《精通Hibernate》学习(1)——第一个Hibernate应用
一、在Java应用中使用Hibernate的步骤
- 创建Hibernate的配置文件
- 创建持久化类
- 创建对象-关系映射文件
- 通过Hibernate API编写访问数据库的代码
二、Helloapp应用的结构
三、Hibernate的配置文件(hibernate.properties)
hibernate.dialect=org.hibernate.dialect.MySQLDialect hibernate.connection.driver_class=com.mysql.jdbc.Driver hibernate.connection.url=jdbc:mysql://localhost:3306/SAMPLEDB hibernate.connection.username=root hibernate.connection.password=1234 hibernate.show_sql=true
四、创建持久化类Customer
- 持久化类符合JavaBean的规范，包含一些属性，以及与之对应的getXXX()和setXXX()方法。
- 持久化类有一个id属性，用来惟一标识Customer类的每个对象。在面向对象术语中，这个id属性被称为对象标识符（OID，Object Identifier），通常它都用整数表示
- Hibernate要求持久化类必须提供一个不带参数的默认构造方法
package mypack;
import java.io.Serializable;
import java.sql.Date;
import java.sql.Timestamp;
public class Customer implements Serializable {
private Long id;
private String name;
private String email;
private String password;
private int phone;
private String address;
private char sex;
private boolean married;
private String description;
private byte[] image;
private Date birthday;
private Timestamp registeredTime;
public Customer(){}
public Long getId(){
return id;
}
private void setId(Long id){
this.id = id;
}
public String getName(){
return name;
}
public void setName(String name){
this.name=name;
}
public String getEmail(){
return email;
}
public void setEmail(String email){
this.email =email ;
}
public String getPassword(){
return password;
}
public void setPassword(String password){
this.password =password ;
}
public int getPhone(){
return phone;
}
public void setPhone(int phone){
this.phone =phone ;
}
public String getAddress(){
return address;
}
public void setAddress(String address){
this.address =address ;
}
public char getSex(){
return sex;
}
public void setSex(char sex){
this.sex =sex ;
}
public boolean isMarried(){
return married;
}
public void setMarried(boolean married){
this.married =married ;
}
public String getDescription(){
return description;
}
public void setDescription(String description){
this.description =description ;
}
public byte[] getImage() {
return this.image;
}
public void setImage(byte[] image) {
this.image = image;
}
public Date getBirthday() {
return this.birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
public Timestamp getRegisteredTime() {
return this.registeredTime;
}
public void setRegisteredTime(Timestamp registeredTime) {
this.registeredTime = registeredTime;
}
}
注意：
- getXXX()和setXXX()方法可以采用任意的访问级别，他的命名规则必须符合特定的命名规则，“get”和“set”后面紧跟属性的名字，并且属性名的首字母为大写，如name属性的get方法为getName()。
- 如果持久化类的属性为boolean类型，那么它的get方法名可以用get做前缀也可以用is做前缀。
五、创建数据库Schema
drop database if exists SAMPLEDB; create database SAMPLEDB; use SAMPLEDB; 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 , ADDRESS varchar(255), SEX char(1) , IS_MARRIED bit, DESCRIPTION text, IMAGE blob, BIRTHDAY date, REGISTERED_TIME timestamp );
六、创建对象-关系映射文件Customer.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC"-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="mypack.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" />
<property name="address" column="ADDRESS" type="string" />
<property name="sex" column="SEX" type="character"/>
<property name="married" column="IS_MARRIED" type="boolean"/>
<property name="description" column="DESCRIPTION" type="text"/>
<property name="image" column="IMAGE" type="binary"/>
<property name="birthday" column="BIRTHDAY" type="date"/>
<property name="registeredTime" column="REGISTERED_TIME" type="timestamp"/>
</class>
</hibernate-mapping>
- <id>元素映射OID
<generator>子元素用来设定标识符生成器。Hibernate提供了提供了多种内置的实现。
- <property>元素映射值类型属性
name属性：指定持久化类的属性的名字。
column属性：指定与类的属性映射的表的字段名。
type属性：指定Hibernate映射类型。Hibernate映射类型是Java类型与SQL类型的桥梁。
采用XML文件来配置对象-关系映射的优点：
