基于springboot2集成jpa,创建dao的案例

springboot中集成jpa需要再pom文件中添加jpa的jar包，使用springboot的话iju不用自己规定版本号了，自动管理依赖版本即可。

<dependency>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

然后我们再添加hibernate和oracle的jar包，同样自动管理版本。

 <dependency>
  <groupId>org.hibernate</groupId>
  <artifactId>hibernate-core</artifactId>
 </dependency>
 <dependency>
  <groupId>com.oracle</groupId>
  <artifactId>ojdbc6</artifactId>
  <version>11.2.0.4.0</version>
 </dependency>

然后我们在配置文件中添加jpa和链接数据库的信息。

spring.datasource.driver-class-name=oracle.jdbc.OracleDriver
spring.datasource.url=jdbc:oracle:thin:@DESKTOP-46DMVCH:1521:orcl
spring.datasource.password=****
spring.datasource.username=****
spring.mvc.date-format=yyyy-MM-dd HH:mm:ss
spring.jpa.database=oracle
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true
spring.datasource.log-abandoned=true
spring.datasource.remove-abandoned=true
spring.datasource.remove-abandoned-timeout=200

添加完成之后我们开始创建jpa使用的公共Repository,创建一个接口。这里的接口可以直接继承JpaRepository，或者可以继承别的Repository.注意要加上@NoRepositoryBean注解，告诉Spring数据：不要创建该接口实例。

当我们在下面使用dao的时候再进行创建实例

@NoRepositoryBean
public interface BaseRepository<T> extends JpaRepository<T,Long> {
}

现在我们创建好了这基础的Repository如果有自己想封装的公用方法的话就可以添加到这个接口中，进行约束。

当我们创建dao接口的时候，直接继承这个基础的Repository;继承之后这个dao再spring中默认识别为一个Repository。

public interface TbUserDao extends BaseRepository<TbUser> {
}

下面我们就可以直接再service中注入这个dao。

@Service
public class UserService {
 @Resource
 private TbUserDao userDao;
}

现在我们看一下JpaRepository源码，其中继承了PagingAndSortingRepository和QueryByExampleExecutor，也就是里面直接有了各种查询的方法，并且在这两个基础上添加了保存和删除的方法。

@NoRepositoryBean
public interface JpaRepository<T, ID> extends PagingAndSortingRepository<T, ID>, QueryByExampleExecutor<T> {
/*
  * (non-Javadoc)
  * @see org.springframework.data.repository.CrudRepository#findAll()
  */
 List<T> findAll();
 /*
  * (non-Javadoc)
  * @see org.springframework.data.repository.PagingAndSortingRepository#findAll(org.springframework.data.domain.Sort)
  */
 List<T> findAll(Sort sort);
 /*
  * (non-Javadoc)
  * @see org.springframework.data.repository.CrudRepository#findAll(java.lang.Iterable)
  */
 List<T> findAllById(Iterable<ID> ids);
 /*
  * (non-Javadoc)
  * @see org.springframework.data.repository.CrudRepository#save(java.lang.Iterable)
  */
 <S extends T> List<S> saveAll(Iterable<S> entities);
 /**
  * Flushes all pending changes to the database.
  */
 void flush();
 /**
  * Saves an entity and flushes changes instantly.
  *
  * @param entity
  * @return the saved entity
  */
 <S extends T> S saveAndFlush(S entity);
 /**
  * Deletes the given entities in a batch which means it will create a single {@link Query}. Assume that we will clear
  * the {@link javax.persistence.EntityManager} after the call.
  *
  * @param entities
  */
 void deleteInBatch(Iterable<T> entities);
 /**
  * Deletes all entities in a batch call.
  */
 void deleteAllInBatch();
 /**
  * Returns a reference to the entity with the given identifier.
  *
  * @param id must not be {@literal null}.
  * @return a reference to the entity with the given identifier.
  * @see EntityManager#getReference(Class, Object)
  * @throws javax.persistence.EntityNotFoundException if no entity exists for given {@code id}.
  */
 T getOne(ID id);
 /*
  * (non-Javadoc)
  * @see org.springframework.data.repository.query.QueryByExampleExecutor#findAll(org.springframework.data.domain.Example)
  */
 @Override
 <S extends T> List<S> findAll(Example<S> example);
 /*
  * (non-Javadoc)
  * @see org.springframework.data.repository.query.QueryByExampleExecutor#findAll(org.springframework.data.domain.Example, org.springframework.data.domain.Sort)
  */
 @Override
 <S extends T> List<S> findAll(Example<S> example, Sort sort);
}

我们再看Jpa继承的两个接口中的代码,PagingAndSortingRepository是继承了CrudRepository的，这个CrudRepository中同样有删除保存查询等方法，是比较全的，但是如果我们直接使用这个CrudRepository的话里面的查询是没有分页的方法。

