集成Spring+SpringDataJpa 01_lt0jpa-01-优快云博客

本文链接：https://blog.youkuaiyun.com/wuguobang_Niko/article/details/95244073

集成Spring+SpringDataJpa

引入项目中所需要的所有包(pom.xml)

<?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>cn.itsource</groupId>
  <artifactId>yxb</artifactId>
  <version>1.0-SNAPSHOT</version>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <org.springframework.version>4.2.5.RELEASE</org.springframework.version>
    <org.hibernate.version>4.3.8.Final</org.hibernate.version>
    <spring-data-jpa.version>1.9.0.RELEASE</spring-data-jpa.version>
    <com.fasterxml.jackson.version>2.5.0</com.fasterxml.jackson.version>
    <org.slf4j.version>1.6.1</org.slf4j.version>
  </properties>
  <dependencies>
    <!-- Spring的支持包 -->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-core</artifactId>
      <version>${org.springframework.version}</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>${org.springframework.version}</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context-support</artifactId>
      <version>${org.springframework.version}</version>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-tx</artifactId>
      <version>${org.springframework.version}</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-jdbc</artifactId>
      <version>${org.springframework.version}</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-orm</artifactId>
      <version>${org.springframework.version}</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-aop</artifactId>
      <version>${org.springframework.version}</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-test</artifactId>
      <version>${org.springframework.version}</version>
      <scope>test</scope>
    </dependency>
    <!-- 引入web前端的支持 -->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-web</artifactId>
      <version>${org.springframework.version}</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-webmvc</artifactId>
      <version>${org.springframework.version}</version>
    </dependency>
    <!-- SpringMCV上传需要用到io包-->
    <dependency>
      <groupId>org.apache.commons</groupId>
      <artifactId>commons-io</artifactId>
      <version>1.3.2</version>
    </dependency>
    <!-- 文件上传用到的包 -->
    <dependency>
      <groupId>commons-fileupload</groupId>
      <artifactId>commons-fileupload</artifactId>
      <version>1.2.2</version>
    </dependency>
    <!-- SpringMVC的json支持包 -->
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-core</artifactId>
      <version>${com.fasterxml.jackson.version}</version>
    </dependency>
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-annotations</artifactId>
      <version>${com.fasterxml.jackson.version}</version>
    </dependency>
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-databind</artifactId>
      <version>${com.fasterxml.jackson.version}</version>
    </dependency>
    <!-- hibernate的支持包 -->
    <dependency>
      <groupId>org.hibernate</groupId>
      <artifactId>hibernate-core</artifactId>
      <version>${org.hibernate.version}</version>
    </dependency>
    <dependency>
      <groupId>org.hibernate</groupId>
      <artifactId>hibernate-entitymanager</artifactId>
      <version>${org.hibernate.version}</version>
    </dependency>
    <!-- SpringData的支持包 -->
    <dependency>
      <groupId>org.springframework.data</groupId>
      <artifactId>spring-data-jpa</artifactId>
      <version>${spring-data-jpa.version}</version>
    </dependency>
    <!-- SpringData的擴展包 -->
    <dependency>
      <groupId>com.github.wenhao</groupId>
      <artifactId>jpa-spec</artifactId>
      <version>3.1.1</version>
      <!-- 把所有的依賴都去掉 -->
      <exclusions>
        <exclusion>
          <groupId>*</groupId>
          <artifactId>*</artifactId>
        </exclusion>
      </exclusions>
    </dependency>

    <dependency>
      <groupId>commons-dbcp</groupId>
      <artifactId>commons-dbcp</artifactId>
      <version>1.2.2</version>
    </dependency>

    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>5.1.6</version>
    </dependency>

