????? 好久没有写博客了，最近比较忙，今天抽时间写点，最近的工作都是围绕EJB及JBoss的，所以这篇博客还是EJB相关。
我们知道EJB环境下Session Bean（两种状态）中可以直接使用EntityManager，使用时只需对EntityManager加一个Annotation（EJB 3）即可，如下：
@PersistenceContext(unitName="com.xxx.xxx.po") EntityManager em=null;
??EJB Container看到PersistenceContext标记是会自动初始化EntityManager，在Session Bean中需要对com.xxx.xxx.po包下面的Entity类进行处理时直接可以用em既可。而实际工作中往往想在自己的代码中控制使用EntityManager，本文就是基于在J2Se环境下使用EntityManager处理POJO类完成对数据库的update。
直接写一个简单Demo：
项目Eclipse下截图：
从下向上，说明：
1 所需Jar包如图中，Jar包添加花了我好多时间，主要是Hibernate相关jar
2 oracle.properties定义数据库连接信息，如下;
hibernate.dialect=org.hibernate.dialect.Oracle10gDialect#connectionhibernate.connection.driver_class=oracle.jdbc.driver.OracleDriverhibernate.connection.username=IPC113hibernate.connection.password=bpmhibernate.connection.url=jdbc:oracle:thin:@//192.168.68.120:1521/orcl#pool hibernate.c3p0.min_size=1hibernate.c3p0.max_size=20hibernate.c3p0.timeout=1800hibernate.c3p0.max_statements=50
?如上显示连接Oracle数据库，用户名IPC113，密码bpm连接URL及数据库池等
3 hibernate.cfg.xml 本来可以不要，但是我不知道用EntityManager直接产生初始化表，我知道是可以产生，但暂时用Hibernate产生初始化表
配置:
<?xml version='1.0' encoding='utf-8'?><!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"><hibernate-configuration> <session-factory> <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property> <property name="connection.url">jdbc:oracle:thin:@192.168.68.120:1521:orcl</property> <property name="connection.username">ipc113</property> <property name="connection.password">bpm</property> <property name="dialect">org.hibernate.dialect.OracleDialect</property> <property name="connection.pool_size">1</property> <property name="current_session_context_class">thread</property> <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property> <property name="show_sql">true</property> <property name="format_sql">true</property> <mapping class="com.kylin.study.po.Person"/> <mapping class="com.kylin.study.po.Husband"/> <mapping class="com.kylin.study.po.Wife"/> </session-factory></hibernate-configuration>
?
4 persistence.xml,Persistence 提供者配置信息
如下：
<persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" version="1.0"> <persistence-unit name="com.kylin.study.po" > <provider>org.hibernate.ejb.HibernatePersistence</provider> <properties> <property name="hibernate.cache.provider_class" value="org.hibernate.cache.EhCacheProvider"/> <property name="hibernate.ejb.classcache.com.kylin.study.po.Person" value="read-write"/> <property name="hibernate.ejb.classcache.com.kylin.study.po.Husband" value="read-write"/> <property name="hibernate.ejb.classcache.com.kylin.study.po.Wife" value="read-write"/> </properties> </persistence-unit></persistence>
5 POJO类，此处用到一对一单向映射的例子，前面http://kylinsoong.iteye.com/blog/739502中第二部分第一个Husband和Wife例子。
代码：
package com.kylin.study.po;import javax.persistence.CascadeType;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.OneToOne;import javax.persistence.Table;@Entity @Table(name="t_husband")public class Husband { private int id; private String name; private Wife wife; @Id @GeneratedValue public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } @OneToOne(cascade=CascadeType.ALL) @JoinColumn(name="wifeId") public Wife getWife() { return wife; } public void setWife(Wife wife) { this.wife = wife; } } ?
package com.kylin.study.po;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.Table;@Entity @Table(name="t_wife")public class Wife { private int id; private String name; @Id @GeneratedValue public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } } ?
package com.kylin.study.po;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.Table;@Entity @Table(name="t_person")public class Person { private int id; private String name; @Id @GeneratedValue public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; }}?
6。测试代码：
package com.kylin.study.jpa;import java.io.IOException;import java.io.InputStream;import java.util.List;import java.util.Properties;import javax.persistence.EntityManager;import javax.persistence.EntityManagerFactory;import javax.persistence.EntityTransaction;import javax.persistence.Persistence;import javax.persistence.Query;import org.hibernate.cfg.AnnotationConfiguration;import org.hibernate.tool.hbm2ddl.SchemaExport;import org.junit.BeforeClass;import org.junit.Test;import com.kylin.study.po.Husband;import com.kylin.study.po.Person;import com.kylin.study.po.Wife;public class JPAJ2SETest { private static EntityManager em ; @BeforeClass public static void beforeClass() { String persistence_unit = "com.kylin.study.po"; Properties prop = new Properties(); InputStream is = JPAJ2SETest.class.getClassLoader().getResourceAsStream("oracle.properties"); try { prop.load(is); } catch (IOException e) { e.printStackTrace(); } finally { try { if(is != null) is.close(); } catch (IOException ignored) { } } EntityManagerFactory emf = Persistence.createEntityManagerFactory(persistence_unit, prop); em = emf.createEntityManager(); } @Test public void createTestTables() { new SchemaExport(new AnnotationConfiguration().configure()).create(true, true); } @Test public void save() { EntityTransaction t = em.getTransaction(); t.begin(); Person kobe = new Person(); kobe.setName("Kobe Bryant"); Person vanessa = new Person(); vanessa.setName("Vanessa Bryant"); em.persist(kobe); em.persist(vanessa); t.commit(); } @Test public void query() { EntityTransaction t = em.getTransaction(); t.begin(); String str = "Kobe Bryant"; Query query = em.createQuery("from Person where name='" + str + "'"); List<Person>lists = query.getResultList(); for(Person p : lists) { System.out.println(p.getId() + " " + p.getName()); } t.commit(); } @Test public void find() { EntityTransaction t = em.getTransaction(); t.begin(); Object obj = em.find(Person.class, 1); t.commit(); System.out.println(obj); } @Test public void delete() { EntityTransaction t = em.getTransaction(); t.begin(); Object obj = em.find(Person.class, 1); em.remove(obj); t.commit(); } @Test public void one2Onesave() { EntityTransaction t = em.getTransaction(); t.begin(); Husband kobe = new Husband(); kobe.setName("Kobe Bryant"); Wife vanessa = new Wife(); vanessa.setName("Vanessa Bryant"); kobe.setWife(vanessa); em.persist(kobe); t.commit(); } @Test public void one2Onequery() { EntityTransaction t = em.getTransaction(); t.begin(); Query query1 = em.createQuery("from Husband"); List<Husband> husbands = query1.getResultList(); for(Husband h : husbands) { System.out.println(h.getId() + " " + h.getName() + " " + h.getWife().getId() + " " + h.getWife().getName()); } Query query2 = em.createQuery("from Wife"); List<Wife> wifes = query2.getResultList(); for(Wife w : wifes) { System.out.println(w.getId() + " " + w.getName()); } t.commit(); } @Test public void one2Onefind() { EntityTransaction t = em.getTransaction(); t.begin(); Husband kobe = em.find(Husband.class, 21); System.out.println(kobe.getId()); System.out.println(kobe.getName()); System.out.println(kobe.getWife().getId()); System.out.println(kobe.getWife().getName()); t.commit(); } @Test public void one2Onedelete() { EntityTransaction t = em.getTransaction(); t.begin(); Husband kobe = em.find(Husband.class, 21); em.remove(kobe); Query query2 = em.createQuery("from Wife"); List<Wife> wifes = query2.getResultList(); for(Wife w : wifes) { System.out.println(w.getId() + " " + w.getName()); } t.commit(); } public static void main(String[] args ) {// JPAJ2SETest test = new JPAJ2SETest();// JPAJ2SETest.beforeClass();// test.save(); }}
?依次向下执行测试类方法：
（1）createTestTables()执行完后，数据库中产生了三张表，如下：
?（2）save()向数据库中存入两个Person，Kobe和他老婆
（3）query()可以查看数据库中所有名字是Kobe Bryant的人，执行结果：
1 Kobe Bryant3 Kobe Bryant
?
（4）find()查找一个Person对象，id为1，执行结果
com.kylin.study.po.Person@16ea269
?
（5） delete()删除一个id为1Person对象；
（6）one2Onesave()同样存储一个一对一的对象，同样是Kobe和他老婆
（7）one2Onequery()查询刚插入的数据，主要验证，一对多单向可以用一方获取另一方，执行结果：
21 Kobe Bryant 22 Vanessa Bryant22 Vanessa Bryant
?
（8）one2Onefind()查找id为21的丈夫，执行结果：
21Kobe Bryant22Vanessa Bryant
?（9）one2Onedelete()删除id为21的Husband，主要验证删除Husband后相关的Wife也删除
?
到此例子结束，有好多问题，比如，如何直接用JPA API生成表等，值得去研究，由于时间不说写……