JPA开发（一）

之前一直在用EJB3，但现在想在J2SE里面使用JPA，因为不大喜欢Hibernate的XML文件配置。

而使用DB4O的时候，出现了一些莫名其妙的问题，一直没解决，就暂时搁下了。

使用myeclipse 6开发jpa如下：

1.创建web project

2.添加jpa capabilities，选择toplink，把自动创建数据库的和更新persistence.xml的勾上

3.切换成database explorer视图，选择表，jpa逆向工程。

4.测试

生成的persistence.xml如下：

<?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"
    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="JPAWebPU"
		transaction-type="RESOURCE_LOCAL">
		<provider>
			oracle.toplink.essentials.PersistenceProvider
		</provider>
		<class>com.persia.entity.Consumer</class>
		<properties>
			<property name="toplink.jdbc.driver"
				value="com.mysql.jdbc.Driver" />
			<property name="toplink.jdbc.url"
				value="jdbc:mysql://localhost:3306/ejb3" />
			<property name="toplink.jdbc.user" value="root" />
			<property name="toplink.jdbc.password" value="root" />
			<property name="toplink.ddl-generation"
				value="create-tables" />
		</properties>
	</persistence-unit>

</persistence>

 

生成的几个类如下：

实体类：

package com.persia.entity;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

/**
 * Consumer entity.
 * 
 * @author MyEclipse Persistence Tools
 */
@Entity
@Table(name = "consumer", catalog = "ejb3", uniqueConstraints = {})
public class Consumer implements java.io.Serializable {

	// Fields

	private Integer id;
	private String name;
	private String password;

	// Constructors

	/** default constructor */
	public Consumer() {
	}

	/** full constructor */
	public Consumer(Integer id, String name, String password) {
		this.id = id;
		this.name = name;
		this.password = password;
	}

	// Property accessors
	@Id
	@Column(name = "id", unique = true, nullable = false, insertable = true, updatable = true)
	public Integer getId() {
		return this.id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	@Column(name = "name", unique = false, nullable = false, insertable = true, updatable = true, length = 45)
	public String getName() {
		return this.name;
	}

	public void setName(String name) {
		this.name = name;
	}

	@Column(name = "password", unique = false, nullable = false, insertable = true, updatable = true, length = 45)
	public String getPassword() {
		return this.password;
	}

	public void setPassword(String password) {
		this.password = password;
	}

}

DAO接口

package com.persia.entity;

import java.util.List;

/**
 * Interface for ConsumerDAO.
 * 
 * @author MyEclipse Persistence Tools
 */

public interface IConsumerDAO {
	/**
	 * Perform an initial save of a previously unsaved Consumer entity. All
	 * subsequent persist actions of this entity should use the #update()
	 * method. This operation must be performed within the a database
	 * transaction context for the entity's data to be permanently saved to the
	 * persistence store, i.e., database. This method uses the
	 * {@link javax.persistence.EntityManager#persist(Object) EntityManager#persist}
	 * operation.
	 * 
	 * <pre>
	 * EntityManagerHelper.beginTransaction();
	 * IConsumerDAO.save(entity);
	 * EntityManagerHelper.commit();
	 * </pre>
	 * 
	 * @param entity
	 *            Consumer entity to persist
	 * @throws RuntimeException
	 *             when the operation fails
	 */
	public void save(Consumer entity);

	/**
	 * Delete a persistent Consumer entity. This operation must be performed
	 * within the a database transaction context for the entity's data to be
	 * permanently deleted from the persistence store, i.e., database. This
	 * method uses the
	 * {@link javax.persistence.EntityManager#remove(Object) EntityManager#delete}
	 * operation.
	 * 
	 * <pre>
	 * EntityManagerHelper.beginTransaction();
	 * IConsumerDAO.delete(entity);
	 * EntityManagerHelper.commit();
	 * entity = null;
	 * </pre>
	 * 
	 * @param entity
	 *            Consumer entity to delete
	 * @throws RuntimeException
	 *             when the operation fails
	 */
	public void delete(Consumer entity);

