SpringBoot具体整合rabbitMQ可参考：SpringBoot2.0应用（四）：SpringBoot2.0之spring-data-jpa

JpaRepositories自动注入

当项目中存在org.springframework.data.jpa.repository.JpaRepository类，并且已经注入过数据源javax.sql.DataSource，同时没有注入过org.springframework.data.jpa.repository.config.JpaRepositoryConfigExtension和org.springframework.data.jpa.repository.support.JpaRepositoryFactoryBean时，会通过@Import注解导入org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfigureRegistrar，由它完成对JPA的支持。JpaRepositoriesAutoConfigureRegistrar又继承自AbstractRepositoryConfigurationSourceSupport。来看下AbstractRepositoryConfigurationSourceSupport的具体内容。

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());
    }

    ......
}

可以看出，到AbstractRepositoryConfigurationSourceSupport对Repository的Bean进行了定义。下面来具体看看Repositoryd的创建。

Repository的创建

我们先来看下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;
    }

到这里其实只是创建了repository的实体Bean的BeanDefinition。前期准备做好了，实际创建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);
    }

首先去获取我们写的repository接口的元数据，包括实体的ID类型，管理的实体类型等。接着获取repository的组合，主要包含repository的方法信息。然后再根据它俩的组合得到一个target。这个target其实就是一个SimpleJpaRepository实体，里面包含了一些通用的方法。只有这些还不够，于是有了后面的代理工厂，对这个target进行进一步处理。包括事务支持，异常处理和SQL创造等。我们主要看一下SQL创建。创建的方法在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));
        }

该方法的逻辑是先找有注解的，这个包括@Query和@Procedure，接着是根据关键字创建，然后是通用方法。

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