浅谈Spring Data如何简化数据操作的方法

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:jpa="http://www.springframework.org/schema/data/jpa"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.3.xsd
    http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.0.xsd
    http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd">
  <context:component-scan base-package="com.kernel.spring.data"/>
  <!--配置数据源-->
  <context:property-placeholder location="classpath:db.properties"/>
  <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
    <property name="driverClass" value="${jdbc.driverClass}"/>
    <property name="jdbcUrl" value="${jdbc.jdbcUrl}"/>
    <property name="user" value="${jdbc.user}"/>
    <property name="password" value="${jdbc.password}"/>
  </bean>
  <!--配置JPA的EntityManagerFactory-->
  <bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
    <property name="dataSource" ref="dataSource"/>
    <property name="jpaVendorAdapter">
      <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter"/>
    </property>
    <property name="packagesToScan" value="com.kernel.spring.data"/>
    <property name="jpaProperties">
      <props>
        <!--生成的数据表的映射策略-->
        <prop key="hibernate.ejb.naming_strategy">org.hibernate.cfg.ImprovedNamingStrategy</prop>
        <!--生成的数据表的列的映射策略-->
        <prop key="hibernate.dialect">org.hibernate.dialect.MySQL5InnoDBDialect</prop>
        <prop key="hibernate.show_sql">true</prop>
        <prop key="hibernate.format_sql">true</prop>
        <prop key="hibernate.hbm2ddl.auto">update</prop>
      </props>
    </property>
  </bean>
  <!--配置事务管理器-->
  <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
    <property name="entityManagerFactory" ref="entityManagerFactory"/>
  </bean>
  <!--配置支持注解的事务-->
  <tx:annotation-driven transaction-manager="transactionManager"/>
  <!--配置Spring Data-->
  <jpa:repositories base-package="com.kernel.spring.data" entity-manager-factory-ref="entityManagerFactory"/>
</beans>

public interface PersonRepository extends Repository<Person, Integer> {
  Person getByLastName(String lastName);

  List<Person> getByLastNameStartingWithAndIdLessThan(String lastName, Integer id);

  List<Person> getByLastNameEndingWithAndIdLessThan(String lastName, Integer id);

  List<Person> getByEmailInAndAgeLessThan(List list, Integer id);

  List<Person> getByAddress_IdGreaterThan(Integer id);
}

@Query("SELECT p FROM Person p WHERE p.lastName = ?1 and p.age = ?2")
Person getByLastNameAndAge(String lastName, int age);

@Query("SELECT p FROM Person p WHERE p.lastName = :lastName and p.id = :id")
Person getByLastNameAndId(@Param("id")int id, @Param("lastName")String lastName);

@Query(value = "SELECT COUNT (id) FROM jpa_persons", nativeQuery = true)
long getTotalCount();

@Test
public void testPagingAndSortingRespository(){
  int pageNo = 3;
  int pageSize = 5;
  Sort.Order order = new Sort.Order(Sort.Direction.DESC, "id");
  Sort.Order order1 = new Sort.Order(Sort.Direction.ASC, "email");
  Sort sort = new Sort(order,order1);
  PageRequest pageable = new PageRequest(pageNo, pageSize, sort);
  Page<Person> page = personRepository.findAll(pageable);
  System.out.println(page.getNumberOfElements());
  System.out.println(page.getContent());
}

@Test
public void testJpaSpecificationExecutor(){
  int pageNo = 3;
  int pageSize = 5;
  PageRequest pageable = new PageRequest(pageNo, pageSize);
  Specification<Person> specification = new Specification<Person>() {
    /**
       * @param root 代表查询的实体类
       * @param criteriaQuery 可以从中得到root对象，即告知 JPA Criteria 查询哪个实体类，
       *           还可以添加查询条件，还可以结合EntityManager对象得到最终查询的                  TypedQuery
       * @param criteriaBuilder 用于创建criteria工厂
       * @return Predicate类型，代表一个查询条件
       */
    @Override
    public Predicate toPredicate(Root<Person> root, CriteriaQuery<?> criteriaQuery, CriteriaBuilder criteriaBuilder) {
      Predicate predicate = criteriaBuilder.ge(root.get("id"),5);
      return predicate;
    }
  };
  Page<Person> page = personRepository.findAll(specification, pageable);
  System.out.println(page.getNumberOfElements());
  System.out.println(page.getContent());
}