none of the above will occur under the
	 * assumption that the user has performed these actions (or not) per his or her
	 * specific needs.
	 * <p>See {@link org.springframework.web.WebApplicationInitializer} for usage examples.
	 * <p>In any case, the given application context will be registered into the
	 * ServletContext under the attribute name {@link
	 * WebApplicationContext#ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE} and the Spring
	 * application context will be closed when the {@link #contextDestroyed} lifecycle
	 * method is invoked on this listener.
	 * @param context the application context to manage
	 * @see #contextInitialized(ServletContextEvent)
	 * @see #contextDestroyed(ServletContextEvent)
	 */
	public ContextLoaderListener(WebApplicationContext context) {
		super(context);
	}


	/**
	 * Initialize the root web application context.
	 */
	@Override
	public void contextInitialized(ServletContextEvent event) {
		initWebApplicationContext(event.getServletContext());
	}


	/**
	 * Close the root web application context.
	 */
	@Override
	public void contextDestroyed(ServletContextEvent event) {
		closeWebApplicationContext(event.getServletContext());
		ContextCleanupListener.cleanupAttributes(event.getServletContext());
	}

}

applicationContext.xml

<context:component-scan base-package="com.hzau">

• 扫描业务类，service，dao

spring-mvc.xml

<!-- 配置自动扫描包 -->
<context:component-scan base-package="com.ssh" />

• 扫描controller

spring5之后上述配置可用

public class MyWebApplicationInitializer implements WebApplicationInitializer {

    @Override
    public void onStartup(ServletContext servletCxt) {

        // Load Spring web application configuration
        AnnotationConfigWebApplicationContext ac = new 
            AnnotationConfigWebApplicationContext();
        ac.register(AppConfig.class);
        ac.refresh();

        // Create and register the DispatcherServlet
        DispatcherServlet servlet = new DispatcherServlet(ac);
        ServletRegistration.Dynamic registration = servletCxt.addServlet("app", servlet);
        registration.setLoadOnStartup(1);
        registration.addMapping("/app/*");
    }
}

//初始化spring的上下文
AnnotationConfigWebApplicationContext ac = new AnnotationConfigWebApplicationContext();
// 配置扫描包
ac.register(AppConfig.class);
//注册一个servlet给容器
DispatcherServlet servlet = new DispatcherServlet(ac);
ServletRegistration.Dynamic registration = servletCxt.addServlet("app", servlet);
//指定处理的请求
 registration.addMapping("/app/*");

Servlet容器启动会扫描当前应用里面每一个jar包的ServletContainerInitializer实现。

实现类必须绑定在META-INF/services/javax.servlet.ServletContainerInitializer的文件中，文件的内容就是实现类的全类名

如果这个类实现了ServletContainerInitializer这个接口，servlet容器会调用其onStartup方法,如果这个类有注解

@HandlesTypes(WebApplicationInitializer.class)

会把所有这个类list当做参数传进来

在spring-web中

\META-INF\services\javax.servlet.ServletContainerInitializer

ServletContainerInitializer文件的内容为

javax.servlet.ServletContainerInitializer

package org.springframework.web;

import java.lang.reflect.Modifier;
import java.util.LinkedList;
import java.util.List;
import java.util.ServiceLoader;
import java.util.Set;

import javax.servlet.ServletContainerInitializer;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.HandlesTypes;

import org.springframework.core.annotation.AnnotationAwareOrderComparator;
import org.springframework.lang.Nullable;
import org.springframework.util.ReflectionUtils;


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

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

		List<WebApplicationInitializer> 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) {
			initializer.onStartup(servletContext);
		}
	}

}

spring最后会执行所有的WebApplicationInitializer.onStartup方法

spring和springmvc去配置化的整合方式。
https://blog.csdn.net/hzau_itdog/article/details/81905685