springboot源码解析-管中窥豹系列之Initializer(四)
2021-01-12 14:14
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一、前言
- Springboot源码解析是一件大工程,逐行逐句的去研究代码,会很枯燥,也不容易坚持下去。
- 我们不追求大而全,而是试着每次去研究一个小知识点,最终聚沙成塔,这就是我们的springboot源码管中窥豹系列。
二、Initializer
- 上一节我们介绍了Runner,它是在项目加载完成之后执行的
- 有后就有前,有没有在项目加载之前执行的呢?
我们今天介绍的ApplicationContextInitializer就是在spring的bean加载之前执行的
public interface ApplicationContextInitializer<C extends ConfigurableApplicationContext> { void initialize(C applicationContext); }
- 使用很简单,实现ApplicationContextInitializer接口就可以了
- 它是先于普通bean加载的,所以不能用@Component的方式
- 具体怎么被springboot加载,往下看,我们分析源码的时候说
三、源码解析
如果对springboot源码一点都不了解的,推荐先看第一节:整体架构
1、获取ApplicationContextInitializer
我们直接先看SpringApplication的构造方法
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) { ... setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class)); ... }
我们先看setInitializers方法,再看里面的getSpringFactoriesInstances方法
public void setInitializers(Collection<? extends ApplicationContextInitializer<?>> initializers) { this.initializers = new ArrayList<>(initializers); }
- 很简单,把查询的initializers集合赋值到本地变量上
- 接着看getSpringFactoriesInstances方法,这个initializers集合怎么查的
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) { return getSpringFactoriesInstances(type, new Class<?>[] {}); } private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) { ClassLoader classLoader = getClassLoader(); // Use names and ensure unique to protect against duplicates Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader)); List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names); AnnotationAwareOrderComparator.sort(instances); return instances; }
- (1) 获取ApplicationContextInitializer实现类的名称集合
- (2) 加载成实例instances
- (3) 排序,返回
我们先研究下SpringFactoriesLoader.loadFactoryNames(type, classLoader)这个方法:
public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) { String factoryTypeName = factoryType.getName(); return l 56c oadSpringFactories(classLoader).getOrDefault(factoryTypeName, Collections.emptyList()); } private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) { MultiValueMap<String, String> result = cache.get(classLoader); if (result != null) { return result; } try { 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 factoryTypeName = ((String) entry.getKey()).trim(); for (String factoryImplementationName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) { result.add(factoryTypeName, factoryImplementationName.trim()); } } } cache.put(classLoader, result); return result; } catch (IOException ex) { throw new IllegalArgumentException("Unable to load fa 56c ctories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex); } }
- 注意:factoryType就是我们传入的参数 ApplicationContextInitializer.class
- 这里有个新的map结构:MultiValueMap<String, String>,它和Map<String, List>是一样的
- 我们先看一下这里:classLoader.getResources(FACTORIES_RESOURCE_LOCATION)
public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
- 加载所有的META-INF/spring.factories,按接口名称放入MultiValueMap<String, String>,并cache
- 注意,这类文件不止一个,它们分布在不同的jar包里面
- 这么说你可能不懂,我们看一下这类文件长什么样,我们看一个系统自带的
# PropertySource Loaders org.springframework.boot.env.PropertySourceLoader=\ org.springframework.boot.env.PropertiesPropertySourceLoader,\ org.springframework.boot.env.YamlPropertySourceLoader # Run Listeners org.springframework.boot.SpringApplicationRunListener=\ org.springframework.boot.context.event.EventPublishingRunListener # Error Reporters org.springframework.boot.SpringBootExceptionReporter=\ org.springframework.boot.diagnostics.FailureAnalyzers # Application Context Initializers org.springframework.context.Ap ad8 plicationContextInitializer=\ org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\ org.springframework.boot.context.ContextIdApplicationContextInitializer,\ org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\ org.springframework.boot.rsocket.context.RSocketPortInfoApplicationContextInitializer,\ org.springframework.boot.web.context.ServerPortInfoApplicationContextInitializer # Application Listeners org.springframework.context.ApplicationListener=\ org.springframework.boot.ClearCachesApplicationListener,\ org.springframework.boot.builder.ParentContextCloserApplicationListener,\ org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\ 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 # Environment Post Processors org.springframework.boot.env.EnvironmentPostProcessor=\ org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\ org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor,\ org.springframework.boot.env.SystemEnvironmentPropertySourceEnvironmentPostProcessor,\ org.springframework.boot.reactor.DebugAgentEnvironmentPostProcessor # Failure Analyzers org.springframework.boot.diagnostics.FailureAnalyzer=\ org.springframework.boot.diagnostics.analyzer.BeanCurrentlyInCreationFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.BeanDefinitionOverrideFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.BeanNotOfRequiredTypeFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.BindFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.BindValidationFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.UnboundConfigurationPropertyFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.ConnectorStartFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.NoSuchMethodFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.NoUniqueBeanDefinitionFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.PortInUseFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.ValidationExceptionFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.InvalidConfigurationPropertyNameFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.InvalidConfigurationPropertyValueFailureA ad0 nalyzer # FailureAnalysisReporters org.springframework.boot.diagnostics.FailureAnalysisReporter=\ org.springframework.boot.diagnostics.LoggingFailureAnalysisReporter
- 接口 = 实现类1,实现类2,实现类3
- 我们假如有了自己的ApplicationContextInitializer实现类,我们在resource下面新建/META-INF/spring.factories文件,按上面的格式写上就可以被加载了
org.springframework.context.ApplicationContextInitializer=\ org.my.zb.MyApplicationContextInitializer
- 我们把思维拉回去,讲完了怎么取的实现类名称集合
- 回去看 createSpringFactoriesInstances();
private <T> List<T> createSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, ClassLoader classLoader, Object[] args, Set<String> names) { List<T> instances = new ArrayList<>(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; }
- (1) 获取Class
- (2) 获取构造函数
- (3) 利用反射新建instance对象
- (4) 加入集合
至此,我们就得到了:List instances
2、执行ApplicationContextInitializer
我们看SpringApplication的run方法:
public ConfigurableApplicationContext run(String... args) { ... try { ... prepareContext(context, environment, listeners, applicationArguments, printedBanner); ... } catch (Throwable ex) { ... } ... return context; }
进入到prepareContext方法:
private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment, SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) { ... applyInitializers(context); ... }
定位到了applyInitializers():
protected void applyInitializers(ConfigurableApplicationContext context) { for (ApplicationContextInitializer initializer : ge 11e1 tInitializers()) { Class<?> requiredType = GenericTypeResolver.resolveTypeArgument(initializer.getClass(), ApplicationContextInitializer.class); Assert.isInstanceOf(requiredType, context, "Unable to call initializer."); initializer.initialize(context); } }
-
前两行判断类型
-
最后一行回调执行
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