1、首先问自己一个问题，为啥要读SpringBoot源码呢？
我们在干一件事情前必须要有自己的目的，不要盲目的跟风。
就比如现在，我们为啥要读SpringBoot源码呢？
对于我来说，最主要的原因是目前技术更新太快，框架层出不穷，越学越迷茫，我到底学了个啥？
像SpringBoot，你难道不好奇他的自动化配置、IOC和AOP的实现原理吗？
带着上面的问题，我们来Debug看看！
2、环境准备
Ⅰ、我的maven依赖关系(不同的SpringBoot版本、不同的依赖关系，运行结果会不一样，因为SpringBoot会自动配置)
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.mybatis.spring.boot</groupId>
<artifactId>mybatis-spring-boot-starter</artifactId>
<version>2.1.4</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-aop</artifactId>
</dependency>
<dependency>
<groupId>io.springfox</groupId>
<artifactId>springfox-boot-starter</artifactId>
<version>3.0.0</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<optional>true</optional>
</dependency>
<dependency>
<groupId>cn.hutool</groupId>
<artifactId>hutool-all</artifactId>
<version>5.7.2</version>
</dependency>
<dependency>
<groupId>com.baomidou</groupId>
<artifactId>mybatis-plus-boot-starter</artifactId>
<version>3.4.0</version>
</dependency>
<dependency>
<groupId>com.baomidou</groupId>
<artifactId>mybatis-plus-generator</artifactId>
<version>3.4.0</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
Ⅱ、Debug前的准备
- clean
- compile
- install
3、开始调试
就想我们学习C语言时的HelloWorld一样，SpringBoot也有一个开场白：
package com.study.redis;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
/**
* @author lemon
*/
@SpringBootApplication
public class RedisApplication {
public static void main(String[] args) {
SpringApplication.run(RedisApplication.class, args);
}
}
然后我们Ctrl+鼠标左键点进SpringApplication的run方法可以看到下图：
首先是调用形参为单个class的run方法，然后调用形参为class数组形式的run方法。
另外需要注意的是上面的那个Decompiled .class file,bytecode version: 52.0(Java 8) Download Sources Choose Sources...
为什么要注意这个呢，因为现在是对.class文件Debug，而不是Java文件，稍后Debug就会出现错误：
Source code does not match the byte code
我们选择Download Sources，如若有必要可以再Choose Sources，选择刚刚下载的Sources，然后就会看到带注释的方法了：
/**
* Static helper that can be used to run a {@link SpringApplication} from the
* specified source using default settings.
* @param primarySource the primary source to load
* @param args the application arguments (usually passed from a Java main method)
* @return the running {@link ApplicationContext}
*/
public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
return run(new Class<?>[] { primarySource }, args);
}
/**
* Static helper that can be used to run a {@link SpringApplication} from the
* specified sources using default settings and user supplied arguments.
* @param primarySources the primary sources to load
* @param args the application arguments (usually passed from a Java main method)
* @return the running {@link ApplicationContext}
*/
public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
return new SpringApplication(primarySources).run(args);
}
这里最终实例化了一个SpringApplication对象，并调用它的run方法，我们先看看初始化函数：
/**
* Create a new {@link SpringApplication} instance. The application context will load
* beans from the specified primary sources (see {@link SpringApplication class-level}
* documentation for details. The instance can be customized before calling
* {@link #run(String...)}.
* @param primarySources the primary bean sources
* @see #run(Class, String[])
* @see #SpringApplication(ResourceLoader, Class...)
* @see #setSources(Set)
*/
public SpringApplication(Class<?>... primarySources) {
this(null, primarySources);
}
/**
* Create a new {@link SpringApplication} instance. The application context will load
* beans from the specified primary sources (see {@link SpringApplication class-level}
* documentation for details. The instance can be customized before calling
* {@link #run(String...)}.
* @param resourceLoader the resource loader to use
* @param primarySources the primary bean sources
* @see #run(Class, String[])
* @see #setSources(Set)
*/
@SuppressWarnings({ "unchecked", "rawtypes" })
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
this.resourceLoader = resourceLoader;
Assert.notNull(primarySources, "PrimarySources must not be null");
this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
this.webApplicationType = WebApplicationType.deduceFromClasspath();
this.bootstrapRegistryInitializers = getBootstrapRegistryInitializersFromSpringFactories();
setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
this.mainApplicationClass = deduceMainApplicationClass();
}
初始化函数就先看到这儿，等要用的时候我们再回来看，接下来我们来看run方法：
/**
* Run the Spring application, creating and refreshing a new
* {@link ApplicationContext}.
