Hibernate提供了另外的操作对象的方法，并提供了RDBMS表中可用的数据.其中一种方法是Criteria API，它允许您以编程方式构建条件查询对象，您可以在其中应用过滤规则和逻辑条件.
Hibernate 会话 interface提供 createCriteria()方法，该方法可用于创建 Criteria 对象，该对象在应用程序执行条件查询时返回持久对象类的实例.
以下是条件查询的最简单示例之一，它将简单地返回与Employee类对应的每个对象.
Criteria cr = session.createCriteria(Employee.class); List results = cr.list();
您可以使用 add()方法为 Criteria 对象添加条件查询的限制.以下是添加限制以返回记录的示例，其中薪水等于2000 :
Criteria cr = session.createCriteria(Employee.class);
cr.add(Restrictions.eq("salary", 2000));
List results = cr.list();下面是几个涵盖不同场景的例子，可以根据要求使用 :
Criteria cr = session.createCriteria(Employee.class);
// To get records having salary more than 2000
cr.add(Restrictions.gt("salary", 2000));
// To get records having salary less than 2000
cr.add(Restrictions.lt("salary", 2000));
// To get records having fistName starting with zara
cr.add(Restrictions.like("firstName", "zara%"));
// Case sensitive form of the above restriction.
cr.add(Restrictions.ilike("firstName", "zara%"));
// To get records having salary in between 1000 and 2000
cr.add(Restrictions.between("salary", 1000, 2000));
// To check if the given property is null
cr.add(Restrictions.isNull("salary"));
// To check if the given property is not null
cr.add(Restrictions.isNotNull("salary"));
// To check if the given property is empty
cr.add(Restrictions.isEmpty("salary"));
// To check if the given property is not empty
cr.add(Restrictions.isNotEmpty("salary"));您可以使用LogicalExpression限制创建AND或OR条件，如下所示 :
Criteria cr = session.createCriteria(Employee.class);
Criterion salary = Restrictions.gt("salary", 2000);
Criterion name = Restrictions.ilike("firstNname","zara%");
// To get records matching with OR conditions
LogicalExpression orExp = Restrictions.or(salary, name);
cr.add( orExp );
// To get records matching with AND conditions
LogicalExpression andExp = Restrictions.and(salary, name);
cr.add( andExp );
List results = cr.list();尽管上述所有条件都可以直接用于HQL，如上一个教程中所述.
分页的Criteria接口有两种方法.
| Sr.No. | 方法&描述 |
|---|---|
| 1 | public Criteria setFirstResult(int firstResult) 此方法采用一个整数，表示结果集中的第一行，从第0行开始. |
| 2 | public Criteria setMaxResults(int maxResults) 此方法告诉Hibernate检索固定数量 maxResults 的对象./p> |
将上述两种方法结合使用，我们可以在网络中构建一个分页组件或者Swing应用程序.下面是一个示例，您可以扩展为一次获取10行 :
Criteria cr = session.createCriteria(Employee.class); cr.setFirstResult(1); cr.setMaxResults(10); List results = cr.list();
Criteria API提供 org.hibernate.criterion.Order class，根据对象的某个属性，按升序或降序对结果集进行排序.此示例演示了如何使用Order类对结果集进行排序 :
Criteria cr = session.createCriteria(Employee.class);
// To get records having salary more than 2000
cr.add(Restrictions.gt("salary", 2000));
// To sort records in descening order
cr.addOrder(Order.desc("salary"));
// To sort records in ascending order
cr.addOrder(Order.asc("salary"));
List results = cr.list();Criteria API提供 org.hibernate.criterion.Projections 类，可用于获取属性值的平均值，最大值或最小值. Projections类类似于Restrictions类，因为它提供了几种静态工厂方法来获取 Projection 实例.
以下是几个涵盖不同场景和可以根据要求使用 :
Criteria cr = session.createCriteria(Employee.class);
// To get total row count.
cr.setProjection(Projections.rowCount());
// To get average of a property.
cr.setProjection(Projections.avg("salary"));
// To get distinct count of a property.
cr.setProjection(Projections.countDistinct("firstName"));
// To get maximum of a property.
cr.setProjection(Projections.max("salary"));
// To get minimum of a property.
cr.setProjection(Projections.min("salary"));
// To get sum of a property.
cr.setProjection(Projections.sum("salary"));考虑以下POJO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;
}
}让我们创建以下EMPLOYEE表来存储Employee对象 :
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) );
以下是映射文件.
<?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，我们将使用main()方法创建我们的应用程序类来运行应用程序，我们将使用 Criteria 查询和减去;
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.Criteria;
import org.hibernate.criterion.Restrictions;
import org.hibernate.criterion.Projections;
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", 2000);
Integer empID2 = ME.addEmployee("Daisy", "Das", 5000);
Integer empID3 = ME.addEmployee("John", "Paul", 5000);
Integer empID4 = ME.addEmployee("Mohd", "Yasee", 3000);
/* List down all the employees */
ME.listEmployees();
/* Print Total employee's count */
ME.countEmployee();
/* Print Total salary */
ME.totalSalary();
}
/* 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 having salary more than 2000 */
public void listEmployees( ) {
Session session = factory.openSession();
Transaction tx = null;
try {
tx = session.beginTransaction();
Criteria cr = session.createCriteria(Employee.class);
// Add restriction.
cr.add(Restrictions.gt("salary", 2000));
List employees = cr.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 print total number of records */
public void countEmployee(){
Session session = factory.openSession();
Transaction tx = null;
try {
tx = session.beginTransaction();
Criteria cr = session.createCriteria(Employee.class);
// To get total row count.
cr.setProjection(Projections.rowCount());
List rowCount = cr.list();
System.out.println("Total Coint: " + rowCount.get(0) );
tx.commit();
} catch (HibernateException e) {
if (tx!=null) tx.rollback();
e.printStackTrace();
} finally {
session.close();
}
}
/* Method to print sum of salaries */
public void totalSalary(){
Session session = factory.openSession();
Transaction tx = null;
try {
tx = session.beginTransaction();
Criteria cr = session.createCriteria(Employee.class);
// To get total salary.
cr.setProjection(Projections.sum("salary"));
List totalSalary = cr.list();
System.out.println("Total Salary: " + totalSalary.get(0) );
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: Daisy Last Name: Das Salary: 5000 First Name: John Last Name: Paul Salary: 5000 First Name: Mohd Last Name: Yasee Salary: 3000 Total Coint: 4 Total Salary: 15000
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 | +----+------------+-----------+--------+ | 14 | Zara | Ali | 2000 | | 15 | Daisy | Das | 5000 | | 16 | John | Paul | 5000 | | 17 | Mohd | Yasee | 3000 | +----+------------+-----------+--------+ 4 rows in set (0.00 sec) mysql>
