springdata jpa 返回dto

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mob64ca13f87273 2024-09-22 15:35:15

文章标签 数据库 spring java hibernate jpa 文章分类 架构后端开发

文章目录

Spring Data JPA是什么？
Spring Data JPA的配置

配置pom.xml
配置applicationContext.xml

Spring Data JPA的使用
Spring Data JPA的运行原理

Spring Data JPA是Spring数据家族的一部分，它使得实现基于JPA访问数据库变得很容易。它增强了对JPA的支持，使得构建使用数据访问技术的spring驱动的应用程序变得更加容易。

Spring Data JPA是什么？

上一期我们讲过了JDBC和原生JPA，而JPA的使用还比较麻烦，每次访问数据库，我们都需要创建EntityManagerFactory工厂类、获得EntityManager、创建事务、提交事务，最后释放资源。这样的操作明显是很繁琐的。

于是，Spring Data JPA出现了。Spring Data JPA是基于原生JPA的封装，它使得我们使用JPA变得更加简单，且拥有更强大的功能。

Spring Data JPA的配置

配置pom.xml

引入以下依赖：

Slf4j日志
Spring核心
Spring Data JPA支持
Druid连接池
Hibernate核心和JPA支持
MySQL驱动
*Junit单元测试
*Lombok

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>org.koorye</groupId>
  <artifactId>hellospringdatajpa</artifactId>
  <version>1.0-SNAPSHOT</version>

  <dependencies>
    <!-- Slf4j -->
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-api</artifactId>
      <version>1.7.25</version>
    </dependency>
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-log4j12</artifactId>
      <version>1.7.25</version>
      <scope>test</scope>
    </dependency>

    <!-- Spring -->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-aop</artifactId>
      <version>5.2.7.RELEASE</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-core</artifactId>
      <version>5.2.7.RELEASE</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-tx</artifactId>
      <version>5.2.7.RELEASE</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-beans</artifactId>
      <version>5.2.7.RELEASE</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring</artifactId>
      <version>5.2.7.RELEASE</version>
      <type>pom</type>
    </dependency>

    <!-- Spring Data JPA -->
    <dependency>
      <groupId>org.springframework.data</groupId>
      <artifactId>spring-data-commons</artifactId>
      <version>2.3.1.RELEASE</version>
    </dependency>
    <dependency>
      <groupId>org.springframework.data</groupId>
      <artifactId>spring-data-jpa</artifactId>
      <version>2.3.1.RELEASE</version>
    </dependency>

    <!-- Druid -->
    <dependency>
      <groupId>com.alibaba</groupId>
      <artifactId>druid</artifactId>
      <version>1.1.21</version>
    </dependency>

    <!-- Hibernate -->
    <dependency>
      <groupId>org.hibernate</groupId>
      <artifactId>hibernate-core</artifactId>
      <version>5.4.10.Final</version>
    </dependency>
    <dependency>
      <groupId>org.hibernate</groupId>
      <artifactId>hibernate-entitymanager</artifactId>
      <version>5.4.10.Final</version>
    </dependency>

    <!-- MySQL -->
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>8.0.20</version>
    </dependency>

    <!-- Test -->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-test</artifactId>
      <version>5.2.7.RELEASE</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.12</version>
      <scope>test</scope>
    </dependency>

    <!-- Lombok -->
    <dependency>
      <groupId>org.projectlombok</groupId>
      <artifactId>lombok</artifactId>
      <version>1.18.12</version>
    </dependency>
  </dependencies>
</project>

配置applicationContext.xml

配置Spring Data JPA分为6步：

配置连接池，此时选用Druid
配置EntityManagerFactory，其中需要指定：

dataSource 连接池
packageToScan 实体类包的位置
persistenceProvider 持久化提供者，此处选择Hibernate提供的持久化
jpaVendorAdapter JPA供应商适配器，其中需要提供一个bean，包含一个jpaVendorAdapter类，而bean有一些配置：

generateDdl 是否自动创建数据表
database 指定数据库类型
showSql 是否显示sql语句
databasePlatform 配置数据库方言

jpaDialect JPA方言

配置transcationManager事务管理器，指定一个JPATranscationManager类，并提供EntityManagerFactory
整合springDataJPA，使用jpa:repository标签，指定以下内容：

base-package 指定JPA方法类包的位置
transaction-manager-ref 引用transactionManager
entity-manager-factory-ref 引用entityManagerFactory