    <dependency>
      <groupId>org.apache.commons</groupId>
      <artifactId>commons-lang3</artifactId>
      <version>3.5</version>
    </dependency>
    <!-- 測試包 -->
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.12</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <version>3.1.0</version>
      <!-- 这个scope 只能作用在编译和测试时，同时没有传递性。表示在运行的时候不添加此jar文件 -->
      <scope>provided</scope>
    </dependency>
    <!-- 日志文件 -->
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-api</artifactId>
      <version>${org.slf4j.version}</version>
    </dependency>
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-log4j12</artifactId>
      <version>${org.slf4j.version}</version>
      <scope>runtime</scope>
    </dependency>
    <dependency>
      <groupId>log4j</groupId>
      <artifactId>log4j</artifactId>
      <version>1.2.14</version>
    </dependency>
    <!-- 代码生成器模版技术 -->
    <dependency>
      <groupId>org.apache.velocity</groupId>
      <artifactId>velocity</artifactId>
      <version>1.6</version>
    </dependency>
  <!-- shiro的支持包 -->
   <dependency>
      <groupId>org.apache.shiro</groupId>
      <artifactId>shiro-all</artifactId>
      <version>1.4.0</version>
      <type>pom</type>
  </dependency>
    <!-- shiro与Spring的集成包 -->
    <dependency>
      <groupId>org.apache.shiro</groupId>
      <artifactId>shiro-spring</artifactId>
      <version>1.4.0</version>
    </dependency>
    <!-- poi支持的jar包 -->
    <dependency>
      <groupId>org.apache.poi</groupId>
      <artifactId>poi</artifactId>
      <version>3.11</version>
    </dependency>
    <dependency>
      <groupId>org.apache.poi</groupId>
      <artifactId>poi-ooxml</artifactId>
      <version>3.11</version>
    </dependency>
    <!-- 图片压缩功能 -->
    <!-- 缩略图 -->
    <dependency>
      <groupId>net.coobird</groupId>
      <artifactId>thumbnailator</artifactId>
      <version>0.4.6</version>
    </dependency>
    <!-- 定时调度 -->
    <dependency>
      <groupId>quartz</groupId>
      <artifactId>quartz</artifactId>
      <version>1.5.2</version>
    </dependency>
    <!-- 邮件支持 -->
    <dependency>
      <groupId>javax.mail</groupId>
      <artifactId>mail</artifactId>
      <version>1.4.1</version>
    </dependency>
  </dependencies>

  <build>
    <finalName>yxb</finalName>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <source>1.8</source>
          <target>1.8</target>
        </configuration>
      </plugin>
      <plugin>
        <groupId>org.mortbay.jetty</groupId>
        <artifactId>jetty-maven-plugin</artifactId>
        <version>8.1.15.v20140411</version>
        <configuration>
          <stopPort>9966</stopPort>
          <stopKey>foo</stopKey>
          <webAppConfig>
            <contextPath>/</contextPath>
          </webAppConfig>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

配置applicationContext.xml文件

修改相应的包扫描(每个系统都会有不一样的地方)
在这里我们加上了SpringDataJpa的配置(红色部分)

<?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">

    <!-- 扫描service部分的包 -->
    <context:component-scan base-package="cn.itsource.aisell.service" />
    <context:property-placeholder location="classpath:jdbc.properties" />

    <!-- 配置连接池 -->
    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
        <!--连接数据4个属性 -->
        <property name="driverClassName" value="${jdbc.driverClassName}" />
        <property name="url" value="${jdbc.url}" />
        <property name="username" value="${jdbc.username}" />
        <property name="password" value="${jdbc.password}" />
        <!--maxActive: 最大连接数量 -->
        <property name="maxActive" value="150" />
        <!--minIdle: 最小空闲连接 -->
        <property name="minIdle" value="5" />
        <!--maxIdle: 最大空闲连接 -->
        <property name="maxIdle" value="20" />
        <!--initialSize: 初始化连接 -->
        <property name="initialSize" value="30" />
        <!-- 用来配置数据库断开后自动连接的 -->
        <!-- 连接被泄露时是否打印 -->
        <property name="logAbandoned" value="true" />
        <!--removeAbandoned: 是否自动回收超时连接 -->
        <property name="removeAbandoned" value="true" />
        <!--removeAbandonedTimeout: 超时时间(以秒数为单位) -->
        <property name="removeAbandonedTimeout" value="10" />
        <!--maxWait: 超时等待时间以毫秒为单位 1000等于60秒 -->
        <property name="maxWait" value="1000" />
        <!-- 在空闲连接回收器线程运行期间休眠的时间值,以毫秒为单位. -->
        <property name="timeBetweenEvictionRunsMillis" value="10000" />
        <!-- 在每次空闲连接回收器线程(如果有)运行时检查的连接数量 -->
        <property name="numTestsPerEvictionRun" value="10" />
        <!-- 1000 * 60 * 30 连接在池中保持空闲而不被空闲连接回收器线程 -->
        <property name="minEvictableIdleTimeMillis" value="10000" />
        <property name="validationQuery" value="SELECT NOW() FROM DUAL" />
    </bean>

    <!-- 集成hibernate的jpa功能 -->
    <bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <!--待扫描的实体类包，不再需要persistence.xml了 -->
        <property name="packagesToScan" value="cn.itsource.aisell.domain" />
        <!-- 3.配置JPA的实现 -->
        <!-- private JpaVendorAdapter jpaVendorAdapter; -->
        <property name="jpaVendorAdapter">
            <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
                <!-- org.springframework.orm.jpa.vendor.AbstractJpaVendorAdapter -->
                <!-- private boolean showSql = false;是否显示sql语句 -->
                <property name="showSql" value="true" />
                <!-- private boolean generateDdl = false;是否建表 -->
                <property name="generateDdl" value="false" />
                <!-- private String databasePlatform;原来方言 -->
                <property name="databasePlatform" value="org.hibernate.dialect.MySQLDialect" />
            </bean>
        </property>
    </bean>

    <!-- Jpa 事务配置 -->
    <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
        <property name="entityManagerFactory" ref="entityManagerFactory" />
    </bean>
    <!-- 注解声明式事务管理 -->
    <tx:annotation-driven />

    <!-- Spring Data Jpa配置 ********************************************-->
    <!-- base-package:扫描的包 -->
    <jpa:repositories base-package="cn.itsource.pss.repository" transaction-manager-ref="transactionManager"
                      entity-manager-factory-ref="entityManagerFactory" />
</beans>

1.1.3. SpringData的结构

Spring Data JPA的七个Repository接口:
Repository（org.springframework.data.repository.Repository）
CrudRepository（org.springframework.data.repository.CrudRepository）
PagingAndSortingRepository（org.springframework.data.repository.PagingAndSortingRepository)
JpaRepository (org.springframework.data.jpa.repository.JpaRepository)
QueryByExampleExecutor(org.springframework.data.repository.query.QueryByExampleExecutor)
JpaSpecificationExecutor (org.springframework.data.jpa.repository.JpaSpecificationExecutor)
QueryDslPredicateExecutor (org.springframework.data.querydsl.QueryDslPredicateExecutor)

两大Repository实现类：
SimpleJpaRepository(org.springframework.data.jpa.repository.support.SimpleJpaRepository)
QueryDslJpaRepository(org.springframework.data.jpa.repository.support.QueryDslJpaRepository)

结构图(通过Intellij Idea,打开SimpleJpaRepository.java,单击鼠标右键show diagrams)

CrudRepository:完成所有基本的增删改查的方法

其中T是要操作的实体类，ID是实体类主键的类型。该接口提供了11个常用操作方法。

package org.springframework.data.repository;
import java.io.Serializable;
@NoRepositoryBean
public interface CrudRepository<T, ID extends Serializable> extends Repository<T, ID> {

   <S extends T> S save(S entity);
   <S extends T> Iterable<S> save(Iterable<S> entities);
   T findOne(ID id);
   boolean exists(ID id);
   Iterable<T> findAll();
   Iterable<T> findAll(Iterable<ID> ids);
   long count();
   void delete(ID id);
   void delete(T entity);
   void delete(Iterable<? extends T> entities);
   void deleteAll();
}

PagingAndSortingRepository:完成分页与排序功能
该接口继承了CrudRepository接口，提供了两个方法，实现了分页和排序的功能了。
package org.springframework.data.repository;

import java.io.Serializable;

import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Sort;

@NoRepositoryBean
public interface PagingAndSortingRepository<T, ID extends Serializable> extends CrudRepository<T, ID> {
   Iterable<T> findAll(Sort sort);
   Page<T> findAll(Pageable pageable);
}

JpaRepository:
该接口继承了PagingAndSortingRepository接口。
package org.springframework.data.jpa.repository;

import java.io.Serializable;
import java.util.List;

import javax.persistence.EntityManager;

import org.springframework.data.domain.Sort;
import org.springframework.data.repository.NoRepositoryBean;
import org.springframework.data.repository.PagingAndSortingRepository;

/**
 * JPA specific extension of {@link org.springframework.data.repository.Repository}.
 * 
 * @author Oliver Gierke
 */
@NoRepositoryBean
public interface JpaRepository<T, ID extends Serializable> extends PagingAndSortingRepository<T, ID> {

   List<T> findAll();
   List<T> findAll(Sort sort);
   List<T> findAll(Iterable<ID> ids);
   <S extends T> List<S> save(Iterable<S> entities);
   void flush();
   <S extends T> S saveAndFlush(S entity);
   void deleteInBatch(Iterable<T> entities);
   void deleteAllInBatch();
   T getOne(ID id);
}

注意与说明：

几个查询、及批量保存方法，和 CrudRepository 接口相比，返回的是 List，使用起来更方便。
增加了 InBatch 删除，实际执行时，后台生成一条sql语句，效率更高些。相比较而言，CrudRepository 接口的删除方法，都是一条一条删除的，即便是 deleteAll 也是一条一条删除的。
增加了 getOne() 方法，切记，该方法返回的是对象引用，当查询的对象不存在时，它的值不是Null。

1.2. @Query注解查询

在Respository方法中一定要按照查询方法的命名规则，其实是比较麻烦的如果我们想不遵循查询方法的命名规则，还可以使用@Query的方法进行查询。
只需要将@Query定义在Respository的方法之上即可。
分页排序功能

//进行分页功能
@Test
public void testPage() {
    //1.需要先创建一个page对象(注意：页数是从0开始计算【0就是第1页】)
    Pageable pageable = new PageRequest(0, 10);
    //2.进行查询
    Page<Employee> page = employeeRepository.findAll(pageable);
    System.out.println(page.getTotalElements()); //总条数
    System.out.println(page.getTotalPages()); //总页数
    System.out.println(page.getContent()); //当前页数据
    System.out.println(page.getNumber()); //第几页
    System.out.println(page.getNumberOfElements()); //当前页有多少个数据
    System.out.println(page.getSize()); //每页条数
}

//进行排序功能
@Test
public void testSort() {
    //排序 ：第一个参数是排序的规则(DESC/ASC)  后面参数是排序的字符
    Sort sort = new Sort(Sort.Direction.DESC,"username");
    List<Employee> emps = employeeRepository.findAll(sort);
    for (Employee emp : emps) {
        System.out.println(emp);
    }
}

//分页与排序的集成
@Test
public void testPageAndSort() {
    //排序 ：第一个参数是排序的规则(DESC/ASC)  后面参数是排序的字符
    Sort sort = new Sort(Sort.Direction.DESC,"username");
    Pageable pageable = new PageRequest(0, 10,sort);
    //2.进行查询
    Page<Employee> page = employeeRepository.findAll(pageable);
    for (Employee employee : page) {
        System.out.println(employee);
    }
}

按照规范创建查询方法，一般按照java驼峰式书写规范加一些特定关键字，例如我们想通过员工的名来获取到对应的员工的对象。
public interface EmployeeRepository extends JpaRepository<Employee, Long> {
    //根据名称模糊查询
    List<Employee> findByUsernameLike(String username);
    //根据名称进行查询
    List<Employee> findByUsername(String username);
}

