1 package com.microservice.framework;
2
3 import org.springframework.boot.SpringApplication;
4 import org.springframework.boot.autoconfigure.SpringBootApplication;
5
6 @SpringBootApplication
7 public class MySpringAplication {
8
9 public void run(String[] args) {
10 SpringApplication sa = new SpringApplication(MySpringAplication.class);
11 sa.run(args);
12 }
13
14 }
SpringBoot启动过程：
1、构建SpringApplication对象
2、执行run()
一、构建SpringApplication对象
1 /**
2 * The application context will load beans from the specified sources
3 */
4 public SpringApplication(Object... sources) {
5 initialize(sources);
6 }
说明：
- 实例化该类的时候会加载bean到applicationContext中去
- 这里的入参是MySpringApplication.class这样一个Class<com.microservice.framework.MySpringApplication>对象
private final Set<Object> sources = new LinkedHashSet<Object>();
private boolean webEnvironment;
private Class<?> mainApplicationClass;
private void initialize(Object[] sources) {
if (sources != null && sources.length > 0) {
this.sources.addAll(Arrays.asList(sources));
}
this.webEnvironment = deduceWebEnvironment();
setInitializers((Collection) getSpringFactoriesInstances(
ApplicationContextInitializer.class));
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
this.mainApplicationClass = deduceMainApplicationClass();
}
步骤：
- 将传入的MySpringApplication.class对象放入Set集合
- 判断是否是web环境
- 创建ApplicationInitializer列表
- 初始化ApplicationListener列表
- 初始化主类mainApplicationClass
1.1、将传入的MySpringApplication.class对象放入Set集合
1.2、判断是否是web环境：
private static final String[] WEB_ENVIRONMENT_CLASSES = { "javax.servlet.Servlet",
"org.springframework.web.context.ConfigurableWebApplicationContext" };
private boolean deduceWebEnvironment() {
for (String className : WEB_ENVIRONMENT_CLASSES) {
if (!ClassUtils.isPresent(className, null)) {
return false;
}
}
return true;
}
说明：通过在classpath中查看是否存在WEB_ENVIRONMENT_CLASSES这个数组中所包含的所有类（实际上就是2个类），如果存在那么当前程序即是一个Web应用程序，反之则不然。
1.3、创建ApplicationContextInitializer列表
1 private List<ApplicationContextInitializer<?>> initializers;
2
3 public void setInitializers(
4 Collection<? extends ApplicationContextInitializer<?>> initializers) {
5 this.initializers = new ArrayList<ApplicationContextInitializer<?>>();
6 this.initializers.addAll(initializers);
7 }
8
9 private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type) {
10 return getSpringFactoriesInstances(type, new Class<?>[] {});
11 }
12
13 private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type,
14 Class<?>[] parameterTypes, Object... args) {
15 ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
16
17 // Use names and ensure unique to protect against duplicates
18 Set<String> names = new LinkedHashSet<String>(
19 SpringFactoriesLoader.loadFactoryNames(type, classLoader));
20 List<T> instances = new ArrayList<T>(names.size());
21
22 // Create instances from the names
23 for (String name : names) {
24 try {
25 Class<?> instanceClass = ClassUtils.forName(name, classLoader);
26 Assert.isAssignable(type, instanceClass);
27 Constructor<?> constructor = instanceClass.getConstructor(parameterTypes);
28 T instance = (T) constructor.newInstance(args);
29 instances.add(instance);
30 }
31 catch (Throwable ex) {
32 throw new IllegalArgumentException(
33 "Cannot instantiate " + type + " : " + name, ex);
34 }
35 }
36
37 AnnotationAwareOrderComparator.sort(instances);
38 return instances;
39 }
步骤：
- 调用SpringFactoriesLoader.loadFactoryNames(type, classLoader)来获取所有Spring Factories的名字，（这里是获取了四个ApplicationContextInitializer实现类的全类名，见下边）
- 为每一个Spring Factories根据读取到的名字创建其对象。（这里创建了4个对象）
- 将创建好的对象列表排序并返回。
其中，SpringFactoriesLoader.loadFactoryNames(type, classLoader)如下：
1 /**
2 * The location to look for factories.
3 * <p>Can be present in multiple JAR files.
4 */
5 public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
6
7 /**
8 * Load the fully qualified class names of factory implementations of the
9 * given type from {@value #FACTORIES_RESOURCE_LOCATION}, using the given
10 * class loader.
