Spring5 全家桶 | 02 - Spring Data JPA

一、什么是Spring Data JPA

Spring Data JPA 概述

Spring Data JPA 是 Spring 基于 ORM 框架、JPA 规范的基础上封装的一套JPA应用框架，可使开发者用极简的代码即可实现对数据库的访问和操作。它提供了包括增删改查等在内的常用功能，且易于扩展！学习并使用 Spring Data JPA 可以极大提高开发效率！

  Spring Data JPA 让我们解脱了DAO层的操作，基本上所有CRUD都可以依赖于它来实现,在实际的工作工程中，推荐使用Spring Data JPA + ORM（如：hibernate）完成操作，这样在切换不同的ORM框架时提供了极大的方便，同时也使数据库层操作更加简单，方便解耦

Spring Data JPA 与 JPA 和 Hibernate 之间的关系

  JPA是一套规范，内部是有接口和抽象类组成的。hibernate是一套成熟的ORM框架，而且Hibernate实现了JPA规范，所以也可以称hibernate为JPA的一种实现方式，我们使用JPA的API编程，意味着站在更高的角度上看待问题（面向接口编程）

  Spring Data JPA是Spring提供的一套对JPA操作更加高级的封装，是在JPA规范下的专门用来进行数据持久化的解决方案。

二、Spring Data JPA 最佳实践

1. 创建maven项目，添加项目依赖

<properties>
    <spring.version>5.2.6.RELEASE</spring.version>
    <hibernate.version>5.0.7.Final</hibernate.version>
    <slf4j.version>1.6.6</slf4j.version>
    <log4j.version>1.2.12</log4j.version>
    <c3p0.version>0.9.1.2</c3p0.version>
    <mysql.version>8.0.19</mysql.version>
</properties>

<dependencies>
    <!-- junit单元测试 -->
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
        <scope>test</scope>
    </dependency>

    <!-- spring beg -->
    <dependency>
        <groupId>org.aspectj</groupId>
        <artifactId>aspectjweaver</artifactId>
        <version>1.6.8</version>
    </dependency>

    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-aop</artifactId>
        <version>${spring.version}</version>
    </dependency>

    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>${spring.version}</version>
    </dependency>

    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context-support</artifactId>
        <version>${spring.version}</version>
    </dependency>

    <!-- spring对orm框架的支持包-->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-orm</artifactId>
        <version>${spring.version}</version>
    </dependency>

    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-beans</artifactId>
        <version>${spring.version}</version>
    </dependency>

    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>${spring.version}</version>
    </dependency>

    <!-- spring end -->

    <!-- hibernate beg -->
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-core</artifactId>
        <version>${hibernate.version}</version>
    </dependency>
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-entitymanager</artifactId>
        <version>${hibernate.version}</version>
    </dependency>
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-validator</artifactId>
        <version>5.2.1.Final</version>
    </dependency>
    <!-- hibernate end -->

    <!-- c3p0 beg -->
    <dependency>
        <groupId>c3p0</groupId>
        <artifactId>c3p0</artifactId>
        <version>${c3p0.version}</version>
    </dependency>
    <!-- c3p0 end -->

    <!-- log end -->
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>${log4j.version}</version>
    </dependency>

    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>
        <version>${slf4j.version}</version>
    </dependency>

    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-log4j12</artifactId>
        <version>${slf4j.version}</version>
    </dependency>
    <!-- log end -->


    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>${mysql.version}</version>
    </dependency>

    <!-- spring data jpa 的坐标-->
    <dependency>
        <groupId>org.springframework.data</groupId>
        <artifactId>spring-data-jpa</artifactId>
        <version>2.3.4
        .RELEASE</version>
    </dependency>

    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-test</artifactId>
        <version>${spring.version}</version>
    </dependency>

    <!-- el beg 使用spring data jpa 必须引入 -->
    <dependency>
        <groupId>javax.el</groupId>
        <artifactId>javax.el-api</artifactId>
        <version>2.2.4</version>
    </dependency>

    <dependency>
        <groupId>org.glassfish.web</groupId>
        <artifactId>javax.el</artifactId>
        <version>2.2.4</version>
    </dependency>
    <!-- el end -->
</dependencies>

2.创建配置文件，进行applicationContext.xml配置，所有的类由Spring管理

<?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:aop="http://www.springframework.org/schema/aop"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:jdbc="http://www.springframework.org/schema/jdbc" xmlns:tx="http://www.springframework.org/schema/tx"
       xmlns:jpa="http://www.springframework.org/schema/data/jpa" xmlns:task="http://www.springframework.org/schema/task"
       xsi:schemaLocation="
      http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
      http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd
      http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
      http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc.xsd
      http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd
      http://www.springframework.org/schema/data/jpa
      http://www.springframework.org/schema/data/jpa/spring-jpa.xsd">

    <!--spring 和 spring data jpa的配置-->

    <!-- 配置包扫描-->
    <context:component-scan base-package="com.citi" ></context:component-scan>

    <!-- 1.创建entityManagerFactory对象交给spring容器管理-->
    <bean id="entityManagerFactoty" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <!--配置的扫描的包（实体类所在的包） -->
        <property name="packagesToScan" value="com.citi.entity" />
        <!-- jpa的实现厂家 -->
        <property name="persistenceProvider">
            <bean class="org.hibernate.jpa.HibernatePersistenceProvider"/>
        </property>

        <!--jpa的供应商适配器 -->
        <property name="jpaVendorAdapter">
            <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
                <!--配置是否自动创建数据库表 -->
                <property name="generateDdl" value="false" />
                <!--指定数据库类型 -->
                <property name="database" value="MYSQL" />
                <!--数据库方言：支持的特有语法 -->
                <property name="databasePlatform" value="org.hibernate.dialect.MySQLDialect" />
                <!--是否显示sql -->
                <property name="showSql" value="true" />
            </bean>
        </property>

        <!--jpa的方言 ：高级的特性 -->
        <property name="jpaDialect" >
            <bean class="org.springframework.orm.jpa.vendor.HibernateJpaDialect" />
        </property>

    </bean>

    <!--2.创建数据库连接池 -->
    <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
        <property name="user" value="root"></property>
        <property name="password" value="root"></property>
        <property name="jdbcUrl" value="jdbc:mysql://localhost:3306/test?useUnicode=true&amp;characterEncoding=utf8&amp;autoReconnect=true&amp;useSSL=false&amp;serverTimezone=Asia/Shanghai" ></property>
        <property name="driverClass" value="com.mysql.cj.jdbc.Driver"></property>
    </bean>

    <!--3.整合spring dataJpa-->
    <jpa:repositories base-package="com.citi.dao" transaction-manager-ref="transactionManager"
                      entity-manager-factory-ref="entityManagerFactoty" ></jpa:repositories>

    <!--4.配置事务管理器 -->
    <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
        <property name="entityManagerFactory" ref="entityManagerFactoty"></property>
    </bean>

    <!-- 4.txAdvice-->
    <tx:advice id="txAdvice" transaction-manager="transactionManager">
        <tx:attributes>
            <tx:method name="save*" propagation="REQUIRED"/>
            <tx:method name="insert*" propagation="REQUIRED"/>
            <tx:method name="update*" propagation="REQUIRED"/>
            <tx:method name="delete*" propagation="REQUIRED"/>
            <tx:method name="get*" read-only="true"/>
            <tx:method name="find*" read-only="true"/>
            <tx:method name="*" propagation="REQUIRED"/>
        </tx:attributes>
    </tx:advice>

    <!-- 5.aop-->
    <aop:config>
        <aop:pointcut id="pointcut" expression="execution(* com.citi.service.*.*(..))" />
        <aop:advisor advice-ref="txAdvice" pointcut-ref="pointcut" />
    </aop:config>
</beans>

3.在entity包中新建实体类Customer，配置实体类与表，属性与字段映射关系

@Entity //表示是一个实体类
@Table(name = "customer") //映射的表明
public class Customer {

    @Id//声明主键
    @GeneratedValue(strategy = GenerationType.IDENTITY)//声明主键生成策略
    @Column(name = "cust_id") //属性和字段映射
    private Long custId;
    @Column(name = "cust_name")
    private String custName;
    @Column(name = "cust_source")
    private String custSource;
    @Column(name = "cust_level")
    private String custLevel;
    @Column(name = "cust_industry")
    private String custIndustry;
    @Column(name = "cust_phone")
    private String custPhone;
    @Column(name = "cust_address")
    private String custAddress;
    // 此处省略getter/setter/toString方法
}    

4.在dao层创建CustomerDao接口类，并继承JpaRepository及JpaSpecificationExecutor

/**
 * JpaRepository泛型第一个是操作的实体类，第二个泛型是主键的类型
 */
public interface CustomerDao extends JpaRepository<Customer,Long>,JpaSpecificationExecutor<Customer> {

}

5.在test包创建CustomerDaoTest测试类，创建testFindById方法

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = "classpath:applicationContext.xml")
public class CustomerDaoTest {

    @Autowired
    private CustomerDao customerDao;

    /**
     * 根据ID查询
     */
    @Test
    public void testFindById(){
        Customer customer = customerDao.findOne(2l);
        System.out.println(customer);
    }

}

save()保存或者更新操作

@Test
public void testSave(){
    // 保存或更新，数据存在就更新，不存在就新建
    Customer customer = new Customer();
    customer.setCustName("Thor");
    customer.setCustSource("Asgard");
    customer.setCustLevel("VIP");
    customer.setCustIndustry("God of Thunder");
    customerDao.save(customer);
}

@Test
public void testUpdate(){
    // 保存或更新，数据存在就更新，不存在就新建
    Customer customer = customerDao.findOne(3l);
    customer.setCustSource("INS");
    customerDao.save(customer);
}

delete()删除操作

@Test
public void testDelete(){
    customerDao.delete(3l);
}

findAll()查询所有操作

@Test
public void testFindAll(){
    List<Customer> customerList = customerDao.findAll();
    for (Customer customer : customerList) {
        System.out.println(customer);
    }
}

