Spring 源码(9)Spring Bean的创建过程的前期准备

回顾总结

到目前为止,Spring源码中AbstractApplicationContext#refresh方法的已经解读到第11个方法finishBeanFactoryInitialization,前10个方法介绍了:

  • BeanFactory的准备,创建,刷新,个性化BeanFactory的扩展点,自定义属性解析;
  • 环境信息Environment的加载(包括环境变量、系统变量等);
  • BeanDefinition的加载,解析,自定义xml的方式;
  • BeanFactoryPostProcessor的注册与执行流程,BeanDefinitionRegistryPostProcessor的解析,ConfigurationClassPostProcessorSpring注解的解析过程(@Component、@PropertySources、@PropertySource、@ComponentScans、@ComponentScan、@Import等注解的解析),Spring Boot 是如何通过@Configuration+@Import + ImportSelector进行自动装配的等;
  • BeanPostProcessor的注册流程;
  • 国际化,Spring事件驱动的加载执行过程;

finishBeanFactoryInitialization 解析过程

接下来开始解析SpringBean的创建过程,上源码:

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
  // Initialize conversion service for this context.
  if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
      beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
    // 设置转换服务,转换服务用来对属性值进行解析的
    beanFactory.setConversionService(
      beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
  }

  // Register a default embedded value resolver if no BeanFactoryPostProcessor
  // (such as a PropertySourcesPlaceholderConfigurer bean) registered any before:
  // at this point, primarily for resolution in annotation attribute values.
  // 如果之前没有注册过任何 BeanFactoryPostProcessor(例如 PropertySourcesPlaceholderConfigurer bean),
  // 则注册一个默认的嵌入值解析器:此时,主要用于解析注释属性值。
  if (!beanFactory.hasEmbeddedValueResolver()) {
    beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
  }

  // Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
  String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
  for (String weaverAwareName : weaverAwareNames) {
    getBean(weaverAwareName);
  }

  // Stop using the temporary ClassLoader for type matching.
  beanFactory.setTempClassLoader(null);

  // Allow for caching all bean definition metadata, not expecting further changes.
  // 允许缓存所有 bean 定义元数据,而不是期望进一步的更改
  beanFactory.freezeConfiguration();

  // Instantiate all remaining (non-lazy-init) singletons.
  // 实例化所有剩余的(非惰性初始化)单例
  beanFactory.preInstantiateSingletons();
}
  • 判断是否存在转换服务,有就设置
  • 判断是否有内置的值解析器,没有就创建一个处理占位符的解析器
  • 实例化LoadTimeWeaverAware,进行早期的Bean的创建
  • 停止使用临时的类加载器
  • 冻结BeanDefinition的元数据信息,防止被修改
  • 开始实例化所有的单例bean对象

除了beanFactory.preInstantiateSingletons() 方法,其他都是Bean创建的准备,接下来一个一个分析,首先是转换服务的设置。

转换服务ConversionService的初始化

方法一开始设置了一个转换服务,这个转换服务在Spring中还是非常的重要的,比如我们xml中配置一个String 类型的属性值,但是在Bean的定义中是一个Integer类型的,这时Spring就会自动帮我们转出来,他是怎么做的呢?

Spring中有几个比较重要的接口:

  • Converer 用于将对象S转换为对象T
  • ConverterFactory 一个转换工厂,能够将对象S转成一类对象R的子集T,比如可以将字符串S转换为TInteger、Long等)Number类型R的子集
  • GenericConverter支持多种类型之间互相转换。

Spring转换器接口ConversionService 的默认实现是DefaultConversionService,这个默认的转换器实现中,内置了很多的转换器,比如:

public static void addDefaultConverters(ConverterRegistry converterRegistry) {
  addScalarConverters(converterRegistry);
  addCollectionConverters(converterRegistry);

  converterRegistry.addConverter(new ByteBufferConverter((ConversionService) converterRegistry));
  converterRegistry.addConverter(new StringToTimeZoneConverter());
  converterRegistry.addConverter(new ZoneIdToTimeZoneConverter());
  converterRegistry.addConverter(new ZonedDateTimeToCalendarConverter());

  converterRegistry.addConverter(new ObjectToObjectConverter());
  converterRegistry.addConverter(new IdToEntityConverter((ConversionService) converterRegistry));
  converterRegistry.addConverter(new FallbackObjectToStringConverter());
  converterRegistry.addConverter(new ObjectToOptionalConverter((ConversionService) converterRegistry));
}

public static void addCollectionConverters(ConverterRegistry converterRegistry) {
  ConversionService conversionService = (ConversionService) converterRegistry;
  // 数组转集合
  converterRegistry.addConverter(new ArrayToCollectionConverter(conversionService));
  // 集合转数组
  converterRegistry.addConverter(new CollectionToArrayConverter(conversionService));

  converterRegistry.addConverter(new ArrayToArrayConverter(conversionService));
  converterRegistry.addConverter(new CollectionToCollectionConverter(conversionService));
  converterRegistry.addConverter(new MapToMapConverter(conversionService));
  // 数组转字符串
  converterRegistry.addConverter(new ArrayToStringConverter(conversionService));
  converterRegistry.addConverter(new StringToArrayConverter(conversionService));

  converterRegistry.addConverter(new ArrayToObjectConverter(conversionService));
  converterRegistry.addConverter(new ObjectToArrayConverter(conversionService));

  converterRegistry.addConverter(new CollectionToStringConverter(conversionService));
  converterRegistry.addConverter(new StringToCollectionConverter(conversionService));

  converterRegistry.addConverter(new CollectionToObjectConverter(conversionService));
  converterRegistry.addConverter(new ObjectToCollectionConverter(conversionService));

  converterRegistry.addConverter(new StreamConverter(conversionService));
}

private static void addScalarConverters(ConverterRegistry converterRegistry) {
  converterRegistry.addConverterFactory(new NumberToNumberConverterFactory());

  converterRegistry.addConverterFactory(new StringToNumberConverterFactory());
  converterRegistry.addConverter(Number.class, String.class, new ObjectToStringConverter());

  converterRegistry.addConverter(new StringToCharacterConverter());
  converterRegistry.addConverter(Character.class, String.class, new ObjectToStringConverter());

  converterRegistry.addConverter(new NumberToCharacterConverter());
  converterRegistry.addConverterFactory(new CharacterToNumberFactory());

  converterRegistry.addConverter(new StringToBooleanConverter());
  converterRegistry.addConverter(Boolean.class, String.class, new ObjectToStringConverter());

  converterRegistry.addConverterFactory(new StringToEnumConverterFactory());
  converterRegistry.addConverter(new EnumToStringConverter((ConversionService) converterRegistry));

  converterRegistry.addConverterFactory(new IntegerToEnumConverterFactory());
  converterRegistry.addConverter(new EnumToIntegerConverter((ConversionService) converterRegistry));

  converterRegistry.addConverter(new StringToLocaleConverter());
  converterRegistry.addConverter(Locale.class, String.class, new ObjectToStringConverter());

  converterRegistry.addConverter(new StringToCharsetConverter());
  converterRegistry.addConverter(Charset.class, String.class, new ObjectToStringConverter());

  converterRegistry.addConverter(new StringToCurrencyConverter());
  converterRegistry.addConverter(Currency.class, String.class, new ObjectToStringConverter());

  converterRegistry.addConverter(new StringToPropertiesConverter());
  converterRegistry.addConverter(new PropertiesToStringConverter());

  converterRegistry.addConverter(new StringToUUIDConverter());
  converterRegistry.addConverter(UUID.class, String.class, new ObjectToStringConverter());
}

可以说是非常的丰富的,基本上常见都是Spring提供了,非常贴心。

那么怎么使用呢?

不懂当然是上官网:https://docs.spring.io/spring-framework/docs/current/reference/html/core.html#core-convert ,这里可以看到我们只需要将ConversionServiceFactoryBean 配置到Spring容器中就可以了,Spring内置的转换器就可以工作了,非常方便。

ConversionServiceFactoryBean实现了FactoryBean接口和InitializingBean 接口,而InitializingBean#afterPropertiesSet是初始化Bean过程中需要执行的。ConversionServiceFactoryBean源码中:

@Override
public void afterPropertiesSet() {
  this.conversionService = createConversionService();
  ConversionServiceFactory.registerConverters(this.converters, this.conversionService);
}

protected GenericConversionService createConversionService() {
  return new DefaultConversionService();
}

// 构造函数
public DefaultConversionService() {
  // 添加默认的转换器
  addDefaultConverters(this);
}

可以看到这个ConversionServiceFactroyBean就是用来初始化转换器的,并且这个类还提供了扩展,可以自定义转换器加入到转换器集合中。

自定义转换器

自定义String转Integer类型的转换器:

/**
 * @author <a href="https://www.cnblogs.com/redwinter/">redwinter</a>
 * @since 1.0
 **/
public class StringToIntegerConverter implements Converter<String,Integer> , ConditionalConverter {
	@Override
	public Integer convert(String source) {
		return NumberUtils.parseNumber(source,Integer.class);
	}

	@Override
	public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
		System.out.println(sourceType.getType());
		System.out.println(targetType.getType());
		return true;
	}
}

