JPA入门之HelloWorld

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利用空余的时间学习了JPA，刚写完一个HelloWorld就来写这篇博客，记录一下自己的编程之路。接下来就步入正题：让我们来搭建一个JPA的环境，小编依旧使用的是IDEA，在这里要特别说明：使用IDEA搭建JPA时，IDE自动生成的persistence.xml不是在resources源码包下，这是运行就会抛出异常，说找不到persistence.xml，因此我们需要把persistence.xml拷贝到resources下。一 ：工程目录结构![工程目录结构图](http://img.blog.csdn.net/20170406102855026?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQveWdlbmdsZW1hbg==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast)二 ：创建实体类

/** * @Table 表明该持久化类生成的数据表的表名称 * @Entity 标识该类是一个持久化类 */@Table(name = "jpa_customer")@Entitypublic class Customer {    private Integer id;    private Integer age;    private String lastName;    private String email;    private Date createDate; //创建时间    private Date birth; //生日    public Customer() {    }    public Customer(Integer age, String lastName, String email) {        this.age = age;        this.lastName = lastName;        this.email = email;    }    public Customer(Integer id, Integer age, String lastName, String email) {        this.id = id;        this.age = age;        this.lastName = lastName;        this.email = email;    }    /**     * @GeneratedValue 标明主键的生成策略     *  1：GenerationType.AUTO 默认的生成策略,JPA会根据数据库选择合适的策略     *  2：GenerationType.SEQUENCE 序列     *  3: GenerationType.IDENTITY 采用数据库自增 oracle不支持此策略     *  @Id ：标明主键     * @return     */    @GeneratedValue(strategy = GenerationType.AUTO)    @Id    public Integer getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    /**     * 对于 Date 类型的属性，若我们不做任何标识     * 那么在生成的数据表所对应的字段类型为 dateTime,     * 然而对于一些特殊的字段就不能满足我们的需求，因此我们可以使用     *     * @return     */    @Temporal(TemporalType.TIMESTAMP)  //时间戳，对应数据表的类型为dateTime    public Date getCreateDate() {        return createDate;    }    public void setCreateDate(Date createDate) {        this.createDate = createDate;    }    @Temporal(TemporalType.DATE)  //精确到年月日, 对应数据表的类型为date    public Date getBirth() {        return birth;    }    public void setBirth(Date birth) {        this.birth = birth;    }    /**     * 若在get方法上没有任何注解，那么Jpa会在该get方法上     * 默认添加 @Basic 注解     * @return     */    @Basic    public Integer getAge() {        return age;    }    public void setAge(Integer age) {        this.age = age;    }    /**     * @Column : 可以定义该字段生成数据表的字段名称，长度....     * @return     */    @Column(name = "last_name", length = 50, nullable = false, unique = true)    public String getLastName() {        return lastName;    }    public void setLastName(String lastName) {        this.lastName = lastName;    }    public String getEmail() {        return email;    }    public void setEmail(String email) {        this.email = email;    }    @Override    public String toString() {        return "Customer{" +                "id=" + id +                ", age=" + age +                ", lastName='" + lastName + '\'' +                ", email='" + email + '\'' +                '}';    }    /**     * 对于这种自定义的方法，我们并不需要将他映射为数据表的字段     * IDEA非常智能，当发现该方法没有对应的setInfo()方法时，IDEA     * 会提示错误，运行时就会抛出异常：     * org.hibernate.PropertyNotFoundException:     * Could not find a setter for property info in class org.jpa.entity.Customer     * 因此我们可以使用 @Transient 注解标识它     * @return     */    @Transient    public String getInfo(){        return "getInfo";    }}

二：编写persistence.xml

<?xml version="1.0" encoding="UTF-8"?><persistence  version="2.0" 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_2_0.xsd">    <persistence-unit name="jpa01" transaction-type="RESOURCE_LOCAL">        <!-- 配置使用什么ORM来实现JPA , 注意由于本人使用的是Hibernate4.1.9.Final,            hibernate-entitymanager 4.1.9.Final，在高版本中此方法已被弃用了        -->        <provider>org.hibernate.ejb.HibernatePersistence</provider>        <!-- 添加持久化类 -->        <class>org.jpa.entity.Customer</class>        <properties>            <!-- 连接数据库的基本信息 -->            <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>            <property name="javax.persistence.jdbc.url" value="jdbc:mysql:///jpa"/>            <property name="javax.persistence.jdbc.user" value="root"/>            <property name="javax.persistence.jdbc.password" value="root"/>            <!-- 配置JPA实现产品的基本信息，实际上是配置Hibernate的基本信息 -->            <!-- 显示SQL语句 -->            <property name="hibernate.show_sql" value="true"/>            <!-- 格式化SQL语句 -->            <property name="hibernate.format_sql" value="true"/>            <!-- 生成表策略 -->            <property name="hibernate.hbm2ddl.auto" value="update"/>        </properties>    </persistence-unit></persistence>

