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spring MVC源码探究之AbstractHandlerMethodMapping
AbstractHandlerMethodMapping 是什么
解释是这样的。
/**
- Abstract base class for {@link HandlerMapping} implementations that define
- a mapping between a request and a {@link HandlerMethod}.
* For each registered handler method, a unique mapping is maintained with
- subclasses defining the details of the mapping type {@code
}. - @param
The mapping for a {@link HandlerMethod} containing the conditions - needed to match the handler method to incoming request.
*/
public abstract class AbstractHandlerMethodMapping
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我的了解为AbstractHandlerMethodMapping为每个注册的handler method，关于每个子类映射类型都维护着其独一的一个映射，就是维护handler method 和URL的关系。主要用于@Controller,@RequestMapping 等注解
AbstractHandlerMethodMapping 完成了InitializingBean接口，InitializingBean是在程序启动的时分执行其独一的afterPropertiesSet()办法，那我们就先看一下启动时分的要做哪些操作。
initHandlerMethods()
/**
在初始化的时分发现 handler methods
* Detects handler methods at initialization.
*/
@Override
public void afterPropertiesSet() {
initHandlerMethods();
}复制代码
在项目启动时会执行initHandlerMethods办法，它的主要功用是扫描应用上下文，发现并注册handler methods。
/**
- Scan beans in the ApplicationContext, detect and register handler methods.
- @see #isHandler(Class)
- @see #getMappingForMethod(Method, Class)
- @see #handlerMethodsInitialized(Map)
*/
protected void initHandlerMethods() {
if (logger.isDebugEnabled()) {
logger.debug("Looking for request mappings in application context: " + getApplicationContext());
}
// 获取IOC容器中一切bean
String[] beanNames = (this.detectHandlerMethodsInAncestorContexts ?
BeanFactoryUtils.beanNamesForTypeIncludingAncestors(obtainApplicationContext(), Object.class) :
obtainApplicationContext().getBeanNamesForType(Object.class));
for (String beanName : beanNames) {
if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
Class beanType = null;
try {
beanType = obtainApplicationContext().getType(beanName);
}
catch (Throwable ex) {
// An unresolvable bean type, probably from a lazy bean - let's ignore it.
if (logger.isDebugEnabled()) {
logger.debug("Could not resolve target class for bean with name '" + beanName + "'", ex);
}
}
// 判别bean 能否有Controller 注解或者RequestMapping 注解
if (beanType != null && isHandler(beanType)) {
detectHandlerMethods(beanName);
}
}
}
handlerMethodsInitialized(getHandlerMethods());}
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isHandler()
AbstractHandlerMethodMapping#isHandler()
RequestMappingHandlerMapping 是目前为止AbstractHandlerMethodMapping的子类中独一完成了isHandler()办法的子类，看下完成
protected boolean isHandler(Class beanType) {
return (AnnotatedElementUtils.hasAnnotation(beanType, Controller.class) ||
AnnotatedElementUtils.hasAnnotation(beanType, RequestMapping.class));
}复制代码
isHandler()办法在这里的作用就是检查beanType能否有@Controller或@RequestMapping注解，这两个注解经常运用，应该都很熟习了。
detectHandlerMethods()
AbstractHandlerMethodMapping#detectHandlerMethods() 这个办法的作用是从handler中获取handler method并注册
protected void detectHandlerMethods(final Object handler) {
Class handlerType = (handler instanceof String ?
obtainApplicationContext().getType((String) handler) : handler.getClass());
if (handlerType != null) {
//为给定的类返回用户定义的类:通常只是给定的类，假如是cglib生成的子类，则返回原始的类。
final Class userType = ClassUtils.getUserClass(handlerType);
Map methods = MethodIntrospector.selectMethods(userType,
(MethodIntrospector.MetadataLookup) method -> {
try {
// 为处置程序办法提供映射
return getMappingForMethod(method, userType);
}
catch (Throwable ex) {
throw new IllegalStateException("Invalid mapping on handler class [" +
userType.getName() + "]: " + method, ex);
}
});
if (logger.isDebugEnabled()) {
logger.debug(methods.size() + " request handler methods found on " + userType + ": " + methods);
}
// 为查找到的handler method 停止注册
methods.forEach((method, mapping) -> {
Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);
registerHandlerMethod(handler, invocableMethod, mapping);
});
}
}
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registerHandlerMethod()
AbstractHandlerMethodMapping#registerHandlerMethod() 的作用是为每个handler method注册它们独一的映射途径，源码如下：
/**
- Register a handler method and its unique mapping. Invoked at startup for
- each detected handler method.
- @param handler the bean name of the handler or the handler instance
- @param method the method to register
- @param mapping the mapping conditions associated with the handler method
- @throws IllegalStateException if another method was already registered
- under the same mapping
*/
protected void registerHandlerMethod(Object handler, Method method, T mapping) {
this.mappingRegistry.register(mapping, handler, method);}
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register办法是AbstractHandlerMethodMapping 内部类MappingRegistry里的办法，