我用JPA的設定檔，persistence.xml，設定以下的資料庫連線資訊：

<persistence 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" 
             version="2.1">

    <persistence-unit name="mydb" transaction-type="RESOURCE_LOCAL">
        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
        <class>com.test.vo.Customer</class>
        <properties>
            <property name="javax.persistence.jdbc.driver" value="oracle.jdbc.driver.OracleDriver" />
            <property name="javax.persistence.jdbc.url" value="jdbc:oracle:thin://localhost:1521/orcl" />
            <property name="javax.persistence.jdbc.user" value="cuser" />
            <property name="javax.persistence.jdbc.password" value="cuser" />
            <property name="hibernate.dialect" value="org.hibernate.dialect.Oracle10gDialect" />
            <property name="hibernate.show_sql" value="true" />
            <property name="hibernate.hbm2ddl.auto" value="none" />
        </properties>
    </persistence-unit>

</persistence>

然後在DAO讀取這個設定檔：

	EntityManagerFactory emf = Persistence.createEntityManagerFactory("mydb");
	EntityManager em = emf.createEntityManager();

而我已經有在Maven repository加入了ojdbc8.jar：
https://i.imgur.com/FGIlQxg.png

也有確定有在專案內引入ojdbc8.jar：
https://i.imgur.com/bkXg65L.png

pom.xml也有加入相關設定：
https://i.imgur.com/koleE8Y.png

但是要連線到資料庫時，仍然會跳出java.lang.ClassNotFoundException: Could not load requested class : oracle.jdbc.driver.OracleDriver

在Maven dependecy的ojdbc8.jar，底下的class確實有oracle.jdbc.driver.OracleDriver

那麼為何還會跳出這樣的錯誤？？

結果我將ojdbc8.jar改放到專案內部的lib資料夾內，再到java build path去add jar，把ojdbc8.jar加進來，就好了。