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Spring Data Jpa 简介
JPA
JPA
(Java Persistence API
)意即Java持久化API,是Sun官方在JDK5.0后提出的Java持久化规范(JSR 338,这些接口所在包为javax.persistence
,详细内容可参考https://github.com/javaee/jpa-spec)
JPA的出现主要是为了简化持久层开发以及整合ORM技术,结束Hibernate、TopLink、JDO等ORM框架各自为营的局面。JPA是在吸收现有ORM框架的基础上发展而来,易于使用,伸缩性强。总的来说,JPA包括以下3方面的技术:
- ORM映射元数据: 支持XML和注解两种元数据的形式,元数据描述对象和表之间的映射关系
- API: 操作实体对象来执行CRUD操作
- 查询语言: 通过面向对象而非面向数据库的查询语言(
JPQL
)查询数据,避免程序的SQL语句紧密耦合
Spring Data Jpa
来看一下Spring官方的解释https://spring.io/projects/spring-data-jpa#overview
Spring Data JPA是Spring Data家族的一部分,可以轻松实现基于JPA的存储库。 此模块处理对基于JPA的数据访问层的增强支持。 它使构建使用数据访问技术的Spring驱动应用程序变得更加容易。
在相当长的一段时间内,实现应用程序的数据访问层一直很麻烦。 必须编写太多样板代码来执行简单查询以及执行分页和审计。 Spring Data JPA旨在通过减少实际需要的工作量来显著改善数据访问层的实现。 作为开发人员,您编写repository接口,包括自定义查找器方法,Spring将自动提供实现。
Jpa、Hibernate、Spring Data Jpa三者之间的关系
这个问题可参考https://stackoverflow.com/questions/16148188/spring-data-jpa-versus-jpa-whats-the-difference及https://blog.csdn.net/u014421556/article/details/52635000
总的来说JPA是ORM规范,Hibernate、TopLink等是JPA规范的具体实现,这样的好处是开发者可以面向JPA规范进行持久层的开发,而底层的实现则是可以切换的。Spring Data Jpa则是在JPA之上添加另一层抽象(Repository层的实现),极大地简化持久层开发及ORM框架切换的成本。
Spring Data Jpa的java配置方案
在Spring Boot没出来之前如果要采用Java Configuration来配置Spring Data Jpa你需要配置如下的Bean
参考自Spring In Action及Spring Data Jpa官方文档5.1.2. Annotation-based Configuration
import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.data.jpa.repository.config.EnableJpaRepositories; import org.springframework.orm.jpa.JpaTransactionManager; import org.springframework.orm.jpa.JpaVendorAdapter; import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean; import org.springframework.orm.jpa.vendor.Database; import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter; import org.springframework.transaction.PlatformTransactionManager; import org.springframework.transaction.annotation.EnableTransactionManagement; import javax.persistence.EntityManagerFactory; import javax.sql.DataSource; /** * 注意:spring-data-jpa2.x版本需要spring版本为5.x * 否则会报Initialization of bean failed; nested exception is java.lang.AbstractMethodError错误 * 参考:https://stackoverflow.com/questions/47558017/error-starting-a-spring-application-initialization-of-bean-failed-nested-excep * 搭配方案:spring4+spring-data-jpa1.x或spring5+spring-data-jpa2.x */ @Configuration // 借助spring data实现自动化的jpa repository,只需编写接口无需编写实现类 // 相当于xml配置的<jpa:repositories base-package="com.example.repository" /> // repositoryImplementationPostfix默认就是Impl // entityManagerFactoryRef默认就是entityManagerFactory // transactionManagerRef默认就是transactionManager @EnableJpaRepositories(basePackages = {"com.example.repository"}, repositoryImplementationPostfix = "Impl", entityManagerFactoryRef = "entityManagerFactory", transactionManagerRef = "transactionManager") @EnableTransactionManagement // 启用事务管理器 public class SpringDataJpaConfig { // 配置jpa厂商适配器(参见spring实战p320) @Bean public JpaVendorAdapter jpaVendorAdapter() { HibernateJpaVendorAdapter jpaVendorAdapter = new HibernateJpaVendorAdapter(); // 设置数据库类型(可使用org.springframework.orm.jpa.vendor包下的Database枚举类) jpaVendorAdapter.setDatabase(Database.MYSQL); // 设置打印sql语句 jpaVendorAdapter.setShowSql(true); // 设置不生成ddl语句 jpaVendorAdapter.setGenerateDdl(false); // 设置hibernate方言 jpaVendorAdapter.setDatabasePlatform("org.hibernate.dialect.MySQL5Dialect"); return jpaVendorAdapter; } // 配置实体管理器工厂 @Bean public LocalContainerEntityManagerFactoryBean entityManagerFactory( DataSource dataSource, JpaVendorAdapter jpaVendorAdapter) { LocalContainerEntityManagerFactoryBean emfb = new LocalContainerEntityManagerFactoryBean(); // 注入数据源 emfb.setDataSource(dataSource); // 注入jpa厂商适配器 emfb.setJpaVendorAdapter(jpaVendorAdapter); // 设置扫描基本包 emfb.setPackagesToScan("com.example.entity"); return emfb; } // 配置jpa事务管理器 @Bean public PlatformTransactionManager transactionManager(EntityManagerFactory emf) { JpaTransactionManager transactionManager = new JpaTransactionManager(); // 配置实体管理器工厂 transactionManager.setEntityManagerFactory(emf); return transactionManager; } }
启用web支持还需要在Spring MVC配置类上添加@EnableSpringDataWebSupport
注解
@Configuration @ComponentScan(basePackages = {"cn.fulgens.controller"}) @EnableWebMvc // 启用spring mvc @EnableSpringDataWebSupport // 启用springmvc对spring data的支持 public class WebMvcConfig extends WebMvcConfigurerAdapter { }
Spring Boot整合Spring Data Jpa
导入依赖
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-jpa</artifactId> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <scope>runtime</scope> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <optional>true</optional> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-devtools</artifactId> <optional>true</optional> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> </dependency>
相关配置
server: port: 8080 servlet: context-path: / spring: datasource: url: jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=UTF-8&zeroDateTimeBehavior=convertToNull&allowMultiQueries=true&useSSL=false username: root password: mysql123 jpa: database: MySQL database-platform: org.hibernate.dialect.MySQL5InnoDBDialect show-sql: true hibernate: ddl-auto: update
create
:每次运行程序时,都会重新创建表,故而数据会丢失create-drop
:每次运行程序时会先创建表结构,然后待程序结束时清空表upadte
:每次运行程序,没有表时会创建表,如果对象发生改变会更新表结构,原有数据不会清空,只会更新(推荐使用)validate
:运行程序会校验数据与数据库的字段类型是否相同,字段不同会报错none
: 禁用DDL处理
Spring Data Jpa的使用
Spring Data Jpa UML类图
简单的REST CRUD示例
实体类
/src/main/java/com/example/springbootjpa/entity/User package com.example.springbootjpa.entity; import lombok.Data; import org.hibernate.annotations.GenericGenerator; import javax.persistence.*; @Entity @Table(name = "tb_user") @Data public class User { @Id @GenericGenerator(name = "idGenerator", strategy = "uuid") @GeneratedValue(generator = "idGenerator") private String id; @Column(name = "username", unique = true, nullable = false, length = 64) private String username; @Column(name = "password", nullable = false, length = 64) private String password; @Column(name = "email", length = 64) private String email; }
一般简单的Demo示例中只会使用@GeneratedValue(strategy = GenerationType.IDENTITY)这种主键自增的策略,而实际数据库中表字段主键类型很少是int型的
Dao层
/src/main/java/com/example/springbootjpa/repository/UserRepository package com.example.springbootjpa.repository; import com.example.springbootjpa.entity.User; import org.springframework.data.jpa.repository.JpaRepository; public interface UserRepository extends JpaRepository<User, String> { }
Controller层
/src/main/java/com/example/springbootjpa/controller/UserController package com.example.springbootjpa.controller; import com.example.springbootjpa.entity.User; import com.example.springbootjpa.repository.UserRepository; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.data.domain.Page; import org.springframework.data.domain.PageRequest; import org.springframework.data.domain.Pageable; import org.springframework.web.bind.annotation.*; import java.util.HashMap; import java.util.Optional; @RestController @RequestMapping("/users") public class UserController { @Autowired private UserRepository userRepository; @PostMapping() public User saveUser(@RequestBody User user) { return userRepository.save(user); } @DeleteMapping("/{id}") public void deleteUser(@PathVariable("id") String userId) { userRepository.deleteById(userId); } @PutMapping("/{id}") public User updateUser(@PathVariable("id") String userId, @RequestBody User user) { user.setId(userId); return userRepository.saveAndFlush(user); } @GetMapping("/{id}") public User getUserInfo(@PathVariable("id") String userId) { Optional<User> optional = userRepository.findById(userId); return optional.orElseGet(User::new); } @GetMapping("/list") public Page<User> pageQuery(@RequestParam(value = "pageNum", defaultValue = "1") Integer pageNum, @RequestParam(value = "pageSize", defaultValue = "10") Integer pageSize) { return userRepository.findAll(PageRequest.of(pageNum - 1, pageSize)); } }
Spring Data Jpa使用详解
Spring Data查询方法
使用Spring Data创建查询只需四步:
- 声明一个接口继承自Repository或Repositoy的一个子接口,对于Spring Data Jpa通常是JpaRepository,如:
interface PersonRepository extends Repository<Person, Long> { … }
- 在接口中声明查询方法,如:
interface PersonRepository extends Repository<Person, Long> { List<Person> findByLastname(String lastname); }
- 使用 JavaConfig 或 XML configuration配置Spring,让 Spring 为声明的接口创建代理对象
3.1 JavaConfig参见上文
3.2 使用Xml配置,可以像下面这样使用jpa命名空间进行配置:
<?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: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.xsd"> <jpa:repositories base-package="com.acme.repositories"/> </beans>
顺带一提,对于不同的Spring Data子项目Spring提供了不同的xml命名空间,如对于Spring Data MongoDB可以将上面的jpa改为mongodb
当然,使用Spring Boot这一步基本可以省略,我们需要做的就是在application.properties或application.yml文件中配置几个属性即可
- 注入Repository实例并使用,如:
class SomeClient { private final PersonRepository repository; SomeClient(PersonRepository repository) { this.repository = repository; } void doSomething() { List<Person> persons = repository.findByLastname("Matthews"); } }
定义Repository接口
选择性暴露CRUD方法
一种方法是定义一个BaseRepository接口继承Repository接口,并从CrudRepository中copy你想暴露的CRUD方法src/main/java/com/example/springbootjpa/repository/MyBaseRepository
package com.example.springbootjpa.repository; import org.springframework.data.repository.NoRepositoryBean; import org.springframework.data.repository.Repository; import java.util.Optional; /** * 自定义Repository,选择性暴露CRUD方法 * @param <T> * @param <ID> */ @NoRepositoryBean public interface MyBaseRepository<T, ID> extends Repository<T, ID> { Optional<T> findById(ID id); <S extends T> S save(S entity); }
src/main/java/com/example/springbootjpa/repository/UserRepository2
package com.example.springbootjpa.repository; import com.example.springbootjpa.entity.User; import org.springframework.stereotype.Repository; public interface UserRepository2 extends MyBaseRepository<User, String> { }
Junit测试
package com.example.springbootjpa.repository; import org.junit.Assert; import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.test.context.SpringBootTest; import org.springframework.test.context.junit4.SpringRunner; import java.util.Optional; @RunWith(SpringRunner.class) @SpringBootTest public class UserRepository2Test { @Autowired private UserRepository2 userRepositoy; @Test public void findByIdTest() { Optional optional = userRepositoy.findById("40289f0c65674a930165674d54940000"); Assert.assertNotNull(optional.get()); } }
这里启动Junit测试时报了一个错,记录一下
java.lang.IllegalStateException: Failed to load ApplicationContext ... Caused by: java.lang.ClassNotFoundException: javax.xml.bind.JAXBException at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:582) at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:190) at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:499) ... 50 more
错误很明显Spring应用上下文加载失败,原因是找不到javax.xml.bind.JAXBException
手贱从java8升级到java10,JAXB API是java EE 的API,在java SE 9.0 中已经不再包含这个 Jar 包。java9 中引入了模块的概念,默认情况下,Java SE中将不再包含java EE 的Jar包,而在 java 6/7 / 8 时关于这个API 都是捆绑在一起的,解决方法添加如下jar包
<dependency> <groupId>javax.xml.bind</groupId> <artifactId>jaxb-api</artifactId> <version>2.3.0</version> </dependency> <dependency> <groupId>com.sun.xml.bind</groupId> <artifactId>jaxb-impl</artifactId> <version>2.3.0</version> </dependency> <dependency> <groupId>com.sun.xml.bind</groupId> <artifactId>jaxb-core</artifactId> <version>2.3.0</version> </dependency> <dependency> <groupId>javax.activation</groupId> <artifactId>activation</artifactId> <version>1.1.1</version> </dependency>
解决方法参考自:https://www.cnblogs.com/newcaoguo/p/8831690.html
另一种方法是使用@RepositoryDefinition
注解,并从CrudRepository中copy你想暴露的CRUD方法src/main/java/com/example/springbootjpa/repository/UserRepository3
package com.example.springbootjpa.repository; import com.example.springbootjpa.entity.User; import org.springframework.data.repository.RepositoryDefinition; import java.util.Optional; @RepositoryDefinition(domainClass = User.class, idClass = String.class) public interface UserRepository3 { Optional<User> findById(String id); User save(User user); }
Repository方法的Null值处理
从Spring Data2.0开始对于返回单个聚合实例的CRUD方法可以使用java8 Optional接口作为方法返回值来表明可能存在的缺省值,典型示例为CrudRepository的findById方法
另外Spring也提供了几个注解来处理Null值
@NonNullApi
: 在包级别使用来声明参数和返回值不能为Null@NonNull
: 在参数或返回值上使用,当它们不能为Null时(如果在包级别上使用了@NonNullApi注解则没有必要再使用@NonNull注解了)@Nullable
: 在参数或返回值上使用,当它们可以为Null时
查询方法
查询创建Query Creation
Spring Data Jpa通过解析方法名创建查询,框架在进行方法名解析时,会先把方法名多余的前缀find…By, read…By, query…By, count…By以及get…By截取掉,然后对剩下部分进行解析,第一个By会被用作分隔符来指示实际查询条件的开始。 我们可以在实体属性
上定义条件,并将它们与And和Or连接起来,从而创建大量查询:
User findByUsername(String username); List<User> findByUsernameIgnoreCase(String username); List<User> findByUsernameLike(String username); User findByUsernameAndPassword(String username, String password); User findByEmail(String email); List<User> findByEmailLike(String email); List<User> findByIdIn(List<String> ids); List<User> findByIdInOrderByUsername(List<String> ids); void deleteByIdIn(List<String> ids); Long countByUsernameLike(String username);
支持的关键字、示例及JPQL片段如下表所示:
And | findByLastnameAndFirstname | … where x.lastname = ?1 and x.firstname = ?2 |
Or | findByLastnameOrFirstname | … where x.lastname = ?1 or x.firstname = ?2 |
Is,Equals | findByFirstname,findByFirstnameIs,findByFirstnameEquals | … where x.firstname = ?1 |
Between | findByStartDateBetween | … where x.startDate between ?1 and ?2 |
LessThan | findByAgeLessThan | … where x.age < ?1 |
LessThanEqual | 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 | ... findByFirstnameNotLike |
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<Age> ages) | … where x.age in ?1 |
NotIn | findByAgeNotIn(Collection<Age> ages) | … 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) |
具体Spring Data Jpa对方法名的解析规则可参看官方文档4.4.3. Property Expressions
限制查询结果
Spring Data Jpa支持使用first
、top
以及Distinct
关键字来限制查询结果,如:
User findFirstByUsernameOrderByUsernameAsc(String username); List<User> findTop10ByUsername(String username, Sort sort); List<User> findTop10ByUsername(String username, Pageable pageable);
自定义查询Using @Query
@Query 注解的使用非常简单,只需在声明的方法上面标注该注解,同时提供一个 JPQL 查询语句即可
@Query("select u from User u where u.email = ?1") User getByEmail(String eamil); @Query("select u from User u where u.username = ?1 and u.password = ?2") User getByUsernameAndPassword(String username, String password); @Query("select u from User u where u.username like %?1%") List<User> getByUsernameLike(String username);
使用命名参数Using Named Parameters
默认情况下,Spring Data JPA使用基于位置的参数绑定,如前面所有示例中所述。 这使得查询方法在重构参数位置时容易出错。 要解决此问题,可以使用@Param
注解为方法参数指定具体名称并在查询中绑定名称,如以下示例所示:
@Query("select u from User u where u.id = :id") User getById(@Param("id") String userId); @Query("select u from User u where u.username = :username or u.email = :email") User getByUsernameOrEmail(@Param("username") String username, @Param("email") String email);
Using SpEL Expressions
从Spring Data JPA release 1.4开始,Spring Data JPA支持名为entityName的变量。 它的用法是select x from #{#entityName} x
。 entityName的解析方式如下:如果实体类在@Entity注解上设置了name属性,则使用它。 否则,使用实体类的简单类名。为避免在@Query注解使用实际的实体类名,就可以使用#{#entityName}
进行代替。如以上示例中,@Query注解的查询字符串里的User都可替换为#{#entityName}
@Query("select u from #{#entityName} u where u.email = ?1")
User getByEmail(String eamil);
原生查询Native Queries
@Query注解还支持通过将nativeQuery
标志设置为true来执行原生查询,同样支持基于位置的参数绑定及命名参数,如:
@Query(value = "select * from tb_user u where u.email = ?1", nativeQuery = true) User queryByEmail(String email); @Query(value = "select * from tb_user u where u.email = :email", nativeQuery = true) User queryByEmail(@Param("email") String email);
@Query(value = "select * from tb_user u where u.username like %?1%", countQuery = "select count(1) from tb_user u where u.username = %?1%", nativeQuery = true) Page<User> queryByUsernameLike(String username, Pageable pageable);
分页查询及排序
Spring Data Jpa可以在方法参数中直接传入Pageable
或Sort
来完成动态分页或排序,通常Pageable或Sort会是方法的最后一个参数,如:
@Query("select u from User u where u.username like %?1%") Page<User> findByUsernameLike(String username, Pageable pageable); @Query("select u from User u where u.username like %?1%") List<User> findByUsernameAndSort(String username, Sort sort);
那调用repository方法时传入什么参数呢?
对于Pageable参数,在Spring Data 2.0之前我们可以new一个org.springframework.data.domain.PageRequest
对象,现在这些构造方法已经废弃,取而代之Spring推荐我们使用PageRequest的of方法
new PageRequest(0, 5); new PageRequest(0, 5, Sort.Direction.ASC, "username"); new PageRequest(0, 5, new Sort(Sort.Direction.ASC, "username")); PageRequest.of(0, 5); PageRequest.of(0, 5, Sort.Direction.ASC, "username"); PageRequest.of(0, 5, Sort.by(Sort.Direction.ASC, "username"));
对于Sort参数,同样可以new一个org.springframework.data.domain.Sort
,但推荐使用Sort.by方法
自定义修改、删除 Modifying Queries
单独使用@Query注解只是查询,如涉及到修改、删除则需要再加上@Modifying
注解,如:
@Transactional() @Modifying @Query("update User u set u.password = ?2 where u.username = ?1") int updatePasswordByUsername(String username, String password); @Transactional() @Modifying @Query("delete from User where username = ?1") void deleteByUsername(String username);
多表查询
这里使用级联查询进行多表的关联查询
多对多
/src/main/java/com/example/springbootjpa/entity/User package com.example.springbootjpa.entity; import lombok.Data; import org.hibernate.annotations.GenericGenerator; import javax.persistence.*; import java.util.Date; import java.util.Set; import java.util.UUID; @Entity @Table(name = "tb_user") @Data public class User { @Id @GenericGenerator(name = "idGenerator", strategy = "uuid") @GeneratedValue(generator = "idGenerator") private String id; @Column(name = "username", unique = true, nullable = false, length = 64) private String username; @Column(name = "password", nullable = false, length = 64) private String password; @Column(name = "email", unique = true, length = 64) private String email; @ManyToMany(targetEntity = Role.class, cascade = {CascadeType.PERSIST, CascadeType.MERGE}, fetch = FetchType.LAZY) @JoinTable(name = "tb_user_role", joinColumns = {@JoinColumn(name = "user_id", referencedColumnName = "id")}, inverseJoinColumns = {@JoinColumn(name = "role_id", referencedColumnName = "id")}) private Set<Role> roles; } /src/main/java/com/example/springbootjpa/entity/Role package com.example.springbootjpa.entity; import lombok.Data; import org.hibernate.annotations.GenericGenerator; import javax.persistence.*; @Entity @Table(name = "tb_role") @Data public class Role { @Id @GenericGenerator(name = "idGenerator", strategy = "uuid") @GeneratedValue(generator = "idGenerator") private String id; @Column(name = "role_name", unique = true, nullable = false, length = 64) private String roleName; }
测试
@Test public void findByIdTest() { Optional<User> optional = userRepository.findById("40289f0c65674a930165674d54940000"); Set<Role> roles = optional.get().getRoles(); System.out.println(optional.get()); }
不出意外会报Hibernate懒加载异常,无法初始化代理类,No Session:
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.example.springbootjpa.entity.User.roles, could not initialize proxy - no Session
原因:Spring Boot整合JPA后Hibernate的Session就交付给Spring去管理。每次数据库操作后,会关闭Session,当我们想要用懒加载方式去获得数据的时候,原来的Session已经关闭,不能获取数据,所以会抛出这样的异常。
解决方法:
在application.yml中做如下配置:
@Test public void findByIdTest() { Optional<User> optional = userRepository.findById("40289f0c65674a930165674d54940000"); Set<Role> roles = optional.get().getRoles(); System.out.println(optional.get()); }
一对多(多对一)
/src/main/java/com/example/springbootjpa/entity/Department package com.example.springbootjpa.entity; import lombok.Data; import org.hibernate.annotations.GenericGenerator; import javax.persistence.*; import java.util.Set; @Entity @Table(name = "tb_dept") @Data public class Department { @Id @GenericGenerator(name = "idGenerator", strategy = "uuid") @GeneratedValue(generator = "idGenerator") private String id; @Column(name = "dept_name", unique = true, nullable = false, length = 64) private String deptName; @OneToMany(mappedBy = "department", cascade = CascadeType.ALL, fetch = FetchType.LAZY) private Set<Employee> employees; } /src/main/java/com/example/springbootjpa/entity/Employee package com.example.springbootjpa.entity; import lombok.Data; import org.hibernate.annotations.GenericGenerator; import javax.persistence.*; import java.util.UUID; @Entity @Table(name = "tb_emp") @Data public class Employee { @Id @GenericGenerator(name = "idGenerator", strategy = "uuid") @GeneratedValue(generator = "idGenerator") private String id; @Column(name = "emp_name", nullable = false, length = 64) private String empName; @Column(name = "emp_job", length = 64) private String empJob; @Column(name = "dept_id", insertable = false, updatable = false) private String deptId; @ManyToOne(targetEntity = Department.class, cascade = CascadeType.ALL, fetch = FetchType.LAZY) @JoinColumn(name = "dept_id") private Department department; } 测试 @Test public void findByIdTest() { Optional<Employee> optional = employeeRepository.findById("93fce66c1ef340fa866d5bd389de3d79"); System.out.println(optional.get()); }
结果报错了...
