OpenJPA超简单入门

环境准备

OpenJPA下载：http://openjpa.apache.org/

Derby下载：http://db.apache.org/derby/

案例源码下载：http://rcom10002.download.csdn.net/user/rcom10002/Java

在学习案例一和二之前，先准备好实验环境，首先准备数据表：

CREATE TABLE AIRLINES ( AIRLINE CHAR(2) NOT NULL , AIRLINE_FULL VARCHAR(24), BASIC_RATE DOUBLE PRECISION, DISTANCE_DISCOUNT DOUBLE PRECISION, BUSINESS_LEVEL_FACTOR DOUBLE PRECISION, FIRSTCLASS_LEVEL_FACTOR DOUBLE PRECISION, ECONOMY_SEATS INTEGER, BUSINESS_SEATS INTEGER, FIRSTCLASS_SEATS INTEGER ) 

然后准备好Java到数据表的映射：

import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.Id;import javax.persistence.Table;@Entity@Table(name = "AIRLINES")public class Airline {@Id@Column(name = "AIRLINE")String airline;@Column(name = "AIRLINE_FULL")String airlineFull;@Column(name = "BASIC_RATE")double basicRate;@Column(name = "DISTANCE_DISCOUNT")double distanceDiscount;@Column(name = "BUSINESS_LEVEL_FACTOR")double businessLevelFactor;@Column(name = "FIRSTCLASS_LEVEL_FACTOR")double firstclassLevelFactor;@Column(name = "ECONOMY_SEATS")int economySeats;@Column(name = "BUSINESS_SEATS")int businessSeats;@Column(name = "FIRSTCLASS_SEATS")int firstclassSeats;/** * @return the airline */public String getAirline() {return airline;}/** * @param airline * the airline to set */public void setAirline(String airline) {this.airline = airline;}/** * @return the airlineFull */public String getAirlineFull() {return airlineFull;}/** * @param airlineFull * the airlineFull to set */public void setAirlineFull(String airlineFull) {this.airlineFull = airlineFull;}/** * @return the basicRate */public double getBasicRate() {return basicRate;}/** * @param basicRate * the basicRate to set */public void setBasicRate(double basicRate) {this.basicRate = basicRate;}/** * @return the distanceDiscount */public double getDistanceDiscount() {return distanceDiscount;}/** * @param distanceDiscount * the distanceDiscount to set */public void setDistanceDiscount(double distanceDiscount) {this.distanceDiscount = distanceDiscount;}/** * @return the businessLevelFactor */public double getBusinessLevelFactor() {return businessLevelFactor;}/** * @param businessLevelFactor * the businessLevelFactor to set */public void setBusinessLevelFactor(double businessLevelFactor) {this.businessLevelFactor = businessLevelFactor;}/** * @return the firstclassLevelFactor */public double getFirstclassLevelFactor() {return firstclassLevelFactor;}/** * @param firstclassLevelFactor * the firstclassLevelFactor to set */public void setFirstclassLevelFactor(double firstclassLevelFactor) {this.firstclassLevelFactor = firstclassLevelFactor;}/** * @return the economySeats */public int getEconomySeats() {return economySeats;}/** * @param economySeats * the economySeats to set */public void setEconomySeats(int economySeats) {this.economySeats = economySeats;}/** * @return the businessSeats */public int getBusinessSeats() {return businessSeats;}/** * @param businessSeats * the businessSeats to set */public void setBusinessSeats(int businessSeats) {this.businessSeats = businessSeats;}/** * @return the firstclassSeats */public int getFirstclassSeats() {return firstclassSeats;}/** * @param firstclassSeats * the firstclassSeats to set */public void setFirstclassSeats(int firstclassSeats) {this.firstclassSeats = firstclassSeats;}/* * (non-Javadoc) * * @see java.lang.Object#hashCode() */@Overridepublic int hashCode() {final int prime = 31;int result = 1;result = prime * result + ((airline == null) ? 0 : airline.hashCode());result = prime * result+ ((airlineFull == null) ? 0 : airlineFull.hashCode());long temp;temp = Double.doubleToLongBits(basicRate);result = prime * result + (int) (temp ^ (temp >>> 32));temp = Double.doubleToLongBits(businessLevelFactor);result = prime * result + (int) (temp ^ (temp >>> 32));result = prime * result + businessSeats;temp = Double.doubleToLongBits(distanceDiscount);result = prime * result + (int) (temp ^ (temp >>> 32));result = prime * result + economySeats;temp = Double.doubleToLongBits(firstclassLevelFactor);result = prime * result + (int) (temp ^ (temp >>> 32));result = prime * result + firstclassSeats;return result;}/* * (non-Javadoc) * * @see java.lang.Object#equals(java.lang.Object) */@Overridepublic boolean equals(Object obj) {if (this == obj)return true;if (obj == null)return false;if (getClass() != obj.getClass())return false;Airline other = (Airline) obj;if (airline == null) {if (other.airline != null)return false;} else if (!airline.equals(other.airline))return false;if (airlineFull == null) {if (other.airlineFull != null)return false;} else if (!airlineFull.equals(other.airlineFull))return false;if (Double.doubleToLongBits(basicRate) != Double.doubleToLongBits(other.basicRate))return false;if (Double.doubleToLongBits(businessLevelFactor) != Double.doubleToLongBits(other.businessLevelFactor))return false;if (businessSeats != other.businessSeats)return false;if (Double.doubleToLongBits(distanceDiscount) != Double.doubleToLongBits(other.distanceDiscount))return false;if (economySeats != other.economySeats)return false;if (Double.doubleToLongBits(firstclassLevelFactor) != Double.doubleToLongBits(other.firstclassLevelFactor))return false;if (firstclassSeats != other.firstclassSeats)return false;return true;}} 

