Question

我正在使用hibernate，stripersist和jpa开发条带样本应用程序。我在访问数据库时遇到错误。我是条纹和冬眠的新手。错误如下

org.apache.jasper.JasperException: javax.el.ELException: Error reading 'contacts' on                                
type com.action.ContactListActionBean
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:54    9)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)


javax.el.ELException: Error reading 'contacts' on type com.action.ContactListActionBean
javax.el.BeanELResolver.getValue(BeanELResolver.java:110)
org.apache.jasper.el.JasperELResolver.getValue(JasperELResolver.java:104)
org.apache.el.parser.AstValue.getValue(AstValue.java:183)
org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:184)
org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate(PageContextImpl.java:967)
org.apache.jsp.WEB_002dINF.jsp.contact_005flist_jsp._jspService(contact_005flist_jsp.jav    a:125)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)


java.lang.NullPointerException
com.dao.impl.stripersist.BaseDaoImpl.read(BaseDaoImpl.java:36)
com.action.ContactListActionBean.getContacts(ContactListActionBean.java:46)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:483)
javax.el.BeanELResolver.getValue(BeanELResolver.java:99)
org.apache.jasper.el.JasperELResolver.getValue(JasperELResolver.java:104)
org.apache.el.parser.AstValue.getValue(AstValue.java:183)
org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:184)
org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluenter code   
hereate(PageContextImpl.java:967)
org.apache.jsp.WEB_002dINF.jsp.contact_005flist_jsp._jspService(contact_005flist_jsp.jav    a:125)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)

BaseDaoImpl.java



public abstract class BaseDaoImpl<T,ID extends Serializable>
implements Dao<T,ID>
{
private Class<T> entityClass;

@SuppressWarnings("unchecked")
public BaseDaoImpl() {
    entityClass = (Class<T>)
        ((ParameterizedType) getClass().getGenericSuperclass())
        .getActualTypeArguments()[0];
}
@SuppressWarnings("unchecked")
public List<T> read() {
    return Stripersist.getEntityManager()
        .createQuery("from " + entityClass.getName())
        .getResultList();
}
public T read(ID id) {
    return Stripersist.getEntityManager().find(entityClass, id);
}
@SuppressWarnings("unchecked")
public void save(T object) {
    Stripersist.getEntityManager().persist(object);
}
public void delete(T object) {
    Stripersist.getEntityManager().remove(object);
}
public void commit() {
    Stripersist.getEntityManager().getTransaction().commit();
}

@SuppressWarnings("unchecked")
private T getSingleResult(Query query) {
    try {
        return (T) query.getSingleResult();
    }
    catch (NonUniqueResultException exc) {
        return (T) query.getResultList().get(0);
    }
    catch (NoResultException exc) {
        return null;
    }
    }
  }


ContactDao.java

public interface ContactDao extends Dao<Contact,Integer> {

}

ContactDaoImpl.java

public class ContactDaoImpl extends BaseDaoImpl<Contact,Integer>
implements ContactDao
{

}

 Contact.java

@Entity
public class Contact extends ModelBase{
private String firstName;
private String lastName;
private String email;  

public String getFirstName() {
    return firstName;
}

public void setFirstName(String firstName) {
    this.firstName = firstName;
}

public String getLastName() {
    return lastName;
}

public void setLastName(String lastName) {
    this.lastName = lastName;
}

public String getEmail() {
    return email;
}

public void setEmail(String email) {
    this.email = email;
}

}

ModelBase.java

@MappedSuperclass
public class ModelBase {
 @Id
@GeneratedValue
private Integer id;
public Integer getId() { return id; }
public void setId(Integer id) { this.id = id; }

@Override
public boolean equals(Object obj) {
    try { return id.equals(((ModelBase) obj).getId()); }
    catch (Exception exc) { return false; }
}
@Override
public int hashCode() {
    return 31 + ((id == null) ? 0 : id.hashCode());
} 
}

ContactListActionBean.java

public class ContactListActionBean extends BaseActionBean{
 private static final String LIST="/WEB-INF/jsp/contact_list.jsp";


@DefaultHandler
public Resolution list() {
    return new ForwardResolution(LIST);
}


public List<Contact> getContacts() {
   return contactDao.read();
} 
}

的persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<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="persistence">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<class>com.model.Contact</class>
<properties>
  <!--  Autodetect entity classes  -->
  <property name="hibernate.archive.autodetection" value="class"/>
  <!--  Automatically create the SQL schema  -->
  <property name="hibernate.hbm2ddl.auto" value="create"/>
  <!--  Tell Hibernate to use HSQLDB  -->
  <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/>
  <property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/>
  <!--  Configure the JDBC database connection  -->
  <property name="hibernate.connection.url" 
  value="jdbc:mysql://localhost:3306/webstore"/>
  <property name="hibernate.connection.username" value="root"/>
  <property name="hibernate.connection.password" value=""/>
  <property name="jdbc.batch_size" value="0"/>
  <!--  Configure the connection pool  -->
  <property name="hibernate.c3p0.min_size" value="5"/>
  <property name="hibernate.c3p0.max_size" value="20"/>
  <property name="hibernate.c3p0.timeout" value="300"/>
  <property name="hibernate.c3p0.max_statements" value="50"/>
  <property name="hibernate.c3p0.idle_test_period" value="3000"/>
  </properties>
  </persistence-unit>
  </persistence>

任何解决方案吗？

Answer 1

您添加的堆栈跟踪在BaseDaoImpl行36上显示NullPointerException。可能在Hibernate / JPA（persistence.xml）中未正确配置EntityManager。

条纹hibernate el异常错误

1 个答案: