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org.hibernate.cfg.Configuration是配置管理类对象。
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加载主配置文件的方法(hibernate.cfg.xml)，默认加载src/hibernate.cfg.xml。
config.configure(“cn/config/hibernate.cfg.xml”); 加载指定路径下指定名称的主配置文件
创建session的工厂对象
Configuration部分源码：
/** * An instance of Configuration allows the application * to specify properties and mapping documents to be used when * creating a SessionFactory. Usually an application will create * a single Configuration, build a single instance of * SessionFactory and then instantiate Sessions in * threads servicing client requests. The Configuration is meant * only as an initialization-time object. SessionFactorys are * immutable and do not retain any association back to the * Configuration.
*
* A new Configuration will use the properties specified in * hibernate.properties by default. * * @author Gavin King * @see org.hibernate.SessionFactory */ public class Configuration implements Serializable { /** * Use the mappings and properties specified in an application resource named hibernate.cfg.xml. * * @return this for method chaining * * @throws HibernateException Generally indicates we cannot find hibernate.cfg.xml * * @see #configure(String) */ public Configuration configure() throws HibernateException { configure( "/hibernate.cfg.xml" ); return this; } /** * Use the mappings and properties specified in the given application resource. The format of the resource is * defined in hibernate-configuration-3.0.dtd. * * The resource is found via {@link #getConfigurationInputStream} * * @param resource The resource to use * * @return this for method chaining * * @throws HibernateException Generally indicates we cannot find the named resource * * @see #doConfigure(java.io.InputStream, String) */ public Configuration configure(String resource) throws HibernateException { log.info( "configuring from resource: " + resource ); InputStream stream = getConfigurationInputStream( resource ); return doConfigure( stream, resource ); } /** * Create a {@link SessionFactory} using the properties and mappings in this configuration. The * {@link SessionFactory} will be immutable, so changes made to {@code this} {@link Configuration} after * building the {@link SessionFactory} will not affect it. * * @return The build {@link SessionFactory} * * @throws HibernateException usually indicates an invalid configuration or invalid mapping information */ public SessionFactory buildSessionFactory() throws HibernateException { log.debug( "Preparing to build session factory with filters : " + filterDefinitions ); secondPassCompile(); if ( ! metadataSourceQueue.isEmpty() ) { log.warn( "mapping metadata cache was not completely processed" ); } enableLegacyHibernateValidator(); enableBeanValidation(); enableHibernateSearch(); validate(); Environment.verifyProperties( properties ); Properties copy = new Properties(); copy.putAll( properties ); PropertiesHelper.resolvePlaceHolders( copy ); Settings settings = buildSettings( copy ); return new SessionFactoryImpl( this, mapping, settings, getInitializedEventListeners(), sessionFactoryObserver ); } }
org.hibernate.SessionFactory
session的工厂（或者说代表了这个hibernate.cfg.xml配置文件）
The main contract here is the creation of Session instances. Usually an application has a single SessionFactory instance and threads servicing client requests obtain Session instances from this factory.
SessionFactory是一个接口，它的主要职责就是创建Session实例。通常情况下，一个application只有一个单独的SessionFactory实例，不同的线程从这个SessionFactory当中获取Session的实例。
The internal state of a SessionFactory is immutable. Once it is created this internal state is set. This internal state includes all of the metadata about Object/Relational Mapping.
SessionFactory的内部状态是不变以，也就是说，一旦SessionFactory被创建，它的内部就不会再发生变化。
创建一个sesison对象
创建session或取出session对象
SessionFactory部分源码：
/**
* The main contract here is the creation of {@link Session} instances. Usually
* an application has a single {@link SessionFactory} instance and threads
* servicing client requests obtain {@link Session} instances from this factory.
*
* The internal state of a {@link SessionFactory} is immutable. Once it is created
* this internal state is set. This internal state includes all of the metadata
* about Object/Relational Mapping.
*
* Implementors must be threadsafe.
*
* @see org.hibernate.cfg.Configuration
*
* @author Gavin King
* @author Steve Ebersole
*/
public interface SessionFactory extends Referenceable, Serializable {
/**
* Open a {@link Session}.
*
* JDBC {@link Connection connection(s} will be obtained from the
* configured {@link org.hibernate.connection.ConnectionProvider} as needed
* to perform requested work.
*
* @return The created session.
*
* @throws HibernateException Indicates a peroblem opening the session; pretty rare here.
*/
public org.hibernate.classic.Session openSession() throws HibernateException;
/**
* Obtains the current session. The definition of what exactly "current"
* means controlled by the {@link org.hibernate.context.CurrentSessionContext} impl configured
* for use.
*
* Note that for backwards compatibility, if a {@link org.hibernate.context.CurrentSessionContext}
* is not configured but a JTA {@link org.hibernate.transaction.TransactionManagerLookup}
* is configured this will default to the {@link org.hibernate.context.JTASessionContext}
* impl.
