须知

• 源码依赖：spring-data-jpa-1.11.11.RELEASE

简介

• JpaQueryLookupStrategy是一个工厂类，通过JpaQueryLookupStrategy#create静态方法生成策略key对应的QueryLookupStrategy实例

官方文档

• docs.spring.io/spring-data…

QueryLookupStrategy接口

源码

/**
 * 策略接口。定义了解析RepositoryQuery的方法
 */
public interface QueryLookupStrategy {
	public static enum Key {
		CREATE, USE_DECLARED_QUERY, CREATE_IF_NOT_FOUND;
		/**
		 * 生成对应的策略key值
		 */
		public static Key create(String xml) {
			if (!StringUtils.hasText(xml)) {
				return null;
			}
			return valueOf(xml.toUpperCase(Locale.US).replace("-", "_"));
		}
	}

	/**
	 * 从给定的QueryMethod中解析出对应的RepositoryQuery
	 */
	RepositoryQuery resolveQuery(Method method, RepositoryMetadata metadata, ProjectionFactory factory,
			NamedQueries namedQueries);
}

UML图

JpaQueryLookupStrategy类

源码

/**
 * 提供创建QueryLookupStrategy的方法
 */
public final class JpaQueryLookupStrategy {

	/**
	 * 私有构造
	 */
	private JpaQueryLookupStrategy() {}

	/**
	 * 带有EntityManager的QueryLookupStrategy抽象类
	 */
	private abstract static class AbstractQueryLookupStrategy implements QueryLookupStrategy {

		private final EntityManager em;
		private final QueryExtractor provider;

		public AbstractQueryLookupStrategy(EntityManager em, QueryExtractor extractor) {

			this.em = em;
			this.provider = extractor;
		}

		@Override
		public final RepositoryQuery resolveQuery(Method method, RepositoryMetadata metadata, ProjectionFactory factory,
				NamedQueries namedQueries) {
			return resolveQuery(new JpaQueryMethod(method, metadata, factory, provider), em, namedQueries);
		}
		//自定义的抽象方法，由子类进行实现
		protected abstract RepositoryQuery resolveQuery(JpaQueryMethod method, EntityManager em, NamedQueries namedQueries);
	}

	/**
	 * 根据方法名创建RepositoryQuery
	 */
	private static class CreateQueryLookupStrategy extends AbstractQueryLookupStrategy {

		private final PersistenceProvider persistenceProvider;

		public CreateQueryLookupStrategy(EntityManager em, QueryExtractor extractor) {

			super(em, extractor);
			this.persistenceProvider = PersistenceProvider.fromEntityManager(em);
		}

		@Override
		protected RepositoryQuery resolveQuery(JpaQueryMethod method, EntityManager em, NamedQueries namedQueries) {
			//解析对应的方法名
			return new PartTreeJpaQuery(method, em, persistenceProvider);
		}

	}

	/**
	 *  解析@Query、@Procedure、@NamedQuery生成对应的RepositoryQuery
	 */
	private static class DeclaredQueryLookupStrategy extends AbstractQueryLookupStrategy {

		private final EvaluationContextProvider evaluationContextProvider;

		public DeclaredQueryLookupStrategy(EntityManager em, QueryExtractor extractor,
				EvaluationContextProvider evaluationContextProvider) {
			super(em, extractor);
			this.evaluationContextProvider = evaluationContextProvider;
		}

		@Override
		protected RepositoryQuery resolveQuery(JpaQueryMethod method, EntityManager em, NamedQueries namedQueries) {
			//解析@Query,底层实现是NativeJpaQuery（nativeQuery=true）或SimpleJpaQuery（nativeQuery=false）
			RepositoryQuery query = JpaQueryFactory.INSTANCE.fromQueryAnnotation(method, em, evaluationContextProvider);
			if (null != query) {
				return query;
			}
			//解析@Procedure，底层实现是StoredProcedureJpaQuery
			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);
			}
			//解析@NamedQuery
			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));
		}
	}

	/**
	 * DeclaredQueryLookupStrategy和CreateQueryLookupStrategy的结合。先按DeclaredQueryLookupStrategy（解析对应的注解，例如：@Query）进行解析，再按CreateQueryLookupStrategy（解析方法名）进行解析
	 */
	private static class CreateIfNotFoundQueryLookupStrategy extends AbstractQueryLookupStrategy {

		private final DeclaredQueryLookupStrategy lookupStrategy;
		private final CreateQueryLookupStrategy createStrategy;

		public CreateIfNotFoundQueryLookupStrategy(EntityManager em, QueryExtractor extractor,
				CreateQueryLookupStrategy createStrategy, DeclaredQueryLookupStrategy lookupStrategy) {

			super(em, extractor);
			this.createStrategy = createStrategy;
			this.lookupStrategy = lookupStrategy;
		}

		@Override
		protected RepositoryQuery resolveQuery(JpaQueryMethod method, EntityManager em, NamedQueries namedQueries) {
			try {
				//先解析对应的注解,例如：@Query
				return lookupStrategy.resolveQuery(method, em, namedQueries);
			} catch (IllegalStateException e) {
 				//如果注解解析不成功,再通过解析方法名进行创建
				return createStrategy.resolveQuery(method, em, namedQueries);
			}
		}
	}

	/**
	 * 创建QueryLookupStrategy
	 */
	public static QueryLookupStrategy create(EntityManager em, Key key, QueryExtractor extractor,
			EvaluationContextProvider evaluationContextProvider) {
 		//默认的key是CREATE_IF_NOT_FOUND
		switch (key != null ? key : Key.CREATE_IF_NOT_FOUND) {
			case CREATE:
				return new CreateQueryLookupStrategy(em, extractor);
			case USE_DECLARED_QUERY:
				return new DeclaredQueryLookupStrategy(em, extractor, evaluationContextProvider);
			case CREATE_IF_NOT_FOUND:
				return new CreateIfNotFoundQueryLookupStrategy(em, extractor, new CreateQueryLookupStrategy(em, extractor),
						new DeclaredQueryLookupStrategy(em, extractor, evaluationContextProvider));
			default:
				throw new IllegalArgumentException(String.format("Unsupported query lookup strategy %s!", key));
		}
	}
}

总结

• AbstractQueryLookupStrategy是QueryLookupStrategy的抽象类,实现了QueryLookupStrategy#resolveQuery。同时抽象出与jpa相关的resolveQuery抽象方法，由子类实现，具体子类如下：
  • CreateQueryLookupStrategy,其resolveQuery方法创建的是PartTreeJpaQuery(解析方法名)
  • DeclaredQueryLookupStrategy,其resolveQuery方法借助JpaQueryFactory.INSTANCE.fromQueryAnnotation(解析@Query注解)、JpaQueryFactory.INSTANCE.fromProcedureAnnotation(解析@Procedure注解)、NamedQuery.lookupFrom(解析@NamedQuery注解)来生成；
  • CreateIfNotFoundQueryLookupStrategy,它的构造器要求传入DeclaredQueryLookupStrategy、CreateQueryLookupStrategy参数，其resolveQuery方法先是借助DeclaredQueryLookupStrategy来创建RepositoryQuery，如果抛出的是IllegalStateException，再借助CreateQueryLookupStrategy来创建RepositoryQuery
• JpaQueryLookupStrategy提供一个静态方法create用于根据不同的QueryLookupStrategy.Key来创建不同的QueryLookupStrategy,默认是Key.CREATE_IF_NOT_FOUND,即创建CreateIfNotFoundQueryLookupStrategy