在META-INF中准备persistence.xml，配置两个持久化单元，一个给案例一使用，另一个给案例二使用。

<persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.0"> <persistence-unit name="OpenJpaExample" transaction-type="RESOURCE_LOCAL"> <class>Airline</class> <properties> <property name="openjpa.ConnectionURL" value="jdbc:derby:jdbcDemoDB;create=true"/> <property name="openjpa.ConnectionDriverName" value="org.apache.derby.jdbc.EmbeddedDriver"/> </properties> </persistence-unit> <!-- <persistence-unit name="OpenJpaSpringExample" transaction-type="JTA"> --> <persistence-unit name="OpenJpaSpringExample" transaction-type="RESOURCE_LOCAL" > <class>Airline</class> <properties> <property name="openjpa.ConnectionURL" value="jdbc:derby:jdbcDemoDB;create=true"/> <property name="openjpa.ConnectionDriverName" value="org.apache.derby.jdbc.EmbeddedDriver"/> </properties> </persistence-unit></persistence> 

案例一 —— OpenJPA在Java应用程序中使用

在这个例子中，重点是如何获取“EntityManagerFactory”，由于是在非JEE容器环境中使用OpenJPA，所以事务类型无法采用JTA形式，我们需要手工进行事务管理。具体的例子源码如下：

