📜  Hibernate-批处理

📅  最后修改于: 2020-11-16 07:04:03             🧑  作者: Mango


考虑一种情况,当您需要使用Hibernate将大量记录上载到数据库中时。以下是使用Hibernate实现此目的的代码片段-

Session session = SessionFactory.openSession();
Transaction tx = session.beginTransaction();
for ( int i=0; i<100000; i++ ) {
   Employee employee = new Employee(.....);
   session.save(employee);
}
tx.commit();
session.close();

默认情况下,Hibernate将所有持久化的对象缓存在会话级缓存中,最终您的应用程序将在第50,000行附近出现OutOfMemoryException崩溃。如果您将批处理与Hibernate一起使用,则可以解决此问题。

要使用批处理功能,首先将hibernate.jdbc.batch_size设置为批处理大小,根据对象大小将其设置为20或50。这将告诉休眠容器每隔X行要批量插入。为了在您的代码中实现这一点,我们需要做一些小的修改,如下所示:

Session session = SessionFactory.openSession();
Transaction tx = session.beginTransaction();
for ( int i=0; i<100000; i++ ) {
   Employee employee = new Employee(.....);
   session.save(employee);
   if( i % 50 == 0 ) { // Same as the JDBC batch size
      //flush a batch of inserts and release memory:
      session.flush();
      session.clear();
   }
}
tx.commit();
session.close();

上面的代码对于INSERT操作可以很好地工作,但是如果您愿意进行UPDATE操作,则可以使用以下代码实现-

Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();

ScrollableResults employeeCursor = session.createQuery("FROM EMPLOYEE").scroll();
int count = 0;

while ( employeeCursor.next() ) {
   Employee employee = (Employee) employeeCursor.get(0);
   employee.updateEmployee();
   seession.update(employee); 
   if ( ++count % 50 == 0 ) {
      session.flush();
      session.clear();
   }
}
tx.commit();
session.close();

批处理示例

让我们修改配置文件以添加hibernate.jdbc.batch_size属性-





   
   
      
         org.hibernate.dialect.MySQLDialect
      
   
      
         com.mysql.jdbc.Driver
      

      
   
      
         jdbc:mysql://localhost/test
      
   
      
         root
      
   
      
         root123
      
   
      
         50
      

      
      

   

考虑以下POJO Employee类-

public class Employee {
   private int id;
   private String firstName; 
   private String lastName;   
   private int salary;  

   public Employee() {}
   
   public Employee(String fname, String lname, int salary) {
      this.firstName = fname;
      this.lastName = lname;
      this.salary = salary;
   }
   
   public int getId() {
      return id;
   }
   
   public void setId( int id ) {
      this.id = id;
   }
   
   public String getFirstName() {
      return firstName;
   }
   
   public void setFirstName( String first_name ) {
      this.firstName = first_name;
   }
   
   public String getLastName() {
      return lastName;
   }
   
   public void setLastName( String last_name ) {
      this.lastName = last_name;
   }
   
   public int getSalary() {
      return salary;
   }
   
   public void setSalary( int salary ) {
      this.salary = salary;
   }
}

让我们创建以下EMPLOYEE表来存储Employee对象-

create table EMPLOYEE (
   id INT NOT NULL auto_increment,
   first_name VARCHAR(20) default NULL,
   last_name  VARCHAR(20) default NULL,
   salary     INT  default NULL,
   PRIMARY KEY (id)
);

以下是将文件映射到EMPLOYEE表的Employee对象的映射文件-


 


   
      
      
         This class contains the employee detail. 
      
      
      
         
      
      
      
      
      
      
   

最后,我们将使用main()方法创建应用程序类以运行应用程序,其中将使用Session对象可用的flush()clear()方法,以便Hibernate继续将这些记录写入数据库,而不是将其缓存在数据库中。记忆。

import java.util.*; 
 
import org.hibernate.HibernateException; 
import org.hibernate.Session; 
import org.hibernate.Transaction;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class ManageEmployee {
   private static SessionFactory factory; 
   public static void main(String[] args) {
      
      try {
         factory = new Configuration().configure().buildSessionFactory();
      } catch (Throwable ex) { 
         System.err.println("Failed to create sessionFactory object." + ex);
         throw new ExceptionInInitializerError(ex); 
      }
      ManageEmployee ME = new ManageEmployee();

      /* Add employee records in batches */
      ME.addEmployees( );
   }
   
   /* Method to create employee records in batches */
   public void addEmployees( ){
      Session session = factory.openSession();
      Transaction tx = null;
      Integer employeeID = null;
      
      try {
         tx = session.beginTransaction();
         for ( int i=0; i<100000; i++ ) {
            String fname = "First Name " + i;
            String lname = "Last Name " + i;
            Integer salary = i;
            Employee employee = new Employee(fname, lname, salary);
            session.save(employee);
             if( i % 50 == 0 ) {
               session.flush();
               session.clear();
            }
         }
         tx.commit();
      } catch (HibernateException e) {
         if (tx!=null) tx.rollback();
         e.printStackTrace(); 
      } finally {
         session.close(); 
      }
      return ;
   }
}

编译与执行

这是编译和运行上述应用程序的步骤。在继续进行编译和执行之前,请确保已正确设置了PATH和CLASSPATH。

  • 如上所述创建hibernate.cfg.xml配置文件。

  • 如上所示,创建Employee.hbm.xml映射文件。

  • 如上所示创建Employee.java源文件并进行编译。

  • 如上所示创建ManageEmployee.java源文件并进行编译。

  • 执行ManageEmployee二进制文件以运行程序,该程序将在EMPLOYEE表中创建100000条记录。