Question

我是JPA和Servlets的新手。我试图创建学生实体并使用Servlet将其插入我的数据库。代码中没有错误。当我去Servlet时，它在浏览器中没有错误。但是这些值没有插入到我的数据库中。

学生实体： -

@Entity
public class Student implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;

@Column(nullable = false)
private String name;

@Column(nullable = false)
private int age;

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public int getAge() {
    return age;
}

public void setAge(int age) {
    this.age = age;
}



public Long getId() {
    return id;
}

public void setId(Long id) {
    this.id = id;
}

@Override
public int hashCode() {
    int hash = 0;
    hash += (id != null ? id.hashCode() : 0);
    return hash;
}

@Override
public boolean equals(Object object) {
    // TODO: Warning - this method won't work in the case the id fields are not set
    if (!(object instanceof Student)) {
        return false;
    }
    Student other = (Student) object;
    if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
        return false;
    }
    return true;
}

@Override
public String toString() {
    return "model.Student[ id=" + id + " ]";
}

}

我的Servlet： -

public class A extends HttpServlet {

@PersistenceUnit(unitName = "persistenceCheckPU")
EntityManagerFactory emf;

@Resource
UserTransaction ut;

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    try (PrintWriter out = response.getWriter()) {

        Student student = new Student();
        student.setName("John");
        student.setAge(22);

        EntityManager em = emf.createEntityManager();
        ut.begin();

        em.persist(student);
        ut.commit();

        out.println("<h2>Success!!!</h2>");

    } catch (SecurityException | IllegalStateException | javax.transaction.RollbackException | HeuristicMixedException | HeuristicRollbackException | SystemException | NotSupportedException ex) {
        Logger.getLogger(A.class.getName()).log(Level.SEVERE, null, ex);
    }
}

我的目标： -

将ID设为唯一且自动增量。

已更新

的persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1" 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">
<persistence-unit name="persistenceCheckPU" transaction-type="JTA">
<jta-data-source>jdbc_persistence</jta-data-source>
<exclude-unlisted-classes>false</exclude-unlisted-classes>
<properties>
  <property name="javax.persistence.schema-generation.database.action" value="create"/>
</properties>
</persistence-unit>
</persistence>

Answer 1

检查您是否有JTA持久性单元（在persistence.xml中），然后在开始交易后致电em.joinTransaction()或在开始交易后致电EntityManager em = emf.createEntityManager();。

Answer 2

您将需要与该操作相关联的交易。有两种方法可以解决这个问题 - 1.使用Spring Transaction 添加此注释

<tx:annotation-driven transaction-manager="transactionManager" proxy-target-class="false"/>

在您的DAO课程中使用@Transactional

为您的方法添加注释

使用Spring AOP 就您的方法提供建议 -

配置您的建议

<aop:config>
        <aop:pointcut id="appControllerTransactionPointCuts"
            expression="execution(* package.structure..*.*(..))" />
<aop:advisor advice-ref="txAdvice" pointcut-ref="appControllerTransactionPointCuts" />
    </aop:config>

现在您的DAO将在事务中运行

EntityManager.persist（）不向DB插入值

2 个答案: