SpringMVC源码解读之 HandlerMapping - AbstractDetectingUrlHandlerM

 AbstractDetectingUrlHandlerMapping是通过扫描方式注册Handler,收到请求时由AbstractUrlHandlerMapping的getHandlerInternal进行分发.

共有5个子类,一个抽象类.

与SimpleUrlHandlerMapping类似,通过覆写initApplicationContext,然后调用detectHandlers进行初始化.

detectHandlers通过BeanFactoryUtils扫描应用下的Object,然后预留determineUrlsForHandler给子类根据Handler生成对应的url.

注册使用的registerHandler依然由AbstractUrlHandlerMapping提供.

// AbstractDetectingUrlHandlerMapping
/**
* Calls the {@link #detectHandlers()} method in addition to the
* superclass's initialization.
*/
@Override
public void initApplicationContext() throws ApplicationContextException {
super.initApplicationContext();
detectHandlers();
}

这边一样是调用AbstractHandlerMapping的initApplicationContext初始化拦截器.

主角上场,detectHandlers,扫描Handlers

// AbstractDetectingUrlHandlerMapping
/**
* Register all handlers found in the current ApplicationContext.
* <p>The actual URL determination for a handler is up to the concrete
* {@link #determineUrlsForHandler(String)} implementation. A bean for
* which no such URLs could be determined is simply not considered a handler.
* @throws org.springframework.beans.BeansException if the handler couldn't be registered
* @see #determineUrlsForHandler(String)
*/
protected void detectHandlers() throws BeansException {
if (logger.isDebugEnabled()) {
logger.debug("Looking for URL mappings in application context: " + getApplicationContext());
}
String[] beanNames = (this.detectHandlersInAncestorContexts ?
BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(),Object.class) :
getApplicationContext().getBeanNamesForType(Object.class));
// Take any bean name that we can determine URLs for.
for (String beanName : beanNames) {
String[] urls = determineUrlsForHandler(beanName);
if (!ObjectUtils.isEmpty(urls)) {
// URL paths found: Let's consider it a handler.
registerHandler(urls,beanName);
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Rejected bean name '" + beanName + "': no URL paths identified");
}
}
}
}

这边预留的模板方法定义如下:

/**
* Determine the URLs for the given handler bean.
* @param beanName the name of the candidate bean
* @return the URLs determined for the bean,* or {@code null} or an empty array if none
*/
protected abstract String[] determineUrlsForHandler(String beanName); 

我们再来看看模板方法在BeanNameUrlHandlerMapping和AbstractControllerUrlHandlerMapping中的实现吧.

BeanNameUrlHandlerMapping非常简单,就实现了determineUrlsForHandler.

其中的alias应该是应该就是通过beanName在配置文件中配置的.

// BeanNameUrlHandlerMapping
/**
* Checks name and aliases of the given bean for URLs,starting with "/".
*/
@Override
protected String[] determineUrlsForHandler(String beanName) {
List<String> urls = new ArrayList<String>();
if (beanName.startsWith("/")) {
urls.add(beanName);
}
String[] aliases = getApplicationContext().getAliases(beanName);
for (String alias : aliases) {
if (alias.startsWith("/")) {
urls.add(alias);
}
}
return StringUtils.toStringArray(urls);
}

再来看看AbstractControllerUrlHandlerMapping中的实现

　　isEligibleForMapping判断controller是否被排除在外(通过包package排除或类class排除).

　　buildUrlsForHandler由子类实现具体的url生成规则

　　isControllerType判断是否Controller的子类

　　buildUrlsForHandler预留给子类生产url的模板方法.

