SpringDataJPA

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Java鱼头

发布于 2022-12-01 22:54:21

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发布于 2022-12-01 22:54:21

文章被收录于专栏：Java-docJava-doc

三、SpringDataJPA介绍

1. 入门案例

1.1 创建项目

创建一个普通的Maven项目

1.2 添加相关的依赖

    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-orm</artifactId>
            <version>5.1.6.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>5.1.6.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.aspectj</groupId>
            <artifactId>aspectjweaver</artifactId>
            <version>1.9.2</version>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.1.8</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.11</version>
        </dependency>
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-entitymanager</artifactId>
            <version>5.0.7.Final</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
            <version>5.1.6.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.data</groupId>
            <artifactId>spring-data-jpa</artifactId>
            <version>1.9.0.RELEASE</version>
        </dependency>
    </dependencies>

1.3 添加配置文件

jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/logistics?characterEncoding=utf-8&serverTimezone=UTC
jdbc.username=root
jdbc.password=123456

Spring的配置文件

<?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/context
       http://www.springframework.org/schema/context/spring-context.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
">
    <!-- 引入db.properties文件 -->
    <context:property-placeholder location="classpath:db.properties" />
    <!-- 创建druid 的数据源 -->
    <bean class="com.alibaba.druid.pool.DruidDataSource" id="dataSource">
        <property name="url" value="${jdbc.url}" />
        <property name="driverClassName" value="${jdbc.driver}" />
        <property name="username" value="${jdbc.username}" />
        <property name="password"  value="${jdbc.password}" />
    </bean>

    <!-- 配置Hibernate的SessionFactory对象 id必须得是 ： entityManagerFactory -->
    <bean class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"
          id="entityManagerFactory">
        <!-- 关联数据源 -->
        <property name="dataSource" ref="dataSource"/>
        <!-- 配置Hibernate的属性信息 -->
        <property name="jpaVendorAdapter">
            <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
                <property name="database" value="MYSQL"/>
                <property name="generateDdl" value="true"/>
                <property name="showSql" value="true"/>
            </bean>
            <!--<props>
                <prop key="show_sql">true</prop>
                <prop key="hibernate.hbm2ddl.auto">update</prop>
            </props>-->
        </property>
        <!-- 扫描路径 -->
        <property name="packagesToScan">
            <list>
                <value>com.bobo.pojo</value>
            </list>
        </property>
    </bean>


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

    <!-- 配置开启事务注解 -->
    <tx:annotation-driven transaction-manager="transactionManager" />

    <!-- 配置扫描路径 -->
    <context:component-scan base-package="com.bobo" />

    <!--  Spring Data Jpa 配置-->
    <!-- 配置Dao的扫描 -->
    <jpa:repositories base-package="com.bobo.dao" />
</beans>

1.4 创建POJO对象

package com.bobo.pojo;


import javax.persistence.*;
import java.io.Serializable;

@Entity
@Table(name="t_user")
public class Users implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name="user_id")
    private Integer userId;

    @Column(name="user_name")
    private String userName;

    @Column(name="real_name")
    private String realName;

    public Integer getUserId() {
        return userId;
    }

    public void setUserId(Integer userId) {
        this.userId = userId;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getRealName() {
        return realName;
    }

    public void setRealName(String realName) {
        this.realName = realName;
    }

    @Override
    public String toString() {
        return "Users{" +
                "userId=" + userId +
                ", userName='" + userName + '\'' +
                ", realName='" + realName + '\'' +
                '}';
    }
}

1.5 创建持久层

import com.bobo.pojo.Users;
import org.springframework.data.jpa.repository.JpaRepository;

public interface UserDao extends JpaRepository<Users,Integer> {

}

1.6 单元测试

package com.bobo.test;

import com.bobo.dao.UserDao;
import com.bobo.pojo.Users;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.annotation.Rollback;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.transaction.annotation.Transactional;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("classpath:applicationContext.xml")
public class Test1 {

    @Autowired
    private UserDao dao;


    @Test
    @Transactional
    @Rollback(false)
    public void test1(){
        Users user = new Users();
        user.setUserName("admin-jpa");
        user.setRealName("测试");
        dao.save(user);
    }
}

2. Repository接口

public interface Repository<T, ID extends Serializable> {
}

Repository 接口是 Spring Data JPA 中为我我们提供的所有接口中的顶层接口,而且是个标志接口，Repository 提供了两种查询方式的支持 1）基于方法名称命名规则查询 2）基于@Query 注解查询

2.1 基于方法名称命名规则查询

package com.bobo.dao;

import com.bobo.pojo.Users;
import org.springframework.data.repository.Repository;

import javax.persistence.criteria.CriteriaBuilder;
import java.util.List;

/**
 * Repository接口的使用
 */
public interface UserDaoRepository extends Repository<Users, Integer> {

    List<Users> findByUserNameIs(String string);

    List<Users> findByUserNameLike(String username);

    List<Users> findByUserNameAndRealNameIs(String name,String realName);
}

测试代码

package com.bobo.test;

import com.bobo.dao.UserDaoRepository;
import com.bobo.pojo.Users;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.annotation.Rollback;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.transaction.annotation.Transactional;

import java.util.List;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("classpath:applicationContext.xml")
public class Test2 {

    @Autowired
    private UserDaoRepository dao;

    @Test
    @Transactional
    @Rollback(false)
    public void query1(){
        List<Users> list = this.dao.findByUserNameIs("Tom");
        for (Users users : list) {
            System.out.println(users);
        }
    }

    @Test
    @Transactional
    @Rollback(false)
    public void query2(){
        List<Users> list = this.dao.findByUserNameLike("Tom");
        for (Users users : list) {
            System.out.println(users);
        }
    }

    @Test
    @Transactional
    @Rollback(false)
    public void query3(){
        List<Users> list = this.dao.findByUserNameAndRealNameIs("Tom","张三丰");
        for (Users users : list) {
            System.out.println(users);
        }
    }
}

2.2 基于@Query 注解查询

通过上面的命令的方式使用的情况，如果查询条件比较复杂的情况下，那么方法的名称会很长，不是很方便而且容易出错，这时我们可以通过@Query注解来实现

2.2.1 JPQL语句

JPQL：是通过Hibernate的HQL语句演变而来的，他和HQL语句很相似

/**
 * Repository接口的使用
 * @Query
 *    JPQL语句
 *    SQL语句
 *    更新操作
 */
public interface UserDaoRepository2 extends Repository<Users, Integer> {

    @Query(value = " from Users where userName =?")
    List<Users> queryUsersByNameUseJPQL(String name);

    @Query(value = " from Users where userName like ?")
    List<Users> queryUserLikeNameUseJPQL(String name);

    @Query(value = " from Users where userName= ? and realName = ?")
    List<Users> queryUserByNameAndRealName(String userName,String realName);

}

单元测试

package com.bobo.test;

import com.bobo.dao.UserDaoRepository;
import com.bobo.dao.UserDaoRepository2;
import com.bobo.pojo.Users;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.annotation.Rollback;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.transaction.annotation.Transactional;

import java.util.List;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("classpath:applicationContext.xml")
public class Test3 {

    @Autowired
    private UserDaoRepository2 dao;

    @Test
    @Transactional
    @Rollback(false)
    public void query1(){
        List<Users> list = this.dao.queryUsersByNameUseJPQL("Tom");
        for (Users users : list) {
            System.out.println(users);
        }
    }

    @Test
    @Transactional
    @Rollback(false)
    public void query2(){
        List<Users> list = this.dao.queryUserLikeNameUseJPQL("Tom");
        for (Users users : list) {
            System.out.println(users);
        }
    }

    @Test
    @Transactional
    @Rollback(false)
    public void query3(){
        List<Users> list = this.dao.queryUserByNameAndRealName("Tom","张三丰");
        for (Users users : list) {
            System.out.println(users);
        }
    }
}

2.2.2 SQL语句

声明接口

package com.bobo.dao;

import com.bobo.pojo.Users;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.Repository;

import java.util.List;

/**
 * Repository接口的使用
 * @Query
 *    JPQL语句
 *    SQL语句
 *    更新操作
 */
public interface UserDaoRepository3 extends Repository<Users, Integer> {

    // 在使用@Query注解 查询SQL语句的时候 nativeQuery默认是false，我们需要设置为true
    @Query(value = "select * from t_user where user_name=?",nativeQuery = true)
    List<Users> queryUsersByNameUseSQL(String name);

    @Query(value = "select * from t_user where user_name like ?" ,nativeQuery = true)
    List<Users> queryUserLikeNameUseSQL(String name);

