[英]Spring beans created but not autowired
我知道有很多類似的問題。 我看了很多,但問題仍然存在。
我有一個已創建但未自動裝配的服務。 在項目和測試中都沒有(!)手動啟動(就像在這個問題中一樣 )
Tomcat輸出說,這兩個bean都被發現並創建。 至少第一項服務不會注入應有的位置。 我不知道第二個。
服務(接口):
public interface SchoolService {
public School getSchool(String id);
}
服務(實施):
@Service
@Transactional
public class SchoolServiceImpl implements SchoolService {
@Autowired
private SchoolDAO schoolDAO;
public School getSchool(String id) {
//database things
return school;
}
}
它被“召喚”的地方
public class SchoolMenu implements Serializable {
@Autowired
private SchoolService schoolService;
public SchoolMenu () {
//here schoolService is null
School school = schoolService.getSchool("id");
}
}
應用程序的context.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:p="http://www.springframework.org/schema/p"
xmlns:aop="http://www.springframework.org/schema/aop"
xmlns:tx="http://www.springframework.org/schema/tx"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.0.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.0.xsd">
<bean id="SchoolServiceImpl" class="content_management.School.service.SchoolServiceImpl"/>
<bean id="SchoolDAOImpl" class="content_management.School.dao.SchoolDAOImpl"/>
</beans>
Tomcat輸出:
org.springframework.beans.factory.support.DefaultListableBeanFactory: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@57003970: defining beans [SchoolServiceImpl,SchoolDAOImpl]; root of factory hierarchy
org.springframework.beans.factory.support.DefaultListableBeanFactory: Creating shared instance of singleton bean 'SchoolServiceImpl'
org.springframework.beans.factory.support.DefaultListableBeanFactory: Creating instance of bean 'SchoolServiceImpl'
org.springframework.beans.factory.support.DefaultListableBeanFactory: Eagerly caching bean 'SchoolServiceImpl' to allow for resolving potential circular references
org.springframework.beans.factory.support.DefaultListableBeanFactory: Finished creating instance of bean 'SchoolServiceImpl'
org.springframework.beans.factory.support.DefaultListableBeanFactory: Creating shared instance of singleton bean 'SchoolDAOImpl'
org.springframework.beans.factory.support.DefaultListableBeanFactory: Creating instance of bean 'SchoolDAOImpl'
org.springframework.beans.factory.support.DefaultListableBeanFactory: Eagerly caching bean 'SchoolDAOImpl' to allow for resolving potential circular references
org.springframework.beans.factory.support.DefaultListableBeanFactory: Finished creating instance of bean 'SchoolDAOImpl'
我的錯誤在哪里?
為了讓@Autowired
工作, SchoolMenu
也必須是一個Spring bean。 如果不是,您可以從應用程序上下文獲取schoolService
。 像這樣的東西
ApplicationContext appContext = new ClassPathXmlApplicationContext("application-context.xml");
SchoolService schoolService = (SchoolService) appContext.getBean(SchoolService.class);
您正在schoolService
的構造函數中訪問SchoolMenu
:
public SchoolMenu () {
//here schoolService is null
School school = schoolService.getSchool("id");
}
那時, schoolService
尚未注入。 它不可能 - 在調用構造函數之前不會發生任何事情。
通過使用javax.annotation.PostConstruct
注釋對bean進行批注,可以在初始化bean之后聲明要調用的方法。 執行需要在該方法中注入依賴項的操作,而不是在構造函數中。
(還有一些其他方法可以實現相同的功能,例如實現InitializingBean
接口,但這些方法有點過時)
例:
public SchoolMenu () {
}
@PostConstruct
public void init() {
// schoolService is NOT null here
School school = schoolService.getSchool("id");
}
您可以通過將此配置添加到應用程序上下文來使用組件掃描,而不是在xml中定義bean,Spring將自動掃描並檢測bean。
<context:component-scan base-package="content_management.School" />
您還需要在上下文命名空間中添加,以便application-context.xml看起來像這樣:
<?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:p="http://www.springframework.org/schema/p"
xmlns:aop="http://www.springframework.org/schema/aop"
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-4.0.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.0.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.0.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
<context:component-scan base-package="content_management.School" />
</beans>
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