扩展JPA方法，重写save方法

为什么要重构save？

jpa提供的save方法会将原有数据置为null，而大多数情况下我们只希望跟新自己传入的参数，所以便有了重写或者新增一个save方法。

本着解决这个问题，网上搜了很多解决方案，但是没有找到合适的，于是自己研究源码，先展示几个重要源码

1、SimpleJpaRepository方法实现类，由于代码过多只展示部分源码

public class SimpleJpaRepository<T, ID> implements JpaRepository<T, ID>, JpaSpecificationExecutor<T> {
    private static final String ID_MUST_NOT_BE_NULL = "The given id must not be null!";
    private final JpaEntityInformation<T, ?> entityInformation;
    private final EntityManager em;
    private final PersistenceProvider provider;
    @Nullable
    private CrudMethodMetadata metadata;

    public SimpleJpaRepository(JpaEntityInformation<T, ?> entityInformation, EntityManager entityManager) {
        Assert.notNull(entityInformation, "JpaEntityInformation must not be null!");
        Assert.notNull(entityManager, "EntityManager must not be null!");
        this.entityInformation = entityInformation;
        this.em = entityManager;
        this.provider = PersistenceProvider.fromEntityManager(entityManager);
    }

    public SimpleJpaRepository(Class<T> domainClass, EntityManager em) {
        this(JpaEntityInformationSupport.getEntityInformation(domainClass, em), em);
    }

    public void setRepositoryMethodMetadata(CrudMethodMetadata crudMethodMetadata) {
        this.metadata = crudMethodMetadata;
    }

    @Nullable
    protected CrudMethodMetadata getRepositoryMethodMetadata() {
        return this.metadata;
    }

    protected Class<T> getDomainClass() {
        return this.entityInformation.getJavaType();
    }

    private String getDeleteAllQueryString() {
        return QueryUtils.getQueryString("delete from %s x", this.entityInformation.getEntityName());
    }
    @Transactional
    public <S extends T> S save(S entity) {
        if (this.entityInformation.isNew(entity)) {
            this.em.persist(entity);
            return entity;
        } else {
            return this.em.merge(entity);
        }
    }
}

2、JpaRepositoryFactoryBean

public class JpaRepositoryFactoryBean<T extends Repository<S, ID>, S, ID> extends TransactionalRepositoryFactoryBeanSupport<T, S, ID> {
    @Nullable
    private EntityManager entityManager;

    public JpaRepositoryFactoryBean(Class<? extends T> repositoryInterface) {
        super(repositoryInterface);
    }

    @PersistenceContext
    public void setEntityManager(EntityManager entityManager) {
        this.entityManager = entityManager;
    }

    public void setMappingContext(MappingContext<?, ?> mappingContext) {
        super.setMappingContext(mappingContext);
    }

    protected RepositoryFactorySupport doCreateRepositoryFactory() {
        Assert.state(this.entityManager != null, "EntityManager must not be null!");
        return this.createRepositoryFactory(this.entityManager);
    }

    protected RepositoryFactorySupport createRepositoryFactory(EntityManager entityManager) {
        return new JpaRepositoryFactory(entityManager);
    }

    public void afterPropertiesSet() {
        Assert.state(this.entityManager != null, "EntityManager must not be null!");
        super.afterPropertiesSet();
    }
}　

根据源码及网上资料总结如下方案

一、重写save

优势：侵入性小，缺点将原方法覆盖。

创建JpaRepositoryReBuild方法继承SimpleJpaRepository。直接上代码

public class JpaRepositoryReBuild<T, ID> extends SimpleJpaRepository<T, ID> {

    private final JpaEntityInformation<T, ?> entityInformation;
    private final EntityManager em;

    @Autowired
    public JpaRepositoryReBuild(JpaEntityInformation<T, ?> entityInformation, EntityManager entityManager) {
        super(entityInformation, entityManager);
        this.entityInformation = entityInformation;
        this.em = entityManager;
    }

    /**
     * 通用save方法 ：新增/选择性更新
     */
    @Override
    @Transactional
    public <S extends T> S save(S entity) {
        
        //获取ID
        ID entityId = (ID) this.entityInformation.getId(entity);
        T managedEntity;
        T mergedEntity;
        if(entityId == null){
            em.persist(entity);
            mergedEntity = entity;
        }else{
            managedEntity = this.findById(entityId).get();
            if (managedEntity == null) {
                em.persist(entity);
                mergedEntity = entity;
            } else {
                BeanUtils.copyProperties(entity, managedEntity, getNullProperties(entity));
                em.merge(managedEntity);
                mergedEntity = managedEntity;
            }
        }
        return entity;
    }

    /**
     * 获取对象的空属性
     */
    private static String[] getNullProperties(Object src) {
        //1.获取Bean
        BeanWrapper srcBean = new BeanWrapperImpl(src);
        //2.获取Bean的属性描述
        PropertyDescriptor[] pds = srcBean.getPropertyDescriptors();
        //3.获取Bean的空属性
        Set<String> properties = new HashSet<>();
        for (PropertyDescriptor propertyDescriptor : pds) {
            String propertyName = propertyDescriptor.getName();
            Object propertyValue = srcBean.getPropertyValue(propertyName);
            if (StringUtils.isEmpty(propertyValue)) {
                srcBean.setPropertyValue(propertyName, null);
                properties.add(propertyName);
            }
        }
        return properties.toArray(new String[0]);
    }
}

启动类加上JpaRepositoryReBuild 方法

@EnableJpaRepositories(value = "com.XXX", repositoryBaseClass = JpaRepositoryReBuild.class)
@SpringBootApplication
@EnableDiscoveryClient // 即消费也注册
public class SystemApplication {

    public static void main(String[] args) {
        SpringApplication.run(SystemApplication.class, args);
    }
    
}

二、扩张jpa方法

1、新建新增方法接口BaseRepository

@NoRepositoryBean
public interface BaseRepository<T, ID extends Serializable> extends JpaRepository<T, ID> {

    /**
     * 保存但不覆盖原有数据
     * @param entity
     * @return
     */
    T saveNotNull(T entity);
}

2、创建BaseRepositoryImpl方法

@NoRepositoryBean
public class BaseRepositoryImpl<T, ID extends Serializable> extends SimpleJpaRepository<T, ID> implements BaseRepository<T, ID> {


    private final JpaEntityInformation<T, ?> entityInformation;
    private final EntityManager em;



    public BaseRepositoryImpl(JpaEntityInformation<T, ?> entityInformation, EntityManager entityManager) {
        super(entityInformation,entityManager);
        this.entityInformation = entityInformation;
        this.em = entityManager;
    }

    public BaseRepositoryImpl(Class<T> domainClass, EntityManager em) {
        this(JpaEntityInformationSupport.getEntityInformation(domainClass, em), em);
    }

    @Override
    @Transactional
    public T saveNotNull(T entity) {

        //获取ID
        ID entityId = (ID) this.entityInformation.getId(entity);
        T managedEntity;
        T mergedEntity;
        if(entityId == null){
            em.persist(entity);
            mergedEntity = entity;
        }else{
            managedEntity = this.findById(entityId).get();
            if (managedEntity == null) {
                em.persist(entity);
                mergedEntity = entity;
            } else {
                BeanUtils.copyProperties(entity, managedEntity, getNullProperties(entity));
                em.merge(managedEntity);
                mergedEntity = managedEntity;
            }
        }
        return mergedEntity;
    }


    private static String[] getNullProperties(Object src) {
        //1.获取Bean
        BeanWrapper srcBean = new BeanWrapperImpl(src);
        //2.获取Bean的属性描述
        PropertyDescriptor[] pds = srcBean.getPropertyDescriptors();
        //3.获取Bean的空属性
        Set<String> properties = new HashSet<>();
        for (PropertyDescriptor propertyDescriptor : pds) {
            String propertyName = propertyDescriptor.getName();
            Object propertyValue = srcBean.getPropertyValue(propertyName);
            if (StringUtils.isEmpty(propertyValue)) {
                srcBean.setPropertyValue(propertyName, null);
                properties.add(propertyName);
            }
        }
        return properties.toArray(new String[0]);
    }
}

3、创建工厂BaseRepositoryFactory

public class BaseRepositoryFactory<R extends JpaRepository<T, ID>, T, ID extends Serializable> extends JpaRepositoryFactoryBean<R, T, ID> {

    public BaseRepositoryFactory(Class<? extends R> repositoryInterface) {
        super(repositoryInterface);
    }

    @Override
    protected RepositoryFactorySupport createRepositoryFactory(EntityManager em) {
        return new MyRepositoryFactory(em);
    }

    private static class MyRepositoryFactory extends JpaRepositoryFactory {

        private final EntityManager em;
        public MyRepositoryFactory(EntityManager em) {
            super(em);
            this.em = em;
        }

        @Override
        protected Object getTargetRepository(RepositoryInformation information) {
            return new BaseRepositoryImpl((Class) information.getDomainType(), em);
        }

        @Override
        protected Class getRepositoryBaseClass(RepositoryMetadata metadata) {
            return BaseRepositoryImpl.class;
        }

    }

}

4、启动类引入

@EnableJpaRepositories(repositoryFactoryBeanClass = BaseRepositoryFactory.class, basePackages ="com.XXX")
@SpringBootApplication
@EnableDiscoveryClient // 即消费也注册
public class SystemApplication {

    public static void main(String[] args) {
        SpringApplication.run(SystemApplication.class, args);
    }
}