Hibernate拦截器

正如前面已经了解到，在Hibernate中，对象将被创建并保存。一旦对象已经改变，它必须被保存到数据库中。这个过程一直持续的对象是需要的，直到下一次，并且它将被从持久存储加载。

因此，一个对象通过不同阶段的生命周期和拦截器接口提供了可以在不同的阶段被调用来执行一些任务所需的方法。这些方法是从session到应用程序的回调，允许它被保存在申请前检查和/或操纵持久化对象的属性，更新，删除或加载。以下是拦截器界面中所有可用的方法列表：

Hibernate拦截器为我们提供了完全控制对象如何将目光转向应用程序和数据库。

如何使用拦截器？

为了建立一个拦截器可以直接实现Interceptor接口的类或继承自EmptyInterceptor类。以下将简单的步骤来使用Hibernate拦截功能。

创建拦截器：

我们将在例子在创建和更新Employee对象时，拦截器的方法将被自动调用继承自EmptyInterceptor。可以实现更多的方法按您的要求。

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，让我们修改一点点，我们使用的EMPLOYEE表和Employee类一起看一个例子：

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。会有一个表对应于每一个对象，愿意提供持久性。考虑上述目的需要存储和检索到下面的RDBMS表：

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：

这一步是创建一个指示Hibernate如何定义的一个或多个类映射到数据库表的映射文件。

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
 "-//Hibernate/Hibernate Mapping DTD//EN"
 "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> 

<hibernate-mapping>
   <class name="Employee" table="EMPLOYEE">
      <meta attribute="class-description">
         This class contains the employee detail. 
      </meta>
      <id name="id" type="int" column="id">
         <generator class="native"/>
      </id>
      <property name="firstName" column="first_name" type="string"/>
      <property name="lastName" column="last_name" type="string"/>
      <property name="salary" column="salary" type="int"/>
   </class>
</hibernate-mapping>

创建应用程序类：

最后，我们将创建应用程序类的main()方法来运行应用程序。这里应该指出的是，在创建会话对象，我们使用了拦截器类作为参数。

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(); 
      }
   }
}

编译和执行：

下面是步骤来编译并运行上述应用程序。请确保已在进行的编译和执行之前，适当地设置PATH和CLASSPATH。

• 创建hibernate.cfg.xml配置文件中配置章节解释。

• 创建Employee.hbm.xml映射文件，如上图所示。

• 创建Employee.java源文件，如上图所示，并编译它。

• 创建MyInterceptor.java源文件，如上图所示，并编译它。

• 创建ManageEmployee.java源文件，如上图所示，并编译它。

• 执行ManageEmployee二进制文件来运行程序。

会得到以下结果，并记录将在EMPLOYEE表中创建。

$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

如果检查EMPLOYEE表，它应该记录信息下：

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>