配置自动装配，使用component-scan标签

<?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: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/context http://www.springframework.org/schema/context/spring-context-4.0.xsd">

  <!-- Data source -->
  <bean id="dataSource" class="com.alibaba.druid.pool.DruidDataSource">
    <property name="driverClassName" value="com.mysql.cj.jdbc.Driver"/>
    <property name="url" value="jdbc:mysql://localhost:3306/demo?useUnicode=true&characterEncoding=UTF-8&serverTimezone=UTC"/>
    <property name="username" value="root"/>
    <property name="password" value="root"/>
  </bean>

  <!-- Entity manager factory, provided by hibernate -->
  <bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
    <property name="dataSource" ref="dataSource"/>
    <property name="packagesToScan" value="org.koorye.pojo"/>
    <property name="persistenceProvider">
      <bean class="org.hibernate.jpa.HibernatePersistenceProvider"/>
    </property>

    <!-- Adapter -->
    <property name="jpaVendorAdapter">
      <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
        <property name="generateDdl" value="false"/>
        <property name="database" value="MYSQL"/>
        <property name="showSql" value="true"/>

        <!-- SQL dialect -->
        <property name="databasePlatform" value="org.hibernate.dialect.MySQL5Dialect"/>
      </bean>
    </property>

    <!-- JPA dialect -->
    <property name="jpaDialect">
      <bean class="org.springframework.orm.jpa.vendor.HibernateJpaDialect"/>
    </property>
  </bean>

  <!-- Transaction manager -->
  <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
    <property name="entityManagerFactory" ref="entityManagerFactory"/>
  </bean>

  <!-- Spring data JPA -->
  <jpa:repositories base-package="org.koorye.dao"
                    transaction-manager-ref="transactionManager"
                    entity-manager-factory-ref="entityManagerFactory"/>

  <!-- Component scan -->
  <context:component-scan base-package="org.koorye"/>
</beans>

Spring Data JPA的使用

Spring Data JPA的使用分为3步：

根据数据表编写实体类，并配置实体类与表、类属性与表字段的映射关系
编写持久层接口，不需要编写实现类！
调用接口方法

首先来实现一个实体类，大部分内容与上一期相同，不再介绍：

package org.koorye.pojo;

import lombok.Getter;
import lombok.Setter;

import javax.persistence.*;

@Getter
@Setter
@Entity
@Table(name = "user")
public class User {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  @Column(name = "u_id")
  private int id;

  @Column(name = "u_name")
  private String name;

  @Override
  public String toString() {
    return "ID: " + id + ", Name: " + name;
  }
}

接下来编写一个接口类，注意此处继承了两个接口：

JpaRepository<实体类名, 主键类型> 提供基本的CRUD功能
JpaSpecificationExecutor<实体类名> 提供多条件查询的支持

package org.koorye.dao;

import org.koorye.pojo.User;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.JpaSpecificationExecutor;

public interface UserDao extends JpaRepository<User, Integer>, JpaSpecificationExecutor<User> {
}

最后来测试一下：

package org.koorye;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.koorye.dao.UserDao;
import org.koorye.pojo.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import java.util.List;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = "classpath:applicationContext.xml")
public class SpringDataJPATest {
  @Autowired
  private UserDao userDao;

  @Test
  public void TestFindAll() {
    List<User> userList = userDao.findAll();
    for (User user : userList) {
      System.out.println(user);
    }
  }
}

注意到，我们的接口类并没有findAll方法，该方法继承自JpaRepository接口。

输出结果，测试成功：

Hibernate: select user0_.u_id as u_id1_0_, user0_.u_name as u_name2_0_ from user user0_
ID: 1, Name: 冬马和纱
ID: 2, Name: 小木曾雪菜

Process finished with exit code 0