正如您已经了解到，在Hibernate中，将创建并保留一个对象.对象更改后，必须将其保存回数据库.这个过程一直持续到下一次需要对象时，它将从持久存储中加载.
因此，一个对象在其生命周期中经过不同的阶段并且拦截器接口提供方法，可以在不同阶段调用这些方法来执行一些必需的任务.这些方法是从会话到应用程序的回调，允许应用程序在保存，更新，删除或加载之前检查和/或操纵持久对象的属性.以下是Interceptor接口中可用的所有方法的列表 :
| Sr.No. | Method&描述 |
|---|---|
| 1 | findDirty() 在Session对象上调用 flush()方法时，将调用此方法. |
| 2 | instantiate() 实例化持久化类时调用此方法. |
| 3 | isUnsaved( ) 将对象传递给 saveOrUpdate()方法/ |
| 4 | onDelete() 在删除对象之前调用此方法. |
| 5 | onFlushDirty() 当Hibernate在刷新即更新操作期间检测到对象变脏(即已更改)时，将调用此方法. |
| 6 | onLoad() 在初始化对象之前调用此方法. |
| 7 | onSave() 在保存对象之前调用此方法. |
| 8 | postFlush() 此方法在刷新后调用已经发生并且对象已在内存中更新. |
| 9 | preFlush() 在刷新之前调用此方法. |
Hibernate Interceptor让我们可以完全控制对象对应用程序和应用程序的外观数据库.
要构建拦截器，您可以直接实现 Interceptor 类或扩展 EmptyInterceptor 类.以下是使用Hibernate Interceptor功能的简单步骤.
我们将在我们的示例中扩展EmptyInterceptor，其中将自动调用Interceptor的方法何时创建并更新 Employee 对象.您可以根据自己的要求实现更多方法.
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");
}
}现在，让我们稍微修改一下我们的第一个例子，我们使用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;
}
}第二步是在你的表中创建表数据库.每个对象都会有一个表，您愿意提供持久性.考虑上面解释的对象，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) );
这一步是创建一个指示Hibernate的映射文件 - 如何映射定义的数据库表的类或类.
<?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>
最后，我们将使用main()方法创建应用程序类来运行应用程序.在这里，应该注意的是，在创建会话对象时，我们使用我们的Interceptor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();
}
}
}这是编译和运行上述应用程序的步骤.确保在进行编译和执行之前已经适当地设置了PATH和CLASSPATH.
创建hibernate.cfg.xml配置文件，如配置章节中所述.
创建Employee.hbm.xml映射文件，如上所示.
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二进制文件来运行程序.
您将获得以下结果，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
如果您检查您的EMPLOYEE表，它应该有以下记录 :
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>
