openjpa postgresql入门

想你了的他他

　　maven pom.xml : 

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.tch.test</groupId>
<artifactId>openjpa</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>openjpa</name>
<url>http://maven.apache.org</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencies>
<dependency>
<groupId>org.apache.openjpa</groupId>
<artifactId>openjpa</artifactId>
<version>2.3.0</version>
</dependency>
<dependency>
<groupId>org.postgresql</groupId>
<artifactId>postgresql</artifactId>
<version>9.3-1102-jdbc41</version>
</dependency>
</dependencies>
</project>

　　src/main/resources 创建META-INF文件夹,创建persistence.xml ：

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
version="1.0">
<persistence-unit name="openjpa" transaction-type="RESOURCE_LOCAL">
<provider>org.apache.openjpa.persistence.PersistenceProviderImpl</provider>  
<class>com.tch.test.openjpa.Point</class>
<exclude-unlisted-classes>true</exclude-unlisted-classes>
<properties>
<property name="javax.persistence.jdbc.driver" value="org.postgresql.Driver" />  
<property name="javax.persistence.jdbc.url" value="jdbc:postgresql://localhost:5432/postgres" />  
<property name="javax.persistence.jdbc.user" value="postgres" />  
<property name="javax.persistence.jdbc.password" value="postgres" />  
<property name="openjpa.jdbc.SynchronizeMappings" value="buildSchema" />
<property name="openjpa.jdbc.DBDictionary" value="postgres(SearchStringEscape=#)" />
<property name="openjpa.Log" value="DefaultLevel=WARN, Runtime=WARN, Tool=INFO, SQL=info" />
</properties>
</persistence-unit>
</persistence>

　　然后创建实体类： 

package com.tch.test.openjpa;
import java.io.Serializable;
import javax.persistence.*;
@Entity
public class Point implements Serializable {
private static final long serialVersionUID = 1L;
@Id @GeneratedValue
private long id;
private int x;
private int y;
public Point() {
}
Point(int x, int y) {
this.x = x;
this.y = y;
}
public Long getId() {
return id;
}
public int getX() {
return x;
}
public int getY() {
return y;
}
@Override
public String toString() {
return String.format("(%d, %d)", this.x, this.y);
}
}
　　测试：

package com.tch.test.openjpa;
import javax.persistence.*;
import java.util.*;
public class Main {
private static EntityManager em;
private static EntityManagerFactory emf;
static {
// Open a database connection
emf = Persistence.createEntityManagerFactory("openjpa");
em = emf.createEntityManager();
}
public static void main(String[] args) {
try{
batchSave();
getCount();
typedQuery();
clearTable();
}catch(Exception e){
e.printStackTrace();
}finally{
// Close the database connection:
em.close();
emf.close();
}
}
private static void clearTable() {
em.getTransaction().begin();
em.createQuery("delete from Point").executeUpdate();
em.getTransaction().commit();
}
private static void typedQuery(){
// Retrieve all the Point objects from the database:
TypedQuery<Point> query =
em.createQuery("SELECT p FROM Point p", Point.class);
List<Point> results = query.setMaxResults(10).getResultList();
System.out.println(results.size());
}
private static void batchSave(){
long startTime = System.currentTimeMillis();
// Store 1000 Point objects in the database:
em.getTransaction().begin();
for (int i = 0; i < 1000; i++) {
Point p = new Point(i, i);
em.persist(p);
}
em.getTransaction().commit();
System.out.println((System.currentTimeMillis()-startTime)+"ms");
}
private static void getCount(){
// Find the number of Point objects in the database:
Query q1 = em.createQuery("SELECT COUNT(p) FROM Point p");
System.out.println("Total Points: " + q1.getSingleResult());
}

}
　　OK