    @Query(value = "select * from t_user where user_name = ? and real_name = ?" , nativeQuery = true)
    List<Users> queryUserByNameAndRealName(String userName,String realName);

}

单元测试

package com.bobo.test;

import com.bobo.dao.UserDaoRepository2;
import com.bobo.dao.UserDaoRepository3;
import com.bobo.pojo.Users;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.annotation.Rollback;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.transaction.annotation.Transactional;

import java.util.List;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("classpath:applicationContext.xml")
public class Test4 {

    @Autowired
    private UserDaoRepository3 dao;

    @Test
    @Transactional
    @Rollback(false)
    public void query1(){
        List<Users> list = this.dao.queryUsersByNameUseSQL("Tom");
        for (Users users : list) {
            System.out.println(users);
        }
    }

    @Test
    @Transactional
    @Rollback(false)
    public void query2(){
        List<Users> list = this.dao.queryUserLikeNameUseSQL("Tom");
        for (Users users : list) {
            System.out.println(users);
        }
    }

    @Test
    @Transactional
    @Rollback(false)
    public void query3(){
        List<Users> list = this.dao.queryUserByNameAndRealName("Tom","张三丰");
        for (Users users : list) {
            System.out.println(users);
        }
    }
}

2.2.3 完成更新数据

@Query注解可以完成数据更新操作，但是不能实现数据的添加和删除操作

    @Query(value = "update Users set userName = ? where userId=?")
    @Modifying// 被@Modifying修饰的方法是一个更新操作
    void updateUserNameById(String userName,Integer userId);

测试

    @Test
    @Transactional
    @Rollback(false)
    public void updateTest(){
        this.dao.updateUserNameById("Tommm",25);
    }

3. CrudRepository接口

CrudRepository接口继承自Repository接口，所以Repository接口具有的功能CrudRepository接口都具有，而且又扩展了CRUD相关的功能


@NoRepositoryBean
public interface CrudRepository<T, ID extends Serializable> extends Repository<T, ID> {
    <S extends T> S save(S var1);

    <S extends T> Iterable<S> save(Iterable<S> var1);

    T findOne(ID var1);

    boolean exists(ID var1);

    Iterable<T> findAll();

    Iterable<T> findAll(Iterable<ID> var1);

    long count();

    void delete(ID var1);

    void delete(T var1);

    void delete(Iterable<? extends T> var1);

    void deleteAll();
}

应用声明接口

/**
 * CrudRepository接口的使用
 */
public interface UserDaoCrudRepository extends CrudRepository<Users,Integer> {
}

单元测试

package com.bobo.test;

import com.bobo.dao.UserDaoCrudRepository;
import com.bobo.dao.UserDaoRepository3;
import com.bobo.pojo.Users;
import org.junit.Test;
import org.junit.experimental.theories.suppliers.TestedOn;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.support.CustomSQLErrorCodesTranslation;
import org.springframework.test.annotation.Rollback;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.transaction.annotation.Transactional;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("classpath:applicationContext.xml")
public class Test5 {

    @Autowired
    private UserDaoCrudRepository dao;

    /**
     * 添加数据
     */
    @Test
    public void test1(){
        Users user = new Users();
        user.setRealName("成龙");
        user.setUserName("chengnong");
        dao.save(user);
    }

    /**
     * 批量添加数据
     */
    @Test
    public void test2(){
        List<Users> list = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            Users user = new Users();
            user.setRealName("成龙"+i);
            user.setUserName("chengnong"+i);
            list.add(user);
        }
        dao.save(list);
    }

    /**
     * 查询单条数据
     */
    @Test
    public void test3(){
        Users user = dao.findOne(25);
        System.out.println(user);
    }

    /**
     * 查询所有的数据
     */
    @Test
    public void test4(){
        Iterable<Users> list = dao.findAll();
        Iterator<Users> iterator = list.iterator();
        while(iterator.hasNext()){
            Users user = iterator.next();
            System.out.println(user);
        }
    }

    /**
     * 删除数据
     */
    @Test
    public void delete1(){
        dao.delete(32);
    }

    /**
     * 更新数据
     */
    @Test
    public void update1(){
        // 根据save方法来实现 如果Users对象的userId属性不为空则update
        Users user = dao.findOne(34);
        user.setUserName("hahahaha");
        dao.save(user);
    }

    /**
     * 更新数据 方式二
     */
    @Test
    @Transactional
    @Rollback(false)
    public void update2(){
        Users user = dao.findOne(34);
        user.setUserName("aaaa"); // User 是一个持久化的状态
    }
}

4.PagingAndSortingRepository接口

PagingAndSortingRepository继承自CrudRepository接口，那么显然PagingAndSortingRepository就具备了CrudRepository接口的相关的功能，同时也扩展了分页和排序的功能

@NoRepositoryBean
public interface PagingAndSortingRepository<T, ID extends Serializable> extends CrudRepository<T, ID> {
    // 排序的支持
    Iterable<T> findAll(Sort var1);
    // 分页的支持
    Page<T> findAll(Pageable var1);
}

创建接口文件

package com.bobo.dao;

import com.bobo.pojo.Users;
import org.springframework.data.repository.PagingAndSortingRepository;

/**
 * PagingAndSortingRepository接口的使用
 *    新增的功能是
 *       分页
 *       排序
 *    注意本接口不支持条件查询
 */
public interface UserDaoPageAndSortRepository extends PagingAndSortingRepository<Users,Integer> {
}

分页测试

package com.bobo.test;

import com.bobo.dao.UserDaoCrudRepository;
import com.bobo.dao.UserDaoPageAndSortRepository;
import com.bobo.pojo.Users;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.test.annotation.Rollback;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.transaction.annotation.Transactional;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("classpath:applicationContext.xml")
public class Test6 {

    @Autowired
    private UserDaoPageAndSortRepository dao;

    /**
     * 分页查询
     */
    @Test
    public void test1(){
        int page = 1; // page:当前分页的索引  从0开始
        int size = 5; // size:每页显示的条数
        PageRequest pageable = new PageRequest(page,size);
        Page<Users> pages = dao.findAll(pageable);
        System.out.println("总的条数:" + pages.getTotalElements());
        System.out.println("总的页数:" + pages.getTotalPages());
        List<Users> list = pages.getContent();
        for (Users user : list) {
            System.out.println(user);
        }
    }
}

排序功能

   /**
     * 排序
     */
    @Test
    public void test2(){

        // Sort.Direction.DESC 降序 ASC 升序
        Sort sort = new Sort(Sort.Direction.DESC,"userId");
        List<Users> list = (List<Users>) this.dao.findAll(sort);
        for (Users users : list) {
            System.out.println(users);
        }
    }

多条件排序

    /**
     * 多条件排序
     */
    @Test
    public void test3(){
        Sort.Order order1 = new Sort.Order(Sort.Direction.DESC,"realName");
        Sort.Order order2 = new Sort.Order(Sort.Direction.ASC,"userId");
        Sort sort = new Sort(order1,order2);
        List<Users> list = (List<Users>) this.dao.findAll(sort);
        for (Users users : list) {
            System.out.println(users);
        }

    }

5. JpaRepository接口

JpaRepository接口是我们开发时使用最多接口，其特点是可以帮助我们将其他接口的方法的返回值做适配处理，可以使我们在开发的时候更方便的使用这些方法

@NoRepositoryBean
public interface JpaRepository<T, ID extends Serializable> extends PagingAndSortingRepository<T, ID> {
    List<T> findAll();

    List<T> findAll(Sort var1);

    List<T> findAll(Iterable<ID> var1);

    <S extends T> List<S> save(Iterable<S> var1);

    void flush();

    <S extends T> S saveAndFlush(S var1);

    void deleteInBatch(Iterable<T> var1);

    void deleteAllInBatch();

    T getOne(ID var1);
}

6. JpaSpecificationExecutor

提供的有多条件查询，并支持分页和排序功能，此接口不能单独使用，需要和其他的接口一块使用

/**
 * JpaSpecificationExecutor的使用
 *    JpaSpecificationExecutor 是不能够单独使用的。需要配置JPA中的其他的接口一块来使用
 */
public interface UserDaoSpecfication extends JpaRepository<Users,Integer>, JpaSpecificationExecutor {
}

6.1 单条件查询

package com.bobo.test;

import com.bobo.dao.UserDaoSpecfication;
import com.bobo.pojo.Users;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.jpa.domain.Specification;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Predicate;
import javax.persistence.criteria.Root;
import java.util.List;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("classpath:applicationContext.xml")
public class Test7 {

    @Autowired
    private UserDaoSpecfication dao;

