Hibernate是一个开源，轻量级的ORM工，它简化了java应用程序与数据库交互的开发，因此在开发项目的时候得到了重用，那hibernate如何使用拦截器?接下来我们就来给大家讲解一下这方面的内容。
创建拦截器
我们将在例子中继承 EmptyInterceptor，当 Employee 对象被创建和更新时拦截器的方法将自动被调用。你可以根据你的需求实现更多的方法。
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
现在让我们稍微修改我们的第一个例子，我们使用 EMPLOYEE 表单和 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;
}
}创建数据库表
第二步将是在你的数据库中创建表。一张表对应每个你提供持久性的对象。考虑以上的对象需要被存储和检索到以下的 RDBM 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 Mapping 配置文件
这个步骤是来创建一个指导 Hibernate 如何将定义的类或者多个类映射到数据库表单中的映射文件。
<?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 Application 类
最后，我们将用 main() 创建 application 类来运行应用程序。这里应该注意当创建 session 对象时我们使用 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();
}
}
}编译和执行
这里是编译和运行上面提及的应用程序的步骤。确保你已经在处理编译和执行前正确设置了 PATH 和 CLASSPATH。
创建在 configuration 章节中解释的 hibernate.cfg.xml 配置文件。
创建如上所示的 Employee.hbm.xml 映射文件。
创建如上所示的 Employee.java 源文件并编译。
创建如上所示的 MyInterceptor.java 源文件并编译。
创建如上所示的 ManageEmployee.java 源文件并编译。
执行 ManageEmployee 来运行程序。
你将得到以下结果，而且记录将在 EMPLOYEE 表单中被创建。
$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
如果你检查你的 EMPLOYEE 表单，它应该有如下结果：
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>
这样就完成了Hibernate 拦截器的创建以及使用，Hibernate 拦截器给予了我们一个对象如何应用到应用程序和数据库的总控制。可见Hibernate 拦截器的重要性!最后大家如果想要了解更多java架构师知识，敬请关注奇Q工具网。
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