逻辑非常简单,直接调用Spring提供的工具类进行转换。

配置xml:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	   xmlns:context="http://www.springframework.org/schema/context"
	   xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">

	<context:component-scan base-package="com.redwinter.selfconverter"/>
	<!--配置转化器-->
	<bean class="org.springframework.context.support.ConversionServiceFactoryBean">
		<property name="converters">
			<set>
				<bean class="com.redwinter.selfconverter.StringToIntegerConverter"/>
			</set>
		</property>
	</bean>

</beans>

创建转换器客户端:

/**
 * @author <a href="https://www.cnblogs.com/redwinter/">redwinter</a>
 * @since 1.0
 **/
@Service
public class MyConverter {

	private final ConversionService conversionService;

	public MyConverter(ConversionService conversionService) {
		this.conversionService = conversionService;
	}

	public void test(String source){
		System.out.println(conversionService.convert(source, Integer.class));
	}
}

创建测试:

/**
 * @author <a href="2360564660@qq.com">redwinter</a>
 * @since 1.0
 **/
public class FactoryBeanTest {

	@Test
	public void test(){
		MyClassPathXmlApplicationContext context = new MyClassPathXmlApplicationContext("spring-factory.xml");
		MyConverter myConverter = context.getBean(MyConverter.class);
		myConverter.test("12345");
	}
}

输出:

class java.lang.String
class java.lang.Integer
12345

分析完转换服务,接下来分析 值解析器的添加。

默认的值解析器

// 省略代码.....
// Register a default embedded value resolver if no BeanFactoryPostProcessor
// (such as a PropertySourcesPlaceholderConfigurer bean) registered any before:
// at this point, primarily for resolution in annotation attribute values.
// 如果之前没有注册过任何 BeanFactoryPostProcessor(例如 PropertySourcesPlaceholderConfigurer bean),
// 则注册一个默认的嵌入值解析器:此时,主要用于解析注释属性值。
if (!beanFactory.hasEmbeddedValueResolver()) {
  beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
}
// 省略代码.....


首先判断了容器中是否存在嵌入的值解析器,如果没有就添加一个进去,这里添加进去的是StringValueResolver,点击resolvePlaceHolders方法进去,最终会在AbstractPropertyResolver#resolvePlaceholders中创建一个PropertyPlaceholderHelper

private PropertyPlaceholderHelper createPlaceholderHelper(boolean ignoreUnresolvablePlaceholders) {
  // 前缀为 ${ ,后缀为 },值的分隔符为 : ,比如 ${username:zhansan} username没有的话,后面的为默认的值
  return new PropertyPlaceholderHelper(this.placeholderPrefix, this.placeholderSuffix,
                                       this.valueSeparator, ignoreUnresolvablePlaceholders);
}

如果已经注册过一个BFPP的占位符解析器的话,就不需要在注册了,BFPP的占位符解析器就是PropertySourcesPlaceholderConfigurer ,专门用于解析占位符的,比如在xml中或者yaml中,配置类似于${jdbc.username} 这种格式的,就会被解析器解析。PropertySourcesPlaceholderConfigurer 这个解析器实现了BeanFactoryPostProcessor接口,能够对BeanDefinition进行处理,当然也可以对属性值进行处理。

分析完值解析器,继续往下分析。

Bean创建前的其他准备

// 省略代码.....
// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
// 在prepareBeanFactory 准备BeanFactory时设置进去的,如果存在,则开始早期Bean的创建
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {
  getBean(weaverAwareName);
}

// Stop using the temporary ClassLoader for type matching.
// 停止使用临时的类加载器,这里也是在准备BeanFactory时设置进去的
beanFactory.setTempClassLoader(null);

// Allow for caching all bean definition metadata, not expecting further changes.
// 允许缓存所有 bean 定义元数据,而不是期望进一步的更改
beanFactory.freezeConfiguration();
// 省略代码.....

这里从容器中获取了AOP的织入,如果有的话就开始进行早期的Bean的创建;然后停止了临时的类加载器;然后就是冻结BeanDefinition的元数据信息。

public void freezeConfiguration() {
  this.configurationFrozen = true;
  this.frozenBeanDefinitionNames = StringUtils.toStringArray(this.beanDefinitionNames);
}

点击进来,其实就是设置了标识,防止后期对BeanDefinition的修改。

这前面的几个判断和方法实际上都是Bean创建的准备工作,接下来开始分析preInstantiateSingletons 预实例化所有的单例Bean

posted @ 2022-05-07 10:10  玲丶蹊  阅读(521)  评论(0编辑  收藏  举报