背景
前一篇文章介绍了EntityManagerFactory的创建过程,有了EntityManagerFactory接下来就是要获取EntityManager了,但EntityManager的创建不再是通过@Conditional注解,而是使用的@PersistenceContext注解,那么Spring Data是如何识别@PersistenceContext注解,并注入EntityManager实例的,又是怎样通过上一步创建的EntityManagerFactory来获取EntityManager的呢?这篇文章就来分析这两个问题。
动态注册Bean
日常开发中我们一般会在类上使用@Service、@Component或者在方法上使用@Bean注解,被注解的类或者方法的返回值的对象实例会被Spring维护到ApplicationContext中,在使用的时可以通过@Autowired、@Resource注解的类变量自动注入对象实例。
如果不使用注解,通过编程的方式也能创建一个对象实例交由ApplicationContext管理。
BeanDefinitionBuilder
/**
* Description:通过编码的方式创建一个Bean实例
*/
public class BeanDefinitionBuilderTest {
public static void main(String[] args) {
DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
//使用builder构建一个MyBean的Bean定义
BeanDefinitionBuilder builder = BeanDefinitionBuilder.rootBeanDefinition(MyBean.class);
//为name属性赋值,会默认调用setName方法,如果没有setName方法会报错
builder.addPropertyValue("name","张三");
//往BeanFactory注册beanName为myBean的Bean定义
beanFactory.registerBeanDefinition("myBean", builder.getRawBeanDefinition());
//获取刚才注册的Bean
MyBean myBean = beanFactory.getBean(MyBean.class);
myBean.say();
}
private static class MyBean{
private String name;
public void setName(String name) {
this.name = name;
}
public void say(){
System.out.println("MyBean name is "+ name);
}
}
}
控制台输出
MyBean name is 张三
可以看到MyBean并未使用任何注解,而是通过BeanDefinitionBuilder创建了一个MyBean的实例并注册到beanFactory中,再从beanFactory获取出来调用say方法,为name设置的值被正确输出。
BeanFactoryPostProcessor
/**
* Description:通过实现BeanFactoryPostProcessor接口创建对象实例
*
* @author fangliangsheng
* @date 2018/11/18
*/
public class BeanFactoryPostProcessorTest {
public static void main(String[] args) {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(MyConfig.class);
MyBean myBean = context.getBean(MyBean.class);
myBean.say();
}
@Configuration
public static class MyConfig{
@Bean
public MyConfigBean myConfigBean(){
return new MyConfigBean();
}
}
private static class MyConfigBean implements BeanFactoryPostProcessor{
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
BeanDefinitionBuilder builder = BeanDefinitionBuilder.rootBeanDefinition(MyBean.class);
builder.addPropertyValue("name","张三");
((DefaultListableBeanFactory) beanFactory)
.registerBeanDefinition("myBean", builder.getRawBeanDefinition());
}
}
private static class MyBean{
private String name;
public void setName(String name) {
this.name = name;
}
public void say(){
System.out.println("MyBean name is "+ name);
}
}
}
控制台输出
MyBean name is 张三
BeanFactoryPostProcessor接口只有一个方法postProcessBeanFactory,该方法的调用时机是Application Context的Bean Factory初始化完成后。
InstantiationAwareBeanPostProcessor
private static class MyConfigBean3 implements InstantiationAwareBeanPostProcessor{
@Override
public PropertyValues postProcessPropertyValues(PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException {
if (bean instanceof MyBean){
System.out.println("set property value:" + beanName +" "+ pvs.getPropertyValues()[0].getName() + " "+pvs.getPropertyValues()[0].getValue());
}
return pvs;
}
}
控制台输出
set property value:myBean name 张三
InstantiationAwareBeanPostProcessor接口能够拦截对象实例化时对属性的赋值操作,实现该接口并判断想要监控的类及属性,在注入值时可以实现自己想要的逻辑。例如根据一个配置再赋值时选择不同的实例,或者通过编程的方式再动态创建一个实例。
这里介绍BeanDefinitionBuilder、BeanFactoryPostProcessor、InstantiationAwareBeanPostProcessor主要是因为在创建EntityManager时Spring Data就是通过这些接口的协作完成的。
