冬眠溫暖,"冬天"快樂(lè),一夜的冬雨在靜靜中把冬衣輕輕換上,Hibernate,就東面一樣,在程序"冬天"里給我們帶來(lái)一絲溫暖,Hibernate的名字真的很優(yōu)美,當(dāng)我曾經(jīng)第一天知道有一種技術(shù)叫"冬眠".我就深深的喜歡上了這種技術(shù).所以產(chǎn)生了一種想法,把這種技術(shù)以最簡(jiǎn)單明了的方式記錄自己的Blog上,一方面能幫助一些剛剛學(xué)習(xí)它的朋友,另一方面也能讓自己對(duì)Hibernate的理解更加深刻.希望大家多多支持我,多光臨我的Blog.好了下面言歸正傳,Hibernate是JAVA應(yīng)用和關(guān)系型數(shù)據(jù)庫(kù)中間的一座橋梁.它負(fù)責(zé)把JAVA對(duì)象和關(guān)系型數(shù)據(jù)庫(kù)映射在一起,其實(shí)簡(jiǎn)單的理解Hibernate可以理解成一種中間件,向下封裝了JDBC對(duì)數(shù)據(jù)庫(kù)的操作,向上提供了面向?qū)ο蟮臄?shù)據(jù)庫(kù)訪問(wèn)API.今天我們不談理論,往往學(xué)習(xí)一種技術(shù)進(jìn)來(lái)就談一些很深的理論會(huì)讓人學(xué)的暈頭轉(zhuǎn)向,我的學(xué)習(xí)方式向來(lái)都是先搞定一個(gè)簡(jiǎn)單明了的小例子,然后在回頭看理論,到時(shí)候總能有事半功倍的感覺(jué).簡(jiǎn)單的說(shuō)一下Hibernate的流程:
      1)創(chuàng)建Hibernate配置文件
      2)創(chuàng)建持久化類
      3)創(chuàng)建對(duì)象和關(guān)系型數(shù)據(jù)庫(kù)的映射文件
      4)通過(guò)Hibernate的API訪問(wèn)數(shù)據(jù)庫(kù)

      好了.既然流程知道了.我們就一步一步來(lái)做吧,首先創(chuàng)建一個(gè)JAVA工程(JAVA工程和WEB工程相比,更加簡(jiǎn)單直觀),然后我們引入必須要有的包,hibernate2包,log4j的包,dom4j的包,MSSQL的3個(gè)驅(qū)動(dòng)包,然后創(chuàng)建Hibernate的配置文件,和其他的properties一樣,都是以鍵=值的形式表示的.當(dāng)然你也可以選擇用XML的形式來(lái)創(chuàng)建hibernate的配置文件,這里用properties方式做演示,名字叫hibernate.properties.為了理解起來(lái)容易些,我們使用最簡(jiǎn)單的數(shù)據(jù)庫(kù)MS SQL Server 2000:

首先要設(shè)置方言,方言的意思就是不同的數(shù)據(jù)庫(kù),有不同的語(yǔ)言規(guī)范,就跟我們現(xiàn)實(shí)中的北京話于廣東話的差距一樣.
hibernate.dialect=net.sf.hibernate.dialect.SQLServerDialect
然后設(shè)置數(shù)據(jù)庫(kù)的驅(qū)動(dòng)類.
hibernate.connection.driver_class=com.microsoft.jdbc.sqlserver.SQLServerDriver
設(shè)置數(shù)據(jù)庫(kù)的路徑
hibernate.connection.url=jdbc:sqlserver://127.0.0.1:1433;charset=GBK;selectMethod=cursor;databaseName=TEMPDB
數(shù)據(jù)庫(kù)登錄名
hibernate.connection.username=sa
數(shù)據(jù)庫(kù)密碼
hibernate.connection.password=555
最后設(shè)置的屬性是是否在控制臺(tái)打印SQL語(yǔ)句,這里我們?cè)O(shè)置為true,因?yàn)榉奖阏{(diào)試,默認(rèn)是false
hibernate.show_sql=true
備注:在Hibernate軟件包的etc目錄下,有一個(gè)hibernate.properties文件,里邊有各種關(guān)系型數(shù)據(jù)庫(kù)的配置樣例.

      OK,配置文件創(chuàng)建完了.就是這么簡(jiǎn)單,現(xiàn)在我們來(lái)創(chuàng)建一個(gè)持久化類.其實(shí)說(shuō)白了持久化類超級(jí)簡(jiǎn)單,就是我們?cè)?jīng)用的JAVABEAN嘛,寫(xiě)幾個(gè)字段Eclipse都能自動(dòng)生成相關(guān)的方法,不過(guò)Hibernate的持久化類要 implements一個(gè)接口,就是Sreializable接口.下面是持久化類的例子,這里省略了大多數(shù)的get,set方法,到時(shí)候自己加上就OK了.
public class Customer implements Serializable {
  private Long id;
  private String name;
  private String email;
  private String password;
  private int phone;
  public Long getId(){
    return id;
  }
  public void setId(Long id){
    this.id = id;
  }
  ........
}

