java如何减少桌面应用程序中的hibernate内存使用？

Question

我正在开发一个桌面应用程序。我正在使用hibernate 4、带嵌入式驱动程序的JavaDB和JavaFx。但我真的很难用冬眠记忆。下面我提供了我的代码

我在一个名为MODEL_E2B_WORDLIST的数据库表中搜索。我有两种方法

1. 冬眠
2. JDBC

我已经用JDBC和Hibernate运行了大约500次相同的搜索操作。我发现JDBC在这个操作中占用的内存不超过100mb，但Hibernate使用的内存约为400mb

现在我想知道我在hibernate中犯了什么错误，占用了这么多内存，或者hibernate是正常的

CFG:

<hibernate-configuration>
  <session-factory>
    <!--.Connection Properties.-->
    <property name="hibernate.dialect">org.hibernate.dialect.DerbyDialect</property>
    <property name="hibernate.connection.driver_class">org.apache.derby.jdbc.EmbeddedDriver</property>
    <property name="hibernate.connection.url">jdbc:derby:vocubulary;create=true;</property>
    <property name="hibernate.connection.username">app</property>
    <property name="hibernate.connection.password">app</property>
    <property name="hibernate.show_sql">true</property>
    <!--done to test.-->
    <property name="hibernate.hbm2ddl.auto">update</property>
    <!--<mapping resource="word.hbm.xml"/>-->
    <mapping class="com.vocubulary.model.Model_E2B_WordList"/>
  </session-factory>
</hibernate-configuration>

DAO Impl类：

public class DAO_e2b_Impl implements DAO_e2b_I
    {

     SessionFactory factory = HibernateUtil.getSessionFactory();
//    Session session = factory.openSession();

    @Override
    public List dao_e2b_get_wordsList_afterSerach(String e2b_searchKey)
        {
//        SessionFactory factory = HibernateUtil.getSessionFactory();
          Session session = factory.openSession();
          List list_word = null;
          try
            {
            Transaction tx = session.beginTransaction();
            Criteria criteria = session.createCriteria(Model_E2B_WordList.class);
            criteria.setProjection(Projections.property("e2b_word")); //Projections.property is used to retrieve specific columns
            criteria.add(Restrictions.ilike("e2b_word", e2b_searchKey, MatchMode.START));
            list_word = criteria.list();
            tx.commit();
          } catch (Exception e)
          {
            e.printStackTrace();
          } finally
          {
            session.close();
//            factory.close();
            System.out.println("\n\n\n Final loadData : all conection closed");
          }
        return list_word;
//        return jdbcDB(e2b_searchKey);  
        }
}

测试类

@Test
     public void search_in_e2b_wordList() throws Exception
         {
            hibernateTest(500);
//             jdbcTest(500);
         }

     public void hibernateTest(int loopCounter) throws  Exception
         {
            DAO_e2b_Impl dAO_e2b_Impl = new DAO_e2b_Impl();
            List l = new ArrayList();
             int x = 0;
             while (x != loopCounter)
               {
                 l = dAO_e2b_Impl.dao_e2b_get_wordsList_afterSerach("Man");
                 System.out.println("Size  :" + l.size());
                 x++;
                 l.clear();
                 System.out.println("count : " + x);
                 Thread.sleep(100);//used, to see the effect in the task manager.
               }
         }
     public void jdbcTest(int loopCounter) throws  Exception
         {
            List l = new ArrayList();
             int x = 0;
             while (x != loopCounter)
               {
                 l = jdbcDB();
                 System.out.println("Size  :" + l.size());
                 x++;
                 l.clear();
                 System.out.println("count : " + x);
                 Thread.sleep(100);//used, to see the effect in the task manager.
               }
         }


    public List jdbcDB()
             {
               // JDBC driver name and database URL
        String JDBC_DRIVER = "org.hibernate.dialect.DerbyDialect";
        String DB_URL = "jdbc:derby:vocubulary;create=true;";

        //  Database credentials
        String USER = "app";
        String PASS = "app";

        Connection conn = null;
        Statement stmt = null;

        List l = new ArrayList();

        try
          {
            //STEP 2: Register JDBC driver
            Class.forName("org.apache.derby.jdbc.EmbeddedDriver");

            //STEP 3: Open a connection
            System.out.println("Connecting to database...");
            conn = DriverManager.getConnection(DB_URL, USER, PASS);

            //STEP 4: Execute a query
            System.out.println("Creating statement...");
            stmt = conn.createStatement();
            String sql;
//            sql = "SELECT app.MODEL_E2B_WORDLIST.E2B_WORD from app.MODEL_E2B_WORDLIST";
            sql = "SELECT app.MODEL_E2B_WORDLIST.E2B_WORD from app.MODEL_E2B_WORDLIST WHERE E2B_WORD LIKE 'MAN%'";
            ResultSet rs = stmt.executeQuery(sql);

            //STEP 5: Extract data from result set
            while (rs.next())
              {
                //Retrieve by column name
                String last = rs.getString("E2B_WORD");
                //Display values
//                System.out.println("Last: " + last);
                l.add(last);
              }
            //STEP 6: Clean-up environment
            rs.close();
            stmt.close();
            conn.close();
          } catch (SQLException se)
          {
            //Handle errors for JDBC
            se.printStackTrace();
          } catch (Exception e)
          {
            //Handle errors for Class.forName
            e.printStackTrace();
          } finally
          {
            //finally block used to close resources
            try
              {
                if (stmt != null)
                  {
                    stmt.close();
                  }
              } catch (SQLException se2)
              {
              }// nothing we can do
            try
              {
                if (conn != null)
                  {
                    conn.close();
                  }
              } catch (SQLException se)
              {
                se.printStackTrace();
              }//end finally try
          }//end try

        System.out.println("Goodbye!");
        return l;
             }

模型类

@ToString
@NoArgsConstructor
@AllArgsConstructor
@Entity
public class Model_E2B_WordList
    {
//          i used "lombok"
            @Id @Getter @Setter
            private String e2b_word;
    }

Answer 1

Hibernate非常灵活，所以您可以调整它，使其使用的内存量与JDBC变体几乎相同

Hibernate使用Session作为一级缓存。您可以尝试使用StatelessSession来减少使用的内存量。你可以用SessionFactory#openStatelessSession()打开StatelessSession

你不需要这个

List l = new ArrayList();

在hibernateTest()中，由于赋值new ArrayList()从不使用。通过这种方式分配一个结果

List l = dAO_e2b_Impl.dao_e2b_get_wordsList_afterSerach("Man");