首页 > 代码库 > springboot源码解析 - 构建SpringApplication

springboot源码解析 - 构建SpringApplication

2024-08-20 17:03:48   221人阅读

 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 duplicates18         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 names23         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 given10      * 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 Initializers2 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：

技术分享

 

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：

技术分享

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 continue14         }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

 

springboot源码解析 - 构建SpringApplication


联系
我们