而PagingAndSortingRepository是在基础上新加了分页查询的方法。

所以我们没有直接使用CrudRepository

@NoRepositoryBean
public interface PagingAndSortingRepository<T, ID> extends CrudRepository<T, ID> {
 Iterable<T> findAll(Sort var1);
 Page<T> findAll(Pageable var1);
}

会有疑问的是我们这里的接口为什么可以直接注入。

因为当我们运行项目的时候，spring识别这个dao是一个Repository会自动为这个接口创建一个接口名+Impl的实现类,如下例子中的就是生成TbUserDaoImpl的实现类。

这个我们可以在EnableJpaRepositories注解源码中可以看到。

里面的repositoryImplementationPostfix()方法是定义repository接口生成的实现类后缀是什么，springboot默认帮我们定义成了Impl。

我们也可以在springboot启动类上面使用这个注解自己定义这个值。

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(JpaRepositoriesRegistrar.class)
public @interface EnableJpaRepositories {
 /**
  * Alias for the {@link #basePackages()} attribute. Allows for more concise annotation declarations e.g.:
  * {@code @EnableJpaRepositories("org.my.pkg")} instead of {@code @EnableJpaRepositories(basePackages="org.my.pkg")}.
  */
 String[] value() default {};
 /**
  * Base packages to scan for annotated components. {@link #value()} is an alias for (and mutually exclusive with) this
  * attribute. Use {@link #basePackageClasses()} for a type-safe alternative to String-based package names.
  */
 String[] basePackages() default {};
 /**
  * Type-safe alternative to {@link #basePackages()} for specifying the packages to scan for annotated components. The
  * package of each class specified will be scanned. Consider creating a special no-op marker class or interface in
  * each package that serves no purpose other than being referenced by this attribute.
  */
 Class<?>[] basePackageClasses() default {};
 /**
  * Specifies which types are eligible for component scanning. Further narrows the set of candidate components from
  * everything in {@link #basePackages()} to everything in the base packages that matches the given filter or filters.
  */
 Filter[] includeFilters() default {};
 /**
  * Specifies which types are not eligible for component scanning.
  */
 Filter[] excludeFilters() default {};
 /**
  * Returns the postfix to be used when looking up custom repository implementations. Defaults to {@literal Impl}. So
  * for a repository named {@code PersonRepository} the corresponding implementation class will be looked up scanning
  * for {@code PersonRepositoryImpl}.
  * 
  * @return
  */
 String repositoryImplementationPostfix() default "Impl";
 /**
  * Configures the location of where to find the Spring Data named queries properties file. Will default to
  * {@code META-INF/jpa-named-queries.properties}.
  * 
  * @return
  */
 String namedQueriesLocation() default "";
 /**
  * Returns the key of the {@link QueryLookupStrategy} to be used for lookup queries for query methods. Defaults to
  * {@link Key#CREATE_IF_NOT_FOUND}.
  * 
  * @return
  */
 Key queryLookupStrategy() default Key.CREATE_IF_NOT_FOUND;
 /**
  * Returns the {@link FactoryBean} class to be used for each repository instance. Defaults to
  * {@link JpaRepositoryFactoryBean}.
  * 
  * @return
  */
 Class<?> repositoryFactoryBeanClass() default JpaRepositoryFactoryBean.class;
 /**
  * Configure the repository base class to be used to create repository proxies for this particular configuration.
  * 
  * @return
  * @since 1.9
  */
 Class<?> repositoryBaseClass() default DefaultRepositoryBaseClass.class;
 // JPA specific configuration
 /**
  * Configures the name of the {@link EntityManagerFactory} bean definition to be used to create repositories
  * discovered through this annotation. Defaults to {@code entityManagerFactory}.
  * 
  * @return
  */
 String entityManagerFactoryRef() default "entityManagerFactory";
 /**
  * Configures the name of the {@link PlatformTransactionManager} bean definition to be used to create repositories
  * discovered through this annotation. Defaults to {@code transactionManager}.
  * 
  * @return
  */
 String transactionManagerRef() default "transactionManager";
 /**
  * Configures whether nested repository-interfaces (e.g. defined as inner classes) should be discovered by the
  * repositories infrastructure.
  */
 boolean considerNestedRepositories() default false;
 /**
  * Configures whether to enable default transactions for Spring Data JPA repositories. Defaults to {@literal true}. If
  * disabled, repositories must be used behind a facade that's configuring transactions (e.g. using Spring's annotation
  * driven transaction facilities) or repository methods have to be used to demarcate transactions.
  * 
  * @return whether to enable default transactions, defaults to {@literal true}.
  */
 boolean enableDefaultTransactions() default true;
}

以上为个人经验，希望能给大家一个参考，也希望大家多多支持小牛知识库。如有错误或未考虑完全的地方，望不吝赐教。