现在让我们举个例子来了解我们如何使用Hibernate在独立应用程序中提供Java持久性.我们将介绍使用Hibernate技术创建Java应用程序所涉及的不同步骤.
创建应用程序的第一步是构建Java POJO类或类，具体取决于将持久保存到数据库的应用程序.让我们考虑使用 getXXX 和 setXXX 方法的 Employee 类，使其符合JavaBeans类.
POJO(Plain Old Java Object)是一个Java对象，它不扩展或实现EJB框架分别需要的某些专用类和接口.所有普通的Java对象都是POJO.
当您设计一个由Hibernate持久化的类时，提供符合JavaBeans的代码以及一个属性非常重要，这些属性可以像
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) );
这一步是创建一个映射文件，指示Hibernate如何映射定义的类或类到数据库表.
<?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>
您应该将映射文档保存在格式为< classname> .hbm.xml的文件中.我们将映射文档保存在Employee.hbm.xml文件中.让我们看一下关于映射文档的一些细节 :
映射文档是一个XML文档，其中包含< hibernate-mapping> ;作为包含所有< class>的根元素元素.
< class> 元素用于定义从Java类到数据库表的特定映射.使用类元素的 name 属性指定Java类名，并使用表属性指定数据库表名.
< meta> 元素是可选元素，可用于创建类描述.
< id> 元素将类中的唯一ID属性映射到数据库表的主键. id元素的 name 属性引用类中的属性，列属性引用数据库表中的列. type 属性保存hibernate映射类型，此映射类型将从Java转换为SQL数据类型.
id元素中的< generator> 元素用于自动生成主键值.生成器元素的 class 属性设置为 native ，让hibernate选择标识，序列或 hilo 根据底层数据库的功能创建主键的算法.
< property> 元素用于映射a Java类属性到数据库表中的一列.元素的 name 属性引用类中的属性，列属性引用数据库表中的列. type 属性保存hibernate映射类型，此映射类型将从Java转换为SQL数据类型.
还有其他可用的属性和元素，这些属性和元素将用于映射文档中，我将尽可能多地讨论其他与Hibernate相关的主题.
最后，我们将使用main（）方法创建应用程序类来运行应用程序。 我们将使用此应用程序来保存很少的员工记录，然后我们将对这些记录应用CRUD操作。
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();
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();
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();
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();
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ManageEmployee.java源文件并进行编译.
执行ManageEmployee二进制文件以运行程序.
你会得到以下结果，并且会在EMPLOYEE表中创建记录.
$java ManageEmployee .......VARIOUS LOG MESSAGES WILL DISPLAY HERE........ First Name: Zara Last Name: Ali Salary: 1000 First Name: Daisy Last Name: Das Salary: 5000 First Name: John Last Name: Paul Salary: 10000 First Name: Zara Last Name: Ali Salary: 5000 First Name: John Last Name: Paul Salary: 10000
如果你检查你的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>
