Java 尝试通过Hibernate访问数据库后发生NullPointerException_Java_Spring

Java 尝试通过Hibernate访问数据库后发生NullPointerException

java spring

Java 尝试通过Hibernate访问数据库后发生NullPointerException,java,spring,Java,Spring,我试图开发一个简单的web应用程序，但为了排除web前端出现错误的所有可能性，我编写了一个小类，并在命令提示符下执行该类 package org.vadim.testmvc; import org.vadim.testmvc.model.*; import org.vadim.testmvc.service.*; public class TestMain { public static void main(String[] args){ Strings s = new

我试图开发一个简单的web应用程序，但为了排除web前端出现错误的所有可能性，我编写了一个小类，并在命令提示符下执行该类

package org.vadim.testmvc;

import org.vadim.testmvc.model.*;
import org.vadim.testmvc.service.*;
public class TestMain {
    public static void main(String[] args){
        Strings s = new Strings();
        TestService ts = new TestService();
        s.setText("StrText");
        ts.addStrings(s);
        System.out.println(ts.listStrings());
    }
}

TestService.java（不带import语句，但确保它们出现在原始列表中）：

hibernate.cfg.xml：

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD//EN"
    "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<mapping class="org.vadim.testmvc.model.Strings"/>
</session-factory>
</hibernate-configuration>

如果我尝试执行TestDAO.addStrings（Strings）方法，也会发生同样的情况，也就是说，问题不在于listStrings（）的返回结果，而在于对数据库的访问。我尝试从mysql命令提示符添加一些条目，使其不为空。我成功地做到了这一点，但这并没有影响程序的行为

如果只声明

TestService-TestService，我得到的结果如下：带有@Autowire注释
ERROR: org.springframework.web.context.ContextLoader - Context initialization failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'testService': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: org.vadim.testmvc.dao.TestDAO org.vadim.testmvc.service.TestService.testdao; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [org.vadim.testmvc.dao.TestDAO] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:285)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1074)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:291)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:288)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:190)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:580)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:895)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:425)
    at org.springframework.web.context.ContextLoader.createWebApplicationContext(ContextLoader.java:276)
    at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:197)
    at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:47)
    at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4723)
    at org.apache.catalina.core.StandardContext$1.call(StandardContext.java:5226)
    at org.apache.catalina.core.StandardContext$1.call(StandardContext.java:5221)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
    at java.util.concurrent.FutureTask.run(FutureTask.java:166)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:722)
Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: org.vadim.testmvc.dao.TestDAO org.vadim.testmvc.service.TestService.testdao; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [org.vadim.testmvc.dao.TestDAO] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:502)
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:84)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:282)
    ... 21 more
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [org.vadim.testmvc.dao.TestDAO] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:920)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:789)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:703)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:474)
    ... 23 more

我不知道你为什么要注释掉Autowired，但这会导致你的问题：
//@Autowired
TestDAO testdao = new TestDAO();

当您手动创建TestDAO
时，Spring无法注入TestDAO.sessionFactory
，它被保留为null
。取消注释此注释并删除=newtestdao（）
：
在main方法中，您没有加载spring配置……因此类成员不会自动连接
加载配置，从context/bean工厂获取TestService bean，并确保自动连接TestDao。
我想您会发现它是@Bozho和@smp7d答案的组合。您需要加载spring配置，确保已在该配置中为TestDao定义了一个bean，并取消对@Autowired的注释。
请尝试在dao中添加它
公共HibernateTemplate HibernateTemplate；
公共会话=空
@Autowired
public void setSessionFactory(SessionFactory sessionFactory) {
    hibernateTemplate = new HibernateTemplate(sessionFactory);
}

ı它无法获取当前会话
您可以使用sessionFactory.openSession（）而不是sessionFactory.getCurrentSession（）
我刚刚编辑了我的文章以显示结果。最初我尝试过这样做，但后来我改变了我展示的视图。确保所有内容都是新部署的。异常意味着dao没有被识别为Springbean，但它应该被识别，因为它是用@repository注释的。问题不在于他没有使用模板。是的，你是对的。你可以尝试sessionFactory.openSession（）而不是sessionFactory.getCurrentSession（）也许这是一个愚蠢的问题，但在spring配置的负载下，您是什么意思？我是否应该向root-context.xml添加类似于的内容？
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:context="http://www.springframework.org/schema/context" xmlns:jee="http://www.springframework.org/schema/jee" xmlns:lang="http://www.springframework.org/schema/lang" xmlns:p="http://www.springframework.org/schema/p" xmlns:tx="http://www.springframework.org/schema/tx" xmlns:util="http://www.springframework.org/schema/util" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.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.xsd http://www.springframework.org/schema/lang http://www.springframework.org/schema/lang/spring-lang.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util.xsd">

<context:annotation-config/>
<context:component-scan base-package="org.vadim.testmvc.dao"/>
<context:component-scan base-package="org.vadim.testmvc.service"/>
<import resource="data.xml"/>
</beans>

<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:context="http://www.springframework.org/schema/context" xmlns:jee="http://www.springframework.org/schema/jee" xmlns:lang="http://www.springframework.org/schema/lang" xmlns:p="http://www.springframework.org/schema/p" xmlns:tx="http://www.springframework.org/schema/tx" xmlns:util="http://www.springframework.org/schema/util" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee.xsd http://www.springframework.org/schema/lang http://www.springframework.org/schema/lang/spring-lang.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util.xsd">

<tx:annotation-driven transaction-manager="transactionManager"/>

<bean id="transactionManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager">
<property name="sessionFactory" ref="sessionFactory"/>
</bean>

<bean id="messageSource" class="org.springframework.context.support.ReloadableResourceBundleMessageSource">
<property name="basename" value="classpath:messages"/>
<property name="defaultEncoding" value="UTF-8"/>
</bean>

    <bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer" p:location="/WEB-INF/jdbc.properties"/>

    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource" p:driverClassName="${jdbc.driverClassName}" p:url="${jdbc.databaseurl}" p:username="${jdbc.username}" p:password="${jdbc.password}"/>

    <bean id="sessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
    <property name="dataSource" ref="dataSource"/>
    <property name="configLocation">
    <value>classpath:hibernate.cfg.xml</value>
    </property>
    <property name="configurationClass">
    <value>org.hibernate.cfg.AnnotationConfiguration</value>
    </property>
    <property name="hibernateProperties">
    <props>
    <prop key="hibernate.show_sql">true</prop>
    <prop key="hibernate.dialect">${jdbc.dialect}</prop>
    <prop key="hibernate.connection.charSet">UTF-8</prop>
    </props>
    </property>
    </bean>
    </beans>

Exception in thread "main" java.lang.NullPointerException
    at org.vadim.testmvc.dao.TestDAO.listStrings(TestDAO.java:23)
    at org.vadim.testmvc.service.TestService.listStrings(TestService.java:18)
    at org.vadim.testmvc.TestMain.main(TestMain.java:11)

ERROR: org.springframework.web.context.ContextLoader - Context initialization failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'testService': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: org.vadim.testmvc.dao.TestDAO org.vadim.testmvc.service.TestService.testdao; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [org.vadim.testmvc.dao.TestDAO] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:285)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1074)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:291)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:288)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:190)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:580)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:895)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:425)
    at org.springframework.web.context.ContextLoader.createWebApplicationContext(ContextLoader.java:276)
    at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:197)
    at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:47)
    at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4723)
    at org.apache.catalina.core.StandardContext$1.call(StandardContext.java:5226)
    at org.apache.catalina.core.StandardContext$1.call(StandardContext.java:5221)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
    at java.util.concurrent.FutureTask.run(FutureTask.java:166)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:722)
Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: org.vadim.testmvc.dao.TestDAO org.vadim.testmvc.service.TestService.testdao; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [org.vadim.testmvc.dao.TestDAO] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:502)
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:84)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:282)
    ... 21 more
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [org.vadim.testmvc.dao.TestDAO] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:920)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:789)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:703)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:474)
    ... 23 more

//@Autowired
TestDAO testdao = new TestDAO();

@Autowired
private TestDAO testdao;

@Autowired
public void setSessionFactory(SessionFactory sessionFactory) {
    hibernateTemplate = new HibernateTemplate(sessionFactory);
}