springboot启动流程
1. 内置容器启动
@SpringBootApplication
public class SpringbootdemoApplication {
public static void main(String[] args) {
SpringApplication.run(SpringbootdemoApplication.class, args);
}
}
springboot启动类入口方法如上，调用了 SpringApplication.run的静态方法run,并将启动类传了进去,如下所示。
public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
return run(new Class<?>[] { primarySource }, args);
}
又调用了重载的run方法。
public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
return new SpringApplication(primarySources).run(args);
}
在重载的run中通过传递进来的启动类，创建了一个SpringApplication对象，并调用了对象的run方法，下面我们先看看spring应用对象的创建
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();
//配置ApplicationContextInitializer，
setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
this.mainApplicationClass = deduceMainApplicationClass();
}
如上的getSpringFactoriesInstances方法，根据参数传递的类型来获取实例。
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
ClassLoader classLoader = getClassLoader();
//SpringFactoriesLoader.loadFactoryNames 通过加载器加载工厂名称，
Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
//根据名称反射创建响应对象。
List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
//排序
AnnotationAwareOrderComparator.sort(instances);
return instances;
}
通过SpringFactoriesLoader.loadFactoryNames(type, classLoader)方法，又调用 loadSpringFactories(classLoader)
private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
MultiValueMap<String, String> result = cache.get(classLoader);
if (result != null) {
return result;
}
try {
//通过FACTORIES_RESOURCE_LOCATION来加载资源，
//FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories"
Enumeration<URL> urls = (classLoader != null ?
classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
result = new LinkedMultiValueMap<>();
while (urls.hasMoreElements()) {
URL url = urls.nextElement();
UrlResource resource = new UrlResource(url);
Properties properties = PropertiesLoaderUtils.loadProperties(resource);
for (Map.Entry<?, ?> entry : properties.entrySet()) {
String factoryClassName = ((String) entry.getKey()).trim();
for (String factoryName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {
result.add(factoryClassName, factoryName.trim());
}
}
}
cache.put(classLoader, result);
return result;
}
catch (IOException ex) {
throw new IllegalArgumentException("Unable to load factories from location [" +
FACTORIES_RESOURCE_LOCATION + "]", ex);
}
}
综上：
创建SpringApplication对象时会查找META-INF/spring.factories文件，并将文件内容读取为properties,保存到缓存中。将其中 ApplicationContextInitializer.class、ApplicationListener.class进行实例化，并保存到对象中。
对象SpringApplication创建好后，会调用它的run方法，也就是spring应用的真正运行过程。
文档信息
- 本文作者：chayedankase
- 本文链接：https://chayedankase.github.io/2020/02/13/SpringBoot%E5%90%AF%E5%8A%A8%E6%B5%81%E7%A8%8B/
- 版权声明：自由转载-非商用-非衍生-保持署名（创意共享3.0许可证）