hibernate 攔截器

hibernate 中的對象將被創建和保持。一旦對象被修改，它必須被保存到數據庫里。這個過程持續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用來進行一些所需要的任務的方法。這些方法是從會話到應用程序的回調函數，允許應用程序檢查或操作一個持續對象的屬性，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。

hibernate 攔截器給予了我們一個對象如何應用到應用程序和數據庫的總控制。

如何使用攔截器？

為了創建一個攔截器你可以直接實現 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。

創建攔截器

我們將在例子中繼承 emptyinterceptor，當 employee 對象被創建和更新時攔截器的方法將自動被調用。你可以根據你的需求實現更多的方法。

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");
   }
}

創建 pojo 類

現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;
   }
}

創建數據庫表

第二步將是在你的數據庫中創建表。一張表對應每個你提供持久性的對象。考慮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)
);

創建 mapping 配置文件

這個步驟是來創建一個指導 hibernate 如何將定義的類或者多個類映射到數據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>

創建 application 類

最后，我們將用 main() 創建 application 類來運行應用程序。這里應該注意當創建 session 對象時我們使用 interceptor 類作為參數。

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();
      }
   }
}

編譯和執行

這里是編譯和運行上面提及的應用程序的步驟。確保你已經在處理編譯和執行前正確設置了 path 和 classpath。

• 創建在 configuration 章節中解釋的 hibernate.cfg.xml 配置文件。
• 創建如上所示的 employee.hbm.xml 映射文件。
• 創建如上所示的 employee.java 源文件并編譯。
• 創建如上所示的 myinterceptor.java 源文件并編譯。
• 創建如上所示的 manageemployee.java 源文件并編譯。
• 執行 manageemployee 來運行程序。

你將得到以下結果，而且記錄將在 employee 表單中被創建。

$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，它應該有如下結果：

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>