springboot原始碼（二）
阿新 • • 發佈：2022-03-26
springboot自動裝配原理分析
- 何為自動裝配？
基於springboot原始碼（一）的內容後，spring一直都在致力於解決一個問題，就是如何讓bean的管理變得更簡單，讓開發者儘可能的少關注一些基礎化bean的配置，多關注業務程式碼。所以實現自動裝配。
自動裝配就是如何自動將bean裝載到IOC容器中。
實際上，在Enablexxxx模組驅動的出現已經有了自動裝配的雛形，真正能夠實現這一機制，還是spring4.0版本中的@Conditional註解的出現。
接下來就聊一下自動裝配到底是個什麼玩應兒......
2.自動裝配的演示（以Redis為類）
新增依賴：
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-redis</artifactId> </dependency>
新增配置：
spring: redis: host: 127.0.0.1 port: 6379
使用：
@Autowired privateStringRedisTemplate stringRedisTemplate;
按照上面的順序新增，就可以使用redisTemplate了。所以就會想redisTemplate為什麼可以被直接注入？什麼時候注入的？
這就是自動裝配，可以把classpath下依賴包的相關的bean，自動裝載到Spring IOC 容器中。怎麼做到的呢？？？？？？
來吧上原始碼
3.自動裝配原始碼分析
@Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @SpringBootConfiguration @EnableAutoConfiguration @ComponentScan(excludeFilters= { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class), @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) }) public @interface SpringBootApplication {
就看這個註解，就能猜到自動裝配大概率跟這個有關。
@EnableAutoConfiguration
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
/**
* Exclude specific auto-configuration classes such that they will never be applied.
* @return the classes to exclude
*/
Class<?>[] exclude() default {};
/**
* Exclude specific auto-configuration class names such that they will never be
* applied.
* @return the class names to exclude
* @since 1.3.0
*/
String[] excludeName() default {};
}
引入了一個AutoConfigurationImportSelector.class 根據上一篇內容會聯想到@import註解，實現ImportSelector的方式 可以把需要納入IOC管理的bean放到一個String[]中。
看一下AutoConfigurationImportSelector這個類
實現了ImportSelector這個介面，來看一下selectImports()方法
public String[] selectImports(AnnotationMetadata annotationMetadata) { if (!isEnabled(annotationMetadata)) { return NO_IMPORTS; } AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(annotationMetadata);
//把autoConfigurationEntry.getConfigurations()轉換成一個String[]，雖然現在還不知道返回的內容是什麼 return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations()); }
//搞清楚autoConfigurationEntry是什麼。
protected AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) { if (!isEnabled(annotationMetadata)) { return EMPTY_ENTRY; } AnnotationAttributes attributes = getAttributes(annotationMetadata);
//從META-INF/spring.factories中獲取EnableAutoConfiguration型別的全類路徑名 List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes); configurations = removeDuplicates(configurations); Set<String> exclusions = getExclusions(annotationMetadata, attributes); checkExcludedClasses(configurations, exclusions); configurations.removeAll(exclusions);
//從META-INF/spring-autoconfigure-metadata.properties中找到自動裝載的條件，類似於@Conditional註解的作用 configurations = getConfigurationClassFilter().filter(configurations); fireAutoConfigurationImportEvents(configurations, exclusions); return new AutoConfigurationEntry(configurations, exclusions); }
protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
//getSpringFactoriesLoaderFactoryClass()-->EnableAutoConfiguration.class List<String> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader()); Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you " + "are using a custom packaging, make sure that file is correct."); return configurations; }
public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {
String factoryTypeName = factoryType.getName();
//只獲得key為EnableAutoConfiguration的
return loadSpringFactories(classLoader).getOrDefault(factoryTypeName, Collections.emptyList());
}
private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) { MultiValueMap<String, String> result = cache.get(classLoader);
//只加載一次 if (result != null) { return result; } try {
//從META-INF/spring.factories下獲取所有的url 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 factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex); } }
得到EnableAutoConfiguration的已經知道，接下來看過濾
private ConfigurationClassFilter getConfigurationClassFilter() { if (this.configurationClassFilter == null) {
//從META-INF/spring.factories中得到key為AutoConfigurationImportFilter的 List<AutoConfigurationImportFilter> filters = getAutoConfigurationImportFilters(); for (AutoConfigurationImportFilter filter : filters) { invokeAwareMethods(filter); }
//從META-INF/spring-autoconfigure-metadata.properties中獲取自動裝載的條件xxxx.conditionalOnBean、conditionalOnClass等 this.configurationClassFilter = new ConfigurationClassFilter(this.beanClassLoader, filters); } return this.configurationClassFilter; }
接下來就是filter()方法，根據configurations 、autoConfigurationMetadata 根據過濾器的條件進行過濾就ok了。
到這springboot的自動裝配機制的主要流程就大致說完了。