创建EntityManager
先看自动配置的入口类
@Configuration
//当存在DataSource实例和JpaRepository类时生效
@ConditionalOnBean(DataSource.class)
@ConditionalOnClass(JpaRepository.class)
//当还没有JpaRepositoryFactoryBean和JpaRepositoryConfigExtension实例时生效
//因为后面会创建这两个类的实例,意思就是不能重复创建
@ConditionalOnMissingBean({ JpaRepositoryFactoryBean.class,
JpaRepositoryConfigExtension.class })
@ConditionalOnProperty(prefix = "spring.data.jpa.repositories", name = "enabled", havingValue = "true", matchIfMissing = true)
//条件校验通过后引入JpaRepositoriesAutoConfigureRegistrar
@Import(JpaRepositoriesAutoConfigureRegistrar.class)
//在HibernateJpaAutoConfiguration之后自动配置,这点很关键,因为要现有EntityManagerFactory,这步的EntityManager才能创建
@AutoConfigureAfter(HibernateJpaAutoConfiguration.class)
public class JpaRepositoriesAutoConfiguration {
}
Import的JpaRepositoriesAutoConfigureRegistrar继承了AbstractRepositoryConfigurationSourceSupport,我们先看这个抽象类。
该抽象类有很多子类,看到类名是不是有点眼熟,这些就是Spring JPA支持的持久化实现。
public abstract class AbstractRepositoryConfigurationSourceSupport
implements BeanFactoryAware, ImportBeanDefinitionRegistrar, ResourceLoaderAware,
EnvironmentAware {
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,
BeanDefinitionRegistry registry) {
new RepositoryConfigurationDelegate(getConfigurationSource(registry),
this.resourceLoader, this.environment).registerRepositoriesIn(registry,
getRepositoryConfigurationExtension());
}
}
它继承了ImportBeanDefinitionRegistrar接口实现了registerBeanDefinitions方法,这是一个重要的切入点。registerBeanDefinitions方法的第二个入参是BeanDefinitionRegistry,通过这个registry接口就可以往Bean Factory注册各种实例了。具体的创建是交给RepositoryConfigurationDelegate待办的。
/**
* 定义Repository的创建步骤
* 通过RepositoryConfigurationSource的配置来源和RepositoryConfigurationExtension的具体实现
*/
public class RepositoryConfigurationDelegate {
private final RepositoryConfigurationSource configurationSource;
/**
* 将找到的repositories注册到BeanDefinitionRegistry中
* 类似于模版方法
*/
public List<BeanComponentDefinition> registerRepositoriesIn(BeanDefinitionRegistry registry,
RepositoryConfigurationExtension extension) {
extension.registerBeansForRoot(registry, configurationSource);
RepositoryBeanDefinitionBuilder builder = new RepositoryBeanDefinitionBuilder(registry, extension, resourceLoader,
environment);
List<BeanComponentDefinition> definitions = new ArrayList<>();
//找到Repository接口的子类并封装为RepositoryConfiguration
//Repository的子类也就是我们平时开发所定义的例如UserRepository
for (RepositoryConfiguration<? extends RepositoryConfigurationSource> configuration : extension
.getRepositoryConfigurations(configurationSource, resourceLoader, inMultiStoreMode)) {
//将configuration转化为BeanDefinitionBuilder,用于创建具体的实例
BeanDefinitionBuilder definitionBuilder = builder.build(configuration);
//EntityManager如何创建的答案就在这个地方了
//这里extension的子类是JpaRepositoryConfigExtension
extension.postProcess(definitionBuilder, configurationSource);
if (isXml) {
extension.postProcess(definitionBuilder, (XmlRepositoryConfigurationSource) configurationSource);
} else {
extension.postProcess(definitionBuilder, (AnnotationRepositoryConfigurationSource) configurationSource);
}
AbstractBeanDefinition beanDefinition = definitionBuilder.getBeanDefinition();
String beanName = configurationSource.generateBeanName(beanDefinition);
