Spring Data JPA 初体验

1.Spring Data JPA的概述

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

1.1Spring Data JPA的特性

SpringData Jpa 极大简化了数据库访问层代码。 如何简化的呢？ 使用了SpringDataJpa，我们的dao层中只需要写接口，就自动具有了增删改查、分页查询等方法。

1.2 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。

2 Spring Data JPA的快速入门

2.1 需求说明

Spring Data JPA完成客户的基本CRUD操作

2.2 搭建Spring Data JPA的开发环境

2.2.1 引入Spring Data JPA的坐标

使用Spring Data JPA，需要整合Spring与Spring Data JPA，并且需要提供JPA的服务提供者hibernate，所以需要导入spring相关坐标，hibernate坐标，数据库驱动坐标等

 <properties>
        <spring.version>4.2.4.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>5.1.6</mysql.version>
    </properties>

    <dependencies>
        <!-- junit单元测试 -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.9</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>

        <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>

</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>

        <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>

<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>

        <dependency>

            <groupId>org.springframework.data</groupId>

            <artifactId>spring-data-jpa</artifactId>

            <version>1.9.0.RELEASE</version>

        </dependency>

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-test</artifactId>

            <version>4.2.4.RELEASE</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>

2.2.2 整合Spring Data JPA与Spring

<?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">
    
    <!-- 1.dataSource 配置数据库连接池-->
    <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
        <property name="driverClass" value="com.mysql.jdbc.Driver" />
        <property name="jdbcUrl" value="jdbc:mysql://localhost:3306/jpa" />
        <property name="user" value="root" />
        <property name="password" value="root" />
    </bean>
    
    <!-- 2.配置entityManagerFactory -->
    <bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="packagesToScan" value="cn.yang.entity" />
        <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">
                <property name="generateDdl" value="false" />
<property name="database" value="MYSQL" />
                <property name="databasePlatform" value="org.hibernate.dialect.MySQLDialect" />
                <property name="showSql" value="true" />
            </bean>
        </property>
        <property name="jpaDialect">
            <bean class="org.springframework.orm.jpa.vendor.HibernateJpaDialect" />
        </property>
    </bean>
    
    
    <!-- 3.事务管理器-->
    <!-- JPA事务管理器  -->
    <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
        <property name="entityManagerFactory" ref="entityManagerFactory" />
    </bean>
    
    <!-- 整合spring data jpa-->
    <jpa:repositories base-package="cn.yang.dao"
        transaction-manager-ref="transactionManager"
        entity-manager-factory-ref="entityManagerFactory"></jpa:repositories>
        
    <!-- 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(* cn.itcast.service.*.*(..))" />
        <aop:advisor advice-ref="txAdvice" pointcut-ref="pointcut" />
    </aop:config>
<context:component-scan base-package="cn.yang"></context:component-scan>
        
    <!--组装其它 配置文件-->
    
</beans>

2.2.3 使用JPA注解配置映射关系

配置Customer实体类对象，并且配置映射关系

数据库为customer

表数据有：

id name source industry level address phone

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

/**
 * 
 *      * 所有的注解都是使用JPA的规范提供的注解，
 *      * 所以在导入注解包的时候，一定要导入javax.persistence下的
 */
@Entity //声明实体类
@Table(name="customer") //建立实体类和表的映射关系
public class Customer {
    
    @Id//声明当前私有属性为主键
    @GeneratedValue(strategy=GenerationType.IDENTITY) //配置主键的生成策略
    @Column(name="id") //指定和表中id字段的映射关系
    private Long Id;
    
    @Column(name="name") //指定和表中name字段的映射关系
    private String Name;
    
    @Column(name="source")//指定和表中source字段的映射关系
    private String Source;
    
    @Column(name="industry")//指定和表中industry字段的映射关系
    private String Industry;
    @Column(name="level")//指定和表中level字段的映射关系
    private String Level;
    
    @Column(name="address")//指定和表中address字段的映射关系
    private String Address;
    
    @Column(name="phone")//指定和表中phone字段的映射关系
    private String Phone;
    
    public Long getId() {
        return Id;
    }
    public void setId(Long Id) {
        this.custId = Id;
    }
    public String getName() {
        return Name;
    }
    public void setName(String Name) {
        this.Name = Name;
    }
    public String getSource() {
        return Source;
    }
    public void setSource(String Source) {
        this.Source = Source;
    }
    public String getIndustry() {
        return Industry;
    }
    public void setIndustry(String Industry) {
        this.Industry = Industry;
    }
    public String getLevel() {
        return Level;
    }
    public void setLevel(String Level) {
        this.Level = Level;
    }
    public String getAddress() {
        return Address;
    }
    public void setAddress(String Address) {
        this.Address = Address;
}
    public String getPhone() {
        return Phone;
    }
    public void setPhone(String Phone) {
        this.Phone =Phone; 
} 
}

2.3 使用Spring Data JPA完成需求

2.3.1 编写符合Spring Data JPA规范的Dao层接口

Spring Data JPA是spring提供的一款对于数据访问层（Dao层）的框架，使用Spring Data JPA，只需要按照框架的规范提供dao接口，不需要实现类就可以完成数据库的增删改查、分页查询等方法的定义，极大的简化了我们的开发过程。

在Spring Data JPA中，对于定义符合规范的Dao层接口，我们只需要遵循以下几点就可以了：

1.创建一个Dao层接口，并实现JpaRepository和JpaSpecificationExecutor

 2.提供相应的泛型

import java.util.List;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.JpaSpecificationExecutor;

import cn.yang.entity.Customer;

/**
 * JpaRepository<实体类类型，主键类型>：用来完成基本CRUD操作
 * JpaSpecificationExecutor<实体类类型>：用于复杂查询（分页等查询操作）
 */
public interface CustomerDao extends JpaRepository<Customer, Long>, JpaSpecificationExecutor<Customer> {
}

这样我们就定义好了一个符合Spring Data JPA规范的Dao层接口

2.3.2 完成基本CRUD操作

完成了Spring Data JPA的环境搭建，并且编写了符合Spring Data JPA 规范的Dao层接口之后，就可以使用定义好的Dao层接口进行客户的基本CRUD操作

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

    @Autowired
    private CustomerDao customerDao;
    
    /**
     * 保存客户：调用save(obj)方法
     */
    @Test
    public void testSave() {
        Customer c = new Customer();
        c.setName("鹿晗");
        customerDao.save(c);
    }
    
    /**
     * 修改客户：调用save(obj)方法
     *      对于save方法的解释：如果执行此方法是对象中存在id属性，即为更新操作会先根据id查询，再更新    
     *                      如果执行此方法中对象中不存在id属性，即为保存操作
     *          
     */
    @Test
    public void testUpdate() {
        //根据id查询id为1的客户
        Customer customer = customerDao.findOne(1l);
        //修改客户名称
        customer.setName("上海堡垒");
        //更新
        customerDao.save(customer);
    }
    
    /**
     * 根据id删除：调用delete(id)方法
     */
    @Test
 public void testDelete() {
        customerDao.delete(1l);
    }
    
    /**
     * 根据id查询：调用findOne(id)方法
     */
    @Test
    public void testFindById() {
        Customer customer = customerDao.findOne(2l);
        System.out.println(customer);
    }
}