- Hibernate既不会渗透到上层域模型中，也不会渗透到下层数据模型中。
- 软件开发人员可以独立设计域模型，不必强迫遵守任何规范。
- 数据库设计人员可以独立设计数据模型，不必强迫遵守任何规范。
- 对象-关系映射不依赖于任何程序代码，如果需要修改对象-关系映射，只需修改XML文件，不需要修改任何程序，提高了软件的灵活性，并且使维护更加方便。
七、创建BusinessService类
package mypack;
import javax.servlet.*;
import org.hibernate.*;
import org.hibernate.cfg.Configuration;
import java.io.*;
import java.sql.Date;
import java.sql.Timestamp;
import java.util.*;
public class BusinessService{
public static SessionFactory sessionFactory;
/** 初始化Hibernate，创建SessionFactory实例 */
static{
try{
// 根据默认位置的Hibernate配置文件的配置信息，创建一个Configuration实例
Configuration config = new Configuration();
//加载Customer类的对象-关系映射文件
config.addClass(Customer.class);
// 创建SessionFactory实例 */
sessionFactory = config.buildSessionFactory();
}catch(RuntimeException e){e.printStackTrace();throw e;}
}
/** 查询所有的Customer对象，然后调用printCustomer()方法打印Customer对象信息 */
public void findAllCustomers(ServletContext context,PrintWriter out) throws Exception{
Session session = sessionFactory.openSession(); //创建一个会话
Transaction tx = null;
try {
tx = session.beginTransaction(); //开始一个事务
Query query=session.createQuery("from Customer as c order by c.name asc");
List customers=query.list();
for (Iterator it = customers.iterator(); it.hasNext();) {
printCustomer(context,out,(Customer) it.next());
}
tx.commit(); //提交事务
}catch (RuntimeException e) {
if (tx != null) {
tx.rollback();
}
throw e;
} finally {
session.close();
}
}
/** 持久化一个Customer对象 */
public void saveCustomer(Customer customer){
Session session = sessionFactory.openSession();
Transaction tx = null;
try {
tx = session.beginTransaction();
session.save(customer);
tx.commit();
}catch (RuntimeException e) {
if (tx != null) {
tx.rollback();
}
throw e;
} finally {
session.close();
}
}
/** 按照OID加载一个Customer对象，然后修改它的属性 */
public void loadAndUpdateCustomer(Long customer_id,String address){
Session session = sessionFactory.openSession();
Transaction tx = null;
try {
tx = session.beginTransaction();
Customer c=(Customer)session.get(Customer.class,customer_id);
c.setAddress(address);
tx.commit();
}catch (RuntimeException e) {
if (tx != null) {
tx.rollback();
}
throw e;
} finally {
session.close();
}
}
/**删除Customer对象 */
public void deleteCustomer(Customer customer){
Session session = sessionFactory.openSession();
Transaction tx = null;
try {
tx = session.beginTransaction();
session.delete(customer);
tx.commit();
}catch (RuntimeException e) {
if (tx != null) {
tx.rollback();
}
throw e;
} finally {
session.close();
}
}
/** 选择向控制台还是Web网页输出Customer对象的信息 */
private void printCustomer(ServletContext context,PrintWriter out,Customer customer)throws Exception{
if(context!=null)
printCustomerInWeb(context,out,customer);
else
printCustomer( out,customer);
}
/** 把Customer对象的信息输出到控制台，如DOS 控制台*/
private void printCustomer(PrintWriter out,Customer customer)throws Exception{
byte[] buffer=customer.getImage();
FileOutputStream fout=new FileOutputStream("photo_copy.gif");
fout.write(buffer);
fout.close();
out.println("------以下是"+customer.getName()+"的个人信息------");
out.println("ID: "+customer.getId());
out.println("口令: "+customer.getPassword());
out.println("E-Mail: "+customer.getEmail());
out.println("电话: "+customer.getPhone());
out.println("地址: "+customer.getAddress());
String sex=customer.getSex()=='M'? "男":"女";
out.println("性别: "+sex);
String marriedStatus=customer.isMarried()? "已婚":"未婚";
out.println("婚姻状况: "+marriedStatus);
out.println("生日: "+customer.getBirthday());
out.println("注册时间: "+customer.getRegisteredTime());
out.println("自我介绍: "+customer.getDescription());
}
/** 把Customer对象的信息输出到动态网页 */
private void printCustomerInWeb(ServletContext context,PrintWriter out,Customer customer)throws Exception{
//保存照片
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()+"的个人信息------"+"<br>");
out.println("ID: "+customer.getId()+"<br>");
out.println("口令: "+customer.getPassword()+"<br>");
out.println("E-Mail: "+customer.getEmail()+"<br>");
out.println("电话: "+customer.getPhone()+"<br>");
out.println("地址: "+customer.getAddress()+"<br>");
String sex=customer.getSex()=='M'? "男":"女";
out.println("性别: "+sex+"<br>");
String marriedStatus=customer.isMarried()? "已婚":"未婚";
out.println("婚姻状况: "+marriedStatus+"<br>");
out.println("生日: "+customer.getBirthday()+"<br>");
out.println("注册时间: "+customer.getRegisteredTime()+"<br>");
out.println("自我介绍: "+customer.getDescription()+"<br>");
out.println("<img src='photo_copy.gif' border=0><p>");
}
public void test(ServletContext context,PrintWriter out) throws Exception{
Customer customer=new Customer();
customer.setName("Tom");
customer.setEmail("[email protected]");
customer.setPassword("1234");
customer.setPhone(55556666);
customer.setAddress("Shanghai");
customer.setSex('M');
customer.setDescription("I am very honest.");
//设置Customer对象的image属性，它是字节数组，存放photo.gif文件中的二进制数据
//photo.gif文件和BusinessService.class文件位于同一个目录下
InputStream in=this.getClass().getResourceAsStream("photo.gif");
byte[] buffer = new byte[in.available()];
in.read(buffer);
customer.setImage(buffer);
//设置Customer对象的birthday属性，它是java.sql.Date类型
customer.setBirthday(Date.valueOf("1980-05-06"));
saveCustomer(customer);
findAllCustomers(context,out);
loadAndUpdateCustomer(customer.getId(),"Beijing");
findAllCustomers(context,out);
deleteCustomer(customer);
}
public static void main(String args[]) throws Exception {
new BusinessService().test(null,new PrintWriter(System.out,true));
sessionFactory.close();
}
}
- saveCustomer()方法
该方法调用Session的save()方法，把Customer对象持久化到数据库中。
tx = session.beginTransaction();
session.save(customer);
tx.commit();
当运行session.save()方法时，Hibernate执行以下SQL语句：
insert into CUSTOMERS (ID, NAME, EMAIL, PASSWORD, PHONE, ADDRESS, SEX,
IS_MARRIED,DESCRIPTION, IMAGE, BIRTHDAY, REGISTERED_TIME)
values(1,'Tom','[email protected]','1234',55556666,'Shanghai','M',0,'I am very honest.', ☺,'1980-05-06',null)
在test()方法中并没有设置Customer对象的id属性，Hibernate会根据映射文件的配置，采用increment标识符生成器自动以递增的方式为OID赋值。在Customer.hbm.xml文件中相关的映射代码如下：
<id name="id" column="ID" type="long">
<generator class="increment"/>
</id>
- findAllCustomers()方法
该方法通过Query接口查询所有的Customer对象。
tx = session.beginTransaction(); //开始一个事务
Query query=session.createQuery("from Customer as c order by c.name asc");
List customers=query.list();
for (Iterator it = customers.iterator(); it.hasNext();) {
printCustomer(context,out,(Customer) it.next());
}
tx.commit(); //提交事务
Session的createQuery()方法的参数“from Customer as c order by c.name asc”使用的是Hibernate查询语言。运行Query.list()方法时， Hibernate执行以下SQL语句：
select * from CUSTOMERS order by NAME asc;
- loadAndUpdateCustomer ()方法
该方法调用Session的get()方法，加载Customer对象，然后再修改Customer对象的属性。
tx = session.beginTransaction();
Customer c=(Customer)session.get(Customer.class,customer_id);
c.setAddress(address); //修改内存中Customer对象的address属性
tx.commit();
以上代码先调用Session的get()方法，它按照参数指定的OID从数据库中检索出匹配的Customer对象，Hibernate会执行以下SQL语句：
select * from CUSTOMERS where ID=1;
loadAndUpdateCustomer()方法接着修改Customer对象的address属性。那么，Hibernate会不会同步更新数据库中相应的CUSTOMERS表的记录呢？答案是肯定的。Hibernate采用脏检查机制，按照内存中的Customer对象的状态的变化，来同步更新数据库中相关的数据，Hibernate会执行以下SQL语句：
update CUSTOMERS set NAME="Tom",EMAIL="[email protected]"…ADDRESS="Beijing"… where ID=1;
尽管只有Customer对象的address属性发生了变化，但是Hibernate执行的update语句中会包含所有的字段。
- deleteCustomer()方法
该方法调用Session的delete()方法，删除特定的Customer对象：
tx = session.beginTransaction();
session.delete(customer);
tx.commit();
运行session.delete()方法时，Hibernate根据Customer对象的OID，执行以下SQL delete语句：
delete from CUSTOMERS where ID=1;
八、效果图
