注释实体管理器空尖例外

问题描述

我做使用JPA一个小项目。我需要插入Employee对象。
对于我使用注释实体管理器时，我得到了空指针异常。
但是，当我用普通的EntityManager不使用它工作正常的注释。
我是否需要配置其他地方其他比的persistence.xml来解决这个〔实施例罚款？

请参阅下面的code。

 公共类EmployeeDao实现IEmployeeDao {     @PersistenceContext（的unitName =时间表）
    私人EntityManager的EntityManager的;    @覆盖
    公共布尔在CreateEmployee（IEmployee员工）{        this.entityManager.persist（员工）;        返回true;
    }
}
 

的persistence.xml

 ＆LT;？XML版本=1.0编码=UTF-8＆GT？;
＆LT;持久性的xmlns：XSI =htt​​p://www.w3.org/2001/XMLSchema-instance
    XSI：的schemaLocation =htt​​p://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd
    版本=2.0的xmlns =htt​​p://java.sun.com/xml/ns/persistence＆GT;
    ＆LT;持久性单位名称=时间表交易型=RESOURCE_LOCAL＆GT;
        ＆LT;类别和GT; com.timesheet.model.Employee＆LT; /班＆GT;
        ＆LT;性状＆gt;
            ＆LT;属性名=javax.persistence.jdbc.driverVALUE =com.mysql.jdbc.Driver/＆GT;
            ＆LT;属性名=javax.persistence.jdbc.url
                值=的jdbc：mysql的：//本地主机：3306 /时间表/＆GT;
            ＆LT;属性名=javax.persistence.jdbc.userVALUE =根/＆GT;
            ＆LT;属性名=javax.persistence.jdbc.passwordVALUE =/＆GT;            ＆LT;！ - 的EclipseLink应该自动创建数据库模式 - ＆GT;
            ＆LT;属性名=eclipselink.ddl代值=创建的表/＆GT;
            ＆LT;属性名=eclipselink.ddl-generation.output模式
                值=数据库/＆GT;
        ＆LT; /性状＆gt;    ＆LT; /持久化部＆gt;
＆LT; /持久＆GT;
 

解决方案

资源注入（在通过使用你的情况的 @PersistenceContext 的），只能在容器管理类（比如EJB和Servlet）。这与Java EE规范的V6更详细的信息为例进行说明，EE5.2.5。

你可以做什么：

• 修改类使其托管类


• 资源的举动注射托管类，并把它传递给
  EmployeeDao，


• 使用JNDI查找和以前一样

I am doing a small project using JPA. I need to insert the employee object.For that when I use the annotated entity manager I got the NullPointer exception.But when I use the Normal EntityManager without using the annotation it is working fine.Do I need to configure somewhere else other than persistence.xml to work this examle fine?

Please see the code below.

public class EmployeeDao implements IEmployeeDao{

     @PersistenceContext(unitName = "timesheet")
    private EntityManager entityManager ;

    @Override
    public boolean createEmployee(IEmployee employee) {

        this.entityManager.persist(employee);

        return true;
    }
}

persistence.xml

<?xml version="1.0" encoding="UTF-8" ?>
<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"
    version="2.0" xmlns="http://java.sun.com/xml/ns/persistence">
    <persistence-unit name="timesheet" transaction-type="RESOURCE_LOCAL">
        <class>com.timesheet.model.Employee</class>
        <properties>
            <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
            <property name="javax.persistence.jdbc.url"
                value="jdbc:mysql://localhost:3306/timesheet" />
            <property name="javax.persistence.jdbc.user" value="root" />
            <property name="javax.persistence.jdbc.password" value="" />

            <!-- EclipseLink should create the database schema automatically -->
            <property name="eclipselink.ddl-generation" value="create-tables" />
            <property name="eclipselink.ddl-generation.output-mode"
                value="database" />
        </properties>

    </persistence-unit>
</persistence>

解决方案

Injection of resources (in your case via use of @PersistenceContext) works only in container managed classes (like EJBs and Servlets). This explained with more details for example in Java EE specification v6, EE5.2.5.

What you can do:

• Modify your class so that it is managed class
• move injection of resources to managed class and pass it toEmployeeDao,
• use JNDI lookup as before

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