*
* @return The current session.
*
* @throws HibernateException Indicates an issue locating a suitable current session.
*/
public org.hibernate.classic.Session getCurrentSession() throws HibernateException;
}注意：openSession()和getCurrentSession()的返回值是 org.hibernate.classic.Session类型。
org.hibernate.classic.Session定义如下：
org.hibernate.classic.Session定义如下：
/**
* An extension of the Session API, including all
* deprecated methods from Hibernate2. This interface is
* provided to allow easier migration of existing applications.
* New code should use org.hibernate.Session.
* @author Gavin King
*/
public interface Session extends org.hibernate.Session {
}org.hibernate.Session定义如下：
/** * The main runtime interface between a Java application and Hibernate. This is the * central API class abstracting the notion of a persistence service.
*
* The lifecycle of a Session is bounded by the beginning and end of a logical * transaction. (Long transactions might span several database transactions.)
*
* The main function of the Session is to offer create, read and delete operations * for instances of mapped entity classes. Instances may exist in one of three states:
*
* transient: never persistent, not associated with any Session
* persistent: associated with a unique Session
* detached: previously persistent, not associated with any Session
*
* Transient instances may be made persistent by calling save(), * persist() or saveOrUpdate(). Persistent instances may be made transient * by calling delete(). Any instance returned by a get() or * load() method is persistent. Detached instances may be made persistent * by calling update(), saveOrUpdate(), lock() or replicate(). * The state of a transient or detached instance may also be made persistent as a new * persistent instance by calling merge().
*
* save() and persist() result in an SQL INSERT, delete() * in an SQL DELETE and update() or merge() in an SQL UPDATE. * Changes to persistent instances are detected at flush time and also result in an SQL * UPDATE. saveOrUpdate() and replicate() result in either an * INSERT or an UPDATE.
*
* It is not intended that implementors be threadsafe. Instead each thread/transaction * should obtain its own instance from a SessionFactory.
*
* A Session instance is serializable if its persistent classes are serializable.
*
* A typical transaction should use the following idiom: ** Session sess = factory.openSession(); * Transaction tx; * try { * tx = sess.beginTransaction(); * //do some work * ... * tx.commit(); * } * catch (Exception e) { * if (tx!=null) tx.rollback(); * throw e; * } * finally { * sess.close(); * } **
* If the Session throws an exception, the transaction must be rolled back * and the session discarded. The internal state of the Session might not * be consistent with the database after the exception occurs. * * @see SessionFactory * @author Gavin King */ public interface Session extends Serializable { /** * Persist the given transient instance, first assigning a generated identifier. (Or * using the current value of the identifier property if the assigned * generator is used.) This operation cascades to associated instances if the * association is mapped with cascade="save-update". * * @param object a transient instance of a persistent class * @return the generated identifier * @throws HibernateException */ public Serializable save(Object object) throws HibernateException; /** * Update the persistent instance with the identifier of the given detached * instance. If there is a persistent instance with the same identifier, * an exception is thrown. This operation cascades to associated instances * if the association is mapped with cascade="save-update". * * @param object a detached instance containing updated state * @throws HibernateException */ public void update(Object object) throws HibernateException; /** * Either {@link #save(Object)} or {@link #update(Object)} the given * instance, depending upon resolution of the unsaved-value checks (see the * manual for discussion of unsaved-value checking). * * This operation cascades to associated instances if the association is mapped * with cascade="save-update". * * @see Session#save(java.lang.Object) * @see Session#update(Object object) * @param object a transient or detached instance containing new or updated state * @throws HibernateException */ public void saveOrUpdate(Object object) throws HibernateException; /** * Return the persistent instance of the given entity class with the given identifier, * or null if there is no such persistent instance. (If the instance is already associated * with the session, return that instance. This method never returns an uninitialized instance.) * * @param clazz a persistent class * @param id an identifier * @return a persistent instance or null * @throws HibernateException */ public Object get(Class clazz, Serializable id) throws HibernateException; /** * Return the persistent instance of the given entity class with the given identifier, * assuming that the instance exists. This method might return a proxied instance that * is initialized on-demand, when a non-identifier method is accessed. *
* You should not use this method to determine if an instance exists (use get() * instead). Use this only to retrieve an instance that you assume exists, where non-existence * would be an actual error. * * @param theClass a persistent class * @param id a valid identifier of an existing persistent instance of the class * @return the persistent instance or proxy * @throws HibernateException */ public Object load(Class theClass, Serializable id) throws HibernateException; }
org.hibernate.Session
session对象维护了一个连接(Connection), 代表了与数据库连接的会话。
Hibernate最重要的对象： 只用使用hibernate与数据库操作，都用到这个对象
beginTransaction()开启一个事务； hibernate要求所有的与数据库的操作必须有事务的环境，否则报错！
save(Object object) 保存一个对象
update(Object object) 更新一个对象
saveOrUpdate(Object object) 保存或者更新的方法：没有设置主键，执行保存；有设置主键，执行更新操作; 如果设置主键不存在报错！
示例代码：
package com.rk.hibernate.a_hello;
import java.util.Date;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.Test;
public class App2
{
private static SessionFactory sessionFactory;
static
{
/*
* //1. 创建配置管理类对象 Configuration config = new Configuration(); // 加载配置文件
* (默认加载src/hibernate.cfg.xml) config.configure(); //2.
