spring注解 构造函数问题 - ITeye问答
我碰到个问题，我项目用的是spring框架，用注解做的
在初始化时候出错了。报的错误是managerContext为空指针，但是把构造函数去掉就没问题，到底怎么回事呀
JAVA类
public class TcpMessageClient implements MessageClient{
@Autowired
private ManagerContext&&& managerC
@Autowired
private ISocketLog&& iSocketL
public& TcpMessageClient(){
socket=new SocketClient(managerContext.getRouterIP(),managerContext.getRouterPort(),managerContext.getTimeout(),iSocketLog);
socket.setProtocol(SocketClient.PROTOCOL_TCP);
}
}
错误
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'messageService': Injection of resource nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'messageClient' defined in file [D:\tomcat\apache-tomcat-6.0.18\webapps\roamer\WEB-INF\classes\com\ultrapower\roamer\common\message\TcpMessageClient.class]: Instanti nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.mon.message.TcpMessageClient]: Constru nested exception is java.lang.NullPointerException
问题补充：public interface ResourceService extends BaseService{
* &p&根据url获取resource&p/&
* @param url
public Resource getResourceByUrl(String url);
}
@Component("resourceService")
public class ResourceServiceImpl extends BaseServiceImpl implements ResourceService{
* @see com.ultrapower.roamer.customer.user.service.ResourceService#getResourceByUrl(java.lang.String)
@SuppressWarnings("unchecked")
public Resource getResourceByUrl(String url) {
List&Resource& resources = createCriteria(Resource.class)
.add(Restrictions.eq("url", url))
if(resources == null || resources.size() == 0){
return resources.get(0);
@Component("tested")
public class TestClass {
private ResourceService resourceS
public ResourceService getResourceService() {
return resourceS
public void setResourceService(ResourceService resourceService) {
this.resourceService = resourceS
}
public class TaskAction&& extends BaseAction{
private static final long serialVersionUID = 1L;
private& TaskService taskS
private TestC
public void query(){
tested.getResourceService();
}
}
在TaskAction中可以看到tested被注入进去了，但是tested中的resourceService是null。测试好多次都是这样
问题补充：&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:mvc="http://www.springframework.org/schema/mvc" xmlns:tx="http://www.springframework.org/schema/tx"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-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/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.0.xsd"&
&context:property-placeholder location="classpath:roamer.properties" /&
&context:annotation-config /&
&context:component-scan base-package="com.ultrapower.roamer" /&
&&& &!-- 国际化 --&
&&& &bean id="messageSource" class="org.springframework.context.support.ReloadableResourceBundleMessageSource"&
&&&
&property name="basename" value="classpath:messages_zh_CN" /&
&&& &/bean&
&&& &!-- import --&
&import resource="application-datasource.xml"/&
&import resource="application-security.xml"/&
&import resource="application-debug.xml"/&
&/beans&
因为类首先被Spring实例化的时候，会调用构造函数。只有实例化后，才会注入。你等于没注入就调用了，所以报错。
spring 在初始化bean的时候要先调用构造函数，再set其它属性；
也就是说在TcpMessageClient实例化的时候（调用public& TcpMessageClient()时），managerContext属性还是空的。
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看例子：public class AnimalServiceImpl implements AnimalService { @Autowired private PersonD public AnimalServiceImpl(){} public AnimalServiceImpl(PersonDao per){
this.per = } public void jump(){
per.add(); }}&&bean id="personDaoB" class="com.dao.person.PersonDaoImpl" &&/bean&& &bean id='animalService' class="com.service.person.AnimalServiceImpl" &AnimalService animal = (AnimalService)cxt.getBean("animalService");animal.jump();那么，能不能让@Autowired以名称查找呢？@Autowired @Qualifier("personDaoB") private PersonD这样就可以了！@Autowired(required=false)当根据类型去找，找不到时，注入一个空。@Autowired(required=true)当根据类型去找，找不到时，抛出异常信息。例如&bean id="personDaoB" class="com.dao.person.PersonDaoImpl" &&/bean&&&bean id='animalService' class="com.service.person.AnimalServiceImpl" &&&/bean&@Autowired(required=false) private PersonSpublic AnimalServiceImpl(PersonDao per,PersonService ps){
this.per =
this.ps = }测试AnimalService animal = (AnimalService)cxt.getBean("animalService");animal.jump();一切正常！如果改为@Autowired(required=true) private PersonS由于找不到PersonService&类型对应的bean，而required=true，所以抛出异常信息！注意，注解注入时一定要同时写带参和不带参的构造方法！如果你不用构造方法行不行呢？就像第一种方式一样：@Autowired private PersonD public void setPd(PersonDao pd) {
this.pd = } public void save(String str){
pd.add(str); }&&context:annotation-config/&&&bean id="personDao" class="com.dao.spring.PersonDaoImpl"&&/bean&&&&bean id='personService' class="com.service.spring.PersonServiceImpl"&同样是可以的！与第一种方式的区别在于，在bean里面，除了配置了两个bean以外，什么也没配，而是在声明属性的时候，写@Autowired之类的注解。而第一种是，在bean的实现类里面，基本什么也没配置，而是在配置文件中写了&property name="personDaoA" ref="personSetDao"&&/property&
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{list wl as x}{/list}@Autowired无法自动注入 - ITeye问答
框架用的是springside4，基于springmvc的，我在我的service的实现类和DAO里面都加了@Component注解，在单元测试的时候可以自动注入，跑项目的时候就报空指针异常了。有没有遇到同样问题的朋友啊
问题补充：问题解决了，因为我引用自动注入的类本身不是spring管理的，给这个类加上@component注解其他spring组件就可以自动注入了
是不是没有扫描到相应的包啊。
如果是必须的对象，试试@Autowired进构造函数，个人感觉@Autowired进构造函数，比@Autowired变量声明要靠谱。
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