mini-spring：03-扩展篇

PropertyPlaceholderConfigurer

经常需要将配置信息配置在properties文件中，然后在XML文件中以占位符的方式引用。

实现思路很简单，在bean实例化之前，编辑BeanDefinition，解析XML文件中的占位符，然后用properties文件中的配置值替换占位符。而BeanFactoryPostProcessor具有编辑BeanDefinition的能力，因此PropertyPlaceholderConfigurer继承自BeanFactoryPostProcessor。

测试： car.properties

1	brand=lamborghini

<?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
		 http://www.springframework.org/schema/context/spring-context-4.0.xsd">

    <bean class="org.springframework.beans.factory.PropertyPlaceholderConfigurer">
        <property name="location" value="classpath:car.properties" />
    </bean>

    <bean id="car" class="org.springframework.test.bean.Car">
        <property name="brand" value="${brand}" />
    </bean>

</beans>

public class PropertyPlaceholderConfigurerTest {

	@Test
	public void test() throws Exception {
		ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:property-placeholder-configurer.xml");

		Car car = applicationContext.getBean("car", Car.class);
		assertThat(car.getBrand()).isEqualTo("lamborghini");
	}
}

包扫描

结合bean的生命周期，包扫描只不过是扫描特定注解的类，提取类的相关信息组装成BeanDefinition注册到容器中。

在XmlBeanDefinitionReader中解析<context:component-scan />标签，扫描类组装BeanDefinition然后注册到容器中的操作在ClassPathBeanDefinitionScanner#doScan中实现。

测试：

@Component
public class Car {

}

package-scan.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
		 http://www.springframework.org/schema/context/spring-context-4.0.xsd">

    <context:component-scan base-package="org.springframework.test.bean"/>

</beans>

public class PackageScanTest {

	@Test
	public void testScanPackage() throws Exception {
		ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:package-scan.xml");

		Car car = applicationContext.getBean("car", Car.class);
		assertThat(car).isNotNull();
	}
}

@Value注解

注解@Value和@Autowired通过BeanPostProcessor处理。InstantiationAwareBeanPostProcessor增加postProcessPropertyValues方法，在bean实例化之后设置属性之前执行，查看AbstractAutowireCapableBeanFactory#doCreateBean方法。

增加AutowiredAnnotationBeanPostProcessor用于处理注解@Value，@Autowired的处理在下一节实现，在ClassPathBeanDefinitionScanner#doScan将其添加到容器中。查看AutowiredAnnotationBeanPostProcessor#postProcessPropertyValues，其中字符解析器StringValueResolver在PropertyPlaceholderConfigurer中添加到BeanFactory中。

测试：

@Component
public class Car {

	@Value("${brand}")
	private String brand;
}

value-annotation.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
		 http://www.springframework.org/schema/context/spring-context-4.0.xsd">

    <bean class="org.springframework.beans.factory.PropertyPlaceholderConfigurer">
        <property name="location" value="classpath:car.properties" />
    </bean>

    <context:component-scan base-package="org.springframework.test.bean"/>

</beans>

car.properties

1	brand=lamborghini

public class ValueAnnotationTest {

	@Test
	public void testValueAnnotation() throws Exception {
		ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:value-annotation.xml");

		Car car = applicationContext.getBean("car", Car.class);
		assertThat(car.getBrand()).isEqualTo("lamborghini");
	}
}

@Autowired注解

@Autowired注解的处理见AutowiredAnnotationBeanPostProcessor#postProcessPropertyValues

测试：

@Component
public class Car {

}

@Component
public class Person implements InitializingBean, DisposableBean {

	@Autowired
	private Car car;
}

autowired-annotation.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
		 http://www.springframework.org/schema/context/spring-context-4.0.xsd">

    <context:component-scan base-package="org.springframework.test.bean"/>

</beans>

public class AutowiredAnnotationTest {

	@Test
	public void testAutowiredAnnotation() throws Exception {
		ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:autowired-annotation.xml");

		Person person = applicationContext.getBean(Person.class);
		assertThat(person.getCar()).isNotNull();
	}
}

bugfix：没有为代理bean设置属性

问题现象：没有为代理bean设置属性

问题原因：织入逻辑在InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation中执行，而该方法如果返回非null，会导致”短路”，不会执行后面的设置属性逻辑。因此如果该方法中返回代理bean后，不会为代理bean设置属性。

修复方案：跟spring保持一致，将织入逻辑迁移到BeanPostProcessor#postProcessAfterInitialization，即将DefaultAdvisorAutoProxyCreator#postProcessBeforeInstantiation的内容迁移到DefaultAdvisorAutoProxyCreator#postProcessAfterInitialization中。

顺便完善spring的扩展机制，为InstantiationAwareBeanPostProcessor增加postProcessAfterInstantiation方法，该方法在bean实例化之后设置属性之前执行。

至此，bean的生命周期比较完整了，如下：

测试： populate-proxy-bean-with-property-values.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
		 http://www.springframework.org/schema/context/spring-context-4.0.xsd">

    <bean id="worldService" class="org.springframework.test.service.WorldServiceImpl">
        <property name="name" value="earth"/>
    </bean>

    <bean class="org.springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator"/>

    <bean id="pointcutAdvisor" class="org.springframework.aop.aspectj.AspectJExpressionPointcutAdvisor">
        <property name="expression" value="execution(* org.springframework.test.service.WorldService.explode(..))"/>
        <property name="advice" ref="methodInterceptor"/>
    </bean>


    <bean id="methodInterceptor" class="org.springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor">
        <property name="advice" ref="beforeAdvice"/>
    </bean>

    <bean id="beforeAdvice" class="org.springframework.test.common.WorldServiceBeforeAdvice"/>

</beans>

public class WorldServiceImpl implements WorldService {

	private String name;

	@Override
	public void explode() {
		System.out.println("The " + name + " is going to explode");
	}

	//setter and getter
}

public class AutoProxyTest {

	@Test
	public void testPopulateProxyBeanWithPropertyValues() throws Exception {
		ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:populate-proxy-bean-with-property-values.xml");

		//获取代理对象
		WorldService worldService = applicationContext.getBean("worldService", WorldService.class);
		worldService.explode();
		assertThat(worldService.getName()).isEqualTo("earth");
	}
}

类型转换（一）

spring在org.springframework.core.convert.converter包中定义了三种类型转换器接口：Converter、ConverterFactory、GenericConverter。

一、Converter

public interface Converter<S, T> {

	/**
	 * 类型转换
	 */
	T convert(S source);
}

Converter能将S类型的对象转换为T类型的对象，比如将String类型的对象转换为Integer类型的对象的实现类：

public class StringToIntegerConverter implements Converter<String, Integer> {
	@Override
	public Integer convert(String source) {
		return Integer.valueOf(source);
	}
}

使用：

1	Integer num = new StringToIntegerConverter().convert("8888");

二、ConverterFactory

public interface ConverterFactory<S, R> {

	<T extends R> Converter<S, T> getConverter(Class<T> targetType);
}

Converter<S,T>接口适合一对一的类型转换，如果要将String类型转换为Ineger/Long/Float/Double/Decimal等类型，就要实现一系列的StringToInteger/StringToLongConverter/StringToFloatConverter转换器，非常不优雅。

ConverterFactory接口则适合一对多的类型转换，可以将一种类型转换为另一种类型及其子类。比如将String类型转换为Ineger/Long/Float/Double/Decimal等Number类型时，只需定义一个ConverterFactory转换器：

public class StringToNumberConverterFactory implements ConverterFactory<String, Number> {

	@Override
	public <T extends Number> Converter<String, T> getConverter(Class<T> targetType) {
		return new StringToNumber<T>(targetType);
	}

	private static final class StringToNumber<T extends Number> implements Converter<String, T> {

		private final Class<T> targetType;

		public StringToNumber(Class<T> targetType) {
			this.targetType = targetType;
		}

		@Override
		public T convert(String source) {
			if (source.length() == 0) {
				return null;
			}

			if (targetType.equals(Integer.class)) {
				return (T) Integer.valueOf(source);
			} else if (targetType.equals(Long.class)) {
				return (T) Long.valueOf(source);
			}
			//TODO 其他数字类型

			else {
				throw new IllegalArgumentException(
						"Cannot convert String [" + source + "] to target class [" + targetType.getName() + "]");
			}
		}
	}

}

使用：

1
2
3

StringToNumberConverterFactory converterFactory = new StringToNumberConverterFactory();
Converter<String, Integer> stringToIntegerConverter = converterFactory.getConverter(Integer.class);
Integer num = stringToIntegerConverter.convert("8888");

三、GenericConverter

public interface GenericConverter {

	Set<ConvertiblePair> getConvertibleTypes();

	Object convert(Object source, Class sourceType, Class targetType);
}

String类型转换为Boolean类型的实现类：

public class StringToBooleanConverter implements GenericConverter {
	@Override
	public Set<ConvertiblePair> getConvertibleTypes() {
		return Collections.singleton(new ConvertiblePair(String.class, Boolean.class));
	}

	@Override
	public Object convert(Object source, Class sourceType, Class targetType) {
		return Boolean.valueOf((String) source);
	}
}