* @param args the application arguments (usually passed from a Java main method)
* @return a running {@link ApplicationContext}
*/
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
DefaultBootstrapContext bootstrapContext = createBootstrapContext();
ConfigurableApplicationContext context = null;
configureHeadlessProperty();
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting(bootstrapContext, this.mainApplicationClass);
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
configureIgnoreBeanInfo(environment);
Banner printedBanner = printBanner(environment);
context = createApplicationContext();
context.setApplicationStartup(this.applicationStartup);
prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
refreshContext(context);
afterRefresh(context, applicationArguments);
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
}
listeners.started(context);
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
handleRunFailure(context, ex, listeners);
throw new IllegalStateException(ex);
}
try {
listeners.running(context);
}
catch (Throwable ex) {
handleRunFailure(context, ex, null);
throw new IllegalStateException(ex);
}
return context;
}
首先实例化了一个StopWatch对象：
/**
* Construct a new {@code StopWatch}.
* <p>Does not start any task.
*/
public StopWatch() {
this("");
}
/**
* Construct a new {@code StopWatch} with the given ID.
* <p>The ID is handy when we have output from multiple stop watches and need
* to distinguish between them.
* <p>Does not start any task.
* @param id identifier for this stop watch
*/
public StopWatch(String id) {
this.id = id;
}
然后调用了start方法，我们看看它的start方法干了啥：
/**
* Start an unnamed task.
* <p>The results are undefined if {@link #stop()} or timing methods are
* called without invoking this method first.
* @see #start(String)
* @see #stop()
*/
public void start() throws IllegalStateException {
start("");
}
/**
* Start a named task.
* <p>The results are undefined if {@link #stop()} or timing methods are
* called without invoking this method first.
* @param taskName the name of the task to start
* @see #start()
* @see #stop()
*/
public void start(String taskName) throws IllegalStateException {
if (this.currentTaskName != null) {
throw new IllegalStateException("Can't start StopWatch: it's already running");
}
this.currentTaskName = taskName;
this.startTimeNanos = System.nanoTime();
}
感觉啥也没干哈哈(菜鸟级理解)
接下来就是createBootstrapContext方法：
private DefaultBootstrapContext createBootstrapContext() {
DefaultBootstrapContext bootstrapContext = new DefaultBootstrapContext();
this.bootstrapRegistryInitializers.forEach((initializer) -> initializer.initialize(bootstrapContext));
return bootstrapContext;
}
首先实例化了一个DefaultBootstrapContext，调用的是默认的构造函数，无代码展示。
然后将bootstrapRegistryInitializer里面的每一个实例都初始化，那我们回来之前SpringApplication的构造函数：
this.bootstrapRegistryInitializers = getBootstrapRegistryInitializersFromSpringFactories();
@SuppressWarnings("deprecation")
private List<BootstrapRegistryInitializer> getBootstrapRegistryInitializersFromSpringFactories() {
ArrayList<BootstrapRegistryInitializer> initializers = new ArrayList<>();
getSpringFactoriesInstances(Bootstrapper.class).stream()
.map((bootstrapper) -> ((BootstrapRegistryInitializer) bootstrapper::initialize))
.forEach(initializers::add);
initializers.addAll(getSpringFactoriesInstances(BootstrapRegistryInitializer.class));
return initializers;
}
看到这个@SuppressWarnings("deprecation")注解，作者估计是不想用这个了吧。
可以看到initializers里面的元素都是从getSpringFactoriesInstances方法中来的：
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {
return getSpringFactoriesInstances(type, new Class<?>[] {});
}
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
ClassLoader classLoader = getClassLoader();
// Use names and ensure unique to protect against duplicates
Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
AnnotationAwareOrderComparator.sort(instances);
return instances;
}
首先它实例化了一个类加载器，其实也就是下面这个：
Thread.currentThread().getContextClassLoader()
然后通过SpringFactoriesLoade的LoadFactoryName方法实例实例化了一个Set<String>集合：
/**
* Load the fully qualified class names of factory implementations of the
* given type from {@value #FACTORIES_RESOURCE_LOCATION}, using the given
* class loader.
* <p>As of Spring Framework 5.3, if a particular implementation class name
* is discovered more than once for the given factory type, duplicates will
* be ignored.
* @param factoryType the interface or abstract class representing the factory
* @param classLoader the ClassLoader to use for loading resources; can be
* {@code null} to use the default
* @throws IllegalArgumentException if an error occurs while loading factory names
* @see #loadFactories
*/
public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {
ClassLoader classLoaderToUse = classLoader;
if (classLoaderToUse == null) {
classLoaderToUse = SpringFactoriesLoader.class.getClassLoader();
}
String factoryTypeName = factoryType.getName();
return loadSpringFactories(classLoaderToUse).getOrDefault(factoryTypeName, Collections.emptyList());
}
最终还是调用的loadSpringFactories方法：
private static Map<String, List<String>> loadSpringFactories(ClassLoader classLoader) {
Map<String, List<String>> result = cache.get(classLoader);
if (result != null) {
return result;
}
result = new HashMap<>();
try {
Enumeration<URL> urls = classLoader.getResources(FACTORIES_RESOURCE_LOCATION);
while (urls.hasMoreElements()) {
URL url = urls.nextElement();
UrlResource resource = new UrlResource(url);
Properties properties = PropertiesLoaderUtils.loadProperties(resource);
for (Map.Entry<?, ?> entry : properties.entrySet()) {
String factoryTypeName = ((String) entry.getKey()).trim();
String[] factoryImplementationNames =
StringUtils.commaDelimitedListToStringArray((String) entry.getValue());
for (String factoryImplementationName : factoryImplementationNames) {
result.computeIfAbsent(factoryTypeName, key -> new ArrayList<>())
.add(factoryImplementationName.trim());
}
}
}
// Replace all lists with unmodifiable lists containing unique elements
result.replaceAll((factoryType, implementations) -> implementations.stream().distinct()
.collect(Collectors.collectingAndThen(Collectors.toList(), Collections::unmodifiableList)));
cache.put(classLoader, result);
}
catch (IOException ex) {
throw new IllegalArgumentException("Unable to load factories from location [" +
FACTORIES_RESOURCE_LOCATION + "]", ex);
}
return result;
}
我们先来看看cache是啥：
static final Map<ClassLoader, Map<String, List<String>>> cache = new ConcurrentReferenceHashMap<>();
很明细，里面是空的，接下来我们看看下面这句：
Enumeration<URL> urls = classLoader.getResources(FACTORIES_RESOURCE_LOCATION);
public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
通过Debug，我们得到如下结果：
算了，这个urls里面东西太多了，反正就是一些包相关信息，我们直接看result吧，反正信息都是从类加载器取出来的：
现在我们回到LoadFactoryNames方法，由于返回的result中没有对应Bootstrapper.class类型的键，所以返回一个空列表。
那我们再看看是否有对应的BootstrapRegistryInitializer.class类型的键，同样也没有。
所以初始化构造的bootstrapRegistryInitializer是一个空列表。
但是initializer和listeners有值：
接下来我们回到createBootstrapContext方法，由于bootstrapRegistryInitializer是一个空列表，
所以该方法相当于直接返回一个默认的DefaultBootstrapContext，没有做其他操作。
现在再回到run方法中的configureHeadlessProperty方法：
private void configureHeadlessProperty() {
System.setProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS,
System.getProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS, Boolean.toString(this.headless)));
}
这一步就简单的设置一下系统所属性，接下来我们看看getRunListeners方法：
private SpringApplicationRunListeners getRunListeners(String[] args) {
Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };
return new SpringApplicationRunListeners(logger,
getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args),
this.applicationStartup);
}
我们先看看构造函数：
SpringApplicationRunListeners(Log log, Collection<? extends SpringApplicationRunListener> listeners,
ApplicationStartup applicationStartup) {
this.log = log;
this.listeners = new ArrayList<>(listeners);
this.applicationStartup = applicationStartup;
}
简单的赋值，没啥好说的，我们回到getSpringFactoriesInstances方法：
可以看到返回了一个listeners，我们再回到run方法：
listeners.starting(bootstrapContext, this.mainApplicationClass);
void starting(ConfigurableBootstrapContext bootstrapContext, Class<?> mainApplicationClass) {
doWithListeners("spring.boot.application.starting", (listener) -> listener.starting(bootstrapContext),
(step) -> {
if (mainApplicationClass != null) {
step.tag("mainApplicationClass", mainApplicationClass.getName());
}
});
}
private void doWithListeners(String stepName, Consumer<SpringApplicationRunListener> listenerAction,
Consumer<StartupStep> stepAction) {
StartupStep step = this.applicationStartup.start(stepName);
this.listeners.forEach(listenerAction);
if (stepAction != null) {
stepAction.accept(step);
}
step.end();
}
通过调用listeners的start方法，最终调用该实例的的listeners的starting方法，我们再看看step干了啥：
private static final DefaultStartupStep DEFAULT_STARTUP_STEP = new DefaultStartupStep();
@Override
public DefaultStartupStep start(String name) {
return DEFAULT_STARTUP_STEP;
}
虽然方法名叫start，但是只是实例化一个DefaultStartupStep对象，接下来再看listener的starting方法：
@Override
public void starting(ConfigurableBootstrapContext bootstrapContext) {
this.initialMulticaster
.multicastEvent(new ApplicationStartingEvent(bootstrapContext, this.application, this.args));
}
该方法属于EventPublishingRunListener类：
public EventPublishingRunListener(SpringApplication application, String[] args) {
this.application = application;
this.args = args;
this.initialMulticaster = new SimpleApplicationEventMulticaster();
for (ApplicationListener<?> listener : application.getListeners()) {
this.initialMulticaster.addApplicationListener(listener);
}
}
可以看到initialMulticaster是SimpleApplicationEventMulticaster的实例，再看看ApplicationStartingEvent构造函数：
/**
* Create a new {@link ApplicationStartingEvent} instance.
* @param bootstrapContext the bootstrap context
* @param application the current application
* @param args the arguments the application is running with
*/
public ApplicationStartingEvent(ConfigurableBootstrapContext bootstrapContext, SpringApplication application,
String[] args) {
super(application, args);
this.bootstrapContext = bootstrapContext;
}
反正就是构造一个实例就完了，那我们再回到initialMulticaster的multicasEvent方法：
@Override
public void multicastEvent(ApplicationEvent event) {
multicastEvent(event, resolveDefaultEventType(event));
}
@Override
public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {
ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
Executor executor = getTaskExecutor();
for (ApplicationListener<?> listener : getApplicationListeners(event, type)) {
if (executor != null) {
executor.execute(() -> invokeListener(listener, event));
}
else {
invokeListener(listener, event);
}
}
}
event就是ApplicationStartingEvent的一个实例，由于SimpleApplicationEventMulticaster的构造函数如下：
/**
* Create a new SimpleApplicationEventMulticaster.
*/
public SimpleApplicationEventMulticaster() {
}
所以Executor是空的，我们看看getApplicationListeners方法：
/**
* Return a Collection of ApplicationListeners matching the given
* event type. Non-matching listeners get excluded early.
* @param event the event to be propagated. Allows for excluding
* non-matching listeners early, based on cached matching information.
* @param eventType the event type
* @return a Collection of ApplicationListeners
* @see org.springframework.context.ApplicationListener
*/
protected Collection<ApplicationListener<?>> getApplicationListeners(
ApplicationEvent event, ResolvableType eventType) {
Object source = event.getSource();
Class<?> sourceType = (source != null ? source.getClass() : null);
ListenerCacheKey cacheKey = new ListenerCacheKey(eventType, sourceType);
// Potential new retriever to populate
CachedListenerRetriever newRetriever = null;
// Quick check for existing entry on ConcurrentHashMap
CachedListenerRetriever existingRetriever = this.retrieverCache.get(cacheKey);
if (existingRetriever == null) {
// Caching a new ListenerRetriever if possible
if (this.beanClassLoader == null ||
(ClassUtils.isCacheSafe(event.getClass(), this.beanClassLoader) &&
(sourceType == null || ClassUtils.isCacheSafe(sourceType, this.beanClassLoader)))) {
newRetriever = new CachedListenerRetriever();
existingRetriever = this.retrieverCache.putIfAbsent(cacheKey, newRetriever);
if (existingRetriever != null) {
newRetriever = null; // no need to populate it in retrieveApplicationListeners
}
}
}
if (existingRetriever != null) {
Collection<ApplicationListener<?>> result = existingRetriever.getApplicationListeners();
if (result != null) {
return result;
}
// If result is null, the existing retriever is not fully populated yet by another thread.
// Proceed like caching wasn't possible for this current local attempt.
