Question

环境：

Ubuntu 14.04
Netbeans 8.0.2
JPA 2.1

我正在使用javaee做一些测试示例，它提出了一些我想要清除它的东西。我刚刚使用持久性单元创建了Entity ToDo，但它确实有用，但我真的不知道实际保存数据的位置。

persistance.xml

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1" xmlns="http://xmlns.jcp.org/xml/ns/persistence" 
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
    <persistence-unit name="prod" transaction-type="JTA">
        <properties>
            <property name="javax.persistence.schema-generation.database.action" value="drop-and-create"/>
        </properties>
    </persistence-unit>
</persistence>

ToDo.java

...
@Entity
@NamedQuery(name=ToDo.findAll, query= "SELECT t FROM ToDo t")
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class ToDo {

    @Id
    @GeneratedValue
    private long id;

    public static final String PREFIX = "reminders.entity.ToDo";
    public static final String findAll = PREFIX + "findAll";

    private String caption;
    private String description;
    private int priority;

    public ToDo(String caption, String description, int priority) {
        this.caption = caption;
        this.description = description;
        this.priority = priority;
    }

    public ToDo() {
    }

    public long getId() {
        return id;
    }

    public static String getFindAll() {
        return findAll;
    }

    public String getCaption() {
        return caption;
    }

    public String getDescription() {
        return description;
    }

}

Answer 1

您没有保存任何数据，因为您没有连接到任何数据库。您需要的要求是：

<property name="javax.persistence.jdbc.driver" value="some.driver"/>
<property name="javax.persistence.jdbc.url" value="location"/>
<property name="javax.persistence.jdbc.user" value="youruser"/>
<property name="javax.persistence.jdbc.password" value="yourpassword"/>

查看Configure the persistence xml file或Persistence Wiki。

的方法

正如您现在所做的那样，您的对象只是存在于应用的上下文中。

Answer 2

首先，安装MySQL：

sudo apt-get install mysql-server mysql-client

下载MySQL JDBC driver（即Connector / J）。如果您正在编写桌面应用程序，只需使用Maven将其添加到您的maven项目中。如果您正在编写Web应用程序，请将驱动程序添加到服务器的类路径中（每个服务器都有所不同，因此请对Stack Overflow进行一些研究。）

假设您正在编写桌面应用程序和eclipselink，请使您的persistence.xml看起来如下所示：

<?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="PU" transaction-type="RESOURCE_LOCAL">
    <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
    <class>com.myPackage.ToDo</class>
    <properties>
      <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/TEST_DB"/>
      <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
      <property name="javax.persistence.jdbc.user" value="user"/>
      <property name="javax.persistence.jdbc.password" value="pass"/>
    </properties>
  </persistence-unit>
</persistence>

如果您在服务器上运行，您需要在服务器的管理控制台中配置JNDI数据源，那么类似以下内容：

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1" xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
    <persistence-unit name="PU" transaction-type="JTA">
        <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
        <jta-data-source>jdbc/MyDBConnection</jta-data-source>
        <class>com.myPackage.ToDo</class>
        <exclude-unlisted-classes>true</exclude-unlisted-classes>
        <properties>
            <property name="eclipselink.logging.level" value="SEVERE"/>
        </properties>
    </persistence-unit>
</persistence>

如果我创建了一个默认持久单元，它在哪里用Netbeans保存持久性数据？

2 个答案: