解决了！
我不知道到底出了什么问题，但是效果很好：
<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="default" transaction-type="RESOURCE_LOCAL"> <provider>org.hibernate.ejb.HibernatePersistence</provider> <properties> <property name="javax.persistence.jdbc.driver" value="org.postgresql.Driver" /> <property name="javax.persistence.jdbc.url" value="jdbc:postgresql://localhost:5432/Automoveis" /> <property name="javax.persistence.jdbc.user" value="postgres" /> <property name="javax.persistence.jdbc.password" value="1234" /> <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect" /> <property name="hibernate.hbm2ddl.auto" value="update" /> <property name="hibernate.show_sql" value="true" /> <property name="hibernate.format_sql" value="true"/> </properties> </persistence-unit>