}
return retrieveApplicationListeners(eventType, sourceType, newRetriever);
}
我们来看看对应的event、eventType是什么：
source就是之前构造的SpringApplication实例：
接下来根据eventType和sourceType创建了一个cacheKey:
public ListenerCacheKey(ResolvableType eventType, @Nullable Class<?> sourceType) {
Assert.notNull(eventType, "Event type must not be null");
this.eventType = eventType;
this.sourceType = sourceType;
}
就是简单的赋值，没啥好说的，然后根据该key获取一个值：
CachedListenerRetriever existingRetriever = this.retrieverCache.get(cacheKey);
final Map<ListenerCacheKey, CachedListenerRetriever> retrieverCache = new ConcurrentHashMap<>(64);
由于retrieverCache是一个空的ConcurrentHashMap()，为啥要用并发Map，我们先不管。
由于existingRetriever是空的，并且beanClassLoader也是空的，所以我们直接看retrieveApplicationListeners方法：
/**
* Actually retrieve the application listeners for the given event and source type.
* @param eventType the event type
* @param sourceType the event source type
* @param retriever the ListenerRetriever, if supposed to populate one (for caching purposes)
* @return the pre-filtered list of application listeners for the given event and source type
*/
private Collection<ApplicationListener<?>> retrieveApplicationListeners(
ResolvableType eventType, @Nullable Class<?> sourceType, @Nullable CachedListenerRetriever retriever) {
List<ApplicationListener<?>> allListeners = new ArrayList<>();
Set<ApplicationListener<?>> filteredListeners = (retriever != null ? new LinkedHashSet<>() : null);
Set<String> filteredListenerBeans = (retriever != null ? new LinkedHashSet<>() : null);
Set<ApplicationListener<?>> listeners;
Set<String> listenerBeans;
synchronized (this.defaultRetriever) {
listeners = new LinkedHashSet<>(this.defaultRetriever.applicationListeners);
listenerBeans = new LinkedHashSet<>(this.defaultRetriever.applicationListenerBeans);
}
// Add programmatically registered listeners, including ones coming
// from ApplicationListenerDetector (singleton beans and inner beans).
for (ApplicationListener<?> listener : listeners) {
if (supportsEvent(listener, eventType, sourceType)) {
if (retriever != null) {
filteredListeners.add(listener);
}
allListeners.add(listener);
}
}
// Add listeners by bean name, potentially overlapping with programmatically
// registered listeners above - but here potentially with additional metadata.
if (!listenerBeans.isEmpty()) {
ConfigurableBeanFactory beanFactory = getBeanFactory();
for (String listenerBeanName : listenerBeans) {
try {
if (supportsEvent(beanFactory, listenerBeanName, eventType)) {
ApplicationListener<?> listener =
beanFactory.getBean(listenerBeanName, ApplicationListener.class);
if (!allListeners.contains(listener) && supportsEvent(listener, eventType, sourceType)) {
if (retriever != null) {
if (beanFactory.isSingleton(listenerBeanName)) {
filteredListeners.add(listener);
}
else {
filteredListenerBeans.add(listenerBeanName);
}
}
allListeners.add(listener);
}
}
else {
// Remove non-matching listeners that originally came from
// ApplicationListenerDetector, possibly ruled out by additional
// BeanDefinition metadata (e.g. factory method generics) above.
Object listener = beanFactory.getSingleton(listenerBeanName);
if (retriever != null) {
filteredListeners.remove(listener);
}
allListeners.remove(listener);
}
}
catch (NoSuchBeanDefinitionException ex) {
// Singleton listener instance (without backing bean definition) disappeared -
// probably in the middle of the destruction phase
}
}
}
AnnotationAwareOrderComparator.sort(allListeners);
if (retriever != null) {
if (filteredListenerBeans.isEmpty()) {
retriever.applicationListeners = new LinkedHashSet<>(allListeners);
retriever.applicationListenerBeans = filteredListenerBeans;
}
else {
retriever.applicationListeners = filteredListeners;
retriever.applicationListenerBeans = filteredListenerBeans;
}
}
return allListeners;
}
我们直接来到下面这段代码：
synchronized (this.defaultRetriever) {
listeners = new LinkedHashSet<>(this.defaultRetriever.applicationListeners);
listenerBeans = new LinkedHashSet<>(this.defaultRetriever.applicationListenerBeans);
}
发现这个defaultRetriever.applicationListeners直接有值了
它是从哪儿来的呢？
private final DefaultListenerRetriever defaultRetriever = new DefaultListenerRetriever();
/**
* Helper class that encapsulates a general set of target listeners.