执行过程

I:实例化的customerDao是一个动态代理对象SimpleJpaRepository

II:SimpleJpaRepository调用findOne()方法，findOne()会通过实体类管理器em调用find()方法完成查询

三、Spring Data JPA 完成复杂查询

统计查询count()

@Test
public void testCount(){
    long count = customerDao.count();
    System.out.println(count);
}

是否存在exists()

@Test
public void testExists(){
    boolean isExists = customerDao.exists(1l);
    System.out.println(isExists);
}

根据ID查询getOne()

@Test
@Transactional
public void testGetOne(){
    Customer one = customerDao.getOne(1l);
    System.out.println(one);
}

底层调用的是EntityManager的getReference()，延迟加载，find()是立即加载

JPA中的查询方法：

使用JPQL完成复杂查询

JPQL：JPA Query Language

特点：语法或关键字与sql语句类似，查询的是类和类中的属性

需要将JPQL语句配置到接口方法上

• 特有的查询，需要在dao接口上配置方法
• 在新添加的方法上使用注解的形式配置JPQL语句
• 注解为@Query

在CustomerDao接口中新增方法，根据客户名称查询客户，使用JPQL语句

@Query(value = "from Customer where custName= ?")
Customer findByCustName(String custName);

在CustomerDao中测试该方法

@Test
public void testFindByCustName(){
    Customer thor = customerDao.findByCustName("Thor");
    System.out.println(thor);
}

输出结果

多条件(多占位符)查询

在CustomerDao接口中新增方法

// 根据客户名称和id查询客户
@Query(value = "from Customer where custName = ? and custId=?")
Customer findByCustNameAndCustId(String custName, Long custId);

在CustomerDaoTest中测试该方法

@Test
public void testFindByCustNameAndCustId(){
    Customer thor = customerDao.findByCustNameAndCustId("Thor",3L);
    System.out.println(thor);
}

通过custId更新custName

CustomerDao接口中新增方法updateCustNameByCustId

// 要指定参数位置
// 声明为更新操作
@Query(value = "update Customer set custName = ?2 where custId = ?1")
@Modifying
@Transactional
void updateCustNameByCustId(Long custId, String custName);

在CustomerDaoTest中测试该方法

@Test
public void testUpdateCustName(){
    customerDao.updateCustNameByCustId(3L,"Thor Odin");
}

使用SQL语句完成复杂查询

• 特有的查询，需要在dao接口上配置方法
• 在新添加的方法上，使用注解的形式配置SQL查询语句
• 注解为@Query(value=,nativeQuery=),value表示jpql语句或者sql语句，nativeQuery为boolean，false表示使用jpql查询，true表示sql查询

SQL语句查询全部

定义方法selectAll()

@Query(value = "SELECT * FROM customer", nativeQuery = true)
List<Customer> selectAll();

测试该方法

@Test
public void testSelectAll(){
    List<Customer> customers = customerDao.selectAll();
    for (Customer customer : customers) {
        System.out.println(customer);
    }
}

输出结果

SQL语句模糊查询

定义方法selectByCustNameLike

@Query(value = "SELECT * FROM customer where cust_name like ?1", nativeQuery = true)
List<Customer> selectByCustNameLike(String like);

测试该方法

@Test
public void testSelectByCustNameLike(){
    List<Customer> customers = customerDao.selectByCustNameLike("Thor%");
    for (Customer customer : customers) {
        System.out.println(customer);
    }
}

输出结果

方法名称规则查询

  是对jpql查询更加深入的一层封装，只需要按照Spring Data JPA提供的方法名规则定义方法，不需要在配置jpql语句即可完成查询

命名规则：查询使用findBy，对象中的属性为查询的条件，如想要通过custName查询Customer，方法名命名为findByCustName,入参为custName,翻译成sql语句就是select * from customer where cust_name = ?，默认使用=,如果是模糊查询需要Like关键字

findByCustName

Customer findByCustName(String custName);

@Test
public void testFindByCustName(){
    Customer thor = customerDao.findByCustName("Thor Odin");
    System.out.println(thor);
}

输出结果

findByCustNameLike 模糊查询

List<Customer> findByCustNameLike(String custName);

@Test
public void testFindByCustNameLike(){
    List<Customer> customers = customerDao.findByCustNameLike("Thor%");
    for (Customer customer : customers) {
        System.out.println(customer);
    }
}

输出结果

findByCustNameAndCustId 多条件查询使用And关键字,查询的属性的顺序要与入参顺序一致

Customer findByCustNameLikeAndCustIndustry(String custName, String custIndustry);

@Test
public void testFindByCustNameLikeAndCustIndustry(){
    Customer stark_industry = customerDao.findByCustNameLikeAndCustIndustry("Iron%", "Military Industry");
    System.out.println(stark_industry);
}