	/**
	 * Persist a previously saved Consumer entity and return it or a copy of it
	 * to the sender. A copy of the Consumer entity parameter is returned when
	 * the JPA persistence mechanism has not previously been tracking the
	 * updated entity. This operation must be performed within the a database
	 * transaction context for the entity's data to be permanently saved to the
	 * persistence store, i.e., database. This method uses the
	 * {@link javax.persistence.EntityManager#merge(Object) EntityManager#merge}
	 * operation.
	 * 
	 * <pre>
	 * EntityManagerHelper.beginTransaction();
	 * entity = IConsumerDAO.update(entity);
	 * EntityManagerHelper.commit();
	 * </pre>
	 * 
	 * @param entity
	 *            Consumer entity to update
	 * @returns Consumer the persisted Consumer entity instance, may not be the
	 *          same
	 * @throws RuntimeException
	 *             if the operation fails
	 */
	public Consumer update(Consumer entity);

	public Consumer findById(Integer id);

	/**
	 * Find all Consumer entities with a specific property value.
	 * 
	 * @param propertyName
	 *            the name of the Consumer property to query
	 * @param value
	 *            the property value to match
	 * @return List<Consumer> found by query
	 */
	public List<Consumer> findByProperty(String propertyName, Object value);

	public List<Consumer> findByName(Object name);

	public List<Consumer> findByPassword(Object password);

	/**
	 * Find all Consumer entities.
	 * 
	 * @return List<Consumer> all Consumer entities
	 */
	public List<Consumer> findAll();
}

 

DAO类

package com.persia.entity;

import java.util.List;
import java.util.logging.Level;
import javax.persistence.EntityManager;
import javax.persistence.Query;

/**
 * A data access object (DAO) providing persistence and search support for
 * Consumer entities. Transaction control of the save(), update() and delete()
 * operations must be handled externally by senders of these methods or must be
 * manually added to each of these methods for data to be persisted to the JPA
 * datastore.
 * 
 * @see com.persia.entity.Consumer
 * @author MyEclipse Persistence Tools
 */

public class ConsumerDAO implements IConsumerDAO {
	// property constants
	public static final String NAME = "name";
	public static final String PASSWORD = "password";

	private EntityManager getEntityManager() {
		return EntityManagerHelper.getEntityManager();
	}

	/**
	 * Perform an initial save of a previously unsaved Consumer entity. All
	 * subsequent persist actions of this entity should use the #update()
	 * method. This operation must be performed within the a database
	 * transaction context for the entity's data to be permanently saved to the
	 * persistence store, i.e., database. This method uses the
	 * {@link javax.persistence.EntityManager#persist(Object) EntityManager#persist}
	 * operation.
	 * 
	 * <pre>
	 * EntityManagerHelper.beginTransaction();
	 * ConsumerDAO.save(entity);
	 * EntityManagerHelper.commit();
	 * </pre>
	 * 
	 * @param entity
	 *            Consumer entity to persist
	 * @throws RuntimeException
	 *             when the operation fails
	 */
	public void save(Consumer entity) {
		EntityManagerHelper.log("saving Consumer instance", Level.INFO, null);
		try {
			getEntityManager().persist(entity);
			EntityManagerHelper.log("save successful", Level.INFO, null);
		} catch (RuntimeException re) {
			EntityManagerHelper.log("save failed", Level.SEVERE, re);
			throw re;
		}
	}

	/**
	 * Delete a persistent Consumer entity. This operation must be performed
	 * within the a database transaction context for the entity's data to be
	 * permanently deleted from the persistence store, i.e., database. This
	 * method uses the
	 * {@link javax.persistence.EntityManager#remove(Object) EntityManager#delete}
	 * operation.
	 * 
	 * <pre>
	 * EntityManagerHelper.beginTransaction();
	 * ConsumerDAO.delete(entity);
	 * EntityManagerHelper.commit();
	 * entity = null;
	 * </pre>
	 * 
	 * @param entity
	 *            Consumer entity to delete
	 * @throws RuntimeException
	 *             when the operation fails
	 */
	public void delete(Consumer entity) {
		EntityManagerHelper.log("deleting Consumer instance", Level.INFO, null);
		try {
			entity = getEntityManager().getReference(Consumer.class,
					entity.getId());
			getEntityManager().remove(entity);
			EntityManagerHelper.log("delete successful", Level.INFO, null);
		} catch (RuntimeException re) {
			EntityManagerHelper.log("delete failed", Level.SEVERE, re);
			throw re;
		}
	}

	/**
	 * Persist a previously saved Consumer entity and return it or a copy of it
	 * to the sender. A copy of the Consumer entity parameter is returned when
	 * the JPA persistence mechanism has not previously been tracking the
	 * updated entity. This operation must be performed within the a database
	 * transaction context for the entity's data to be permanently saved to the
	 * persistence store, i.e., database. This method uses the
	 * {@link javax.persistence.EntityManager#merge(Object) EntityManager#merge}
	 * operation.
	 * 
	 * <pre>
	 * EntityManagerHelper.beginTransaction();
	 * entity = ConsumerDAO.update(entity);
	 * EntityManagerHelper.commit();
	 * </pre>
	 * 
	 * @param entity
	 *            Consumer entity to update
	 * @returns Consumer the persisted Consumer entity instance, may not be the
	 *          same
	 * @throws RuntimeException
	 *             if the operation fails
	 */
	public Consumer update(Consumer entity) {
		EntityManagerHelper.log("updating Consumer instance", Level.INFO, null);
		try {
			Consumer result = getEntityManager().merge(entity);
			EntityManagerHelper.log("update successful", Level.INFO, null);
			return result;
		} catch (RuntimeException re) {
			EntityManagerHelper.log("update failed", Level.SEVERE, re);
			throw re;
		}
	}

	public Consumer findById(Integer id) {
		EntityManagerHelper.log("finding Consumer instance with id: " + id,
				Level.INFO, null);
		try {
			Consumer instance = getEntityManager().find(Consumer.class, id);
			return instance;
		} catch (RuntimeException re) {
			EntityManagerHelper.log("find failed", Level.SEVERE, re);
			throw re;
		}
	}

	/**
	 * Find all Consumer entities with a specific property value.
	 * 
	 * @param propertyName
	 *            the name of the Consumer property to query
	 * @param value
	 *            the property value to match
	 * @return List<Consumer> found by query
	 */
	@SuppressWarnings("unchecked")
	public List<Consumer> findByProperty(String propertyName, final Object value) {
		EntityManagerHelper.log("finding Consumer instance with property: "
				+ propertyName + ", value: " + value, Level.INFO, null);
		try {
			final String queryString = "select model from Consumer model where model."
					+ propertyName + "= :propertyValue";
			Query query = getEntityManager().createQuery(queryString);
			query.setParameter("propertyValue", value);
			return query.getResultList();
		} catch (RuntimeException re) {
			EntityManagerHelper.log("find by property name failed",
					Level.SEVERE, re);
			throw re;
		}
	}

	public List<Consumer> findByName(Object name) {
		return findByProperty(NAME, name);
	}

	public List<Consumer> findByPassword(Object password) {
		return findByProperty(PASSWORD, password);
	}

	/**
	 * Find all Consumer entities.
	 * 
	 * @return List<Consumer> all Consumer entities
	 */
	@SuppressWarnings("unchecked")
	public List<Consumer> findAll() {
		EntityManagerHelper.log("finding all Consumer instances", Level.INFO,
				null);
		try {
			final String queryString = "select model from Consumer model";
			Query query = getEntityManager().createQuery(queryString);
			return query.getResultList();
		} catch (RuntimeException re) {
			EntityManagerHelper.log("find all failed", Level.SEVERE, re);
			throw re;
		}
	}

}

 

还有一个非常有用的helper

package com.persia.entity;

import java.util.logging.Level;
import java.util.logging.Logger;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.Query;
/**
 * @author MyEclipse Persistence Tools
 */
public class EntityManagerHelper {
	
	private static final EntityManagerFactory emf; 
	private static final ThreadLocal<EntityManager> threadLocal;
	private static final Logger logger;
	
	static {
		emf = Persistence.createEntityManagerFactory("JPAWebPU"); 		
		threadLocal = new ThreadLocal<EntityManager>();
		logger = Logger.getLogger("JPAWebPU");
		logger.setLevel(Level.ALL);
	}
		
	public static EntityManager getEntityManager() {
		EntityManager manager = threadLocal.get();		
		if (manager == null || !manager.isOpen()) {
			manager = emf.createEntityManager();
			threadLocal.set(manager);
		}
		return manager;
	}
	
	 public static void closeEntityManager() {
        EntityManager em = threadLocal.get();
        threadLocal.set(null);
        if (em != null) em.close();
    }
    
    public static void beginTransaction() {
    	getEntityManager().getTransaction().begin();
    }
    
    public static void commit() {
    	getEntityManager().getTransaction().commit();
    }  
    
    public static void rollback() {
    	getEntityManager().getTransaction().rollback();
    } 
    
    public static Query createQuery(String query) {
		return getEntityManager().createQuery(query);
	}
	
	public static void log(String info, Level level, Throwable ex) {
    	logger.log(level, info, ex);
    }
    
}

 

然后使用helper和dao进行测试

package com.jpa.test;

import java.util.List;

import com.persia.entity.Consumer;
import com.persia.entity.ConsumerDAO;
import com.persia.entity.EntityManagerHelper;

public class JPATest {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// 1.创建 DAO
		ConsumerDAO dao = new ConsumerDAO();
		// 2.创建实体类
		Consumer c = new Consumer();
		c.setName("jpa01");
		c.setPassword("jianchi");
		
		
		// 开始事务 
		EntityManagerHelper.beginTransaction();
		// 3. 保存
		dao.save(c);
		
		// 提交事务真正保存实体到数据库
		EntityManagerHelper.commit();
		
		// 4. 列出数据库中所有对象
		List<Consumer> result = dao.findAll();
		
		for(Consumer o : result) {
			System.out.println(o.getId());
			System.out.println(o.getName());
		}
	
	}

}

 

测试实例如下：

package test;
import java.util.List;
import dao.*;

public class JPATest {
	public static void main(String[] args) {
		// 1.创建 DAO
		StudentDAO dao = new StudentDAO();
		// 2.创建实体类
		Student user = new Student();
		user.setUsername("hellojpa test");
		user.setPassword("jpa password");
		user.setAge(20);
		
		// 开始事务 
		EntityManagerHelper.beginTransaction();
		// 3. 保存
		dao.save(user);
		
		// 提交事务真正保存实体到数据库
		EntityManagerHelper.commit();
		
		// 4. 列出数据库中所有对象
		List<Student> result = dao.findAll();
		
		for(Student o : result) {
			System.out.println(o.getId());
			System.out.println(o.getUsername());
		}
		// 5. 更改用户名
		user.setUsername("测试JPA");
		
		// 开始事务 
		EntityManagerHelper.beginTransaction();
		// 保存（JPA会自动更新变动过的字段）
		dao.update(user);
		
		// 提交事务真正保存实体到数据库
		EntityManagerHelper.commit();
		
		// 6. 查找所有年龄为20的用户，从第1个开始获取（第0个是第一条记录）
		result = dao.findByAge(20, 1);
		
		for(Student o : result) {
			System.out.println(o.getId());
			System.out.println(o.getUsername());
		}
		
		// 7. 根据 ID 查找
		user = dao.findById(2);
		
		System.out.println(user.getUsername());	
		
		// 8. 删除
		// 开始事务 
		EntityManagerHelper.beginTransaction();
		// 保存（JPA会自动更新变动过的字段）
		dao.delete(user);
		
		// 提交事务真正保存实体到数据库
		EntityManagerHelper.commit();		
	}
}

 

若部署到tomcat，没有什么问题，也不要额外添加什么。