前言
不知道从啥时候开始项目上就一直用MyBatis,其实我个人更新JPA些,因为JPA看起来OO的思想更强烈些,所以这才最近把JPA拿出来再看一看,使用起来也很简单,除了定义Entity实体外,声明自己的业务接口继承JpaRepository接口,什么逻辑也不用写,基本的增删改查,分页,排序就都搞定了。
我在实现JpaRepository接口时就有个疑问,那么实现类是什么?如果用过MyBatis肯定也知道,是接口和实现类之间有一个代理类专门来处理这块的业务,那么JPA这块是否也会有一个代理类来处理同样的业务呢? 总体来说我们有两个疑问,关键字分别是: 接口实现类,代理类是什么 。
工作原理分析
首先从spring-boot-autoconfiguration.jar中下的spring.factories中我们可以看到JPA的自动配置需要从JpaRepositoriesAutoConfiguration开始着手。 我先画了一张总的Spring Data JPA自动配置流程图,可以有个大概的认识,下面会从源代码层面再来读一读其工作原理,和关键代码都分布在那里。
JpaRepositoriesAutoConfiguration 自动配置
因为我们在pom中导入了spring-data-jpa.jar,数据库驱动jar包为系统默认jar,也就是说他们会出现在程序运行的classpath上,并且我们在yml文件中配置了数据源,所以在springboot程序启动中,springboot自动配置中关于JPA的自动配置就已经开始工作了,具体的自动配置类会从JpaRepositoriesAutoConfiguration开始。
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3307/readinglist?serverTimezone=UTC&useSSL=false&allowPublicKeyRetrieval\
=true
spring.datasource.username=root
spring.datasource.password=000
spring.jpa.generate-ddl=false
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true
从代码中可以看到JPA的默认实现是Hibernate,所以会先配置HibernateJpaAutoConfiguration,并且是在DataSource bean已经存在的情况下。
@Configuration(proxyBeanMethods = false)
@ConditionalOnBean(DataSource.class)
@ConditionalOnClass(JpaRepository.class)
@ConditionalOnMissingBean({ JpaRepositoryFactoryBean.class, JpaRepositoryConfigExtension.class })
@ConditionalOnProperty(prefix = "spring.data.jpa.repositories", name = "enabled", havingValue = "true",
matchIfMissing = true)
//导入JpaRepositoriesRegistrar
@Import(JpaRepositoriesRegistrar.class)
//先自动配置HibernateJpaAutoConfiguration, TaskExecutionAutoConfiguration
@AutoConfigureAfter({ HibernateJpaAutoConfiguration.class, TaskExecutionAutoConfiguration.class })
public class JpaRepositoriesAutoConfiguration {
}
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass({ LocalContainerEntityManagerFactoryBean.class, EntityManager.class, SessionImplementor.class })
@EnableConfigurationProperties(JpaProperties.class)
@AutoConfigureAfter({ DataSourceAutoConfiguration.class })
@Import(HibernateJpaConfiguration.class)
public class HibernateJpaAutoConfiguration {
}
这里你首先会看到必须是DataSource bean存在的情况下,其次还有一个关键信息就是不存在JpaRepositoryFactoryBean bean的情况下才会执行该自动配置,也就是说如果你想根据自己的业务重新实现一个FactoryBean,那么该自动配置则不会执行。 那么看起来JpaRepositoryFactoryBean可能看起来有点眼熟哦。
JpaRepositoryFactoryBean位于org.springframework.data.jpa.repository.support包下
用户自定义的JpaRepository作为bean注入Spring容器中
JpaRepositoriesRegistrar中静态内部类使用了@EnableJpaRepositories开启JPA。如果不是SpringBoot项目中该注解是需要手动开启。
class JpaRepositoriesRegistrar extends AbstractRepositoryConfigurationSourceSupport {
@EnableJpaRepositories
private static class EnableJpaRepositoriesConfiguration {
}
}
JpaRepositoriesRegistrar又继承了抽象类AbstractRepositoryConfigurationSourceSupport类。这是一个ImportBeanDefinitionRegistrar,设计目的就是在SpringBoot自动发现机制中发现用户自定义的JpaRepository。在Spring容器启动中,该ImportBeanDefinitionRegistrar就会执行。
public abstract class AbstractRepositoryConfigurationSourceSupport
implements ImportBeanDefinitionRegistrar, BeanFactoryAware, ResourceLoaderAware, EnvironmentAware {
}
在AbstractRepositoryConfigurationSourceSupport类中重写了registerBeanDefinitions方法,这个方法里又把实例化的任务交给了RepositoryConfigurationDelegate#registerRepositoriesIn()。
