SpringBoot2.0原始碼分析（四）：spring-data-jpa分析

摘要： 當專案中存在org.springframework.data.jpa.repository.JpaRepository 類，並且已經注入過資料來源javax.sql.DataSource ，同時沒有注入過org.springframework.data.jpa.rep...

當專案中存在org.springframework.data.jpa.repository.JpaRepository 類，並且已經注入過資料來源javax.sql.DataSource ，同時沒有注入過org.springframework.data.jpa.repository.config.JpaRepositoryConfigExtension 和org.springframework.data.jpa.repository.support.JpaRepositoryFactoryBean 時，會通過@Import 註解匯入org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfigureRegistrar ，由它完成對JPA的支援。JpaRepositoriesAutoConfigureRegistrar 又繼承自AbstractRepositoryConfigurationSourceSupport 。來看下AbstractRepositoryConfigurationSourceSupport 的具體內容。

public abstract class AbstractRepositoryConfigurationSourceSupport
implements BeanFactoryAware, ImportBeanDefinitionRegistrar, ResourceLoaderAware,
EnvironmentAware {

private ResourceLoader resourceLoader;

private BeanFactory beanFactory;

private Environment environment;

@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,
BeanDefinitionRegistry registry) {
new RepositoryConfigurationDelegate(getConfigurationSource(registry),
this.resourceLoader, this.environment).registerRepositoriesIn(registry,
getRepositoryConfigurationExtension());
}

......
}
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可以看出，到AbstractRepositoryConfigurationSourceSupport 對Repository 的Bean進行了定義。下面來具體看看Repositoryd的建立。

Repositoryd的建立

我們先來看下RepositoryConfigurationDelegate 的registerRepositoriesIn 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<>();

for (RepositoryConfiguration<? extends RepositoryConfigurationSource> configuration : extension
.getRepositoryConfigurations(configurationSource, resourceLoader, inMultiStoreMode)) {

BeanDefinitionBuilder definitionBuilder = builder.build(configuration);

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);
......
beanDefinition.setAttribute(FACTORY_BEAN_OBJECT_TYPE, configuration.getRepositoryInterface());

registry.registerBeanDefinition(beanName, beanDefinition);
definitions.add(new BeanComponentDefinition(beanDefinition, beanName));
}

return definitions;
}
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到這裡其實只是建立了repository的實體Bean的BeanDefinition。前期準備做好了，實際建立repository是在RepositoryFactorySupport 的getRepository方法。

public <T> T getRepository(Class<T> repositoryInterface, RepositoryFragments fragments) {
Assert.notNull(repositoryInterface, "Repository interface must not be null!");
Assert.notNull(fragments, "RepositoryFragments must not be null!");

RepositoryMetadata metadata = getRepositoryMetadata(repositoryInterface);
RepositoryComposition composition = getRepositoryComposition(metadata, fragments);
RepositoryInformation information = getRepositoryInformation(metadata, composition);

validate(information, composition);

Object target = getTargetRepository(information);

// Create proxy
ProxyFactory result = new ProxyFactory();
result.setTarget(target);
result.setInterfaces(repositoryInterface, Repository.class, TransactionalProxy.class);

if (MethodInvocationValidator.supports(repositoryInterface)) {
result.addAdvice(new MethodInvocationValidator());
}

result.addAdvice(SurroundingTransactionDetectorMethodInterceptor.INSTANCE);
result.addAdvisor(ExposeInvocationInterceptor.ADVISOR);

postProcessors.forEach(processor -> processor.postProcess(result, information));

result.addAdvice(new DefaultMethodInvokingMethodInterceptor());

ProjectionFactory projectionFactory = getProjectionFactory(classLoader, beanFactory);
result.addAdvice(new QueryExecutorMethodInterceptor(information, projectionFactory));

composition = composition.append(RepositoryFragment.implemented(target));
result.addAdvice(new ImplementationMethodExecutionInterceptor(composition));

return (T) result.getProxy(classLoader);
}
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首先去獲取我們寫的repository介面的元資料，包括實體的ID型別，管理的實體型別等。接著獲取repository的組合，主要包含repository的方法資訊。然後再根據它倆的組合得到一個target。這個target其實就是一個SimpleJpaRepository實體，裡面包含了一些通用的方法。只有這些還不夠，於是有了後面的代理工廠，對這個target進行進一步處理。包括事務支援，異常處理和SQL創造等。我們主要看一下SQL建立。建立的方法在DeclaredQueryLookupStrategy 的resolveQuery 中。

protected RepositoryQuery resolveQuery(JpaQueryMethod method, EntityManager em, NamedQueries namedQueries) {

RepositoryQuery query = JpaQueryFactory.INSTANCE.fromQueryAnnotation(method, em, evaluationContextProvider);

if (null != query) {
return query;
}

query = JpaQueryFactory.INSTANCE.fromProcedureAnnotation(method, em);

if (null != query) {
return query;
}

String name = method.getNamedQueryName();
if (namedQueries.hasQuery(name)) {
return JpaQueryFactory.INSTANCE.fromMethodWithQueryString(method, em, namedQueries.getQuery(name),
evaluationContextProvider);
}

query = NamedQuery.lookupFrom(method, em);

if (null != query) {
return query;
}

throw new IllegalStateException(
String.format("Did neither find a NamedQuery nor an annotated query for method %s!", method));
}
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該方法的邏輯是先找有註解的，這個包括@Query 和@Procedure ，接著是根據關鍵字建立，然後是通用方法。