      OK持久化類也一樣簡(jiǎn)單,下面我們要做的事情更簡(jiǎn)單,就是到我們的數(shù)據(jù)庫(kù)中,創(chuàng)建一個(gè)和持久化類字段對(duì)應(yīng)的表.例子如下:
create database TEMPDB;

create table CUSTOMERS (
  ID bigint not null primary key,
  NAME varchar(15) not null,
  EMAIL varchar(128) not null,
  PASSWORD varchar(8) not null, 
  PHONE  int
)

      數(shù)據(jù)庫(kù)搞定了.下面來(lái)完成一件比較重要的事情,就是創(chuàng)建對(duì)象-關(guān)系映射文件.,Hibernate采用XML格式的文件來(lái)指定對(duì)象和關(guān)系型數(shù)據(jù)庫(kù)之間的映射,在運(yùn)行的時(shí)候Hibernate將根據(jù)這個(gè)映射文件來(lái)生成各種SQL語(yǔ)句.下面我們創(chuàng)建一個(gè)Customer.hbm.xml的文件,這個(gè)文件和Customer.class放在同一個(gè)目錄下.
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 2.0//EN"
"<hibernate-mapping>
  <class name="com.Customer" table="CUSTOMERS">
    <id name="id" column="ID" type="long">
      <generator class="increment"/>
    </id>
    <property name="name"  column="NAME"  type="string" not-null="true" /> 
    <property name="email"     column="EMAIL"     type="string" not-null="true" />
    <property name="password"  column="PASSWORD"  type="string" not-null="true"/>
    <property name="phone"     column="PHONE"     type="int" /> 
  </class>
</hibernate-mapping>

      首先<class 標(biāo)簽的name屬性指定的是類名,table屬性指定的和這個(gè)類映射的表名.<id 標(biāo)簽的<generator 子標(biāo)簽指定對(duì)象標(biāo)識(shí)符生成器,他負(fù)責(zé)在對(duì)象里產(chǎn)生表的唯一標(biāo)識(shí)符.<property標(biāo)簽的name屬性指定持久化類中屬性的名字,clumn屬性顧名思義,列的意思,這里是指定了數(shù)據(jù)庫(kù)中的字段.type屬性指定Hibernate的映射類型,Hibernate映射類型是JAVA類型和SQL類型之間的橋梁,先簡(jiǎn)單的知道JAVA里的String和數(shù)據(jù)庫(kù)里的varchar這里配置為string,而JAVA里的int和數(shù)據(jù)庫(kù)里的int配置為int.還有N多我們以后深入使用Hibernate的時(shí)候在深入的了解就OK了.現(xiàn)在知道簡(jiǎn)單的足以.最后說(shuō)一下<property標(biāo)簽的not-null屬性是設(shè)置這個(gè)字段是否為空.值得我們關(guān)注的是,在實(shí)際的項(xiàng)目開(kāi)發(fā)中,我們不應(yīng)該以來(lái)Hibernate或者數(shù)據(jù)庫(kù)來(lái)做數(shù)據(jù)的驗(yàn)證.全部在業(yè)務(wù)羅基層處理好就OK了.下面說(shuō)一下Hibernate采用XML文件來(lái)配置對(duì)象-關(guān)系映射的優(yōu)點(diǎn):
   1)Hibernate既不會(huì)滲透到上層的業(yè)務(wù)模型中,也不會(huì)泄漏到下層的數(shù)據(jù)模型中
   2)軟件開(kāi)發(fā)人員可以獨(dú)立設(shè)計(jì)業(yè)務(wù)模型,數(shù)據(jù)庫(kù)設(shè)計(jì)人員可以獨(dú)立設(shè)計(jì)數(shù)據(jù)模型,互相不受拘束.
   2)對(duì)象-關(guān)系映射不依賴于任何代碼,提高了程序的靈活性,使得維護(hù)更加方便.

      這里說(shuō)一下映射文件的類型定義DTD,在我們的Customer.hbm.xml中,文件開(kāi)頭就聲明了DTD類型,DTD的意思就是對(duì)XML文件的語(yǔ)法做定義,在實(shí)際編程中,我們引入正確的DTD規(guī)范,讓我們編寫(xiě)XML非常方便.每一種XML文件都有獨(dú)自的DTD文件.Hibernate的DTD文件下載地址是:http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd,在Hibernate的軟件包src\net\sf\hibernate目錄下也提供了hibernate-mapping-2.0.dtd文件.