java.lang.StackOverflowError at java.base/java.lang.Exception.<init>(Exception.java:102) at java.base/java.lang.ReflectiveOperationException.<init>(ReflectiveOperationException.java:89) at java.base/java.lang.reflect.InvocationTargetException.<init>(InvocationTargetException.java:73) at jdk.internal.reflect.GeneratedConstructorAccessor54.newInstance(Unknown Source) at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:488) at com.mysql.jdbc.Util.handleNewInstance(Util.java:425) at com.mysql.jdbc.PreparedStatement.getInstance(PreparedStatement.java:761) at com.mysql.jdbc.ConnectionImpl.clientPrepareStatement(ConnectionImpl.java:1404) at com.mysql.jdbc.ConnectionImpl.prepareStatement(ConnectionImpl.java:4121) at com.mysql.jdbc.ConnectionImpl.prepareStatement(ConnectionImpl.java:4025) at com.zaxxer.hikari.pool.ProxyConnection.prepareStatement(ProxyConnection.java:318) at com.zaxxer.hikari.pool.HikariProxyConnection.prepareStatement(HikariProxyConnection.java) at org.hibernate.engine.jdbc.internal.StatementPreparerImpl$5.doPrepare(StatementPreparerImpl.java:145) at org.hibernate.engine.jdbc.internal.StatementPreparerImpl$StatementPreparationTemplate.prepareStatement(StatementPreparerImpl.java:171) at org.hibernate.engine.jdbc.internal.StatementPreparerImpl.prepareQueryStatement(StatementPreparerImpl.java:147) at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.prepareQueryStatement(AbstractLoadPlanBasedLoader.java:226) at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeQueryStatement(AbstractLoadPlanBasedLoader.java:190) at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeLoad(AbstractLoadPlanBasedLoader.java:121) at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeLoad(AbstractLoadPlanBasedLoader.java:86) at org.hibernate.loader.collection.plan.AbstractLoadPlanBasedCollectionInitializer.initialize(AbstractLoadPlanBasedCollectionInitializer.java:87) at org.hibernate.persister.collection.AbstractCollectionPersister.initialize(AbstractCollectionPersister.java:688) at org.hibernate.event.internal.DefaultInitializeCollectionEventListener.onInitializeCollection(DefaultInitializeCollectionEventListener.java:75) at org.hibernate.internal.SessionImpl.initializeCollection(SessionImpl.java:2223) at org.hibernate.collection.internal.AbstractPersistentCollection$4.doWork(AbstractPersistentCollection.java:565) at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:247) at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:561) at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:132) at org.hibernate.collection.internal.PersistentSet.hashCode(PersistentSet.java:430) at com.example.springbootjpa.entity.Department.hashCode(Department.java:14)
通过日志看sql的输出,发现了sql重复执行了好多次。以下我截取了前10条sql记录。
Hibernate: select employee0_.id as id1_1_0_, employee0_.dept_id as dept_id2_1_0_, employee0_.emp_job as emp_job3_1_0_, employee0_.emp_name as emp_name4_1_0_ from tb_emp employee0_ where employee0_.id=? Hibernate: select department0_.id as id1_0_0_, department0_.dept_name as dept_nam2_0_0_ from tb_dept department0_ where department0_.id=? Hibernate: select employees0_.dept_id as dept_id2_1_0_, employees0_.id as id1_1_0_, employees0_.id as id1_1_1_, employees0_.dept_id as dept_id2_1_1_, employees0_.emp_job as emp_job3_1_1_, employees0_.emp_name as emp_name4_1_1_ from tb_emp employees0_ where employees0_.dept_id=? Hibernate: select department0_.id as id1_0_0_, department0_.dept_name as dept_nam2_0_0_ from tb_dept department0_ where department0_.id=? Hibernate: select employees0_.dept_id as dept_id2_1_0_, employees0_.id as id1_1_0_, employees0_.id as id1_1_1_, employees0_.dept_id as dept_id2_1_1_, employees0_.emp_job as emp_job3_1_1_, employees0_.emp_name as emp_name4_1_1_ from tb_emp employees0_ where employees0_.dept_id=? Hibernate: select employees0_.dept_id as dept_id2_1_0_, employees0_.id as id1_1_0_, employees0_.id as id1_1_1_, employees0_.dept_id as dept_id2_1_1_, employees0_.emp_job as emp_job3_1_1_, employees0_.emp_name as emp_name4_1_1_ from tb_emp employees0_ where employees0_.dept_id=? Hibernate: select employees0_.dept_id as dept_id2_1_0_, employees0_.id as id1_1_0_, employees0_.id as id1_1_1_, employees0_.dept_id as dept_id2_1_1_, employees0_.emp_job as emp_job3_1_1_, employees0_.emp_name as emp_name4_1_1_ from tb_emp employees0_ where employees0_.dept_id=? Hibernate: select employees0_.dept_id as dept_id2_1_0_, employees0_.id as id1_1_0_, employees0_.id as id1_1_1_, employees0_.dept_id as dept_id2_1_1_, employees0_.emp_job as emp_job3_1_1_, employees0_.emp_name as emp_name4_1_1_ from tb_emp employees0_ where employees0_.dept_id=? Hibernate: select employees0_.dept_id as dept_id2_1_0_, employees0_.id as id1_1_0_, employees0_.id as id1_1_1_, employees0_.dept_id as dept_id2_1_1_, employees0_.emp_job as emp_job3_1_1_, employees0_.emp_name as emp_name4_1_1_ from tb_emp employees0_ where employees0_.dept_id=? Hibernate: select employees0_.dept_id as dept_id2_1_0_, employees0_.id as id1_1_0_, employees0_.id as id1_1_1_, employees0_.dept_id as dept_id2_1_1_, employees0_.emp_job as emp_job3_1_1_, employees0_.emp_name as emp_name4_1_1_ from tb_emp employees0_ where employees0_.dept_id=?
通过观察发现,第一条sql是执行查询Employee的sql,第二条sql是执行查询Department的sql,第三条sql是执行Department里面所有员工的sql,第四条sql是执行查询Department的sql,后面所有的sql都是执行查询Department里面所有员工的sql。
很明显发生了循环依赖的情况。这是Lombok的@Data注解的锅。Lombok的@Data注解相当于@Getter、@Setter、@RequiredArgsConstructor、@ToString、@EqualsAndHashCode这几个注解。
我们可以通过反编译看一下Lombok生成的toString()方法
// Employee public String toString() { return "Employee(id=" + getId() + ", empName=" + getEmpName() + ", empJob=" + getEmpJob() + ", deptId=" + getDeptId() + ", department=" + getDepartment() + ")"; } // Department public String toString() { return "Department(id=" + getId() + ", deptName=" + getDeptName() + ", employees=" + getEmployees() + ")"; }
可以发现Lombok为我们生成的toString()方法覆盖了整个类的所有属性
现在将@Data注解去掉,替换为@Setter、@Getter、@EqualsAndHashCode,重写toString()方法
// Department @Override public String toString() { return "Department{" + "id='" + id + '\'' + ", deptName='" + deptName + '\'' + '}'; } // Employee @Override public String toString() { return "Employee{" + "id='" + id + '\'' + ", empName='" + empName + '\'' + ", empJob='" + empJob + '\'' + ", deptId='" + deptId + '\'' + ", department=" + department + '}'; }
再次运行测试用例,测试通过,以上Employee toString()方法打印的department会触发懒加载,最终日志输出的sql如下:
Hibernate: select employee0_.id as id1_1_0_, employee0_.dept_id as dept_id2_1_0_, employee0_.emp_job as emp_job3_1_0_, employee0_.emp_name as emp_name4_1_0_ from tb_emp employee0_ where employee0_.id=? Hibernate: select department0_.id as id1_0_0_, department0_.dept_name as dept_nam2_0_0_ from tb_dept department0_ where department0_.id=? Employee{id='93fce66c1ef340fa866d5bd389de3d79', empName='jack', empJob='hr', deptId='0a4fe7234fff42afad34f6a06a8e1821', department=Department{id='0a4fe7234fff42afad34f6a06a8e1821', deptName='人事部'}}
再来测试查询Department
@Test public void findByIdTest() { Optional<Department> optional = departmentRepository.findById("0a4fe7234fff42afad34f6a06a8e1821"); Set<Employee> employees = optional.get().getEmployees(); Assert.assertNotEquals(0, employees.size()); }
同样还是报了堆栈溢出,错误定位在Department和Employee的hashCode()方法上
java.lang.StackOverflowError at com.mysql.jdbc.Util.handleNewInstance(Util.java:439) at com.mysql.jdbc.ResultSetImpl.getInstance(ResultSetImpl.java:342) at com.mysql.jdbc.MysqlIO.buildResultSetWithRows(MysqlIO.java:3132) at com.mysql.jdbc.MysqlIO.getResultSet(MysqlIO.java:477) at com.mysql.jdbc.MysqlIO.readResultsForQueryOrUpdate(MysqlIO.java:3115) at com.mysql.jdbc.MysqlIO.readAllResults(MysqlIO.java:2344) at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2739) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2486) at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1858) at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:1966) at com.zaxxer.hikari.pool.ProxyPreparedStatement.executeQuery(ProxyPreparedStatement.java:52) at com.zaxxer.hikari.pool.HikariProxyPreparedStatement.executeQuery(HikariProxyPreparedStatement.java) at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.extract(ResultSetReturnImpl.java:60) at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.getResultSet(AbstractLoadPlanBasedLoader.java:419) at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeQueryStatement(AbstractLoadPlanBasedLoader.java:191) at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeLoad(AbstractLoadPlanBasedLoader.java:121) at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeLoad(AbstractLoadPlanBasedLoader.java:86) at org.hibernate.loader.collection.plan.AbstractLoadPlanBasedCollectionInitializer.initialize(AbstractLoadPlanBasedCollectionInitializer.java:87) at org.hibernate.persister.collection.AbstractCollectionPersister.initialize(AbstractCollectionPersister.java:688) at org.hibernate.event.internal.DefaultInitializeCollectionEventListener.onInitializeCollection(DefaultInitializeCollectionEventListener.java:75) at org.hibernate.internal.SessionImpl.initializeCollection(SessionImpl.java:2223) at org.hibernate.collection.internal.AbstractPersistentCollection$4.doWork(AbstractPersistentCollection.java:565) at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:247) at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:561) at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:132) at org.hibernate.collection.internal.PersistentSet.hashCode(PersistentSet.java:430) at com.example.springbootjpa.entity.Department.hashCode(Department.java:17)
依旧是Lombok的锅,@EqualsAndHashCode为我们生成的equals()和hashCode()方法会使用所有属性,注意,Department中employees是Set集合,当我们调用department.getEmployees()时,Employee的hashCode()方法会被调用,Employee中的hashCode()又依赖于Department的HashCode()方法,这样又形成了循环引用...
// Department public int hashCode() { int i = 43; String $id = getId(); int result = ($id == null ? 43 : $id.hashCode()) + 59; String $deptName = getDeptName(); result = (result * 59) + ($deptName == null ? 43 : $deptName.hashCode()); Set $employees = getEmployees(); int i2 = result * 59; if ($employees != null) { i = $employees.hashCode(); } return i2 + i; } // Employee public int hashCode() { int i = 43; String $id = getId(); int result = ($id == null ? 43 : $id.hashCode()) + 59; String $empName = getEmpName(); result = (result * 59) + ($empName == null ? 43 : $empName.hashCode()); String $empJob = getEmpJob(); result = (result * 59) + ($empJob == null ? 43 : $empJob.hashCode()); String $deptId = getDeptId(); result = (result * 59) + ($deptId == null ? 43 : $deptId.hashCode()); Department $department = getDepartment(); int i2 = result * 59; if ($department != null) { i = $department.hashCode(); } return i2 + i; }
自己动手重写equals()和hashCode()方法,去掉@EqualsAndHashCode注解
// Department @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Department that = (Department) o; return Objects.equals(id, that.id) && Objects.equals(deptName, that.deptName); } @Override public int hashCode() { return Objects.hash(id, deptName); } // Employee @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Employee employee = (Employee) o; return Objects.equals(id, employee.id) && Objects.equals(empName, employee.empName) && Objects.equals(empJob, employee.empJob) && Objects.equals(deptId, employee.deptId); } @Override public int hashCode() { return Objects.hash(id, empName, empJob, deptId); }
再次运行测试用例,测试通过
审计Auditing
参考自官方文档5.9Auditing
一般数据库表在设计时都会添加4个审计字段,Spring Data Jpa同样支持审计功能。Spring Data提供了@CreatedBy
,@LastModifiedBy
,@CreatedDate
,@LastModifiedDate
4个注解来记录表中记录的创建及修改信息。
实体类
package com.example.springbootjpa.entity; import lombok.Data; import org.hibernate.annotations.GenericGenerator; import org.springframework.data.annotation.CreatedBy; import org.springframework.data.annotation.CreatedDate; import org.springframework.data.annotation.LastModifiedBy; import org.springframework.data.annotation.LastModifiedDate; import org.springframework.data.jpa.domain.support.AuditingEntityListener; import javax.persistence.*; import java.util.Date; import java.util.Set; @Entity @EntityListeners(AuditingEntityListener.class) @Table(name = "tb_user") @Data public class User { @Id @GenericGenerator(name = "idGenerator", strategy = "uuid") @GeneratedValue(generator = "idGenerator") private String id; @Column(name = "username", unique = true, nullable = false, length = 64) private String username; @Column(name = "password", nullable = false, length = 64) private String password; @Column(name = "email", unique = true, length = 64) private String email; @ManyToMany(targetEntity = Role.class, cascade = CascadeType.ALL, fetch = FetchType.LAZY) @JoinTable(name = "tb_user_role", joinColumns = {@JoinColumn(name = "user_id", referencedColumnName = "id")}, inverseJoinColumns = {@JoinColumn(name = "role_id", referencedColumnName = "id")}) private Set<Role> roles; @CreatedDate @Column(name = "created_date", updatable = false) private Date createdDate; @CreatedBy @Column(name = "created_by", updatable = false, length = 64) private String createdBy; @LastModifiedDate @Column(name = "updated_date") private Date updatedDate; @LastModifiedBy @Column(name = "updated_by", length = 64) private String updatedBy; }
实现AuditorAware接口
光添加了4个审计注解还不够,得告诉程序到底是谁在创建和修改表记录/src/main/java/com/example/springbootjpa/auditing/AuditorAwareImpl
package com.example.springbootjpa.auditing; import org.springframework.data.domain.AuditorAware; import org.springframework.stereotype.Component; import java.util.Optional; @Component public class AuditorAwareImpl implements AuditorAware<String> { @Override public Optional<String> getCurrentAuditor() { return Optional.of("admin"); } }
这里简单的返回了一个"admin"字符串来代表当前用户名
启用Jpa审计功能
在Spring Boot启动类上添加@EnableJpaAuditing
注解用于启用Jpa的审计功能
package com.example.springbootjpa; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.data.jpa.repository.config.EnableJpaAuditing; @SpringBootApplication @EnableJpaAuditing public class SpringBootJpaApplication { public static void main(String[] args) { SpringApplication.run(SpringBootJpaApplication.class, args); } }
更多关于Jpa Specifications、Example查询请查阅官方文档
参考资料:
Spring Data Jpa官方文档
使用Hibernate、JPA、Lombok遇到的有趣问题
SpringData Jpa、Hibernate、Jpa 三者之间的关系
Spring Data-JPA versus JPA: What's the difference?