本文介绍了Spring注入引起空指针异常的注释的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
这篇文章是的连续性
我有一个使用Spring 3和Hibernate 4的JSF2的小应用程序，当我运行我正在运行的应用程序时。
java.lang.NullPointerException在
net.test.managed.bean.EmployeesManagedBean.getEmpList（EmployeesManagedBean.java： 53）
我做错了什么来获取空指针异常？任何帮助都是非常可观的。
ManagedBean：
@ManagedBean（名称=empMB）
@Named
@Scope（request）
public class EmployeesManagedBean实现可序列化{
public List< Employees> getEmpList（）{
try {
empList = new ArrayList< Employees>（）;
empList.addAll（getEmployeesService（）。getEmployees（））;
} catch（Exception e）{
e.printStackTrace（）;
}
返回empList;
我注入了注解：
@Inject
EmployeesService employeesService;
在EmployeesService中，我有如下注释：
@Named
public class EmployeesService实现IEmployeesService {
@Inject
EmployeesDAO employeesDAO;
@Override
公共列表<雇员> getEmployees（）{
return getEmployeesDAO（）。getEmployees（）;
}
在EmployeesDAO中，我有如下注释：
@Named
public class EmployeesDAO implements IEmployeesDAO {
@Override
public List< Employees> getEmployees（）{
List query = this.getSessionFactory（）。getCurrentSession（）。getNamedQuery（getEmp）。list（）;
返回查询;
$ b实体类：
$ b pre> @Entity
@ javax.persistence.NamedNativeQuery（name =getEmp，query ={？= call getemployees}，resultClass = Employees.class，hints = { @ javax.persistence.QueryHint（name =org.hibernate.callable，value =true）}）
@Table（name =EMPLOYEES）
public class Employees {
最后在applicationContext.xml中我有
< context：component-scan base-package =net.test/>
更新1：
@Component（empMB）或@Named（empMB）我得到以下例外：
'empMB'：注入自动装配的
依赖项失败;
嵌套异常是org.springframework.beans.factory.BeanCreationException：
无法自动装载字段：net.test.employees.service.EmployeesService
net.test.managed.bean.EmployeesManagedBean.employeesService ;
嵌套异常是org.springframework.beans.factory。
NoSuchBeanDefinitionException：没有为
依赖关系找到类型为
[net.test.employees.service.EmployeesService]的匹配bean：预计至少有1个符合自动布线的bean
此候选人依赖。依赖注释：{@ javax.inject.Inject（）}
更新2
applicationContext.xml：
< beans xmlns =http：//www.springframework .org / schema / beans
xmlns：xsi =http://www.w3.org/2001/XMLSchema-instancexmlns：tx =http://www.springframework.org/schema/tx
xmlns：context =http://www.springframework.org/schema/context
xsi：schemaLocation =http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/tx
http：//www.springframework。 org / schema / tx / spring-tx-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-上下文3.0.xsd>
< context：component-scan base-package =net.test/>
< bean id =DataSourceclass =com.mchange.v2.c3p0.ComboPooledDataSource
destroy-method =close>
< property name =driverClassvalue =oracle.jdbc/>
< property name =jdbcUrlvalue =jdbc：oracle：thin：@server：1521：DEV/>
< property name =uservalue =scott/>
< property name =passwordvalue =tiger/>
< property name =maxPoolSizevalue =10/>
< property name =maxStatementsvalue =0/>
< property name =minPoolSizevalue =5/>
< / bean>
< bean id =SessionFactory
class =org.springframework.orm.hibernate4.LocalSessionFactoryBean>
< property name =dataSourceref =DataSource/>
< property name =hibernateProperties>
<道具>
< prop key =hibernate.dialect> org.hibernate.dialect.Oracle10gDialect< / prop>
< prop key =hibernate.show_sql> true< / prop>
< /道具>
< / property>
< / bean>
< tx：annotation-driven transaction-manager =txManager/>
< bean id =txManager
class =org.springframework.orm.hibernate4.HibernateTransactionManager>
< property name =sessionFactoryref =SessionFactory/>
< / bean>
< / beans>
解决方案
我设法解决了获取空指针的问题例外，礼貌
我在做的错误是没有DAO类的 @Inject ，I已修改我的DAO类为
@Named
public class EmployeesDAO implements IEmployeesDAO {
@Inject
private SessionFactory sessionFactory;
@Override
公共列表<雇员> getEmployees（）{
List query = sessionFactory.getCurrentSession（）。getNamedQuery（getEmp）。list（）;
返回查询;
在ManagedBean中， Daniel使用 @Named 而不是 @ManagedBean 。修改后的ManagedBean
$ $ p $ code $ @ $（b
$ b $ public $ EmployeesManagedBean实现Serializable {
@Inject
IEmployeesService employeesService;
当然，在 applicationContext.xml 中添加以下内容来扫描实体类
< property name =annotatedClasses>
< list>
< value> net.test.model.Employees< / value>
< / list>
< / property>
This post is continuity of Declaration of beans in applicationContext.xml
I have a small application using Spring 3 and Hibernate 4 with JSF2, When I am running the application I am getting.
java.lang.NullPointerException at
net.test.managed.bean.EmployeesManagedBean.getEmpList(EmployeesManagedBean.java:53)
What am I doing wrongly to get nullpointer exception? Any help is highly appreciable.
ManagedBean:
@ManagedBean(name="empMB")
@Named
@Scope("request")
public class EmployeesManagedBean implements Serializable {
public List<Employees> getEmpList() {
try {
empList = new ArrayList<Employees>();
empList.addAll(getEmployeesService().getEmployees());
} catch (Exception e) {
e.printStackTrace();
}
return empList;
}
}
and I have Inject annotation:
@Inject
EmployeesService employeesService;
In EmployeesService I have annotations like:
@Named
public class EmployeesService implements IEmployeesService {
@Inject
EmployeesDAO employeesDAO;
@Override
public List<Employees> getEmployees() {
return getEmployeesDAO().getEmployees();
}
In EmployeesDAO I have annotations like:
@Named
public class EmployeesDAO implements IEmployeesDAO {
@Override
public List<Employees> getEmployees() {
List query = this.getSessionFactory().getCurrentSession().getNamedQuery("getEmp").list();
return query;
}
Entity class:
@Entity
@javax.persistence.NamedNativeQuery(name = "getEmp", query = "{ ? = call getemployees }", resultClass = Employees.class, hints = { @javax.persistence.QueryHint(name = "org.hibernate.callable", value = "true") })
@Table(name = "EMPLOYEES")
public class Employees {
and finally in applicationContext.xml I have
<context:component-scan base-package="net.test" />
Update 1:
When I use @Component("empMB") or @Named("empMB") I am getting the following exceptions
Error creating bean with name 'empMB': Injection of autowired
dependencies failed;
nested exception is org.springframework.beans.factory.BeanCreationException:
Could not autowire field: net.test.employees.service.EmployeesService
net.test.managed.bean.EmployeesManagedBean.employeesService;
nested exception is org.springframework.beans.factory.
NoSuchBeanDefinitionException: No matching bean of type
[net.test.employees.service.EmployeesService] found for
dependency: expected at least 1 bean which qualifies as autowire
candidate for this dependency. Dependency annotations: {@javax.inject.Inject()}
Update 2
applicationContext.xml:
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:tx="http://www.springframework.org/schema/tx"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/tx
http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd">
<context:component-scan base-package="net.test" />
<!-- Data Source Declaration -->
<bean id="DataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource"
destroy-method="close">
<property name="driverClass" value="oracle.jdbc" />
<property name="jdbcUrl" value="jdbc:oracle:thin:@server:1521:DEV" />
<property name="user" value="scott" />
<property name="password" value="tiger" />
<property name="maxPoolSize" value="10" />
<property name="maxStatements" value="0" />
<property name="minPoolSize" value="5" />
</bean>
<!-- Session Factory Declaration -->
<bean id="SessionFactory"
class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
<property name="dataSource" ref="DataSource" />
<property name="hibernateProperties">
<props>
<prop key="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</prop>
<prop key="hibernate.show_sql">true</prop>
</props>
</property>
</bean>
<!-- Enable the configuration of transactional behavior based on annotations -->
<tx:annotation-driven transaction-manager="txManager" />
<!-- Transaction Manager is defined -->
<bean id="txManager"
class="org.springframework.orm.hibernate4.HibernateTransactionManager">
<property name="sessionFactory" ref="SessionFactory" />
</bean>
</beans>
解决方案
I have managed to resolve the issue of getting null pointer exception, courtesy toMarten Deinum
The mistake what I was doing was there were no @Inject for DAO class, I have modified my DAO class as
@Named
public class EmployeesDAO implements IEmployeesDAO {
@Inject
private SessionFactory sessionFactory;
@Override
public List<Employees> getEmployees() {
List query = sessionFactory.getCurrentSession().getNamedQuery("getEmp").list();
return query;
}
}
and in ManagedBean I have made the changes as mentioned by Daniel to use @Named instead of @ManagedBean. Modified ManagedBean
@Named("empMB")
@Scope("request")
public class EmployeesManagedBean implements Serializable {
@Inject
IEmployeesService employeesService;
And of course added the following in applicationContext.xml to scan Entity class
<property name="annotatedClasses">
<list>
<value>net.test.model.Employees</value>
</list>
</property>
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