之前一直在用EJB3，但現在想在J2SE里面使用JPA，因為不大喜歡Hibernate的XML文件配置。

而使用DB4O的時候，出現了一些莫名其妙的問題，一直沒解決，就暫時擱下了。

使用myeclipse 6開發jpa如下：

1.創建web project

2.添加jpa capabilities，選擇toplink，把自動創建數據庫的和更新persistence.xml的勾上

3.切換成database explorer視圖，選擇表，jpa逆向工程。

4.測試

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/persistencehttp://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>

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生成的幾個類如下：

實體類：

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 {// Fieldsprivate 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(); }

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DAO類

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 constantspublic 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;}}}

?

還有一個非常有用的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);}}

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然后使用helper和dao進行測試

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.創建 DAOConsumerDAO dao = new ConsumerDAO();// 2.創建實體類Consumer c = new Consumer();c.setName("jpa01");c.setPassword("jianchi");// 開始事務 EntityManagerHelper.beginTransaction();// 3. 保存dao.save(c);// 提交事務真正保存實體到數據庫EntityManagerHelper.commit();// 4. 列出數據庫中所有對象List<Consumer> result = dao.findAll();for(Consumer o : result) {System.out.println(o.getId());System.out.println(o.getName());}}}

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測試實例如下：

package test; import java.util.List; import dao.*;public class JPATest {public static void main(String[] args) {// 1.創建 DAOStudentDAO dao = new StudentDAO();// 2.創建實體類Student user = new Student();user.setUsername("hellojpa test");user.setPassword("jpa password");user.setAge(20);// 開始事務 EntityManagerHelper.beginTransaction();// 3. 保存dao.save(user);// 提交事務真正保存實體到數據庫EntityManagerHelper.commit();// 4. 列出數據庫中所有對象List<Student> result = dao.findAll();for(Student o : result) {System.out.println(o.getId());System.out.println(o.getUsername());}// 5. 更改用戶名user.setUsername("測試JPA");// 開始事務 EntityManagerHelper.beginTransaction();// 保存（JPA會自動更新變動過的字段）dao.update(user);// 提交事務真正保存實體到數據庫EntityManagerHelper.commit();// 6. 查找所有年齡為20的用戶，從第1個開始獲取（第0個是第一條記錄）result = dao.findByAge(20, 1);for(Student o : result) {System.out.println(o.getId());System.out.println(o.getUsername());}// 7. 根據 ID 查找user = dao.findById(2);System.out.println(user.getUsername()); // 8. 刪除// 開始事務 EntityManagerHelper.beginTransaction();// 保存（JPA會自動更新變動過的字段）dao.delete(user);// 提交事務真正保存實體到數據庫EntityManagerHelper.commit(); } }

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若部署到tomcat，沒有什么問題，也不要額外添加什么。

轉載于:https://www.cnblogs.com/cxccbv/archive/2009/02/25/1397928.html

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