Hibernate-拦截器 - 芒果文档

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📜 Hibernate-拦截器

📅 最后修改于: 2020-11-16 07:04:52 🧑 作者: Mango

如您所知，在Hibernate中，将创建并保留一个对象。更改对象后，必须将其保存回数据库。该过程将一直持续到下一次需要该对象为止，然后将从持久性存储中加载该对象。

因此，对象在其生命周期中经历了不同的阶段，并且拦截器接口提供了可以在不同的阶段调用以执行某些所需任务的方法。这些方法是从会话到应用程序的回调，从而允许应用程序在保存，更新，删除或加载持久对象之前检查和/或操纵该对象的属性。以下是Interceptor接口中可用的所有方法的列表-

Sr.No.	Method & Description
1	findDirty() This method is be called when the flush() method is called on a Session object.
2	instantiate() This method is called when a persisted class is instantiated.
3	isUnsaved() This method is called when an object is passed to the saveOrUpdate() method/
4	onDelete() This method is called before an object is deleted.
5	onFlushDirty() This method is called when Hibernate detects that an object is dirty (i.e. have been changed) during a flush i.e. update operation.
6	onLoad() This method is called before an object is initialized.
7	onSave() This method is called before an object is saved.
8	postFlush() This method is called after a flush has occurred and an object has been updated in memory.
9	preFlush() This method is called before a flush.

Hibernate Interceptor使我们可以完全控制对象在应用程序和数据库中的外观。

如何使用拦截器?

要构建拦截器，可以直接实现Interceptor类，也可以扩展EmptyInterceptor类。以下是使用休眠拦截器功能的简单步骤。

创建拦截器

我们将在示例中扩展EmptyInterceptor，其中在创建和更新Employee对象时将自动调用Interceptor的方法。您可以根据需要实现更多方法。

import java.io.Serializable;
import java.util.Date;
import java.util.Iterator;

import org.hibernate.EmptyInterceptor;
import org.hibernate.Transaction;
import org.hibernate.type.Type;

public class MyInterceptor extends EmptyInterceptor {
   private int updates;
   private int creates;
   private int loads;

   public void onDelete(Object entity, Serializable id,
      Object[] state, String[] propertyNames, Type[] types) {
       // do nothing
   }

   // This method is called when Employee object gets updated.
   public boolean onFlushDirty(Object entity, Serializable id,
      Object[] currentState, Object[] previousState, String[] propertyNames,
      Type[] types) {
         if ( entity instanceof Employee ) {
            System.out.println("Update Operation");
            return true; 
         }
         return false;
   }
    
   public boolean onLoad(Object entity, Serializable id,
      Object[] state, String[] propertyNames, Type[] types) {
         // do nothing
         return true;
   }
   
   // This method is called when Employee object gets created.
   public boolean onSave(Object entity, Serializable id,
      Object[] state, String[] propertyNames, Type[] types) {
         if ( entity instanceof Employee ) {
            System.out.println("Create Operation");
            return true; 
         }
         return false;
   }
   
   //called before commit into database
   public void preFlush(Iterator iterator) {
      System.out.println("preFlush");
   }
   
   //called after committed into database
   public void postFlush(Iterator iterator) {
      System.out.println("postFlush");
   }
}

创建POJO类

现在，让我们修改一下第一个示例，其中我们使用了EMPLOYEE表和Employee类来玩-

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;
   }
}

创建数据库表

第二步是在数据库中创建表。每个对象对应一个表，您愿意提供持久性。考虑上述对象，需要将其存储并检索到以下RDBMS表中-

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)
);

创建映射配置文件

此步骤是创建一个指示Hibernate的映射文件-如何将已定义的一个或多个类映射到数据库表。


 


   
      
      
         This class contains the employee detail.

创建应用程序类

最后，我们将使用main()方法创建应用程序类以运行该应用程序。在这里，应该注意，在创建会话对象时，我们将Interceptor类用作参数。

import java.util.List; 
import java.util.Date;
import java.util.Iterator; 
 
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 few employee records in database */
      Integer empID1 = ME.addEmployee("Zara", "Ali", 1000);
      Integer empID2 = ME.addEmployee("Daisy", "Das", 5000);
      Integer empID3 = ME.addEmployee("John", "Paul", 10000);

      /* List down all the employees */
      ME.listEmployees();

      /* Update employee's records */
      ME.updateEmployee(empID1, 5000);

      /* Delete an employee from the database */
      ME.deleteEmployee(empID2);

      /* List down new list of the employees */
      ME.listEmployees();
   }
   
   /* Method to CREATE an employee in the database */
   public Integer addEmployee(String fname, String lname, int salary){
      Session session = factory.openSession( new MyInterceptor() );
      Transaction tx = null;
      Integer employeeID = null;
      
      try {
         tx = session.beginTransaction();
         Employee employee = new Employee(fname, lname, salary);
         employeeID = (Integer) session.save(employee); 
         tx.commit();
      } catch (HibernateException e) {
         if (tx!=null) tx.rollback();
         e.printStackTrace(); 
      } finally {
         session.close(); 
      }
      return employeeID;
   }
   
   /* Method to  READ all the employees */
   public void listEmployees( ){
      Session session = factory.openSession( new MyInterceptor() );
      Transaction tx = null;
      
      try {
         tx = session.beginTransaction();
         List employees = session.createQuery("FROM Employee").list(); 
         for (Iterator iterator = employees.iterator(); iterator.hasNext();){
            Employee employee = (Employee) iterator.next(); 
            System.out.print("First Name: " + employee.getFirstName()); 
            System.out.print("  Last Name: " + employee.getLastName()); 
            System.out.println("  Salary: " + employee.getSalary()); 
         }
         tx.commit();
      } catch (HibernateException e) {
         if (tx!=null) tx.rollback();
         e.printStackTrace(); 
      } finally {
         session.close(); 
      }
   }
   
   /* Method to UPDATE salary for an employee */
   public void updateEmployee(Integer EmployeeID, int salary ){
      Session session = factory.openSession( new MyInterceptor() );
      Transaction tx = null;
      
      try {
         tx = session.beginTransaction();
         Employee employee = (Employee)session.get(Employee.class, EmployeeID); 
         employee.setSalary( salary );
         session.update(employee); 
         tx.commit();
      } catch (HibernateException e) {
         if (tx!=null) tx.rollback();
         e.printStackTrace(); 
      } finally {
         session.close(); 
      }
   }
   
   /* Method to DELETE an employee from the records */
   public void deleteEmployee(Integer EmployeeID){
      Session session = factory.openSession( new MyInterceptor() );
      Transaction tx = null;
      
      try {
         tx = session.beginTransaction();
         Employee employee = (Employee)session.get(Employee.class, EmployeeID); 
         session.delete(employee); 
         tx.commit();
      } catch (HibernateException e) {
         if (tx!=null) tx.rollback();
         e.printStackTrace(); 
      } finally {
         session.close(); 
      }
   }
}

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。

按照配置章节中的说明创建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MyInterceptor.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。

您将得到以下结果，并且将在EMPLOYEE表中创建记录。

$java ManageEmployee
.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........

Create Operation
preFlush
postFlush
Create Operation
preFlush
postFlush
Create Operation
preFlush
postFlush
First Name: Zara  Last Name: Ali  Salary: 1000
First Name: Daisy  Last Name: Das  Salary: 5000
First Name: John  Last Name: Paul  Salary: 10000
preFlush
postFlush
preFlush
Update Operation
postFlush
preFlush
postFlush
First Name: Zara  Last Name: Ali  Salary: 5000
First Name: John  Last Name: Paul  Salary: 10000
preFlush
postFlush

如果您检查EMPLOYEE表，则该表应具有以下记录-

mysql> select * from EMPLOYEE;
+----+------------+-----------+--------+
| id | first_name | last_name | salary |
+----+------------+-----------+--------+
| 29 | Zara       | Ali       |   5000 |
| 31 | John       | Paul      |  10000 |
+----+------------+-----------+--------+
2 rows in set (0.00 sec
mysql>