*/
private class DefaultListenerRetriever {
public final Set<ApplicationListener<?>> applicationListeners = new LinkedHashSet<>();
public final Set<String> applicationListenerBeans = new LinkedHashSet<>();
public Collection<ApplicationListener<?>> getApplicationListeners() {
List<ApplicationListener<?>> allListeners = new ArrayList<>(
this.applicationListeners.size() + this.applicationListenerBeans.size());
allListeners.addAll(this.applicationListeners);
if (!this.applicationListenerBeans.isEmpty()) {
BeanFactory beanFactory = getBeanFactory();
for (String listenerBeanName : this.applicationListenerBeans) {
try {
ApplicationListener<?> listener =
beanFactory.getBean(listenerBeanName, ApplicationListener.class);
if (!allListeners.contains(listener)) {
allListeners.add(listener);
}
}
catch (NoSuchBeanDefinitionException ex) {
// Singleton listener instance (without backing bean definition) disappeared -
// probably in the middle of the destruction phase
}
}
}
AnnotationAwareOrderComparator.sort(allListeners);
return allListeners;
}
}
这里我们并未找到该值的来源，那我们找一下哪些地方用到了这个defaultRetriever：
@Override
public void addApplicationListener(ApplicationListener<?> listener) {
synchronized (this.defaultRetriever) {
// Explicitly remove target for a proxy, if registered already,
// in order to avoid double invocations of the same listener.
Object singletonTarget = AopProxyUtils.getSingletonTarget(listener);
if (singletonTarget instanceof ApplicationListener) {
this.defaultRetriever.applicationListeners.remove(singletonTarget);
}
this.defaultRetriever.applicationListeners.add(listener);
this.retrieverCache.clear();
}
}
这里向里面添加listener的，我们再看看有那个地方调用了这个方法：
public EventPublishingRunListener(SpringApplication application, String[] args) {
this.application = application;
this.args = args;
this.initialMulticaster = new SimpleApplicationEventMulticaster();
for (ApplicationListener<?> listener : application.getListeners()) {
this.initialMulticaster.addApplicationListener(listener);
}
}
发现原来是在最开始初始化EventPublishRunListener的时候添加的。
接下来就是判断是否支持事件，添加到对应的listeners中去，另外由于listenersBean是空的，所以没啥好说的。
我们直接看返回结果：
分析这么多，我们终于可以回到以下代码了：
invokeListener(listener, event);
/**
* Invoke the given listener with the given event.
* @param listener the ApplicationListener to invoke
* @param event the current event to propagate
* @since 4.1
*/
protected void invokeListener(ApplicationListener<?> listener, ApplicationEvent event) {
ErrorHandler errorHandler = getErrorHandler();
if (errorHandler != null) {
try {
doInvokeListener(listener, event);
}
catch (Throwable err) {
errorHandler.handleError(err);
}
}
else {
doInvokeListener(listener, event);
}
}
@SuppressWarnings({"rawtypes", "unchecked"})
private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) {
try {
listener.onApplicationEvent(event);
}
catch (ClassCastException ex) {
String msg = ex.getMessage();
if (msg == null || matchesClassCastMessage(msg, event.getClass()) ||
(event instanceof PayloadApplicationEvent &&
matchesClassCastMessage(msg, ((PayloadApplicationEvent) event).getPayload().getClass()))) {
// Possibly a lambda-defined listener which we could not resolve the generic event type for
// -> let's suppress the exception.
Log loggerToUse = this.lazyLogger;
if (loggerToUse == null) {
loggerToUse = LogFactory.getLog(getClass());
this.lazyLogger = loggerToUse;
}
if (loggerToUse.isTraceEnabled()) {
loggerToUse.trace("Non-matching event type for listener: " + listener, ex);
}
}
else {
throw ex;
}
}
}
最终调用的是onApplicationEvent方法，不同的listener该方法不一样：
以上就是为了让listeners跑起来，感觉啥也没干哈哈，可能我想要的东西在下面，接下来我们看看run方法中try语句块的代码：
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
configureIgnoreBeanInfo(environment);
Banner printedBanner = printBanner(environment);
context = createApplicationContext();
context.setApplicationStartup(this.applicationStartup);
prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
refreshContext(context);
afterRefresh(context, applicationArguments);
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
}
listeners.started(context);
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
handleRunFailure(context, ex, listeners);
throw new IllegalStateException(ex);
}
try {
listeners.running(context);
}
catch (Throwable ex) {
handleRunFailure(context, ex, null);
throw new IllegalStateException(ex);
}
return context;
自动化配置应该就是通过使用类加载器机制实现的吧...
草，写不下去了，好多，下一篇吧！！！