无法实例化 bean：构造函数抛出异常；嵌套异常是 java.lang.NullPointerException答案

【问题标题】：Could not instantiate bean : Constructor threw exception; nested exception is java.lang.NullPointerException无法实例化 bean：构造函数抛出异常；嵌套异常是 java.lang.NullPointerException
【发布时间】：2013-05-09 19:19:15
【问题描述】：

package baseDao;

public interface BaseDao {

    public void create(Object obj);
    public void delete(Object obj);
    public void update(Object obj);
    public void get(Object obj);
}

package baseDao;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.springframework.beans.factory.annotation.Autowired;


public abstract  class BaseDaoImpl implements BaseDao {

    @Autowired
    private  SessionFactory usermanagementSessionFactory;
    private  Session session = usermanagementSessionFactory.getCurrentSession();

    /*-----------------To save an object--------------*/

    public void create(Object obj){
        session.save(obj);
    }

    /*-----------------To delete an object--------------*/


    public void delete(Object obj){
        session.delete(obj);
    }

    /*-----------------To update an object--------------*/

    public void update(Object obj){
        session.update(obj);
    }

    /*-----------------To find/Get an object--------------*/

    public void get(Object obj){

    }



    protected SessionFactory getUsermanagementSessionFactory() {
        return usermanagementSessionFactory;
    }


    protected void setUsermanagementSessionFactory(
            SessionFactory usermanagementSessionFactory) {
        this.usermanagementSessionFactory = usermanagementSessionFactory;
    }

}




<?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:util="http://www.springframework.org/schema/util"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:jee="http://www.springframework.org/schema/jee"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
        http://www.springframework.org/schema/util
        http://www.springframework.org/schema/util/spring-util-3.0.xsd
        http://www.springframework.org/schema/context 
        http://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/jee 
        http://www.springframework.org/schema/jee/spring-jee-3.0.xsd">

    <util:properties id="usermanagementHibernateProperties" location="classpath:usermanagement-hibernate.properties" />

    <bean id="usermanagementSessionFactory"
        class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
        <property name="dataSource" ref="usermanagementDataSource" />
        <property name="configLocation" value="classpath:hibernate.cfg.usermanagement.xml" />
        <property name="configurationClass" value="org.hibernate.cfg.AnnotationConfiguration" />
        <property name="hibernateProperties" ref="usermanagementHibernateProperties" />
    </bean>

    <jee:jndi-lookup id="usermanagementDataSource" jndi-name="java:usermanagementDS" />

    <bean id="city" class="com.ecom.data.entities.user.City"/>
    <bean id="state" class="com.ecom.data.entities.user.State"/>
    <bean id="country" class="com.ecom.data.entities.user.Country"/>
    <bean id="pincodes" class="com.ecom.data.entities.user.Pincodes"/>
    <bean id="notification" class="com.ecom.data.entities.notification.Notifications"/>
    <bean id="notification_types" class="com.ecom.data.entities.notification.Notification_Types"/>
    <bean id="transactions" class="com.ecom.data.entities.transaction.Transactions"/>
    <bean id="address" class="com.ecom.data.entities.user.Address"/>
    <bean id="user_master" class="com.ecom.data.entities.user.User_Master"/>
    <bean id="notification_channels" class="com.ecom.data.entities.notification.Notification_Channels"/>
    <bean id="notification_time" class="com.ecom.data.entities.notification.Notification_Time"/>
    <bean id="prefilled_response" class="com.ecom.data.entities.product.Prefilled_Response"/>
    <bean id="payment_options" class="com.ecom.data.entities.transaction.Payment_Options"/>
    <bean id="catagory" class="com.ecom.data.entities.product.Catagory"/>
    <bean id="vendor" class="com.ecom.data.entities.product.Vendor"/>
    <bean id="requester" class="com.ecom.data.entities.product.Requester"/>
    <bean id="requirement_type" class="com.ecom.data.entities.product.Requirement_type"/>
    <bean id="discount_offer_type" class="com.ecom.data.entities.product.Discount_Offer_Type"/>
    <bean id="discount_offers" class="com.ecom.data.entities.product.Discount_Offers"/>
    <bean id="requirements" class="com.ecom.data.entities.product.Requirements"/>
    <bean id="product_catalog" class="com.ecom.data.entities.product.Product_Catalog"/>
    <bean id="product_catalog_vendor" class="com.ecom.data.entities.product.Product_Catalog_Vendor"/>
    <bean id="product_vendor_payment_option_location" class="com.ecom.data.entities.product.PRODUCT_VENDOR_PAYMENT_OPTION_LOCATION"/>

    <bean id="baseDaoImpl" abstract="true"  class="baseDao.BaseDaoImpl"> </bean>
    <bean id="pincodeDao" parent="baseDaoImpl" class="com.ecom.data.access.user.PincodeDao"> </bean>


</beans>





package com.ecom.data.access.user;

import junit.framework.Assert;

import org.junit.BeforeClass;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.AbstractTransactionalJUnit4SpringContextTests;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import com.ecom.data.entities.user.Pincodes;


@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = {"/applicationContext-usermanagement-dao.xml",
        "/applicationContext-usermanagement-dao-test.xml" })
public class PiccodeTest extends AbstractTransactionalJUnit4SpringContextTests {


    @BeforeClass
    public static void setup(){}


    @Test
    public void pincodeTest(){

        PincodeDao pinDao = new PincodeDao();   // object of dao class to call the create method
        pinDao.save();

    }

}
______________________________________________________________________
when i run this code with junit with maven it gives the error
-------------------->

SEVERE: Caught exception while allowing TestExecutionListener [org.springframework.test.context.support.DependencyInjectionTestExecutionListener@1f2edd2] to prepare test instance [com.ecom.data.access.user.PiccodeTest@1dbb27d]
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'pincodeDao' defined in class path resource [applicationContext-usermanagement-dao.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.ecom.data.access.user.PincodeDao]: 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:626)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:932)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:479)
    at org.springframework.test.context.support.AbstractGenericContextLoader.loadContext(AbstractGenericContextLoader.java:96)
    at org.springframework.test.context.support.AbstractGenericContextLoader.loadContext(AbstractGenericContextLoader.java:44)
    at org.springframework.test.context.TestContext.buildApplicationContext(TestContext.java:198)
    at org.springframework.test.context.TestContext.getApplicationContext(TestContext.java:233)
    at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.injectDependencies(DependencyInjectionTestExecutionListener.java:126)
    at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.prepareTestInstance(DependencyInjectionTestExecutionListener.java:85)
    at org.springframework.test.context.TestContextManager.prepareTestInstance(TestContextManager.java:231)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.createTest(SpringJUnit4ClassRunner.java:95)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.invokeTestMethod(SpringJUnit4ClassRunner.java:139)
    at org.junit.internal.runners.JUnit4ClassRunner.runMethods(JUnit4ClassRunner.java:51)
    at org.junit.internal.runners.JUnit4ClassRunner$1.run(JUnit4ClassRunner.java:44)
    at org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:27)
    at org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:37)
    at org.junit.internal.runners.JUnit4ClassRunner.run(JUnit4ClassRunner.java:42)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
Caused by: org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.ecom.data.access.user.PincodeDao]: 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)
    ... 30 more
Caused by: java.lang.NullPointerException
    at baseDao.BaseDaoImpl.<init>(BaseDaoImpl.java:11)
    at com.ecom.data.access.user.PincodeDao.<init>(PincodeDao.java:7)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:148)
    ... 32 more

在这段代码中，我正在尝试运行我的实体我有一个带有 getter setter 的 pincode 实体，现在我只想在我的测试范围内使用此代码保存数据

我正在使用 hibernate 4 spring 3 和 maven 3

【问题讨论】：

你试过使用 sessionfactory.openSession()

标签： spring hibernate maven

【解决方案1】：

问题出在这里：

@Autowired
private  SessionFactory usermanagementSessionFactory;
private  Session session = usermanagementSessionFactory.getCurrentSession();

sessionFactory 需要自动装配，但这只发生在构造之后。施工涉及正在执行的第二条生产线 - 它使用未设置的工厂。因此你会得到一个空指针异常。

即使你的类没有构造函数，实例的构造仍然可以作为字段初始化的结果抛出异常，如本例所示。

【讨论】：

所以对于这个我现在应该怎么做我该如何解决这个问题
@user2385113 使用构造函数注入或@PostContruct注解的方法来做需要按特定顺序进行的初始化。

【解决方案2】：

将会话初始化移动到下面的方法

@PostConstruct
public void init(){
      session = usermanagementSessionFactory.getCurrentSession();
}

【讨论】：

需要换行 private Session session = usermanagementSessionFactory.getCurrentSession();与会话会话。如果您已经这样做了，但仍然出现错误，请检查您的 Spring Configuration xml 或放置您的 Spring 配置和堆栈跟踪
你也可以查看我今年早些时候问过的这个问题stackoverflow.com/questions/14953410/…

【解决方案3】：

当 usernameSessionFactory 对象尚未初始化时，您正在尝试初始化会话对象。

在一个类中，所有 Spring @Autowired 对象都在该类的实例构造完成后初始化。

private  Session session = usermanagementSessionFactory.getCurrentSession();

但是如果一个实例以上述代码的方式清除，将在构造之前初始化，它们甚至可以用作构造的参数。

@Autowired
private  SessionFactory usermanagementSessionFactory;
private  Session session;

@PostConstruct
public void init() {
    session = usermanagementSessionFactory.getCurrentSession();
}

以上代码，在构造完成后会初始化会话对象，也就是说usermanagementSessionFactory已经准备好，不为空。

希望对您有所帮助..

【讨论】：

请考虑添加一些说明
谢谢 yahya，我没有时间解释任何事情，只是尝试提供一些可能有用的代码