if (LOGGER.isDebugEnabled()) {
LOGGER.debug(REPOSITORY_REGISTRATION, extension.getModuleName(), beanName,
configuration.getRepositoryInterface(), configuration.getRepositoryFactoryBeanClassName());
}
beanDefinition.setAttribute(FACTORY_BEAN_OBJECT_TYPE, configuration.getRepositoryInterface());
registry.registerBeanDefinition(beanName, beanDefinition);
definitions.add(new BeanComponentDefinition(beanDefinition, beanName));
}
return definitions;
}
}
接下来看下JpaRepositoryConfigExtension的实现
public class JpaRepositoryConfigExtension extends RepositoryConfigurationExtensionSupport
//该方法是在上一个类的registerRepositoriesIn中调用的
//给builder指定类entityManager属性的赋值方法
@Override
public void postProcess(BeanDefinitionBuilder builder, RepositoryConfigurationSource source) {
Optional<String> transactionManagerRef = source.getAttribute("transactionManagerRef");
builder.addPropertyValue("transactionManager", transactionManagerRef.orElse(DEFAULT_TRANSACTION_MANAGER_BEAN_NAME));
builder.addPropertyValue("entityManager", getEntityManagerBeanDefinitionFor(source, source.getSource()));
builder.addPropertyReference("mappingContext", JPA_MAPPING_CONTEXT_BEAN_NAME);
}
//通过BeanDefinitionBuilder定义了SharedEntityManagerCreator的createSharedEntityManager
//为entityManager的创建方法
private static AbstractBeanDefinition getEntityManagerBeanDefinitionFor(RepositoryConfigurationSource config,
@Nullable Object source) {
BeanDefinitionBuilder builder = BeanDefinitionBuilder
.rootBeanDefinition("org.springframework.orm.jpa.SharedEntityManagerCreator");
builder.setFactoryMethod("createSharedEntityManager");
builder.addConstructorArgReference(getEntityManagerBeanRef(config));
AbstractBeanDefinition bean = builder.getRawBeanDefinition();
bean.setSource(source);
return bean;
}
}
结合动态注册Bean章节的内容,可以知道BeanDefinitionBuilder的作用。所以EntityManager的实际创建是通过SharedEntityManagerCreator的createSharedEntityManager方法。以上只是定义好了BeanDefinitionBuilder,builder中属性的赋值操作是对象实际实例时调用的。
接下来我们再看PersistenceAnnotationBeanPostProcessor,该类继承了InstantiationAwareBeanPostProcessor实现了postProcessPropertyValues方法,在动态注册Bean章节中,介绍了postProcessPropertyValues的作用。
public class PersistenceAnnotationBeanPostProcessor
implements InstantiationAwareBeanPostProcessor, DestructionAwareBeanPostProcessor,
MergedBeanDefinitionPostProcessor, PriorityOrdered, BeanFactoryAware, Serializable{
//拦截实例化对象时的赋值操作
@Override
public PropertyValues postProcessPropertyValues(
PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) {
//找到@PersistenceContext、@PersistenceUnit注解的方法
InjectionMetadata metadata = findPersistenceMetadata(beanName, bean.getClass(), pvs);
try {
metadata.inject(bean, beanName, pvs);
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "Injection of persistence dependencies failed", ex);
}
return pvs;
}
}
PersistenceAnnotationBeanPostProcessor的作用是实现PersistenceContext和PersistenceUnit注解的作用,即JPA规范定义通过@PersistenceContext注解的方法或者属性将会注入EntityManger实例,@PersistenceUnit注解的方法或者属性将会注入EntityManagerFactory实例.
结束
这篇文章主要分析了EntityManger的创建过程,
- AbstractRepositoryConfigurationSourceSupport的registerBeanDefinitions为切入点
- RepositoryConfigurationDelegate定义创建步骤
- JpaRepositoryConfigExtension通过BeanDefinitionBuilder指定了EntityManager的具体创建方法
以上涉及到的相关类,用一张类图展示
EntityManager是为谁创建的呢,创建出来后又是如何使用的呢,下一篇文章继续分析。