规则如下：
表达式例子 hql查询语句
And findByLastnameAndFirstname … where x.lastname = ?1 and x.firstname = ?2
Or findByLastnameOrFirstname … where x.lastname = ?1 or x.firstname = ?2
Is,Equals findByFirstname,findByFirstnameIs,findByFirstnameEqual … where x.firstname = 1?
Between findByStartDateBetween … where x.startDate between 1? and ?2
LessThan(lt) findByAgeLessThan … where x.age < ?1
LessThanEqual(le) findByAgeLessThanEqual … where x.age <= ?1
GreaterThan findByAgeGreaterThan … where x.age > ?1
GreaterThanEqual findByAgeGreaterThanEqual … where x.age >= ?1
After findByStartDateAfter … where x.startDate > ?1
Before findByStartDateBefore … where x.startDate < ?1
IsNull findByAgeIsNull … where x.age is null
IsNotNull,NotNull findByAge(Is)NotNull … where x.age not null
Like findByFirstnameLike … where x.firstname like ?1
NotLike findByFirstnameNotLike … where x.firstname not like ?1
StartingWith findByFirstnameStartingWith … where x.firstname like ?1 (parameter bound with appended %)
EndingWith findByFirstnameEndingWith … where x.firstname like ?1 (parameter bound with prepended %)
Containing findByFirstnameContaining … where x.firstname like ?1 (parameter bound wrapped in %)
OrderBy findByAgeOrderByLastnameDesc … where x.age = ?1 order by x.lastname desc
Not findByLastnameNot … where x.lastname <> ?1
In findByAgeIn(Collection ages) … where x.age in ?1
NotIn findByAgeNotIn(Collection age) … where x.age not in ?1
True findByActiveTrue() … where x.active = true
False findByActiveFalse() … where x.active = false
IgnoreCase findByFirstnameIgnoreCase … where UPPER(x.firstame) = UPPER(?1)

#1.3. JpaSpecificationExecutor的认识

单个条件的查询

@Test
public void testFind() {
    /**
*官方解释:
     * Root<T> root:代表了可以查询和操作的实体对象的根，
     *              可以通过它的 Path<Y> get(String attributeName); 这个方法拿到我们要操作的字段
     *              注意:只可以拿到对应的T的字段(Employee)
     * CriteriaQuery<?> query:代表一个specific的顶层查询对象
     *              包含查询的各个部分,比如select,from,where,group by ,order by 等
     *              简单理解 就是它提供 了查询ROOT的方法(where,select,having)
     * CriteriaBuilder cb:用来构建CriteriaQuery的构建器对象(相当于条件或者说条件组合)
     *              构造好后以Predicate的形式返回
     */
/**
* 非官方理解:
 * 查询的时候就需要给一个标准（规范）
 *  -》 根据规范（这个规范我们可以先简单理解为查询的条件）进行查询
 *
 *      Root：查询哪个表（定位到表和字段-> 用于拿到表中的字段）
 *            可以查询和操作的实体的根
 *              Root接口：代表Criteria查询的根对象，Criteria查询的查询根定义了实体类型，能为将来导航获得想要的结果，它与SQL查询中的FROM子句类似
 *             Root<Employee> 相当于 from Employee
 *             Root<Product> 相当于  from Product
 *      CriteriaQuery：查询哪些字段，排序是什么(主要是把多个查询的条件连系起来)
 *      CriteriaBuilder：字段之间是什么关系，如何生成一个查询条件，每一个查询条件都是什么方式
 *                      主要判断关系（和这个字段是相等，大于，小于like等）
 *      Predicate（Expression）：单独每一条查询条件的详细描述 整个 where xxx=xx and yyy=yy ...
 */
    List<Employee> emps = employeeRepository.findAll(
            new Specification<Employee>() {
                @Override
                public Predicate toPredicate(Root<Employee> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
                    Path path = root.get("username");//拿到要做查询的字段
                    Predicate p = cb.like(path, "%1%");//like代表做模糊查询，后面就是它的条件值
                    return p;
                }
            }
    );
    for (Employee emp : emps) {
        System.out.println(emp);
    }
}


