學習hibernate筆記

標籤：hibernate   java   資料庫   singleton   

       以前學習java的時候，一開始就學習了hibernate，那時候總覺得ssh非常高大上，所以就急忙看了下相關視頻。不過因為實際需要不高，所以後來一直沒有使用上hibernate組件。現在一年過去了，也瘋狂學習了java一段時間了，做過幾個不大的項目，但是總算對java有些瞭解。現在參加了工作，公司使用的就是ssh，所以這兩天又重新開始搗鼓hibernate。這次學習直接使用editplus，直接開發。看了官網的demo，發現英語也沒有想象中那麼困難。哈哈，把自己的學習記錄下來吧。這裡主要記錄三個方面：

       1.如何搭建hibernate

       2.幾種常用映射關係（one - to -one，one - to - many, many - to - one, many - to - many）

搭建hibernate（直接使用文字編輯器）

第一步：這個過程也不複雜，主要是下載到hibernate相關jar包，然後將必要的jar引入到classpath中，具體什麼是classpath，大家可以百度下。如果不匯入到classpath中，會出現不能找到類的異常。為什麼會出現這種情況呢？大家可以百度下，java 的類載入過程。

第二步：編寫hibernate.cfg.xml檔案。這個大家不用手寫，直接去hibernate文章中copy一個即可。下面給出My Code

<?xml version='1.0' encoding='utf-8' ?><!DOCTYPE hibernate-configuration PUBLIC       "-//Hibernate/Hibernate Configuration DTD 3.0//EN"        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"><hibernate-configuration>      <session-factory>             <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>             <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/hibernate_demo</property>             <property name="hibernate.connection.username">root</property>             <property name="hibernate.connection.password">root</property>             <property name="dialect">org.hibernate.dialect.MySQLDialect</property>             <property name="hibernate.show_sql">true</property>     <!--if the value='create, means create table, every time open hibernate, if will drop the old scheme'-->   <property name="hbm2ddl.auto">update</property>    <mapping resource="User.xml"/>    <mapping resource="Address.xml"/>        </session-factory></hibernate-configuration>

第三步：開始製作一個工具類，用來初始化hibernate組件。由於難度不高，直接給出代碼，這些在文章中都已經有了，大家可以自己下載document看看。下面是代碼：

import java.io.*;import org.hibernate.*;import org.hibernate.cfg.*;/** * that is a hibernate config util * */public class HibernateConfigurationUtil{    private static HibernateConfigurationUtil singleton = new HibernateConfigurationUtil("hibernate.cfg.xml");    private static SessionFactory factory;/** * singleton pattern * */private HibernateConfigurationUtil(String configXml){    init(configXml);}    public void init(String configXml){     Configuration cfg = new Configuration().configure(new File("hibernate.cfg.xml")); factory = cfg.buildSessionFactory();   // build the session factory}    public static SessionFactory getSessionFactory(){    if(factory == null) return null;return factory;}    /** * open a new Session * * */public static Session openSession(){    Session session = factory.openSession();return session;}}

注意下，這個類使用單例設計模式，因為hibernate組建在啟動Configuration時，是非常耗時的，而且這個對象在啟動之後不能改變，所以每個工程中，啟動一次即可。

第三步：編寫BaseHibernateDao，這個類注意是封裝了save, delete, update, load這四個方法。

import java.io.*;import org.hibernate.*;import org.hibernate.cfg.*;/** * that is the base hibernate dao, * it define a series of method to access database * if you want to 'delete, update a object, the object must exists in hibernate memery' * * @author luohong * @date 2014-08-07  * */public class BaseHibernateDao{public BaseHibernateDao(){}    /** * try to save a object * */public void save(Object object){    Session session = HibernateConfigurationUtil.openSession();// open transactionTransaction transaction = session.beginTransaction();session.save(object);// commint transactiontransaction.commit();}/** * try to update a object * */public void update(Object object){    Session session = HibernateConfigurationUtil.openSession();// open transactionTransaction transaction = session.beginTransaction();session.update(object);// commint transactiontransaction.commit();}        /** * try to delete a object * */public void delete(Object object){    Session session = HibernateConfigurationUtil.openSession();// open transactionTransaction transaction = session.beginTransaction();session.delete(object);// commint transactiontransaction.commit();}    /** * try to load a object from database by className and id * */public Object load(Class<?> className, Serializable id){Session session = HibernateConfigurationUtil.openSession();        // there is no need for transactionreturn session.load(className, id);}}