    @Test
    public void test1(){
        Specification<Users> speci = new Specification<Users>() {
            /**
             * 定义查询条件
             * @param root 根对象  封装查询条件的对象
             * @param criteriaQuery 基本的查询
             * @param criteriaBuilder 创建查询条件
             * @return
             */
            @Override
            public Predicate toPredicate(Root<Users> root
                    , CriteriaQuery<?> criteriaQuery
                    , CriteriaBuilder criteriaBuilder) {
                Predicate pre = criteriaBuilder.equal(root.get("userName"),"Tommm");
                return pre;
            }
        };

        List<Users> list = dao.findAll(speci);
        for (Users users : list) {
            System.out.println(users);
        }
    }
}

6.2 多条件

    /**
     * 多条件查询
     */
    @Test
    public void test2(){
        Specification<Users> spec = new Specification<Users>() {
            /**
             * 指定查询的条件
             * @param root
             * @param criteriaQuery
             * @param criteriaBuilder
             * @return
             */
            @Override
            public Predicate toPredicate(Root<Users> root, CriteriaQuery<?> criteriaQuery, CriteriaBuilder criteriaBuilder) {
                List<Predicate> list = new ArrayList<>();
                list.add(criteriaBuilder.equal(root.get("userName"),"Tommm"));
                list.add(criteriaBuilder.equal(root.get("realName"),"张三丰"));
                Predicate[] arr = new Predicate[list.size()];
                return criteriaBuilder.and(list.toArray(arr));
            }
        };
        List<Users> list = dao.findAll(spec);
        for (Users users : list) {
            System.out.println(users);
        }
    }

6.3 分页

    /**
     * 单条件+分页
     */
    @Test
    public void test3(){
        Specification<Users> speci = new Specification<Users>() {
            /**
             * 定义查询条件
             * @param root 根对象  封装查询条件的对象
             * @param criteriaQuery 基本的查询
             * @param criteriaBuilder 创建查询条件
             * @return
             */
            @Override
            public Predicate toPredicate(Root<Users> root
                    , CriteriaQuery<?> criteriaQuery
                    , CriteriaBuilder criteriaBuilder) {
                Predicate pre = criteriaBuilder.equal(root.get("userName"),"Tommm");
                return pre;
            }
        };

        Pageable pagealbe = (Pageable) new PageRequest(0,3);
        Page page = dao.findAll(speci, pagealbe);
        System.out.println(page.getTotalElements());
        System.out.println(page.getTotalPages());
        List content = page.getContent();
        System.out.println(content);

    }

6.4 排序

    /**
     * 单条件+排序
     */
    @Test
    public void test4(){
        Specification<Users> speci = new Specification<Users>() {
            /**
             * 定义查询条件
             * @param root 根对象  封装查询条件的对象
             * @param criteriaQuery 基本的查询
             * @param criteriaBuilder 创建查询条件
             * @return
             */
            @Override
            public Predicate toPredicate(Root<Users> root
                    , CriteriaQuery<?> criteriaQuery
                    , CriteriaBuilder criteriaBuilder) {
                Predicate pre = criteriaBuilder.equal(root.get("userName"),"Tommm");
                return pre;
            }
        };

        Sort sort = new Sort(Sort.Direction.DESC,"userId");
        List<Users> list = dao.findAll(speci, sort);
        System.out.println(list);

    }

6.5 分页和排序

    /**
     * 单条件+分页 + 排序
     */
    @Test
    public void test5(){
        Specification<Users> speci = new Specification<Users>() {
            /**
             * 定义查询条件
             * @param root 根对象  封装查询条件的对象
             * @param criteriaQuery 基本的查询
             * @param criteriaBuilder 创建查询条件
             * @return
             */
            @Override
            public Predicate toPredicate(Root<Users> root
                    , CriteriaQuery<?> criteriaQuery
                    , CriteriaBuilder criteriaBuilder) {
                Predicate pre = criteriaBuilder.equal(root.get("userName"),"Tommm");
                return pre;
            }
        };
        Sort sort = new Sort(Sort.Direction.DESC,"userId");
        // 封装分页对象的时候我们可以直接指定 排序的规则
        Pageable pagealbe = (Pageable) new PageRequest(0,3,sort);
        Page page = dao.findAll(speci, pagealbe);
        System.out.println(page.getTotalElements());
        System.out.println(page.getTotalPages());
        List content = page.getContent();
        System.out.println(content);

    }