AbstractRepositoryConfigurationSourceSupport#registerBeanDefinitions
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry,
BeanNameGenerator importBeanNameGenerator) {
RepositoryConfigurationDelegate delegate = new RepositoryConfigurationDelegate(
getConfigurationSource(registry, importBeanNameGenerator), this.resourceLoader, this.environment);
delegate.registerRepositoriesIn(registry, getRepositoryConfigurationExtension());
}
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
registerBeanDefinitions(importingClassMetadata, registry, null);
}
RepositoryConfigurationDelegate#registerRepositoriesIn
public class RepositoryConfigurationDelegate {
public List registerRepositoriesIn(BeanDefinitionRegistry registry, RepositoryConfigurationExtension extension) {
extension.registerBeansForRoot(registry, this.configurationSource);
RepositoryBeanDefinitionBuilder builder = new RepositoryBeanDefinitionBuilder(registry, extension, this.configurationSource, this.resourceLoader, this.environment);
List definitions = new ArrayList();
StopWatch watch = new StopWatch();
watch.start();
//extension.getRepositoryConfigurations() 会扫描相应的包并找到用户自定义JpaRepository接口
Collection> configurations = extension.getRepositoryConfigurations(this.configurationSource, this.resourceLoader, this.inMultiStoreMode);
Map> configurationsByRepositoryName = new HashMap(configurations.size());
Iterator var8 = configurations.iterator();
while(var8.hasNext()) {
RepositoryConfiguration configuration = (RepositoryConfiguration)var8.next();
configurationsByRepositoryName.put(configuration.getRepositoryInterface(), configuration);
//对于每个扫描找到的用户自定义JpaRepository,构建一个BeanDefinitionBuilder,
//就是在这个步骤中将该BeanDefinition同JpaRepositoryFactoryBean建立关系
BeanDefinitionBuilder definitionBuilder = builder.build(configuration);
extension.postProcess(definitionBuilder, this.configurationSource);
if (this.isXml) {
extension.postProcess(definitionBuilder, (XmlRepositoryConfigurationSource)this.configurationSource);
} else {
extension.postProcess(definitionBuilder, (AnnotationRepositoryConfigurationSource)this.configurationSource);
}
//这里根据所发现的用户自定义JpaRepository接口的名字构造一个bean名称
AbstractBeanDefinition beanDefinition = definitionBuilder.getBeanDefinition();
beanDefinition.setResourceDescription(configuration.getResourceDescription());
String beanName = this.configurationSource.generateBeanName(beanDefinition);
if (logger.isTraceEnabled()) {
logger.trace(LogMessage.format("Spring Data %s - Registering repository: %s - Interface: %s - Factory: %s", extension.getModuleName(), beanName, configuration.getRepositoryInterface(), configuration.getRepositoryFactoryBeanClassName()));
}
//设置当前BeanDefinition的属性factoryBeanObjectType为用户自定义JpaRepository接口的全限定名
beanDefinition.setAttribute("factoryBeanObjectType", configuration.getRepositoryInterface());
// 现在把这个bean注册到容器
registry.registerBeanDefinition(beanName, beanDefinition);
definitions.add(new BeanComponentDefinition(beanDefinition, beanName));
}
potentiallyLazifyRepositories(configurationsByRepositoryName, registry, this.configurationSource.getBootstrapMode());
watch.stop();
return definitions;
}
}
RepositoryBeanDefinitionBuilder#build
public BeanDefinitionBuilder build(RepositoryConfiguration configuration) {
