Question

是否可以在普通的JAVA类中使用PersistenceContext作为JPA的注释？如果没有，你能告诉我如何在没有任何注释的情况下使用PersistenceContext吗？

Answer 1

是的，您可以在任何Java类中使用@PersistenceContext。但是，您必须在Spring配置中指定annotation-config，如以下示例所示：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd">

    <context:annotation-config/>
</beans>

指定后，您可以使用@PersistenceContext，如下所示：

package com.sample.dao.impl

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.Query;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;

public class CustomerDaoImpl {

    @PersistenceContext
    private EntityManager em;

    public Customer getCustomerByName(String customerName) {
        Query query = em.createQuery("SELECT c FROM Customer c WHERE c.name = ?1");
        query.setParameter(1, customerName);
        List<Customer> results = query.getResultList();
        if (results.size() > 0) {
            return results.get(0);
        }
        return null;
    }
}

在注释中使用PersistenceContext

1 个答案: