hibernate 拦截器

hibernate 中的对象将被创建和保持。一旦对象被修改，它必须被保存到数据库里。这个过程持续直到下一次对象被需要，它将被从持久的存储中加载。

因此一个对象通过它生命周期中的不同阶段，并且 interceptor 接口提供了在不同阶段能被调用来进行一些所需要的任务的方法。这些方法是从会话到应用程序的回调函数，允许应用程序检查或操作一个持续对象的属性，在它被保存，更新，删除或上传之前。以下是在 interceptor 接口中可用的所有方法的列表。

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。

如何使用拦截器？

为了创建一个拦截器你可以直接实现 interceptor 类或者继承 emptyinterceptor 类。以下是简单的使用 hibernate 拦截器功能的步骤。

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 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>