使用JPA persistence.xml报错:A ResourcePool could not acquire a resource from its primary factory or sour

使用JPA persistence.xml 配置时，报错:

Unable to acquire JDBC Connection

Caused by: java.sql.SQLException: Connections could not be acquired from the underlying database!

Caused by: com.mchange.v2.resourcepool.CannotAcquireResourceException: A ResourcePool could not acquire a resource from its primary factory or source.

首先检查persistence.xml中url，driver，username，password的写法是否正确，我是直接把hibernate.cfg.xml下面的拷贝过来的，所以写错了，对比如下：

hibernate：

<property name="connection.url">jdbc:mysql://localhost:3306/hibernate</property>
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="connection.username">root</property>
<property name="connection.password">123456</property>

JPA:

<property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/hibernate"/>
<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
<property name="javax.persistence.jdbc.user" value="root"/>
<property name="javax.persistence.jdbc.password" value="123456"/>

注意driver_class 变为driver，username变为user，还有前缀也要变为 javax.persistence.jdbc，最后附上正确的persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<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_2.xsd"
             version="2.2">
    <!--transaction-type:事务类型-->
        <!--JTA:JAVA Transaction API-->
        <!--RESOURCE_LOCAL:本地代码事务-->
    <persistence-unit name="myJPAUnit" transaction-type="RESOURCE_LOCAL">
        <!--JPA提供商，可以不写-->
        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
        <!--JPA注解的实体类位置，可以不写-->
        <class>domain.CstCustomer</class>
        <class>domain.CstLinkman</class>

        <!--以下只要把cfg.xml文件中的拷贝过来稍加改动即可-->
        <!--1.连接数据库的信息-->
        <properties>
            <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/hibernate"/>
            <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
            <property name="javax.persistence.jdbc.user" value="root"/>
            <property name="javax.persistence.jdbc.password" value="123456"/>
            <!--2.hibernate可选配置-->
            <!--检测实体类的映射配置和数据库的表结构是否一致，如果不一致，更新表结构-->
            <property name="hbm2ddl.auto" value="update"/>
            <!--数据库方言-->
            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5Dialect"/>
            <!--是否显示hibernate生成的sql语句-->
            <property name="hibernate.show_sql" value="true"/>
            <!--是否使用格式化输出sql语句-->
            <property name="hibernate.format_sql" value="true"/>
            <!--3.设置hibernate的连接池提供商-->
            <property name="hibernate.connection.provider_class" value="org.hibernate.c3p0.internal.C3P0ConnectionProvider"/>

        </properties>
    </persistence-unit>
</persistence>

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