三：测试类

public class Main {    public static void main(String[] args) {        //创建EntityManagerFactory        String name = "jpa01" ;        EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory(name);        //创建EntityManager        EntityManager entityManager = entityManagerFactory.createEntityManager();        //开启事务        EntityTransaction transaction = entityManager.getTransaction();        transaction.begin();        //持久化数据        Customer customer = new Customer(21, "Jerry", "Jerry@163.com");        customer.setCreateDate(new Date());        customer.setBirth(new Date());        entityManager.persist(customer);        //提交事务        transaction.commit();        //关闭EntityManagerFactory        entityManagerFactory.close();        //关闭EntityManager        entityManager.close();    }}

四：pom.xml

<dependencies>    <dependency>      <groupId>junit</groupId>      <artifactId>junit</artifactId>      <version>4.11</version>      <scope>test</scope>    </dependency>    <dependency>      <groupId>org.hibernate.common</groupId>      <artifactId>hibernate-commons-annotations</artifactId>      <version>4.0.2.Final</version>    </dependency>    <dependency>      <groupId>org.hibernate</groupId>      <artifactId>hibernate-core</artifactId>      <version>4.1.9.Final</version>    </dependency>    <dependency>      <groupId>org.hibernate.javax.persistence</groupId>      <artifactId>hibernate-jpa-2.0-api</artifactId>      <version>1.0.1.Final</version>    </dependency>    <dependency>      <groupId>org.jboss.logging</groupId>      <artifactId>jboss-logging</artifactId>      <version>3.1.0.GA</version>    </dependency>    <dependency>      <groupId>org.slf4j</groupId>      <artifactId>slf4j-api</artifactId>      <version>1.6.0</version>    </dependency>    <dependency>      <groupId>org.jboss.spec.javax.transaction</groupId>      <artifactId>jboss-transaction-api_1.1_spec</artifactId>      <version>1.0.1.Final</version>    </dependency>    <dependency>      <groupId>org.hibernate</groupId>      <artifactId>hibernate-entitymanager</artifactId>      <version>4.1.9.Final</version>    </dependency>    <dependency>      <groupId>org.eclipse.persistence</groupId>      <artifactId>javax.persistence</artifactId>      <version>2.1.0-RC2</version>    </dependency>    <dependency>      <groupId>dom4j</groupId>      <artifactId>dom4j</artifactId>      <version>1.6.1</version>    </dependency>    <dependency>      <groupId>antlr</groupId>      <artifactId>antlr</artifactId>      <version>2.7.7</version>    </dependency>    <dependency>      <groupId>org.javassist</groupId>      <artifactId>javassist</artifactId>      <version>3.15.0-GA</version>    </dependency>    <dependency>      <groupId>mysql</groupId>      <artifactId>mysql-connector-java</artifactId>      <version>5.1.18</version>    </dependency>    <!-- hibernate 二级缓存 -->    <dependency>      <groupId>net.sf.ehcache</groupId>      <artifactId>ehcache-core</artifactId>      <version>2.4.3</version>    </dependency>    <dependency>      <groupId>org.hibernate</groupId>      <artifactId>hibernate-ehcache</artifactId>      <version>4.2.4.Final</version>    </dependency>    <dependency>      <groupId>org.jboss.logging</groupId>      <artifactId>jboss-logging</artifactId>      <version>3.1.0.CR2</version>    </dependency>    <dependency>      <groupId>commons-collections</groupId>      <artifactId>commons-collections</artifactId>      <version>3.1</version>    </dependency>    <dependency>      <groupId>org.hibernate</groupId>      <artifactId>hibernate-validator</artifactId>      <version>4.2.0.Final</version>    </dependency>    <dependency>      <groupId>commons-logging</groupId>      <artifactId>commons-logging</artifactId>      <version></version>    </dependency>  </dependencies>

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