·康忙，先跟着下圖走一遍靜靜心...
-
建立SpringBoot項目 -> main 啟動
@SpringBootApplication
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
}
-
-> SpringApplication.run(DemoApplication.class, args)
public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
return run(new Class[]{primarySource}, args);
}
public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
return (new SpringApplication(primarySources)).run(args);
}
-
-> new SpringApplication，這裡隻分析初始化，run啟動後面分析
public SpringApplication(Class<?>... primarySources) {
this((ResourceLoader)null, primarySources);
}
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
this.sources = new LinkedHashSet();
this.bannerMode = Mode.CONSOLE;
this.logStartupInfo = true;
this.addCommandLineProperties = true;
this.addConversionService = true;
this.headless = true;
this.registerShutdownHook = true;
this.additionalProfiles = new HashSet();
this.isCustomEnvironment = false;
// 資源加載器
this.resourceLoader = resourceLoader;
Assert.notNull(primarySources, "PrimarySources must not be null");
// Set<Class<?>> primarySources:意義在于存放 Java Config 類，這裡就是 DemoApplication
this.primarySources = new LinkedHashSet(Arrays.asList(primarySources));
// 1.通過 classpath ，判斷 Web 應用類型
this.webApplicationType = WebApplicationType.deduceFromClasspath();
// 2.設定 List<ApplicationContextInitializer<?>> initializers
this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));
// 3.設定 List<ApplicationListener<?>> listeners
this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));
// 4.擷取調用 main 方法的啟動類：Class<?> mainApplicationClass
this.mainApplicationClass = this.deduceMainApplicationClass();
}
目錄. 第1. --> WebApplicationType.deduceFromClasspath()
第2與3. --> 都調用 SpringApplication.getSpringFactoriesInstances()，這裡拿 type=ApplicationContextInitializer.class 做分析
第4. --> SpringApplication.deduceMainApplicationClass()
第1. --> WebApplicationType.deduceFromClasspath()
static WebApplicationType deduceFromClasspath() {
if (ClassUtils.isPresent("org.springframework.web.reactive.DispatcherHandler", (ClassLoader)null) && !ClassUtils.isPresent("org.springframework.web.servlet.DispatcherServlet", (ClassLoader)null) && !ClassUtils.isPresent("org.glassfish.jersey.servlet.ServletContainer", (ClassLoader)null)) {
return REACTIVE;
} else {
String[] var0 = SERVLET_INDICATOR_CLASSES;
int var1 = var0.length;
for(int var2 = 0; var2 < var1; ++var2) {
String className = var0[var2];
if (!ClassUtils.isPresent(className, (ClassLoader)null)) {
return NONE;
}
}
//private static final String[] SERVLET_INDICATOR_CLASSES = new String[]
//{"javax.servlet.Servlet","org.springframework.web.context.ConfigurableWebApplicationContext"}
// 判斷classpath下是否存在該數組裡面的class,存在則傳回 SERVLET
return SERVLET;
}
}
第2與3. --> 都調用 SpringApplication.getSpringFactoriesInstances()，這裡拿 type=ApplicationContextInitializer.class 做分析
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {
return this.getSpringFactoriesInstances(type, new Class[0]);
}
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
ClassLoader classLoader = this.getClassLoader();
// 1. 加載配置檔案 'META-INF/spring.factories'，并且從中擷取指定類型的類名的數組，放入set去重
Set<String> names = new LinkedHashSet(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
// 2. 建立對象執行個體
List<T> instances = this.createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
// 3. 排序對象集合
AnnotationAwareOrderComparator.sort(instances);
return instances;
}
·這裡隻分析介紹 --> SpringFactoriesLoader.loadFactoryNames()
public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
// 獲得factoryClassName,我們在這裡的 factoryClassName =org.springframework.context.ApplicationContextInitializer.
String factoryClassName = factoryClass.getName();
// 擷取 factoryClassName 為key下的 className 集合
return (List)loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
}
// 加載 META-INF/spring.factories 檔案，資訊以 key-value 形式存入 map
private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
// 首先從緩存 Map<ClassLoader, MultiValueMap<String, String>> cache 中擷取
MultiValueMap<String, String> result = (MultiValueMap)cache.get(classLoader);
if (result != null) {
return result;// 緩存中存在，傳回
} else {
try {
// 加載 META-INF/spring.factories 檔案
Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");
LinkedMultiValueMap result = new LinkedMultiValueMap();
while(urls.hasMoreElements()) {
URL url = (URL)urls.nextElement();
UrlResource resource = new UrlResource(url);
// 把resource 轉為 properties
Properties properties = PropertiesLoaderUtils.loadProperties(resource);
Iterator var6 = properties.entrySet().iterator();
while(var6.hasNext()) {
Entry<?, ?> entry = (Entry)var6.next();
String factoryClassName = ((String)entry.getKey()).trim();
String[] var9 = StringUtils.commaDelimitedListToStringArray((String)entry.getValue());
int var10 = var9.length;
for(int var11 = 0; var11 < var10; ++var11) {
String factoryName = var9[var11];
// 把 factoryClassName 下的所有 className 存入 result中
result.add(factoryClassName, factoryName.trim());
}
}
}
// 放入緩存
cache.put(classLoader, result);
return result;
} catch (IOException var13) {
throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", var13);
}
}
}
斷點調試檢視 result
·以 org.springframework.context.ApplicationContextInitializer 為key的集合中共有6個元素
因為 /Users/～/.m2/repository/org/springframework/boot/spring-boot/2.1.6.RELEASE/spring-boot-2.1.6.RELEASE.jar!/META-INF/spring.factories 中有4個，/Users/～/.m2/repository/org/springframework/boot/spring-boot-autoconfigure/2.1.6.RELEASE/spring-boot-autoconfigure-2.1.6.RELEASE.jar!/META-INF/spring.factories有2個
# Application Context Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\
org.springframework.boot.context.ContextIdApplicationContextInitializer,\
org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\
org.springframework.boot.web.context.ServerPortInfoApplicationContextInitializer
# Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener
·以 org.springframework.context.ApplicationListener 為key的集合中共有10個元素
因為 /Users/～/.m2/repository/org/springframework/boot/spring-boot/2.1.6.RELEASE/spring-boot-2.1.6.RELEASE.jar!/META-INF/spring.factories 中有9個，/Users/～/.m2/repository/org/springframework/boot/spring-boot-autoconfigure/2.1.6.RELEASE/spring-boot-autoconfigure-2.1.6.RELEASE.jar!/META-INF/spring.factories有1個
# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.ClearCachesApplicationListener,\
org.springframework.boot.builder.ParentContextCloserApplicationListener,\
org.springframework.boot.context.FileEncodingApplicationListener,\
org.springframework.boot.context.config.AnsiOutputApplicationListener,\
org.springframework.boot.context.config.ConfigFileApplicationListener,\
org.springframework.boot.context.config.DelegatingApplicationListener,\
org.springframework.boot.context.logging.ClasspathLoggingApplicationListener,\
org.springframework.boot.context.logging.LoggingApplicationListener,\
org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener
# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.autoconfigure.BackgroundPreinitializer
· 然後拿着目前class類型下的 names集合，進行執行個體化(利用反射，就不詳細介紹)，最後進行排序。
--> classType=ApplicationContextInitializer.class 時擷取到的執行個體如下
--> classType=ApplicationListener.class 時擷取到的執行個體如下
stop......... 從第2、3步中的思緒中跳出來，分析初始化 SpringApplication 的最後一步
第4. --> SpringApplication.deduceMainApplicationClass()
private Class<?> deduceMainApplicationClass() {
try {
// 擷取目前方法調用棧元素
StackTraceElement[] stackTrace = (new RuntimeException()).getStackTrace();
StackTraceElement[] var2 = stackTrace;
int var3 = stackTrace.length;
for(int var4 = 0; var4 < var3; ++var4) {
StackTraceElement stackTraceElement = var2[var4];
// 找到 main 函數的類
if ("main".equals(stackTraceElement.getMethodName())) {
// 擷取擷取啟動類
return Class.forName(stackTraceElement.getClassName());
}
}
} catch (ClassNotFoundException var6) {
}
return null;
}
debug --> 通過尋找 main 方法找到啟動類 DemoApplication
賦與私有屬性 private Class<?> mainApplicationClass ;主要用于日志的列印
至此，SpringApplication 的初始化就完成啦!