SpringMvc组件初始化

SpringMVC 9大组件初始化

由上面的断点流程，可以看出来其实是在spring容器初始化完成的最后一步，通过发送event事件

@Override
	public void publishEvent(ApplicationEvent event) {
		Assert.notNull(event, "Event must not be null");
		if (logger.isTraceEnabled()) {
			logger.trace("Publishing event in " + getDisplayName() + ": " + event);
		}
		getApplicationEventMulticaster().multicastEvent(event);
		if (this.parent != null) {
			this.parent.publishEvent(event);
		}
	}

然后进入下面的SimpleApplicationEventMulticaster的类中，去遍历所有的监听类

@Override
	@SuppressWarnings({ "unchecked", "rawtypes" })
	public void multicastEvent(final ApplicationEvent event) {
		for (final ApplicationListener listener : getApplicationListeners(event)) {
			Executor executor = getTaskExecutor();
			if (executor != null) {
				executor.execute(new Runnable() {
					@Override
					public void run() {
						listener.onApplicationEvent(event);
					}
				});
			}
			else {
				listener.onApplicationEvent(event);
			}
		}
	}

onApplicationEvent这个方法一直被重写，最后执行的是FrameworkServlet的onApplicationEvent方法，在去调用DispatcherServlet的onRefresh方法。

@Override
	protected void onRefresh(ApplicationContext context) {
		initStrategies(context);
	}

	/**
	 * Initialize the strategy objects that this servlet uses.
	 * <p>May be overridden in subclasses in order to initialize further strategy objects.
	 */
	protected void initStrategies(ApplicationContext context) {
		initMultipartResolver(context);
		initLocaleResolver(context);
		initThemeResolver(context);
		initHandlerMappings(context);
		initHandlerAdapters(context);
		initHandlerExceptionResolvers(context);
		initRequestToViewNameTranslator(context);
		initViewResolvers(context);
		initFlashMapManager(context);
	}

再去初始化9大组件，这里就简单的介绍其中的一个组件的初始化过程。

private void initHandlerMappings(ApplicationContext context) {
		this.handlerMappings = null;

		if (this.detectAllHandlerMappings) {
			// Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
			Map<String, HandlerMapping> matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.handlerMappings = new ArrayList<HandlerMapping>(matchingBeans.values());
				// We keep HandlerMappings in sorted order.
				OrderComparator.sort(this.handlerMappings);
			}
		}
		else {
			try {
				HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
				this.handlerMappings = Collections.singletonList(hm);
			}
			catch (NoSuchBeanDefinitionException ex) {
				// Ignore, we'll add a default HandlerMapping later.
			}
		}

		// Ensure we have at least one HandlerMapping, by registering
		// a default HandlerMapping if no other mappings are found.
		if (this.handlerMappings == null) {
			this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
			if (logger.isDebugEnabled()) {
				logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");
			}
		}
	}

其中：detectAllHandlerMappings这个值为true，也可以在配置文件里面设置false，当true的时候，值为下面。

其中：this.handlerMappings == null，当走进这个方法的时候，回去读取配置文件中默认的处理器映射器。

protected <T> List<T> getDefaultStrategies(ApplicationContext context, Class<T> strategyInterface) {
		String key = strategyInterface.getName();
		String value = defaultStrategies.getProperty(key);
		if (value != null) {
			String[] classNames = StringUtils.commaDelimitedListToStringArray(value);
			List<T> strategies = new ArrayList<T>(classNames.length);
			for (String className : classNames) {
				try {
					Class<?> clazz = ClassUtils.forName(className, DispatcherServlet.class.getClassLoader());
					Object strategy = createDefaultStrategy(context, clazz);
					strategies.add((T) strategy);
				}
				catch (ClassNotFoundException ex) {
					throw new BeanInitializationException(
							"Could not find DispatcherServlet's default strategy class [" + className +
									"] for interface [" + key + "]", ex);
				}
				catch (LinkageError err) {
					throw new BeanInitializationException(
							"Error loading DispatcherServlet's default strategy class [" + className +
									"] for interface [" + key + "]: problem with class file or dependent class", err);
				}
			}
			return strategies;
		}
		else {
			return new LinkedList<T>();
		}
	}

其中

	private static final Properties defaultStrategies;

	static {
		// Load default strategy implementations from properties file.
		// This is currently strictly internal and not meant to be customized
		// by application developers.
		try {
			ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
			defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
		}
		catch (IOException ex) {
			throw new IllegalStateException("Could not load 'DispatcherServlet.properties': " + ex.getMessage());
		}
	}

回去加载配置文件里面的默认值。

先简单的记录一下，等后面在结合SpringMVC源码的书，在进行补充。

个人感觉这个工具类还是挺有用的，其中springboot的自动配置原理也有用到，下面就简单测试一下。

/**
 * @author WGR
 * @create 2021/4/14 -- 22:27
 */
public class Test {

    @SneakyThrows
    public static void main(String[] args) {
        ClassPathResource resource = new ClassPathResource("test.properties", Test.class);
        Properties properties = PropertiesLoaderUtils.loadProperties(resource);
        System.out.println(properties.getProperty("org.springframework.web.servlet.HandlerAdapter"));

    }
}
org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
	org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
	org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter

我这里是idea，跑起来的时候，直接报错，然后百度了一下，要在pom.xml配置.因为IDEA有个配置项，默认只把.class的文件放到编译目录中，也就是target目录。

 <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.*</include>
                </includes>
                <excludes>
                    <exclude>**/*.java</exclude>
                </excludes>
            </resource>
        </resources>