import java.io.BufferedReader;import java.io.InputStream;import java.io.InputStreamReader;import java.io.Reader;import java.io.StringWriter;import java.io.Writer;import java.sql.Connection;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.Statement;import java.util.List;import javax.persistence.EntityManager;import javax.persistence.EntityManagerFactory;import javax.persistence.Persistence;public class OpenJpaExample {public static void main(String[] args) {String driver = "org.apache.derby.jdbc.EmbeddedDriver";String connectionURL = "jdbc:derby:jdbcDemoDB;create=true";try {Class.forName(driver);} catch (java.lang.ClassNotFoundException e) {e.printStackTrace();}Connection conn = null;Statement s = null;ResultSet rs = null;try {conn = DriverManager.getConnection(connectionURL);rs = conn.getMetaData().getTables(null, null, "AIRLINES", new String[] {"TABLE"});if (rs.next()) {rs.close();} else {s = conn.createStatement();s.executeUpdate(readSql());}} catch (Throwable e) {e.printStackTrace();} finally {try {if (rs != null) {rs.close();}if (s != null) {s.close();}if (conn != null) {conn.close();}} catch (Exception e) {e.printStackTrace();}}EntityManagerFactory factory = Persistence.createEntityManagerFactory("OpenJpaExample", System.getProperties());EntityManager em = factory.createEntityManager();em.getTransaction().begin();Airline airline = null;airline = new Airline();airline.setAirline("CZ");airline.setAirlineFull("CZ12345");airline.setFirstclassSeats(10);airline.setBusinessSeats(20);airline.setEconomySeats(50);em.persist(airline);airline = new Airline();airline.setAirline("MU");airline.setAirlineFull("MU54321");airline.setFirstclassSeats(10);airline.setBusinessSeats(20);airline.setEconomySeats(50);em.persist(airline);@SuppressWarnings("unchecked")List<Airline> airlines = em.createNativeQuery("select * from airlines", Airline.class).getResultList();for (Airline eachAirline: airlines) {System.out.println(eachAirline.getAirline());System.out.println(eachAirline.getAirlineFull());System.out.println(eachAirline.getFirstclassSeats());System.out.println(eachAirline.getBusinessSeats());System.out.println(eachAirline.getEconomySeats());System.out.println("-----------------------------");}//airline = em.find(Airline.class, "MU");em.createNativeQuery("DELETE FROM AIRLINES").executeUpdate();em.getTransaction().commit();}private static String readSql() {InputStream stream = OpenJpaExample.class.getResourceAsStream("/ToursDB_schema.sql"); return StreamToString.convertStreamToString(stream);}private static class StreamToString { public static String convertStreamToString(InputStream is) { if (is != null) { Writer writer = new StringWriter(); char[] buffer = new char[1024]; try { Reader reader = new BufferedReader( new InputStreamReader(is, "UTF-8")); int n; while ((n = reader.read(buffer)) != -1) { writer.write(buffer, 0, n); } } catch (Exception e) { e.printStackTrace();} finally {try {is.close();} catch (Exception e) {e.printStackTrace();} } return writer.toString(); } else { return ""; } }}} 

案例二 —— 从Spring中获取OpenJPA编程接口

与上面的例子类似，只是在这里我们改换另一种从Spring中获取“EntityManagerFactory”的方法，Spring的配置如下：

<?xml version="1.0" encoding="UTF-8"?><beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> <bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalEntityManagerFactoryBean"> <property name="persistenceUnitName" value="OpenJpaSpringExample"/> </bean></beans> 

Java实例代码如下：

import java.util.Date;import java.util.List;import javax.persistence.EntityManager;import javax.persistence.EntityManagerFactory;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;public class OpenJpaSpringExample {public static void main(String[] args) {ApplicationContext context = new ClassPathXmlApplicationContext(new String[] { "applicationContext.xml" }); EntityManagerFactory emf = (EntityManagerFactory)context.getBean("entityManagerFactory"); EntityManager em = emf.createEntityManager(); em.getTransaction().begin(); // remove all airlines em.createNativeQuery("DELETE FROM airlines").executeUpdate(); // create a new airline Airline airline = new Airline();airline.setAirline("CZ");airline.setAirlineFull("CZ" + new Date().getTime());airline.setFirstclassSeats(10);airline.setBusinessSeats(20);airline.setEconomySeats(50);// save the new airlineem.persist(airline);em.getTransaction().commit();@SuppressWarnings("unchecked")// list all saved airlinesList<Airline> airlines = em.createNativeQuery("SELECT * FROM AIRLINES", Airline.class).getResultList();for (Airline eachAirline : airlines) {System.out.println(eachAirline.getAirline());System.out.println(eachAirline.getAirlineFull());}}}