不知道大家和我有没有相同的疑惑，就是Spring什么时候把RequestMapping加载的，在类上声明@Controller或@RestController注解，只是声明注册一个bean，那么@RequestMapping又是在什么时候加载的呢？
@RequestMapping加载依赖的是RequestMappingHandlerMapping，所以这节主要分析RequestMappingHandlerMapping。
RequestMappingHandlerMapping创建
不知道大家是否还有印象，我们在二十三、spring mvc之简单使用中的WebConfig上使用了@EnableWebMvc注解，这个注解导入了DelegatingWebMvcConfiguration配置，在DelegatingWebMvcConfiguration的父类WebMvcConfigurationSupport创建了RequestMappingHandlerMapping。
@Bean
public RequestMappingHandlerMapping requestMappingHandlerMapping() {
RequestMappingHandlerMapping mapping = createRequestMappingHandlerMapping();
//...省略属性设置
return mapping;
}
RequestMappingHandlerMapping加载@RequestMapping
我一开始也不知道创建RequestMappingHandlerMapping作用，后来看到它的类图就明白加载过程。
RequestMappingHandlerMapping的父类实现了InitializingBean，那么在初始化的时候就会调用afterPropertiesSet方法。看下父类afterPropertiesSet的实现:
@Override
public void afterPropertiesSet() {
initHandlerMethods();
}
protected void initHandlerMethods() {
if (logger.isDebugEnabled()) {
logger.debug("Looking for request mappings in application context: " + getApplicationContext());
}
//detectHandlerMethodsInAncestorContexts默认false，所以是得到所有的beanNames
String[] beanNames = (this.detectHandlerMethodsInAncestorContexts ?
BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) :
getApplicationContext().getBeanNamesForType(Object.class));
for (String beanName : beanNames) {
if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
Class<?> beanType = null;
try {
beanType = getApplicationContext().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);
}
}
//2. isHandler由子类实现
if (beanType != null && isHandler(beanType)) {
//3. 查找controller中有@RequestMapping注解的方法,并注册到请求
detectHandlerMethods(beanName);
}
}
}
//空方法
handlerMethodsInitialized(getHandlerMethods());
}
afterPropertiesSet实现交给了initHandlerMethods，initHandlerMethods的执行流程如下:
- 得到所有的beanName
- 遍历beanNames,调用isHandler判断bean是不是一个controller，isHandler由子类实现，RequestMappingHandlerMapping的实现如下，判断bean中有没有Controller或RequestMapping
@Override
protected boolean isHandler(Class<?> beanType) {
return (AnnotatedElementUtils.hasAnnotation(beanType, Controller.class) ||
AnnotatedElementUtils.hasAnnotation(beanType, RequestMapping.class));
}
- 查找controller中有@RequestMapping注解的方法,并注册到请求容器中
protected void detectHandlerMethods(final Object handler) {
//1. 得到controller真实类型
Class<?> handlerType = (handler instanceof String ?
getApplicationContext().getType((String) handler) : handler.getClass());
final Class<?> userType = ClassUtils.getUserClass(handlerType);
//3. 封装所有的Method和RequestMappingInfo到Map中
Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
new MethodIntrospector.MetadataLookup<T>() {
@Override
public T inspect(Method method) {
try {
//2. 根据方法上的@RequestMapping信息构建RequestMappingInfo
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);
}
for (Map.Entry<Method, T> entry : methods.entrySet()) {
Method invocableMethod = AopUtils.selectInvocableMethod(entry.getKey(), userType);
T mapping = entry.getValue();
//4. 将RequestMappingInfo注册到请求容器中
registerHandlerMethod(handler, invocableMethod, mapping);
}
}
detectHandlerMethods是加载请求核心方法，执行流程如下:
(1) 得到controller真实类型,controller可能被代理
(2) 根据方法上的@RequestMapping信息构建RequestMappingInfo,由RequestMappingHandlerMapping实现。从代码上可以看出，必须方法上声明@RequestMapping，类上的@RequestMapping才会生效。
@Override
protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) {
//1. 根据方法上的@RequestMapping创建RequestMappingInfo
RequestMappingInfo info = createRequestMappingInfo(method);
if (info != null) {
//2. 查找类上是否有@RequestMapping，如果有则和方法上的组合
RequestMappingInfo typeInfo = createRequestMappingInfo(handlerType);
if (typeInfo != null) {
info = typeInfo.combine(info);
}
}
return info;
}
- 封装所有的Method和RequestMappingInfo到Map中
- 将RequestMappingInfo注册到请求容器中
protected void registerHandlerMethod(Object handler, Method method, T mapping) {
this.mappingRegistry.register(mapping, handler, method);
}
这里就不再分析register方法的实现过程，主要是根据handler，method封装成HandlerMethod，再请求的时候会得到HandlerMethod，然后反射调用。