使用:

1	Boolean flag = new StringToBooleanConverter().convert("true", String.class, Boolean.class);

ConversionService是类型转换体系的核心接口，将以上三种类型转换器整合到一起，GenericConversionService是其实现类，DefaultConversionService在GenericConversionService的基础上添加内置转换器。

测试见TypeConversionFirstPartTest。

public class TypeConversionFirstPartTest {

	@Test
	public void testStringToIntegerConverter() throws Exception {
		StringToIntegerConverter converter = new StringToIntegerConverter();
		Integer num = converter.convert("8888");
		assertThat(num).isEqualTo(8888);
	}

	@Test
	public void testStringToNumberConverterFactory() throws Exception {
		StringToNumberConverterFactory converterFactory = new StringToNumberConverterFactory();

		Converter<String, Integer> stringToIntegerConverter = converterFactory.getConverter(Integer.class);
		Integer intNum = stringToIntegerConverter.convert("8888");
		assertThat(intNum).isEqualTo(8888);

		Converter<String, Long> stringToLongConverter = converterFactory.getConverter(Long.class);
		Long longNum = stringToLongConverter.convert("8888");
		assertThat(longNum).isEqualTo(8888L);
	}

	@Test
	public void testGenericConverter() throws Exception {
		StringToBooleanConverter converter = new StringToBooleanConverter();

		Boolean flag = (Boolean) converter.convert("true", String.class, Boolean.class);
		assertThat(flag).isTrue();
	}

	@Test
	public void testGenericConversionService() throws Exception {
		GenericConversionService conversionService = new GenericConversionService();
		conversionService.addConverter(new StringToIntegerConverter());

		Integer intNum = conversionService.convert("8888", Integer.class);
		assertThat(conversionService.canConvert(String.class, Integer.class)).isTrue();
		assertThat(intNum).isEqualTo(8888);

		conversionService.addConverterFactory(new StringToNumberConverterFactory());
		assertThat(conversionService.canConvert(String.class, Long.class)).isTrue();
		Long longNum = conversionService.convert("8888", Long.class);
		assertThat(longNum).isEqualTo(8888L);

		conversionService.addConverter(new StringToBooleanConverter());
		assertThat(conversionService.canConvert(String.class, Boolean.class)).isTrue();
		Boolean flag = conversionService.convert("true", Boolean.class);
		assertThat(flag).isTrue();
	}
}

类型转换（二）

上一节实现了spring中的类型转换体系，本节将类型转换的能力整合到容器中。

为了方便使用，提供了创建ConversionService的FactoryBean——ConversionServiceFactoryBean。

如果有定义ConversionService，在AbstractApplicationContext#finishBeanFactoryInitialization方法中设置到容器中。

类型转换的时机有两个：

为bean填充属性时，见AbstractAutowireCapableBeanFactory#applyPropertyValues
处理@Value注解时，见AutowiredAnnotationBeanPostProcessor#postProcessPropertyValues

你可能会有疑问，如果没有定义ConversionService，是怎么进行基本类型的转换的？其实spring为了向下兼容保留了一套比较旧的类型转换机制，没有定义ConversionService时会使用其进行基本类型的转换工作，不必关注旧的类型转换机制。

测试：

public class Car {

	private int price;

	private LocalDate produceDate;
}

public class StringToLocalDateConverter implements Converter<String, LocalDate> {

	private final DateTimeFormatter DATE_TIME_FORMATTER;

	public StringToLocalDateConverter(String pattern) {
		DATE_TIME_FORMATTER = DateTimeFormatter.ofPattern(pattern);
	}

	@Override
	public LocalDate convert(String source) {
		return LocalDate.parse(source, DATE_TIME_FORMATTER);
	}
}

type-conversion-second-part.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
		 http://www.springframework.org/schema/context/spring-context-4.0.xsd">

    <bean id="car" class="org.springframework.test.bean.Car">
        <property name="price" value="1000000"/>
        <property name="produceDate" value="2021-01-01"/>
    </bean>

    <bean id="conversionService" class="org.springframework.context.support.ConversionServiceFactoryBean">
        <property name="converters" ref="converters"/>
    </bean>

    <bean id="converters" class="org.springframework.test.common.ConvertersFactoryBean"/>

</beans>

public class TypeConversionSecondPartTest {

	@Test
	public void testConversionService() throws Exception {
		ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:type-conversion-second-part.xml");

		Car car = applicationContext.getBean("car", Car.class);
		assertThat(car.getPrice()).isEqualTo(1000000);
		assertThat(car.getProduceDate()).isEqualTo(LocalDate.of(2021, 1, 1));
	}
}