BeanDefinitionBuilder builder = BeanDefinitionBuilder.rootBeanDefinition(configuration.getRepositoryFactoryBeanClassName());
builder.getRawBeanDefinition().setSource(configuration.getSource());
builder.addConstructorArgValue(configuration.getRepositoryInterface());
builder.addPropertyValue("queryLookupStrategyKey", configuration.getQueryLookupStrategyKey());
builder.addPropertyValue("lazyInit", configuration.isLazyInit());
builder.setLazyInit(configuration.isLazyInit());
builder.setPrimary(configuration.isPrimary());
configuration.getRepositoryBaseClassName().ifPresent((it) -> {
builder.addPropertyValue("repositoryBaseClass", it);
});
NamedQueriesBeanDefinitionBuilder definitionBuilder = new NamedQueriesBeanDefinitionBuilder(this.extension.getDefaultNamedQueryLocation());
configuration.getNamedQueriesLocation().ifPresent(definitionBuilder::setLocations);
builder.addPropertyValue("namedQueries", definitionBuilder.build(configuration.getSource()));
this.registerCustomImplementation(configuration).ifPresent((it) -> {
builder.addPropertyReference("customImplementation", it);
builder.addDependsOn(it);
});
BeanDefinitionBuilder fragmentsBuilder = BeanDefinitionBuilder.rootBeanDefinition(RepositoryFragmentsFactoryBean.class);
List fragmentBeanNames = (List)this.registerRepositoryFragmentsImplementation(configuration).map(RepositoryFragmentConfiguration::getFragmentBeanName).collect(Collectors.toList());
fragmentsBuilder.addConstructorArgValue(fragmentBeanNames);
builder.addPropertyValue("repositoryFragments", ParsingUtils.getSourceBeanDefinition(fragmentsBuilder, configuration.getSource()));
return builder;
}
我在builder()里调试了一下代码,程序执行到该方法倒数第二行代码时,可以BeanDefinitionBuilder#beanClass就是org.springframework.data.jpa.repository.support.JpaRepositoryFactoryBean。
从上面两段代码分析来看,不管用户创建多少个JpaRepository,最终注入Spring容器的bean都是来自JpaRepositoryFactoryBean工厂来创建。每个开发人员自定义的JpqRepository又都是针对不同的领域模型的,比如说UserRepository,OrderRepository,OrderLineItemRepository。
使用用户自定义的JpaRepository
@Autowired
private BookRepository bookRepository;
当你定义了的BookRepository后,在使用时又是如何从Spring容器中获取bean的。上面既然说了BeanDefinitionBuilder会和JpaRepositoryFactoryBean建立联系,那我们还是从JpaRepositoryFactoryBean入手。
public class JpaRepositoryFactoryBean, S, ID>
extends TransactionalRepositoryFactoryBeanSupport {
//构造函数,这里repositoryInter就是你自定义的JpaRepository
public JpaRepositoryFactoryBean(Class repositoryInterface) {
super(repositoryInterface);
}
@Override
protected RepositoryFactorySupport doCreateRepositoryFactory() {
Assert.state(entityManager != null, "EntityManager must not be null!");
return createRepositoryFactory(entityManager);
}
//这个方法会返回JpaRepositoryFactory
protected RepositoryFactorySupport createRepositoryFactory(EntityManager entityManager) {
JpaRepositoryFactory jpaRepositoryFactory = new JpaRepositoryFactory(entityManager);
jpaRepositoryFactory.setEntityPathResolver(entityPathResolver);
jpaRepositoryFactory.setEscapeCharacter(escapeCharacter);
if (queryMethodFactory != null) {
jpaRepositoryFactory.setQueryMethodFactory(queryMethodFactory);
}
return jpaRepositoryFactory;
}
}
这段代码我们会关注两个地方,一个是构造函数,构造函数的参数repositoryInterface就是用户自定义的接口,一个是createRepositoryFactory(),Spring要创建JpaRepository的实现类,会先创建一个JpaRepositoryFactory,然后具体接口的实现类,或者叫做代理会交给该工厂类实现。