      下面看一個(gè)重點(diǎn)吧,通過(guò)Hibernate的API操作數(shù)據(jù)庫(kù):
public class BusinessService{
  public static SessionFactory sessionFactory;
  static{
    try{
      // Create a configuration based on the properties file we've put
      // in the standard place.
      Configuration config = new Configuration();
      config.addClass(Customer.class);
      // Get the session factory we can use for persistence
      sessionFactory = config.buildSessionFactory();
    }catch(Exception e){e.printStackTrace();}
  }

  public void findAllCustomers(ServletContext context,OutputStream out) throws Exception{
    // Ask for a session using the JDBC information we've configured
    Session session = sessionFactory.openSession();
    Transaction tx = null;
    try {
      tx = session.beginTransaction();
      List customers=session.find("from Customer as c order by c.name asc");
      for (Iterator it = customers.iterator(); it.hasNext();) {
         printCustomer(context,out,(Customer) it.next());
      }

      // We're done; make our changes permanent
      tx.commit();

    }catch (Exception e) {
      if (tx != null) {
        // Something went wrong; discard all partial changes
        tx.rollback();
      }
      throw e;
    } finally {
      // No matter what, close the session
      session.close();
    }
  }
  public void saveCustomer(Customer customer) throws Exception{
     // Ask for a session using the JDBC information we've configured
    Session session = sessionFactory.openSession();
    Transaction tx = null;
    try {
      tx = session.beginTransaction();
      session.save(customer);
      // We're done; make our changes permanent
      tx.commit();

    }catch (Exception e) {
      if (tx != null) {
        // Something went wrong; discard all partial changes
        tx.rollback();
      }
      throw e;
    } finally {
      // No matter what, close the session
      session.close();
    }
  }

  public void loadAndUpdateCustomer(Long customer_id,String address) throws Exception{
    // Ask for a session using the JDBC information we've configured
    Session session = sessionFactory.openSession();
    Transaction tx = null;
    try {
      tx = session.beginTransaction();

      Customer c=(Customer)session.load(Customer.class,customer_id);
      c.setAddress(address);
      // We're done; make our changes permanent
      tx.commit();

    }catch (Exception e) {
      if (tx != null) {
        // Something went wrong; discard all partial changes
        tx.rollback();
      }
      throw e;
    } finally {
      // No matter what, close the session
      session.close();
    }
  }
  public void deleteAllCustomers() throws Exception{
    // Ask for a session using the JDBC information we've configured
    Session session = sessionFactory.openSession();
    Transaction tx = null;
    try {
      tx = session.beginTransaction();
      session.delete("from Customer as c");
      // We're done; make our changes permanent
      tx.commit();

    }catch (Exception e) {
      if (tx != null) {
        // Something went wrong; discard all partial changes
        tx.rollback();
      }
      throw e;
    } finally {
      // No matter what, close the session
      session.close();
    }
  }

  private void printCustomer(ServletContext context,OutputStream out,Customer customer)throws Exception{
   if(out instanceof ServletOutputStream)
           printCustomer(context,(ServletOutputStream) out,customer);
       else
          printCustomer((PrintStream) out,customer);
  }
  private void printCustomer(PrintStream out,Customer customer)throws Exception{
   //save photo
    byte[] buffer=customer.getImage();
    FileOutputStream fout=new FileOutputStream("photo_copy.gif");
    fout.write(buffer);
    fout.close();

    out.println("------以下是"+customer.getName()+"的個(gè)人信息------");
    out.println("ID: "+customer.getId());
    out.println("口令: "+customer.getPassword());
    out.println("E-Mail: "+customer.getEmail());
    out.println("電話: "+customer.getPhone());

  }
  private void printCustomer(ServletContext context,ServletOutputStream out,Customer customer)throws Exception{
    //save photo
    byte[] buffer=customer.getImage();
    String path=context.getRealPath("/");
    FileOutputStream fout=new FileOutputStream(path+"photo_copy.gif");
    fout.write(buffer);
    fout.close();

    out.println("------以下是"+customer.getName()+"的個(gè)人信息------"+"<br>");
    out.println("ID: "+customer.getId()+"<br>");
    out.println("口令: "+customer.getPassword()+"<br>");
    out.println("E-Mail: "+customer.getEmail()+"<br>");
    out.println("電話: "+customer.getPhone()+"<br>");
  }
   public void test(ServletContext context,OutputStream out) throws Exception{

    Customer customer=new Customer();
    customer.setName("我心依舊");
    customer.setEmail("it5719@163.com");
    customer.setPassword("666");
    customer.setPhone(5555555);
 
    saveCustomer(customer);

    findAllCustomers(context,out);
    loadAndUpdateCustomer(customer.getId(),"Beijing");
    findAllCustomers(context,out);

    deleteAllCustomers();
  }

  public static void main(String args[]) throws Exception {
    new BusinessService().test(null,System.out);
    sessionFactory.close();
  }

}

      OK最后一步我們還需要配置LOG4J的屬性文件.下面是LOG4J的配置文件,如果想了解LOG4J,請(qǐng)看我的前一篇隨筆,有簡(jiǎn)單明了的介紹.然后調(diào)試過(guò)這個(gè)程序看看結(jié)果.如果通過(guò)了,恭喜你,你已經(jīng)進(jìn)入了"冬天"正式開(kāi)始了Hibernae.
#init log4j level console file
log4j.rootLogger=ERROR,console,file

#create log4j console
log4j.appender.console=org.apache.log4j.ConsoleAppender
log4j.appender.console.layout=org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=%-5p %d [%t] (%F,%L) - %m%n

#create log4j file
log4j.appender.file=org.apache.log4j.RollingFileAppender
log4j.appender.file.File=debug.log
log4j.appender.file.MaxFileSize=100KB
log4j.appender.file.MaxBackupIndex=1
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%-5p %d [%t] (%F,%L) - %m%n