(02)Hibernate核心API
1、Configuration
org.hibernate.cfg.Configuration是配置管理类对象。
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1.1、configure()
加载主配置文件的方法(hibernate.cfg.xml),默认加载src/hibernate.cfg.xml。
1.2、configure(String resource)
config.configure(“cn/config/hibernate.cfg.xml”); 加载指定路径下指定名称的主配置文件
1.3、buildSessionFactory()
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 ); } }
2、SessionFactory
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。
2.1、openSession()
创建一个sesison对象
2.2、getCurrentSession()
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; }
3、Session
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
3.1、事务
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!
3.2、保存和更新
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!"); } }
3.3、主键查询
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!"); }
3.4、HQL查询
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"); Listlist = q.list(); System.out.println(list); tx.commit(); session.close(); System.out.println("执行结束!"); }
3.5、Criteria查询
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)); Listlist = criteria.list(); System.out.println(list); tx.commit(); session.close(); System.out.println("执行结束!"); }
3.6、本地SQL查询
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); Listlist = 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"); Listlist = 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!"); } }
4、Transaction
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); }
5、共性问题
(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!
文章标题:(02)Hibernate核心API
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