public class JpaRepositoryFactory extends RepositoryFactorySupport {
}
JpaRepositoryFactory继承了抽象类RepositoryFactorySupport,而RepositoryFactorySupport又实现了两个Spring接口BeanClassLoaderAware,BeanFactoryAware。
RepositoryFactorySupport位于spring-data-common.jar内。
RepositoryFactorySupport#getRepository
public T getRepository(Class repositoryInterface, RepositoryFragments fragments) {
//repositoryInterface为用户自定义的JpaRepository,这里为BookRepository。
RepositoryMetadata metadata = this.getRepositoryMetadata(repositoryInterface);
RepositoryComposition composition = this.getRepositoryComposition(metadata, fragments);
RepositoryInformation information = this.getRepositoryInformation(metadata, composition);
this.validate(information, composition);
//target为SimpleJpaRepository。
Object target = this.getTargetRepository(information);
ProxyFactory result = new ProxyFactory();
result.setTarget(target);
result.setInterfaces(new Class[]{repositoryInterface, Repository.class, TransactionalProxy.class});
if (MethodInvocationValidator.supports(repositoryInterface)) {
result.addAdvice(new MethodInvocationValidator());
}
result.addAdvisor(ExposeInvocationInterceptor.ADVISOR);
this.postProcessors.forEach((processor) -> {
processor.postProcess(result, information);
});
if (DefaultMethodInvokingMethodInterceptor.hasDefaultMethods(repositoryInterface)) {
result.addAdvice(new DefaultMethodInvokingMethodInterceptor());
}
ProjectionFactory projectionFactory = this.getProjectionFactory(this.classLoader, this.beanFactory);
Optional queryLookupStrategy = this.getQueryLookupStrategy(this.queryLookupStrategyKey, this.evaluationContextProvider);
result.addAdvice(new QueryExecutorMethodInterceptor(information, projectionFactory, queryLookupStrategy, this.namedQueries, this.queryPostProcessors, this.methodInvocationListeners));
composition = composition.append(RepositoryFragment.implemented(target));
result.addAdvice(new RepositoryFactorySupport.ImplementationMethodExecutionInterceptor(information, composition, this.methodInvocationListeners));
//repository为SimpleJpaRepository
T repository = result.getProxy(this.classLoader);
return repository;
}
这是一个关键方法,this.getTargetRepository会创建一个SimpleJpaRepository对象。该对象知道自己具体操作那个领域对象,随后又基于此类创建一个代理对象,设置Interceptor对象后返回该代理对象。 当真正的SimpleJpaRepository代理对象被创建之后,包裹该对象的JpaRepositoryFactoryBean对象就是我们最终要使用bean的FactoryBean,Spring容器中,用户自定义的bean保存的实际上是一个JpaRepositoryFactoryBean。
@Repository
@Transactional(readOnly = true)
public class SimpleJpaRepository implements JpaRepositoryImplementation {
//这里就是我们常用的CURD方法了,终于看到了庐山真面目。
}
综上所述,注入bean实例化过程就结束了,可以进行注入了,根据上面的分析,每个用户自定义的JpaRepository实际上在Spring容器中保存的是一个JpaRepositoryFactoryBean,这是一个FactoryBean。当对JpaRepository进行注入并调用时会FactoryBean#getObject()获取要调用SimpleJpaRepository的代理对象。
总结
上面我自己提到的两个问题,到了这里我们就有一个明确的答案了,首先回答代理是什么,从上面调试代码可以看出来repository的h属性是JdkDynamicAopProxy对象。当程序执行的时候会通过调用JdkDynamicAopProxy.invoke(),比如说调用JpaRepository.findAll(), 代理对象的创建逻辑都隐藏在JdkDynamicAopProxy中,而在这里这个代理对象就是SimpleJpaRepository 对象,也是你的自定义JpaRepository的实现类。
SimpleJpaRepository对象位于 org.springframework.data.jpa.repository.support包下。
来源:https://www.tuicool.com/articles/qaYvM3b