多个条件查询
@Test
public void testFind02() {
    Specification spec = new Specification<Employee>() {
        @Override
        public Predicate toPredicate(Root root, CriteriaQuery query, CriteriaBuilder cb) {
            //加上第一个条件: username like '%1%'
            Path path1 = root.get("username");
            Predicate p1 = cb.like(path1, "%1%");
            //加上第二个条件: email like '%2%'
            Path path2 = root.get("email");
            Predicate p2 = cb.like(path2,"%2%");
            //加上第二个条件: age < 20
            Path path3 = root.get("age");
            Predicate p3 = cb.lt(path3, 20);
           //下面是加上or的条件的方案
           //Predicate p3 = cb.or(p1,p2);

            //把两个查询条件放到query对象中去(条件使用where)
            CriteriaQuery where = query.where(p1, p2, p3);
            //返回查询条件
            return where.getRestriction();
        }
    };

    List<Employee> emps = employeeRepository.findAll(spec);
    for (Employee emp : emps) {
        System.out.println(emp);
    }

}

条件查询+分页排序
@Test
public void testFind03() {
    Specification spec = new Specification<Employee>() {
        @Override
        public Predicate toPredicate(Root root, CriteriaQuery query, CriteriaBuilder cb) {
            //加上条件: username like '%1%'
            Path path1 = root.get("username");
            Predicate p1 = cb.and(cb.like(path1, "%1%"));
            //把两个查询条件放到query对象中去(条件使用where)
            CriteriaQuery where = query.where(p1);
            //返回查询条件
            return where.getRestriction();
        }
    };

    //排序 ：第一个参数是排序的规则(DESC/ASC)  后面参数是排序的字符
    Sort sort = new Sort(Sort.Direction.DESC,"username");
    Pageable pageable = new PageRequest(0, 10,sort);

    Page<Employee> page = employeeRepository.findAll(spec, pageable);
    for (Employee emp : page) {
        System.out.println(emp);
    }
}

1.4.	jpa-spec插件
这是一个对于咱们刚才的动态生成Query功能的一个封装版，如果我们使用这个插件，在完成查询与分页的时候功能会简单不少。基于Spring Data Jpa的动态查询库 https://github.com/wenhao/jpa-spec
1.	兼容Spring Data Jpa 和JPA2.1接口。
2.	Equal/NotEqual/Like/NotLike/In/NotIn支持可变参数, Equal/NotEqual 支持空(Null)值。
3.	每个条件支持关联查询。
4.	支持自定义条件查询。
5.	条件构建器。
6.	支持分页和排序。
在Maven中引入相应的包
pom.xml(咱们项目中已经引入):
<!--  jpa的SpecificationSpecification功能封装 -->
<dependency>
  <groupId>com.github.wenhao</groupId>
  <artifactId>jpa-spec</artifactId>
  <version>3.1.1</version>
  <!-- 把所有依赖都过滤 -->
  <exclusions>
    <exclusion>
      <groupId>*</groupId>
      <artifactId>*</artifactId>
    </exclusion>
  </exclusions>
</dependency>

1.5. Query查询条件

BaseQuery:公共的分页条件
package cn.itsource.pss.query;
/**
* 公共的条件与规范
*/
public abstract class BaseQuery {

   //当前页(从1开始)
   private int currentPage = 1;
   //每页条数
   private int pageSize = 10;

