spring boot 源码解析2-SpringApplication初始化

2018-06-18 01:05:37来源：未知阅读 ()

前?

我们?成?个spring boot 项?时,会?带?个启动类. 代码如下:

@SpringBootApplication
public class SpringBootAnalysisApplication {
 public static void main(String[] args) {
 SpringApplication.run(SpringBootAnalysisApplication.class, args);
 }
}

就是这么简单的代码,构成了spring boot的世界. 那么代码中只有?个@SpringBootApplication 注解和调?了SpringApplication#run

?法.那么我们先来解析SpringApplication的run?法.

解析

?先调?了org.springframework.boot.SpringApplication#run(Object, String...) ?法.代码如下:

public static ConfigurableApplicationContext run(Object source, String... args) {
 return run(new Object[] { source }, args);
}

接着调?如下代码:

public static ConfigurableApplicationContext run(Object[] sources, String[] args) {
 return new SpringApplication(sources).run(args);
}

可以发现 ?先初始化了SpringApplication,然后调?其实例?法:run.

2. 在 SpringApplication 的构造器中,调?了 initialize ?法.

public SpringApplication(Object... sources) {
 initialize(sources);
}

3. SpringApplication#initialize?法代码如下:

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();
}

可以看到做了如下5件事:

1. 如果sources?度?于0的话,加?到SpringApplication的sources中,该sources是?个LinkedHashSet.

2. 调?deduceWebEnvironment?法判断是否是web环境

3. 设置initializers.

4. 设置Listeners.

5. 设置mainApplicationClass.

4. deduceWebEnvironment代码如下:

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;
}

可以发现会调?ClassUtils类的isPresent?法，检查classpath中是否存在javax.servlet.Servlet类和

org.springframework.web.context.ConfigurableWebApplicationContext类,如果存在的话,返回true.否则返回false.

5. 在设置Initializers时?先调?getSpringFactoriesInstances?法加载ApplicationContextInitializer.然后直接赋值给initializers.代码如下:

private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type) {
 return getSpringFactoriesInstances(type, new Class<?>[] {});
}

转?调?如下代码:

private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type,
 Class<?>[] parameterTypes, Object... args) {
 ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
 // Use names and ensure unique to protect against duplicates
 // 使?Set保存names来避免重复元素
 Set<String> names = new LinkedHashSet<String>(
 SpringFactoriesLoader.loadFactoryNames(type, classLoader));
 // 根据names来进?实例化
 List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
 classLoader, args, names);
 // 对实例进?排序
 AnnotationAwareOrderComparator.sort(instances);
 return instances;
}

该?法逻辑如下:

1. ?先获得ClassLoader.

2. 调?SpringFactoriesLoader#loadFactoryNames进?加载,然后放?到LinkedHashSet进?去重.

3. 调?createSpringFactoriesInstances进?初始化

4. 排序

其中SpringFactoriesLoader#loadFactoryNames代码如下:

public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
 String factoryClassName = factoryClass.getName();
 try {
 Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURC
E_LOCATION) :
 ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
 List<String> result = new ArrayList<String>();
 while (urls.hasMoreElements()) {
 URL url = urls.nextElement();
 Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
 String factoryClassNames = properties.getProperty(factoryClassName);
 result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassN
ames)));
 }
 return result;
 }
 catch (IOException ex) {
 throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() +
 "] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex);
 }
}

逻辑如下:

1. 获得factoryClassName,对于当前来说factoryClassName =org.springframework.context.ApplicationContextInitializer.

2. 通过传?的classLoader加载META-INF/spring.factories?件.

3. 通过调?PropertiesLoaderUtils#loadProperties将其转为Properties.

4. 获得factoryClassName对应的值进?返回.

对于当前来说,由于我们只加?了spring-boot-starter-web的依赖,因此会加载如下的配置:

1. 在spring-boot/META-INF/spring.factories中.org.springframework.context.ApplicationContextInitializer值如下:

org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\
org.springframework.boot.context.ContextIdApplicationContextInitializer,\
org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\
org.springframework.boot.context.embedded.ServerPortInfoApplicationContextInitializer

2. 在spring-boot-autoconfigure/src/main/resources/META-INF/spring.factories

中.org.springframework.context.ApplicationContextInitializer值如下:

org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
org.springframework.boot.autoconfigure.logging.AutoConfigurationReportLoggingInitializer

因此会加载6个.

SpringApplication#createSpringFactoriesInstances?法如下:

private <T> List<T> createSpringFactoriesInstances(Class<T> type,
 Class<?>[] parameterTypes, ClassLoader classLoader, Object[] args,
 Set<String> names) {
 List<T> instances = new ArrayList<T>(names.size());
 for (String name : names) {
 try {
 Class<?> instanceClass = ClassUtils.forName(name, classLoader);
 Assert.isAssignable(type, instanceClass);
 Constructor<?> constructor = instanceClass
 .getDeclaredConstructor(parameterTypes);
 T instance = (T) BeanUtils.instantiateClass(constructor, args);
 instances.add(instance);
 }
 catch (Throwable ex) {
 throw new IllegalArgumentException(
 "Cannot instantiate " + type + " : " + name, ex);
 }
 }
 return instances;
}

逻辑如下:遍历传?的names,也就是之前通过SpringFactoriesLoader加载的类名.通过遍历,依次调?其构造器进?初始化.加?到

instances.然后进?返回.

对于当前场景来说:

ConfigurationWarningsApplicationContextInitializer,DelegatingApplicationContextInitializer,ServerPortInfoApplicationContextInitializer

初始化没有做任何事.

ContextIdApplicationContextInitializer在初始化时.会获得spring boot的应?名.搜索路径如下:

1. spring.application.name

2. vcap.application.name

3. spring.config.name

4. 如果都没有配置的话,返回application.

代码如下:

private static final String NAME_PATTERN = "${spring.application.name:${vcap.application.name:${s
pring.config.name:application}}}";
public ContextIdApplicationContextInitializer() {
 this(NAME_PATTERN);
}
public ContextIdApplicationContextInitializer(String name) {
 this.name = name;
}

6. 设置SpringApplication#setListeners时,还是同样的套路.调?getSpringFactoriesInstances加载META-INF/spring.factories中配置

的org.springframework.context.ApplicationListener. 对于当前来说.加载的类如下:

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.liquibase.LiquibaseServiceLocatorApplicationListener,\
org.springframework.boot.logging.ClasspathLoggingApplicationListener,\
org.springframework.boot.logging.LoggingApplicationListener

这些类在构造器中都没有做任何事.

7. 调?SpringApplication#deduceMainApplicationClass?法.获得应?的启动类.该?法通过获取当前?法调?栈，找到main函数的

类.代码如下:

private Class<?> deduceMainApplicationClass() {
 try {
 StackTraceElement[] stackTrace = new RuntimeException().getStackTrace();
 for (StackTraceElement stackTraceElement : stackTrace) {
 if ("main".equals(stackTraceElement.getMethodName())) {
 return Class.forName(stackTraceElement.getClassName());
 }
 }
 }
 catch (ClassNotFoundException ex) {
 // Swallow and continue
 }
 return null;
}