你已經(jīng)學(xué)到，在 Hibernate 中，一個對象將被創(chuàng)建和保持。一旦對象已經(jīng)被修改，它必須被保存到數(shù)據(jù)庫里。這個過程持續(xù)直到下一次對象被需要，它將被從持久的存儲中加載。
因此一個對象通過它生命周期中的不同階段，并且 Interceptor 接口提供了在不同階段能被調(diào)用來進行一些所需要的任務(wù)的方法。這些方法是從會話到應(yīng)用程序的回調(diào)函數(shù)，允許應(yīng)用程序檢查或操作一個持續(xù)對象的屬性，在它被保存，更新，刪除或上傳之前。以下是在 Interceptor 接口中可用的所有方法的列表。
| S.N. | 方法和描述 |
|---|---|
| 1 | findDirty() 這個方法在當(dāng) flush() 方法在一個 Session 對象上被調(diào)用時被調(diào)用。 |
| 2 | instantiate() 這個方法在一個持續(xù)的類被實例化時被調(diào)用。 |
| 3 | isUnsaved() 這個方法在當(dāng)一個對象被傳到 saveOrUpdate() 方法時被調(diào)用。 |
| 4 | onDelete() 這個方法在一個對象被刪除前被調(diào)用。 |
| 5 | onFlushDirty() 這個方法在當(dāng) Hibernate 探測到一個對象在一次 flush（例如，更新操作）中是臟的（例如，被修改）時被調(diào)用。 |
| 6 | onLoad() 這個方法在一個對象被初始化之前被調(diào)用。 |
| 7 | onSave() 這個方法在一個對象被保存前被調(diào)用。 |
| 8 | postFlush() 這個方法在一次 flush 已經(jīng)發(fā)生并且一個對象已經(jīng)在內(nèi)存中被更新后被調(diào)用。 |
| 9 | preFlush() 這個方法在一次 flush 前被調(diào)用。 |
Hibernate 攔截器給予了我們一個對象如何應(yīng)用到應(yīng)用程序和數(shù)據(jù)庫的總控制。
為了創(chuàng)建一個攔截器你可以直接實現(xiàn) Interceptor 類或者繼承 EmptyInterceptor 類。以下是簡單的使用 Hibernate 攔截器功能的步驟。
我們將在例子中繼承 EmptyInterceptor，當(dāng) Employee 對象被創(chuàng)建和更新時攔截器的方法將自動被調(diào)用。你可以根據(jù)你的需求實現(xiàn)更多的方法。
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");
}
}現(xiàn)在讓我們稍微修改我們的第一個例子，我們使用 EMPLOYEE 表單和 Employee 類：
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;
}
}第二步將是在你的數(shù)據(jù)庫中創(chuàng)建表。一張表對應(yīng)每個你提供持久性的對象?？紤]以上的對象需要被存儲和檢索到以下的 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)
);這個步驟是來創(chuàng)建一個指導(dǎo) Hibernate 如何將定義的類或者多個類映射到數(shù)據(jù)庫表單中的映射文件。
<?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>最后，我們將用 main() 創(chuàng)建 application 類來運行應(yīng)用程序。這里應(yīng)該注意當(dāng)創(chuàng)建 session 對象時我們使用 Interceptor 類作為參數(shù)。
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();
}
}
}這里是編譯和運行上面提及的應(yīng)用程序的步驟。確保你已經(jīng)在處理編譯和執(zhí)行前正確設(shè)置了 PATH 和 CLASSPATH。
你將得到以下結(jié)果，而且記錄將在 EMPLOYEE 表單中被創(chuàng)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如果你檢查你的 EMPLOYEE 表單，它應(yīng)該有如下結(jié)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>
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