SpringBoot自动装配深入理解(12)

在这里大家留意一下最后一句processDeferredImportSelectors方法,在这里将会对DeferredImportSelector进行处理,这样我们就和AutoConfigurationSelectImporter结合到一起了:

private void processDeferredImportSelectors() {
        List<DeferredImportSelectorHolder> deferredImports = this.deferredImportSelectors;
        this.deferredImportSelectors = null;
        Collections.sort(deferredImports, DEFERRED_IMPORT_COMPARATOR);

for (DeferredImportSelectorHolder deferredImport : deferredImports) {
            ConfigurationClass configClass = deferredImport.getConfigurationClass();
            try {
                String[] imports = deferredImport.getImportSelector().selectImports(configClass.getMetadata());
                processImports(configClass, asSourceClass(configClass), asSourceClasses(imports), false);
            }
            catch (BeanDefinitionStoreException ex) {
                throw ex;
            }
            catch (Throwable ex) {
                throw new BeanDefinitionStoreException(
                        "Failed to process import candidates for configuration class [" +
                        configClass.getMetadata().getClassName() + "]", ex);
            }
        }
    }

请大家关注这句代码:String[] imports = deferredImport.getImportSelector().selectImports(configClass.getMetadata());在这里deferredImport的类型为DeferredImportSelectorHolder:

private static class DeferredImportSelectorHolder {

private final ConfigurationClass configurationClass;

private final DeferredImportSelector importSelector;

public DeferredImportSelectorHolder(ConfigurationClass configClass, DeferredImportSelector selector) {
            this.configurationClass = configClass;
            this.importSelector = selector;
        }

public ConfigurationClass getConfigurationClass() {
            return this.configurationClass;
        }

public DeferredImportSelector getImportSelector() {
            return this.importSelector;
        }
    }

在这个内部类里持有了一个DeferredImportSelector的引用,至此将会执行自动装配的所有操作

三、总结

  1)自动装配还是利用了SpringFactoriesLoader来加载META-INF/spring.factoires文件里所有配置的EnableAutoConfgruation,它会经过exclude和filter等操作,最终确定要装配的类

  2)  处理@Configuration的核心还是ConfigurationClassPostProcessor,这个类实现了BeanFactoryPostProcessor, 因此当AbstractApplicationContext执行refresh方法里的invokeBeanFactoryPostProcessors(beanFactory)方法时会执行自动装配。

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