Spring Boot 2.2.6 源码之旅四十三SpringMVC源码细节之BeanNameUrlHandlerMapping处理器
- BeanNameUrlHandlerMapping是什么
- BeanNameUrlHandlerMapping初始化
-
- AbstractDetectingUrlHandlerMapping的detectHandlers
-
- BeanNameUrlHandlerMapping的determineUrlsForHandler
- AbstractUrlHandlerMapping的registerHandler注册处理器
- 处理原理
BeanNameUrlHandlerMapping是什么
其实这个就是在用bean注解方法的时候填写的名字作为uri和bean处理器映射。先看例子，比如我定义了两种老的写法的处理器：
然后我在配置文件中注入他们，都命名了：
然后访问：
好像也挺方便哦，但是都要实现接口，而且方法参数是死的，无法做到直接获取需要的参数值，而ResourceHttpRequestHandler更强大，他可以任意传参数，只要能匹配的上都可以匹配，等于定制化，灵活，你可以实现任何你想要的参数类型，只要你编写解析器。我们来说说原理吧。
BeanNameUrlHandlerMapping初始化
他也是EnableWebMvcConfiguration创建的：
AbstractDetectingUrlHandlerMapping的detectHandlers
但是在ApplicationContextAwareProcessor的初始化之前的方法postProcessBeforeInitialization中，最后进行了处理器探测detectHandlers：
protected void detectHandlers() throws BeansException {
ApplicationContext applicationContext = obtainApplicationContext();
String[] beanNames = (this.detectHandlersInAncestorContexts ?
BeanFactoryUtils.beanNamesForTypeIncludingAncestors(applicationContext, Object.class) :
applicationContext.getBeanNamesForType(Object.class));
// 遍历所有容器里的beanName，找出beanName有uri的注册进去
for (String beanName : beanNames) {
String[] urls = determineUrlsForHandler(beanName);
if (!ObjectUtils.isEmpty(urls)) {
// URL paths found: Let's consider it a handler.
registerHandler(urls, beanName);
}
}
if ((logger.isDebugEnabled() && !getHandlerMap().isEmpty()) || logger.isTraceEnabled()) {
logger.debug("Detected " + getHandlerMap().size() + " mappings in " + formatMappingName());
}
}
BeanNameUrlHandlerMapping的determineUrlsForHandler
名字或者别名以/开头的都放入url集合里。
@Override
protected String[] determineUrlsForHandler(String beanName) {
List<String> urls = new ArrayList<>();
if (beanName.startsWith("/")) {
urls.add(beanName);
}
String[] aliases = obtainApplicationContext().getAliases(beanName);
for (String alias : aliases) {
if (alias.startsWith("/")) {
urls.add(alias);
}
}
return StringUtils.toStringArray(urls);
}
AbstractUrlHandlerMapping的registerHandler注册处理器
protected void registerHandler(String[] urlPaths, String beanName) throws BeansException, IllegalStateException {
Assert.notNull(urlPaths, "URL path array must not be null");
for (String urlPath : urlPaths) {
registerHandler(urlPath, beanName);
}
}
首先看不是懒初始化的单例且处理器只是个名字的话就直接实例化，然后判断重复，根据url的不同，设置不同的处理器，一般的就是放入url和处理器的映射集合。
protected void registerHandler(String urlPath, Object handler) throws BeansException, IllegalStateException {
Assert.notNull(urlPath, "URL path must not be null");
Assert.notNull(handler, "Handler object must not be null");
Object resolvedHandler = handler;
// Eagerly resolve handler if referencing singleton via name.
if (!this.lazyInitHandlers && handler instanceof String) {
String handlerName = (String) handler;
ApplicationContext applicationContext = obtainApplicationContext();
if (applicationContext.isSingleton(handlerName)) {
resolvedHandler = applicationContext.getBean(handlerName);
}
}
Object mappedHandler = this.handlerMap.get(urlPath);
if (mappedHandler != null) {
if (mappedHandler != resolvedHandler) {
throw new IllegalStateException(
"Cannot map " + getHandlerDescription(handler) + " to URL path [" + urlPath +
"]: There is already " + getHandlerDescription(mappedHandler) + " mapped.");
}
}
else {
if (urlPath.equals("/")) {
if (logger.isTraceEnabled()) {
logger.trace("Root mapping to " + getHandlerDescription(handler));
}
setRootHandler(resolvedHandler);
}
else if (urlPath.equals("/*")) {
if (logger.isTraceEnabled()) {
logger.trace("Default mapping to " + getHandlerDescription(handler));
}
setDefaultHandler(resolvedHandler);
}
else {
this.handlerMap.put(urlPath, resolvedHandler);
if (logger.isTraceEnabled()) {
logger.trace("Mapped [" + urlPath + "] onto " + getHandlerDescription(handler));
}
}
}
}
处理原理
至于他的处理原理，还是获取处理器的方法lookupHandler，其实他和SimpleUrlHandlerMapping一样，都是AbstractDetectingUrlHandlerMapping的子类，所以实现是一样的，都是AbstractDetectingUrlHandlerMapping实现的，这个上几篇有讲过了，就不多说了。
好了，今天就到这里了，希望对学习理解有帮助，大神看见勿喷，仅为自己的学习理解，能力有限，请多包涵。