注意：在save, update, delete方法中，只用了Transaction，要開啟事務，否則資料庫找不到相關記錄。

第四步：到了這裡之後，就非常簡單了，只需要針對具體的類，擴充BaseHibernateDao即可。下面給出一個一對多的例子。類比情景：使用者（User）擁有多個住址（Address）首先給出兩個類：

import java.util.*;public class User{private int id;private String password;private String name;    private Set<Address> addressSet;public void setAddressSet(Set<Address> addressSet){    this.addressSet = addressSet;}public Set<Address> getAddressSet(){    return addressSet;}public void setName(String name){    this.name = name;}public String getName(){    return name;}public void setId(int id){    this.id = id;}public int getId(){    return id;}public void setPassword(String password){    this.password = password;}public String getPassword(){    return password;}public String toString(){    return "id = " + id + ", name = " + name + ", password = " + password + ", addressSet = " + addressSet;}}

/** * that is the user address * a user have many address, but a adress belong to a user * It is the classical 1 * n relationship * @author luohong * @date 2014-08-07 * */ public class Address {//=====================properties============================= private int id; //private User belongTo; private String code; private String city; private String street; private String homeNumber;//===================setter and getter======================== public void setId(int id){     this.id = id; } public int getId(){     return id; }/* public void setBelongTo(User user){     this.belongTo = belongTo; } public User getBelongTo(){     return belongTo; }*/ public void setCode(String code){     this.code = code; } public String getCode(){     return code; } public void setCity(String city){     this.city = city; } public String getCity(){     return city; } public void setHomeNumber(String homeNumber){     this.homeNumber = homeNumber; } public String getHomeNumber(){ return homeNumber; } public String getStreet(){     return street; } public void setStreet(String street){         this.street = street; }//========================toString================================ public String toString(){     return "id = " + id + ", city = " + city + ", street = " + street + ", homeNumber = " + homeNumber  + ", code = " + code;// + ", belongTo = " + belongTo; }       }

給出相關的User.xml, Address.xml；這個例子使用的是單向一對多。

<?xml version="1.0"?>  <!DOCTYPE hibernate-mapping PUBLIC          "-//Hibernate/Hibernate Mapping DTD 3.0//EN"          "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">  <hibernate-mapping><class name="User" table="user"><id name="id"><generator class="increment"/></id> <property name="password"/><property name="name"/><!--one to many--><set name="addressSet" cascade="all">    <!--define the foreight column name-->    <key column="user_id"/><!--define the foreight table name--><one-to-many class="Address"/> </set></class></hibernate-mapping>  

<?xml version="1.0"?>  <!DOCTYPE hibernate-mapping PUBLIC          "-//Hibernate/Hibernate Mapping DTD 3.0//EN"          "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">  <hibernate-mapping><class name="Address" table="address"><id name="id"><generator class="increment"/></id><property name="code"/><property name="city"/><property name="street"/><property name="homeNumber"/></class></hibernate-mapping>  

然後編寫一個UserDao，繼承BaseHibernateDao，也很簡單，哈哈，一看就懂，這就是hibernate的厲害之處。

import java.util.*;import org.hibernate.*;/** * user dao extends BaseHibernateDao * you can add new functions to the custom dao *  *  * @author luohong * @date 2014-08-07 * */public class UserDao extends BaseHibernateDao{    /** * delete a user by userId * * */public void deleteById(String id){if (id == null) return;  // do nothingString hql = "delete User where id=?";// 1 open session    Session session = HibernateConfigurationUtil.openSession(); // 2 create a queryQuery query = session.createQuery(hql);// 3 set the parameter to queryquery.setString(1, id);// 4 execute queryquery.executeUpdate();}    /** * find all user from database * */public List<User> findAllUsers(){    String hql = "from User";Session session = HibernateConfigurationUtil.openSession();Query query = session.createQuery(hql);List userList = query.list();return (List<User>)userList;}}

剩下的就是測試啦，come on...

import java.io.*;import java.util.*;/** * hibernate orm 架構demo * @author luohong * @date 2014-08-06  *  * */public class HibernateDemo{public static void main(String[] args) throws Exception{    UserDao userDao = new UserDao();        User user = new User();user.setName("luohong");user.setPassword("luohong");        Set<Address> addressSet = new HashSet<Address>();for(int i=0; i<3; i++){Address address = new Address();address.setCode("111");address.setCity("hongkang");address.setStreet("universal street");address.setHomeNumber("a-2846");//address.setBelongTo(user);addressSet.add(address);}user.setAddressSet(addressSet);userDao.save(user);}}