java - EntityManager.persist() 不将值插入数据库

Question

我对 JPA 和 Servlet 还不熟悉。我正在尝试创建学生实体并使用 Servlet 将其插入到我的数据库中。代码中没有错误。当我访问 Servlet 时，它在浏览器中运行正常，没有错误。但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 创建为唯一且自动递增的 ID。

已更新

持久性.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)，然后在开始事务后调用 em.joinTransaction() 或调用 EntityManager em = emf.createEntityManager(); 开始事务后。