* 根据加载的配置管理类对象，创建SessionFactory对象 sessionFactory =
* config.buildSessionFactory();
*/
// 创建SessionFactory对象
sessionFactory = new Configuration().configure().buildSessionFactory();
}
// 1. 保存对象
@Test
public void testSave()
{
// 对象
Employee emp = new Employee();
emp.setEmpName("张三");
emp.setWorkDate(new Date());
// 根据session的工厂，创建session对象
Session session = sessionFactory.openSession();
// 开启事务
Transaction transaction = session.beginTransaction();
// -----执行操作-----
session.save(emp);
// 提交事务
transaction.commit();
// 关闭
session.close();
System.out.println("执行结束！");
}
// 2. 更新对象
@Test
public void testUpdate()
{
// 对象
Employee emp = new Employee();
emp.setEmpId(20);
emp.setEmpName("小明");
// 创建session
Session session = sessionFactory.openSession();
// 开启事务
Transaction tx = session.beginTransaction();
// 更新。如果不提供id，则报错；如果提供的id不存在，也报错
session.update(emp);
// 提交事务
tx.commit();
// 关闭
session.close();
System.out.println("执行结束！");
}
// 3. 保存或更新对象
@Test
public void testSaveOrUpdate()
{
// 对象
Employee emp = new Employee();
emp.setEmpId(3);
emp.setEmpName("小红");
// 创建session
Session session = sessionFactory.openSession();
// 开启事务
Transaction tx = session.beginTransaction();
// -------执行操作-------
// 没有设置主键，执行保存。
//有设置主键，执行更新操作; 如果设置主键不存在，则报错！
session.saveOrUpdate(emp);
// 提交事务
tx.commit();
// 关闭
session.close();
System.out.println("执行结束！");
}
}get(Class clazz, Serializable id) 主键查询
load(Class theClass, Serializable id) 主键查询 (支持懒加载)
示例代码：
@Test
public void testQuery()
{
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
// get主键查询
Employee emp1 = (Employee) session.get(Employee.class, 2);
System.out.println(emp1);
// load主键查询
Employee emp2 = (Employee) session.load(Employee.class, 3);
System.out.println(emp2);
tx.commit();
session.close();
System.out.println("执行结束！");
}HQL查询与SQL查询区别：
SQL: (结构化查询语句)查询的是表(table)以及字段(column); 不区分大小写。
HQL: hibernate query language 即hibernate提供的面向对象的查询语言，查询的是对象以及对象的属性(property)，区分大小写。
示例代码：
// HQL查询 【适合有数据库基础的】
@Test
public void testHQL()
{
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
// HQL查询
Query q = session.createQuery("From Employee where empId=2 or empId=3");
List list = q.list();
System.out.println(list);
tx.commit();
session.close();
System.out.println("执行结束！");
} 完全面向对象的查询
示例代码：
//QBC查询 , query by criteria 完全面向对象的查询
@Test
public void testQBC()
{
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
Criteria criteria = session.createCriteria(Employee.class);
// 条件
criteria.add(Restrictions.eq("empId", 2));
List list = criteria.list();
System.out.println(list);
tx.commit();
session.close();
System.out.println("执行结束！");
} 复杂的查询，就要使用原生态的sql查询也可以，就是本地sql查询的支持！缺点： 不能跨数据库平台！
示例代码：
//SQL
@Test
public void testSQL()
{
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
// 把每一行记录封装为对象数组，再添加到list集合
//SQLQuery sqlQuery = session.createSQLQuery("select * from employee");
// 把每一行记录封装为 指定的对象类型
SQLQuery sqlQuery = session.createSQLQuery("select * from employee").addEntity(Employee.class);
List list = sqlQuery.list();
System.out.println(list);
tx.commit();
session.close();
System.out.println("执行结束！");
} 完整示例代码：
package com.rk.hibernate.a_hello;
import java.util.LinkedList;
import java.util.List;
import org.hibernate.Criteria;
import org.hibernate.Query;
import org.hibernate.SQLQuery;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.classic.Session;
import org.hibernate.criterion.Restrictions;
import org.junit.Test;
public class App3
{
private static SessionFactory sessionFactory;
static
{
// 创建SessionFactory对象
sessionFactory = new Configuration().configure().buildSessionFactory();
}
@Test
public void testQuery()
{
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
// get主键查询
Employee emp1 = (Employee) session.get(Employee.class, 2);
System.out.println(emp1);
// load主键查询
Employee emp2 = (Employee) session.load(Employee.class, 3);
System.out.println(emp2);
tx.commit();
session.close();
System.out.println("执行结束！");
}
// HQL查询 【适合有数据库基础的】
@Test
public void testHQL()
{
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
// HQL查询
Query q = session.createQuery("From Employee where empId=2 or empId=3");
List list = q.list();
System.out.println(list);
tx.commit();
session.close();
System.out.println("执行结束！");
}
//QBC查询 , query by criteria 完全面向对象的查询
@Test
public void testQBC()
{
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
Criteria criteria = session.createCriteria(Employee.class);
// 条件
criteria.add(Restrictions.eq("empId", 2));
List list = criteria.list();
System.out.println(list);
tx.commit();
session.close();
System.out.println("执行结束！");
}
//SQL
@Test
public void testSQL()
{
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
// 把每一行记录封装为对象数组，再添加到list集合
//SQLQuery sqlQuery = session.createSQLQuery("select * from employee");
// 把每一行记录封装为 指定的对象类型
SQLQuery sqlQuery = session.createSQLQuery("select * from employee").addEntity(Employee.class);
List list = sqlQuery.list();
System.out.println(list);
tx.commit();
session.close();
System.out.println("执行结束！");
}
} org.hibernate.Transaction是hibernate事务对象
A transaction is associated with a Session and is usually instantiated by a call to Session.beginTransaction().
transaction与Session相关联，通常由Session.beginTransaction()方法创建。
A single session might span multiple transactions since the notion of a session (a conversation between the application and the datastore) is of coarser granularity than the notion of a transaction. However, it is intended that there be at most one uncommitted Transaction associated with a particular Session at any time.
session可以理解为application和datastore之间一次conversation。在一个session产生多个transactions，但是在同一时间内，只只能有一个未提交的transaction。
package org.hibernate; import javax.transaction.Synchronization; /** * Allows the application to define units of work, while * maintaining abstraction from the underlying transaction * implementation (eg. JTA, JDBC).
*
* A transaction is associated with a Session and is * usually instantiated by a call to Session.beginTransaction(). * A single session might span multiple transactions since * the notion of a session (a conversation between the application * and the datastore) is of coarser granularity than the notion of * a transaction. However, it is intended that there be at most one * uncommitted Transaction associated with a particular * Session at any time.
*
* Implementors are not intended to be threadsafe. * * @see Session#beginTransaction() * @see org.hibernate.transaction.TransactionFactory * @author Anton van Straaten */ public interface Transaction { /** * Begin a new transaction. */ public void begin() throws HibernateException; /** * Flush the associated Session and end the unit of work (unless * we are in {@link FlushMode#MANUAL}. * * This method will commit the underlying transaction if and only * if the underlying transaction was initiated by this object. * * @throws HibernateException */ public void commit() throws HibernateException; /** * Force the underlying transaction to roll back. * * @throws HibernateException */ public void rollback() throws HibernateException; /** * Was this transaction rolled back or set to rollback only? * * This only accounts for actions initiated from this local transaction. * If, for example, the underlying transaction is forced to rollback via * some other means, this method still reports false because the rollback * was not initiated from here. * * @return boolean True if the transaction was rolled back via this * local transaction; false otherwise. * @throws HibernateException */ public boolean wasRolledBack() throws HibernateException; /** * Check if this transaction was successfully committed. * * This method could return false even after successful invocation * of {@link #commit}. As an example, JTA based strategies no-op on * {@link #commit} calls if they did not start the transaction; in that case, * they also report {@link #wasCommitted} as false. * * @return boolean True if the transaction was (unequivocally) committed * via this local transaction; false otherwise. * @throws HibernateException */ public boolean wasCommitted() throws HibernateException; /** * Is this transaction still active? * * Again, this only returns information in relation to the * local transaction, not the actual underlying transaction. * * @return boolean Treu if this local transaction is still active. */ public boolean isActive() throws HibernateException; /** * Register a user synchronization callback for this transaction. * * @param synchronization The Synchronization callback to register. * @throws HibernateException */ public void registerSynchronization(Synchronization synchronization) throws HibernateException; /** * Set the transaction timeout for any transaction started by * a subsequent call to begin() on this instance. * * @param seconds The number of seconds before a timeout. */ public void setTimeout(int seconds); }
（1）ClassNotFoundException…., 缺少jar文件！
（2）如果程序执行程序，hibernate也有生成sql语句，但数据没有结果影响。问题一般是事务忘记提交…….遇到问题，一定看错误提示!
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