我正在尝试从会话工厂获取会话以使用我的CRUD方法。我试图在构造函数中设置会话,但是那时bean尚未初始化。在创建bean之后如何初始化它?
堆栈跟踪
Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userDaoImpl' defined in file [/home/ryan/workspace/com-byteslounge-spring-tx/target/classes/com/byteslounge/spring/tx/dao/impl/UserDaoImpl.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.byteslounge.spring.tx.dao.impl.UserDaoImpl]: Constructor threw exception; nested exception is java.lang.NullPointerException
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1011)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:957)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:490)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:461)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:295)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:223)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:292)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:607)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:932)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:479)
at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
at com.byteslounge.spring.tx.Main.main(Main.java:19)
Caused by: org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.byteslounge.spring.tx.dao.impl.UserDaoImpl]: Constructor threw exception; nested exception is java.lang.NullPointerException
at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:163)
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:87)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1004)
... 13 more
Caused by: java.lang.NullPointerException
at com.byteslounge.spring.tx.dao.impl.UserDaoImpl.<init>(UserDaoImpl.java:24)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:525)
at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:148)
... 15 more
UserDaoImpl.java
package com.byteslounge.spring.tx.dao.impl;
import java.util.List;
import org.hibernate.Criteria;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.byteslounge.spring.tx.dao.UserDao;
import com.byteslounge.spring.tx.domain.User;
@Service
public class UserDaoImpl implements UserDao {
@Autowired
private SessionFactory sessionFactory;
private Session session;
public UserDaoImpl() {
session = sessionFactory.getCurrentSession();
}
public SessionFactory getSessionFactory() {
return this.sessionFactory;
}
public void setSessionFactory(SessionFactory sessionFactory) {
this.sessionFactory = sessionFactory;
}
public void insertUser(User user) {
session.save(user);
}
public void removeUserByName(String username) {
User user = null;
try {
getUser(username);
} catch (IndexOutOfBoundsException e) {
System.out.println(username + " does not exist!");
} finally {
if (user != null)
session.delete(user);
}
}
public User getUserById(int userId) {
return (User) session.get(User.class, userId);
}
public User getUser(String username) {
// Query query = sessionFactory.getCurrentSession().createQuery("from User where username = :username");
// query.setParameter("username", username);
Query query = session.getNamedQuery(User.FIND_USER_BY_USERNAME).setString("username", username);
return (User) query.list().get(0);
}
@SuppressWarnings("unchecked")
public List<User> getUsers() {
Criteria criteria = session.createCriteria(User.class);
return criteria.list();
}
}
的applicationContext.xml
<?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"
xmlns:tx="http://www.springframework.org/schema/tx" xmlns:p="http://www.springframework.org/schema/p"
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
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd">
<tx:annotation-driven />
<context:component-scan base-package="com.byteslounge.spring.tx.dao.impl" />
<context:component-scan base-package="com.byteslounge.spring.tx.user.impl" />
<bean
class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<property name="location">
<value>database.properties</value>
</property>
</bean>
<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
destroy-method="close">
<property name="driverClassName" value="${jdbc.driverClassName}" />
<property name="url" value="${jdbc.url}" />
<property name="username" value="${jdbc.username}" />
<property name="password" value="${jdbc.password}" />
</bean>
<bean id="sessionFactory"
class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
<property name="dataSource" ref="dataSource"></property>
<property name="hibernateProperties">
<props>
<prop key="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</prop>
<prop key="hibernate.show_sql">true</prop>
</props>
</property>
<property name="packagesToScan" value="com.byteslounge.spring.tx.domain" />
</bean>
<bean id="transactionManager"
class="org.springframework.orm.hibernate4.HibernateTransactionManager"
p:sessionFactory-ref="sessionFactory">
</bean>
</beans>
答案 0 :(得分:3)
使用@PostConstruct
标记然后获取会话。只有在创建UserDaoImpl
后才会注入您的bean,并且只有在注入所有bean后,Spring才会调用@PostConstruct
方法。
@Service
public class UserDaoImpl implements UserDao {
@Autowired
private SessionFactory sessionFactory;
private Session session;
public UserDaoImpl() {
}
@PostConstruct
public void init() {
this.session = sessionFactory.getCurrentSession();
}
...
}
另一种方式(在我的opnion中更好)是通过构造函数注入并仅在需要时获取当前会话。
...
private final SessionFactory sessionFactory;
@Autowired
public UserDaoImpl(SessionFactory sessionFactory) {
this.sessionFactory = sessionFactory;
}
private Session currentSession() {
return this.sessionFactory.getCurrentSession();
}
修改强>
最好使用第二种方式,因为如果只在构造之后才获得会话,那么一旦会话过期,对DAO的调用将不起作用。在您的交易方法开始拨打电话时始终使用SessionFactory#getCurrentSession()
。
答案 1 :(得分:1)
正如拉尔夫指出的那样,构造函数执行得太早,而Spring此时没有注入任何东西。
此外,您可能不会引用会话,因为它依赖于SessionContext机制,而机制又可能是线程绑定或servlet请求绑定。您的bean可能具有更宽的范围(例如,单例),您将永久存储来自第一个调用者的会话或其他东西!
我建议总是在bean内部从sessionFactory获取会话。