springboot jpa oracle實體類中配置註解沒法在數據庫中生成註釋的一種解決方式

需求

對於oracle數據庫，jpa的Entity即便配置了註釋註解@Column(columnDefinition = '列註釋')，沒法在數據庫層生成列的註釋

解決方案

自定義註解，配置在Entity類上，項目初始化時，經過EntityManager獲取全部的實體類，遍歷實體類中是否配置了註解，若是配置了，動態拼接DDL語句並執行

• 自定義註解：

  import java.lang.annotation.*;
  /**
  * description: * 解決jap根據實體類建立建表過程當中沒法添加字段註釋
  * @author MorningSun
  * @version 1.0 * @since JDK1.8 * date 11/6/2020 10:45 AM */@Target({ElementType.TYPE, ElementType.FIELD})
  @Retention(RetentionPolicy.RUNTIME)
  @Documented
  public @interface JPAOracleComment {
     /**
  * spring jpa + oracle add comment * @return */ String value() default "";
  }

  import com.orient.cssrc.jpa.model.JpaOracleComment;
  import lombok.extern.slf4j.Slf4j;
  import org.hibernate.SessionFactory;
  import org.hibernate.internal.SessionFactoryImpl;
  import org.hibernate.persister.entity.EntityPersister;
  import org.hibernate.persister.entity.SingleTableEntityPersister;
  import org.hibernate.persister.walking.spi.AttributeDefinition;
  import org.springframework.boot.CommandLineRunner;
  import org.springframework.boot.autoconfigure.orm.jpa.HibernateProperties;
  import org.springframework.jdbc.core.JdbcTemplate;
  import org.springframework.stereotype.Component;
  import javax.annotation.Resource;
  import javax.persistence.EntityManager;
  import javax.persistence.EntityManagerFactory;
  import javax.persistence.PersistenceContext;
  import java.lang.reflect.Field;
  import java.util.Map;
  import java.util.Objects;
  /**
  * description: * * @author MorningSun * @version V1.0 * @since date 2020/12/25 */@Slf4j
  @Component
  public class JpaOracleCommentInit implements CommandLineRunner {
     @PersistenceContext
  private EntityManager entityManager;
     @Resource
  private JdbcTemplate jdbcTemplate;
     @Resource
  private HibernateProperties hibernateProperties;
     @Override
  public void run(String... args) throws Exception {
         String ddlAuto = this.hibernateProperties.getDdlAuto();
         if(Objects.nonNull(ddlAuto) && "update".equalsIgnoreCase(ddlAuto)){
             this.scanCommentAnnotationOnEntityAndCreate();
         }
     }
     private void scanCommentAnnotationOnEntityAndCreate(){
         EntityManagerFactory entityManagerFactory = this.entityManager.getEntityManagerFactory();
         SessionFactoryImpl sessionFactory = (SessionFactoryImpl)entityManagerFactory.unwrap(SessionFactory.class);
         Map<String, EntityPersister> persisterMap = sessionFactory.getMetamodel().entityPersisters();
         if(Objects.nonNull(persisterMap) && persisterMap.keySet().size() > 0){
             for(Map.Entry<String, EntityPersister> entry: persisterMap.entrySet()){
                 Class<?> targetClazz = entry.getValue().getMappedClass();
                 SingleTableEntityPersister persister = (SingleTableEntityPersister)entry.getValue();
                 //數據表名
  String tableName = persister.getTableName();
                 //添加表的註釋
  JpaOracleComment targetClazzAnno = targetClazz.getAnnotation(JpaOracleComment.class);
                 if(Objects.nonNull(targetClazzAnno)){
                     String sql = "comment on table " +
                             tableName +
                             " is " +
                             "'" + targetClazzAnno.value() + "'";
                     this.jdbcTemplate.execute(sql);
                 }
                 for (AttributeDefinition attributeDefinition : persister.getAttributes()) {
                     //屬性名稱
  String propertyName = attributeDefinition.getName();
                     if (propertyName.equalsIgnoreCase("_identifierMapper")) {
                         log.warn("嘗試爲實體類:" + targetClazz.getSimpleName() + "生成註解，發現了聯合主鍵，暫時沒法處理，已忽略對應字段");
                         continue;
                     }
                     Field field;
                     try {
                         field = targetClazz.getDeclaredField(propertyName);
                         JpaOracleComment anno = field.getAnnotation(JpaOracleComment.class);
                         if (Objects.nonNull(anno)) {
                             //數據庫字段名
  String[] columns = persister.getPropertyColumnNames(propertyName);
                             String sql = "comment on column " +
                                     tableName +
                                     "." +
                                     columns[0] +
                                     " is " +
                                     "'" + anno.value() + "'";
                             this.jdbcTemplate.execute(sql);
                         }
                     } catch (NoSuchFieldException ex) {
                         ex.printStackTrace();
                     }
                 }
             }
         }
     }
  }