简介
在上篇文章中,大致解析了 Spring 如何将请求路径与处理方法进行映射,但映射相关的初始化对于我们来说还是一团迷雾
本篇文章就来探索下,请求路径和处理方法的映射,是如何进行初始化的
概览
基于上篇文章:Spring 源码解析 -- SpringWeb请求映射解析
本篇文章本来想早点写完,但一直卡着,没有找到想要的切入点,还好在周四左右定位到了相关的关键代码,初步探索到相关初始化的代码过程
接下来就展示这段时间的定位和解析过程,下面是自己这段时间探索历程:
想定位 handlerMappings 的初始化,但没有定位请求 URL 和处理方法相关初始化的东西
回过来头来看 handlerMappings ,看其有哪些东西,发现这个 Map 中并没有自定义的 HelloWorld
意识到关键的 RequestMappingHandlerMapping,跟踪发送只有在这个类型才成功匹配
回顾上篇的请求映射解析,在 RequestMappingHandlerMapping 细致初始化相关的代码
成功找到相关的路径和处理方法初始化的关键代码
接下来详细看下:
源码解析
初步探索初始化:误入歧途
在类: DispatcherServlet.java 中,我们定位到 mappedHandler 获取的关键代码
@Nullable
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
if (this.handlerMappings != null) {
for (HandlerMapping mapping : this.handlerMappings) {
HandlerExecutionChain handler = mapping.getHandler(request);
if (handler != null) {
return handler;
}
}
}
return null;
}
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它就是遍历了: handlerMappings ,于是去跟踪了 handlerMappings 初始化过程
结果失败而归,没有找到自己想要的东西,并没有发现自定义类: HelloWorld 的相关东西
这块有很多的代码,里面也有很多的东西,但在这里就不展示出来了,感兴趣的老哥可自行探索
回顾请求映射查找匹配:幡然醒悟
探索 handlerMappings 无果,于是回到上面那段遍历处理
经过调试 handlerMappings 基本是固定的,包含下面的类:
this.handlerMappings
RequestMappingHandlerMapping
BeanNameUrlHandlerMapping
RouterFunctionMapping
SimpleUrlHandlerMapping
WelcomePageHandlerMapping
而匹配的成功的是: RequestMappingHandlerMapping ,其返回了我们想要的处理方法 HelloWorld
调试中很疑惑为啥初期要初始化这几个了,并且再套了一层请求匹配,目前掌握的知识还不足于破解,只能后面再探索了
于是开始梳理 RequestMappingHandlerMapping 的请求匹配,在下面的一段关键代码匹配成功了:
# AbstractHandlerMethodMapping.java
@Nullable
protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
List<Match> matches = new ArrayList<>();
// 在这里拿到了匹配结果
List<T> directPathMatches = this.mappingRegistry.getMappingsByDirectPath(lookupPath);
if (directPathMatches != null) {
addMatchingMappings(directPathMatches, matches, request);
}
if (matches.isEmpty()) {
addMatchingMappings(this.mappingRegistry.getRegistrations().keySet(), matches, request);
}
.......
}
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在上面的代码中就匹配成功了,其中匹配的方法很简单粗暴:
# AbstractHandlerMethodMapping.java -- MappingRegistry
@Nullable
public List<T> getMappingsByDirectPath(String urlPath) {
return this.pathLookup.get(urlPath);
}
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于是关键点到了 this.mappingRegistry 的初始化,找到初始化的代码,打上断点
期间以为是在类:AbstractHandlerMethodMapping 中进行的初始的,在下面的函数打上了断点:
# AbstractHandlerMethodMapping.java
public void setPatternParser(PathPatternParser patternParser) {
Assert.state(this.mappingRegistry.getRegistrations().isEmpty(),
"PathPatternParser must be set before the initialization of " +
"request mappings through InitializingBean#afterPropertiesSet.");
super.setPatternParser(patternParser);
}
public void registerMapping(T mapping, Object handler, Method method) {
if (logger.isTraceEnabled()) {
logger.trace("Register \"" + mapping + "\" to " + method.toGenericString());
}
this.mappingRegistry.register(mapping, handler, method);
}
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但一直进不去,于是直接在其定义的内部类中: MappingRegistry 中进行寻找,并成功定位到想要的关键代码
请求映射关键代码定位:柳暗花明
阅读类: MappingRegistry 的相关代码,发现下面的方法和可以,我们直接打上断点,重启程序:
发现了前面的: this.pathLookup 的相关添加操作
public void register(T mapping, Object handler, Method method) {
this.readWriteLock.writeLock().lock();
try {
HandlerMethod handlerMethod = createHandlerMethod(handler, method);
validateMethodMapping(handlerMethod, mapping);
Set<String> directPaths = AbstractHandlerMethodMapping.this.getDirectPaths(mapping);
for (String path : directPaths) {
// 这段代码是关键
this.pathLookup.add(path, mapping);
}
String name = null;
if (getNamingStrategy() != null) {
name = getNamingStrategy().getName(handlerMethod, mapping);
addMappingName(name, handlerMethod);
}
CorsConfiguration corsConfig = initCorsConfiguration(handler, method, mapping);
if (corsConfig != null) {
corsConfig.validateAllowCredentials();
this.corsLookup.put(handlerMethod, corsConfig);
}
this.registry.put(mapping,
new MappingRegistration<>(mapping, handlerMethod, directPaths, name, corsConfig != null));
}
finally {
this.readWriteLock.writeLock().unlock();
}
}
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应用重启后,果然顺利来到我们打上的断点处,通过分析调用栈,我们确实找到了请求映射的关键代码
我们将调用栈从下网上分析查看:
应用启动相关
开始就是熟悉 Spring 启动相关,这些代码相信大家尝试阅读源码的时候读过很多遍了
跟踪发现在: DefaultListableBeanFactory.class 的 preInstantiateSingletons 方法中个,一大段嵌套循环,心想这段代码目前能优化吗?
public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
return (new SpringApplication(primarySources)).run(args);
}
public static void main(String[] args) throws Exception {
run(new Class[0], args);
}
public ConfigurableApplicationContext run(String... args) {
......
try {
......
this.prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
// 从下面这个进入
this.refreshContext(context);
this.afterRefresh(context, applicationArguments);
......
} catch (Throwable var10) {
......
this.handleRunFailure(context, var10, listeners);
throw new IllegalStateException(var10);
}
......
}
public void refresh() throws BeansException, IllegalStateException {
synchronized(this.startupShutdownMonitor) {
.......
try {
this.postProcessBeanFactory(beanFactory);
StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
this.invokeBeanFactoryPostProcessors(beanFactory);
this.registerBeanPostProcessors(beanFactory);
beanPostProcess.end();
this.initMessageSource();
this.initApplicationEventMulticaster();
this.onRefresh();
this.registerListeners();
// 从这里进入
this.finishBeanFactoryInitialization(beanFactory);
this.finishRefresh();
} catch (BeansException var10) {
} finally {
......
}
......
}
}
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RequestMappingHandlerMapping 相关初始化
继续跟踪下面的,看到了属性的 CreateBean 和 afterPropertiesSet
# AbstractAutowireCapableBeanFactory.class
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) throws BeanCreationException {
......
try {
// 这里初始化了 RequestMappingHandlerMapping
beanInstance = this.doCreateBean(beanName, mbdToUse, args);
if (this.logger.isTraceEnabled()) {
this.logger.trace("Finished creating instance of bean '" + beanName + "'");
}
return beanInstance;
} catch (ImplicitlyAppearedSingletonException | BeanCreationException var7) {
throw var7;
} catch (Throwable var8) {
throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", var8);
}
}
# AbstractAutowireCapableBeanFactory.class
protected void invokeInitMethods(String beanName, Object bean, @Nullable RootBeanDefinition mbd) throws Throwable {
boolean isInitializingBean = bean instanceof InitializingBean;
if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
if (this.logger.isTraceEnabled()) {
this.logger.trace("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
}
if (System.getSecurityManager() != null) {
try {
AccessController.doPrivileged(() -> {
((InitializingBean)bean).afterPropertiesSet();
return null;
}, this.getAccessControlContext());
} catch (PrivilegedActionException var6) {
throw var6.getException();
}
} else {
// 这里进入请求映射的相关操作
((InitializingBean)bean).afterPropertiesSet();
}
}
......
}
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请求映射初始化
继续跟踪下去,看看了循环遍历 Controllers 相关的代码(还有很多细节没搞清,后面再继续了,先梳理主线)
# AbstractHandlerMethodMapping.java
@Override
public void afterPropertiesSet() {
// 初始化请求映射
initHandlerMethods();
}
protected void initHandlerMethods() {
// 遍历所有的自定义的Controllers,后面自己又定义了一个Controllers
for (String beanName : getCandidateBeanNames()) {
if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
// 在这里看到了我们定义的HelloWorld
processCandidateBean(beanName);
}
}
handlerMethodsInitialized(getHandlerMethods());
}
protected String[] getCandidateBeanNames() {
return (this.detectHandlerMethodsInAncestorContexts ?
BeanFactoryUtils.beanNamesForTypeIncludingAncestors(obtainApplicationContext(), Object.class) :
obtainApplicationContext().getBeanNamesForType(Object.class));
}
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继续跟踪下去,看到了下面的获取类中具体请求路径相关的代码,并且到了具体的初始化请求映射的代码
# AbstractHandlerMethodMapping.java
protected void processCandidateBean(String beanName) {
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.isTraceEnabled()) {
logger.trace("Could not resolve type for bean '" + beanName + "'", ex);
}
}
if (beanType != null && isHandler(beanType)) {
// 得到Controller Bean后的入口
detectHandlerMethods(beanName);
}
}
protected void detectHandlerMethods(Object handler) {
Class<?> handlerType = (handler instanceof String ?
obtainApplicationContext().getType((String) handler) : handler.getClass());
if (handlerType != null) {
// 处理得到所有的Controllers method
Class<?> userType = ClassUtils.getUserClass(handlerType);
Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
(MethodIntrospector.MetadataLookup<T>) method -> {
try {
return getMappingForMethod(method, userType);
}
catch (Throwable ex) {
throw new IllegalStateException("Invalid mapping on handler class [" +
userType.getName() + "]: " + method, ex);
}
});
if (logger.isTraceEnabled()) {
logger.trace(formatMappings(userType, methods));
}
else if (mappingsLogger.isDebugEnabled()) {
mappingsLogger.debug(formatMappings(userType, methods));
}
methods.forEach((method, mapping) -> {
Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);
// 注册
registerHandlerMethod(handler, invocableMethod, mapping);
});
}
}
public void register(T mapping, Object handler, Method method) {
this.readWriteLock.writeLock().lock();
try {
HandlerMethod handlerMethod = createHandlerMethod(handler, method);
validateMethodMapping(handlerMethod, mapping);
Set<String> directPaths = AbstractHandlerMethodMapping.this.getDirectPaths(mapping);
for (String path : directPaths) {
// 映射添加
this.pathLookup.add(path, mapping);
}
}
finally {
this.readWriteLock.writeLock().unlock();
}
}
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总结
经过一段时间的探索的整理,我们终于得到了大致的请求路径映射初始化的代码
经过调试,我们还发现虽然 RequestMappingHandlerMapping 是一开始就初始化了,但加载到 handlerMappings 是第一次请求的时候才加载进去的
本篇虽然得到了大致的请求路径初始化的代码,但其中有很多细节是值得探索的,比如 Bean 中 Method 的处理
之前自己写过一些 DI 和 Web 相关的 Demo,停在了 Servlet,卡在了请求映射初始化和匹配,这个给了我一些思路,后面详细看看这块代码,完善下之前的 Demo
参考链接
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