// AbstractControllerUrlHandlerMapping
/**
* This implementation delegates to {@link #buildUrlsForHandler},* provided that {@link #isEligibleForMapping} returns {@code true}.
*/
@Override
protected String[] determineUrlsForHandler(String beanName) {
Class beanClass = getApplicationContext().getType(beanName);
if (isEligibleForMapping(beanName,beanClass)) {
return buildUrlsForHandler(beanName,beanClass);
}
else {
return null;
}
} 
// AbstractControllerUrlHandlerMapping
/**判断controller是否被排除在外(通过包package排除或类class排除).
* Determine whether the specified controller is excluded from this mapping.
* @param beanName the name of the controller bean
* @param beanClass the concrete class of the controller bean
* @return whether the specified class is excluded
* @see #setExcludedPackages
* @see #setExcludedClasses
*/
protected boolean isEligibleForMapping(String beanName,Class beanClass) {
if (beanClass == null) {
if (logger.isDebugEnabled()) {
logger.debug("Excluding controller bean '" + beanName + "' from class name mapping " +
"because its bean type could not be determined");
}
return false;
}
if (this.excludedClasses.contains(beanClass)) {
if (logger.isDebugEnabled()) {
logger.debug("Excluding controller bean '" + beanName + "' from class name mapping " +
"because its bean class is explicitly excluded: " + beanClass.getName());
}
return false;
}
String beanClassName = beanClass.getName();
for (String packageName : this.excludedPackages) {
if (beanClassName.startsWith(packageName)) {
if (logger.isDebugEnabled()) {
logger.debug("Excluding controller bean '" + beanName + "' from class name mapping " +
"because its bean class is defined in an excluded package: " + beanClass.getName());
}
return false;
}
}
return isControllerType(beanClass);
} 
// AbstractControllerUrlHandlerMapping
/**
* Determine whether the given bean class indicates a controller type
* that is supported by this mapping strategy.
* @param beanClass the class to introspect
*/
protected boolean isControllerType(Class beanClass) {
return this.predicate.isControllerType(beanClass);
} 
// ControllerTypePredicate

这边提供2个api,分别判断是Controller的子类还是MultiActionController的子类.

/**
* Internal helper class that identifies controller types.
*
* @author Juergen Hoeller
* @since ..
*/
class ControllerTypePredicate {
public boolean isControllerType(Class beanClass) {
return Controller.class.isAssignableFrom(beanClass);
}
public boolean isMultiActionControllerType(Class beanClass) {
return MultiActionController.class.isAssignableFrom(beanClass);
}
}

预留生成url的模板方法

// AbstractControllerUrlHandlerMapping
/**
* Abstract template method to be implemented by subclasses.
* @param beanName the name of the bean
* @param beanClass the type of the bean
* @return the URLs determined for the bean
*/
protected abstract String[] buildUrlsForHandler(String beanName,Class beanClass); 

再来看看AbstractControllerUrlHandlerMapping的2个实现ControllerBeanNameUrlHandlerMapping和ControllerClassNameUrlHandlerMapping.

其实这两个,很简单,一个是根据beanName来生产url,一个是根据className来生产url.

// ControllerBeanNameUrlHandlerMapping
@Override
protected String[] buildUrlsForHandler(String beanName,Class beanClass) {
List<String> urls = new ArrayList<String>();
urls.add(generatePathMapping(beanName));
String[] aliases = getApplicationContext().getAliases(beanName);// 也获取配置的别名
for (String alias : aliases) {
urls.add(generatePathMapping(alias));
}
return StringUtils.toStringArray(urls);
} 
// ControllerBeanNameUrlHandlerMapping
/**对path添加前后缀,还有/
* Prepends a '/' if required and appends the URL suffix to the name.
*/
protected String generatePathMapping(String beanName) {
String name = (beanName.startsWith("/") ? beanName : "/" + beanName);
StringBuilder path = new StringBuilder();
if (!name.startsWith(this.urlPrefix)) {
path.append(this.urlPrefix);
}
path.append(name);
if (!name.endsWith(this.urlSuffix)) {
path.append(this.urlSuffix);
}
return path.toString();
} 
// ControllerClassNameUrlHandlerMapping

直接委托给generatePathMappings实现

@Override
protected String[] buildUrlsForHandler(String beanName,Class beanClass) {
return generatePathMappings(beanClass);
} 
// ControllerClassNameUrlHandlerMapping

　　通过buildPathPrefix获取path的前缀

　　通过ClassUtils获取className,如BookController(不带包名),同时使用cglib代理的问题一并解决

　　根据大小写是否敏感,转换className(默认caseSensitive = false;)

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