11 */
12 public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
13 String factoryClassName = factoryClass.getName();
14 try {
15 Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
16 ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
17 List<String> result = new ArrayList<String>();
18 while (urls.hasMoreElements()) {
19 URL url = urls.nextElement();
20 Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
21 String factoryClassNames = properties.getProperty(factoryClassName);
22 result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
23 }
24 return result;
25 }
26 catch (IOException ex) {
27 throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() +
28 "] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex);
29 }
30 }
META-INF/spring-factories
1 # Application Context Initializers 2 org.springframework.context.ApplicationContextInitializer=\ 3 org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\ 4 org.springframework.boot.context.ContextIdApplicationContextInitializer,\ 5 org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\ 6 org.springframework.boot.context.web.ServerPortInfoApplicationContextInitializer
说明：
- 从所有jar获取所有的META-INF/spring-factories文件。（这里只有spring-boot-1.3.0.RELEASE.jar下有一个）
- 遍历每一个spring-factories文件，并获取其下key为factoryClass.getName()（这里是入参
org.springframework.context.ApplicationContextInitializer）的value（这里有以上四个ApplicationContextInitializer实现类）
以上四个类的作用：
至此，设置ApplicationContextInitialize就完成了。
总结：整个setInitializers实际上就是初始化了SpringApplication的属性List<ApplicationContextInitializer<?>> initializers为一个ArrayList列表，该列表中有四个实例：
- ConfigurationWarningsApplicationContextInitializer的实例
- ContextIdApplicationContextInitializer的实例
- DelegatingApplicationContextInitializer实例
- ServerPortInfoApplicationContextInitializer实例
1.4、初始化ApplicationListener列表
1 private List<ApplicationListener<?>> listeners;
2
3 /**
4 * Sets the {@link ApplicationListener}s that will be applied to the SpringApplication
5 * and registered with the {@link ApplicationContext}.
6 * @param listeners the listeners to set
7 */
8 public void setListeners(Collection<? extends ApplicationListener<?>> listeners) {
9 this.listeners = new ArrayList<ApplicationListener<?>>();
10 this.listeners.addAll(listeners);
11 }
META-INF/spring-factories
1 # Application Listeners 2 org.springframework.context.ApplicationListener=\ 3 org.springframework.boot.builder.ParentContextCloserApplicationListener,\ 4 org.springframework.boot.context.FileEncodingApplicationListener,\ 5 org.springframework.boot.context.config.AnsiOutputApplicationListener,\ 6 org.springframework.boot.context.config.ConfigFileApplicationListener,\ 7 org.springframework.boot.context.config.DelegatingApplicationListener,\ 8 org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener,\ 9 org.springframework.boot.logging.ClasspathLoggingApplicationListener,\ 10 org.springframework.boot.logging.LoggingApplicationListener
以上八个listener的作用如下：
至此，整个setListeners方法结束，初始化了一个包含以上8个ApplicationListener实例的List集合。
1.5、初始化主类mainApplicationClass
1 private Class<?> mainApplicationClass;
2
3 private Class<?> deduceMainApplicationClass() {
4 try {
5 StackTraceElement[] stackTrace = new RuntimeException().getStackTrace();
6 for (StackTraceElement stackTraceElement : stackTrace) {
7 if ("main".equals(stackTraceElement.getMethodName())) {
8 return Class.forName(stackTraceElement.getClassName());
9 }
10 }
11 }
12 catch (ClassNotFoundException ex) {
13 // Swallow and continue
14 }
15 return null;
16 }
说明：获取main()方法所在的主类Class对象，并赋值给SpringApplication的mainApplicationClass属性。
至此，SpringApplication对象初始化完成了。
总结：整个SpringApplication初始化的过程，就是初始化了
- 一个包含入参MySpringApplication.class的sources的Set<Object>
- 一个当前环境是否是web环境的boolean webEnvironment
- 一个包含4个ApplicationContextInitializer实例的List
- 一个包含8个ApplicationListener实例的List
- 一个main方法所在的主类的Class对象。
注意：
本文基本参照http://zhaox.github.io/java/2016/03/22/spring-boot-start-flow 完成，该文的作者已经解析的很好了，我这里再抄一遍，只是为了加深记忆！！！
http://www.cnblogs.com/java-zhao/p/5540309.html