   //排序方式 ASC/DESC
   private String orderByType ="ASC";
   //排序字段
   private String orderByName;

   public int getCurrentPage() {
       return currentPage;
   }
   /**
    * 专门准备的方法，因为前台用户传的是从第1页开始，而我们后台分页又是从0开的
    * @return
    */
   public int getJpaPage() {
       return currentPage - 1;
   }

   public void setCurrentPage(int currentPage) {
       this.currentPage = currentPage;
   }
   public int getPageSize() {
       return pageSize;
   }

   public void setPageSize(int pageSize) {
       this.pageSize = pageSize;
   }
   public String getOrderByType() {
       return orderByType;
   }

   public void setOrderByType(String orderByType) {
       this.orderByType = orderByType;
   }

   public String getOrderByName() {
       return orderByName;
   }

   public void setOrderByName(String orderByName) {
       this.orderByName = orderByName;
   }
}

EmployeeQuery:Employee特有的一些条件
package cn.itsource.pss.query;

public class EmployeeQuery extends BaseQuery {

   private String username;//姓名
   private String email;//邮件
   private Integer age;//年龄

   public String getUsername() {
       return username;
   }
   public void setUsername(String username) {
       this.username = username;
   }
   public String getEmail() {
       return email;
   }
   public void setEmail(String email) {
       this.email = email;
   }
   public Integer getAge() {
       return age;
   }

   public void setAge(Integer age) {
       this.age = age;
   }
}

功能测试
//根据Query对象进行查询
@Test
public void testSpecFindByQuery() {
   //创建模块一个Query对象
   EmployeeQuery baseQuery = new EmployeeQuery();
//下面的都是测试的条件，可以任何放开进行测试
   //baseQuery.setUsername("1");
   //baseQuery.setAge(20);
   //baseQuery.setEmail("2");
   //baseQuery.setOrderByName("username");
   //baseQuery.setOrderByType("DESC");
   //baseQuery.setCurrentPage(2);
   //baseQuery.setPageSize(5);

   //like(条件boolean值,字段,值)
   Specification<Employee> spec = Specifications.<Employee>and()
           .like(StringUtils.isNotBlank(baseQuery.getUsername()), "username","%"+baseQuery.getUsername()+"%")
           .like(StringUtils.isNotBlank(baseQuery.getEmail()), "email","%"+baseQuery.getEmail()+"%")
           .lt(baseQuery.getAge()!=null, "age",baseQuery.getAge())
           .build();


   //这里确定是否需要排序
   Sort sort = null;
   if(baseQuery.getOrderByName()!=null){
       Sort.Direction desc = "DESC".equals(baseQuery.getOrderByType())?Sort.Direction.DESC:Sort.Direction.ASC;
       sort = new Sort(desc,baseQuery.getOrderByName());
   }
   Pageable pageable = new PageRequest(baseQuery.getJpaPage(), baseQuery.getPageSize(),sort);

   Page<Employee> page = employeeRepository.findAll(spec, pageable);
   for (Employee emp : page) {
       System.out.println(emp);
   }
}

通过上面的功能测试，我们已经知道如果前台传数据过来，后面的查询应该怎么处理了。但是大家也应该发现了，除了创建Specification对象这一，分页排序的部分每次查询的代码都应该是一样的，所以我们现在需要做的就是把代码开始进行功能抽取。

6.4 创建Specification的流程放到Query里

BaseQuery中添加抽象方法
public abstract class BaseQuery {
...
//拿到查询的条件对象(由子类实现)
	public abstract Specification createSpecification();
//拿到排序的数据
	public Sort createSort() {
    		Sort sort = null;
    		if (StringUtils.isNotBlank(orderByName)) {
        		Sort.Direction type=  "ASC".equals(orderByType.toUpperCase())? Sort.Direction.ASC:Sort.Direction.DESC;
       		 sort = new Sort(type,orderByName);
    		}
    		return sort;
	}
...
}

EmployeeQuery中实现相应方法
(以后每一个Query要做高级查询都写在这个位置)
public class EmployeeQuery extends BaseQuery {
    ...
@Override
	public Specification createSpecification() {
    	//根据条件把数据返回即可
   	return  Specifications.<Employee>and()
            .like(StringUtils.isNotBlank(username), "username","%"+username+"%")
            .like(StringUtils.isNotBlank(email), "email","%"+email+"%")
            .lt(age!=null, "age",age)
            .build();
	}
...
}