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[英]How to use @Inject annotation properly in spring Java based configuration?
[英]inject prototype into singleton(java configuration + annotation)
我在采访中被问到有关将单体原型注入单例的问题。 我很难回答,现在我正在尝试对此进行研究。
我写了以下代码(启动时启动)
豆1:
@Service
@Scope(value = "prototype")
public class MyValidator {
}
豆2:
@Service
public class ValidatorHolder {
@Autowired
MyValidator myValidator;
public MyValidator getMyValidator() {
return myValidator;
}
}
组态:
@SpringBootApplication
@Configuration
@ComponentScan("com.example.domain")
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
ApplicationContext context = new AnnotationConfigApplicationContext(DemoApplication.class);
ValidatorHolder validatorHolder1 = (ValidatorHolder) context.getBean("validatorHolder");
ValidatorHolder validatorHolder2 = (ValidatorHolder) context.getBean("validatorHolder");
System.out.println("=====================================");
System.out.println(validatorHolder1.getMyValidator() == validatorHolder2.getMyValidator());
System.out.println("=====================================");
}
}
该代码为true。
据我了解,在阅读文章链接时 ,可以配置为返回false。
如何在我的代码中执行? (没有xml)
我试图像文章中那样重写代码:
<bean id="validatorHolder" class="com.example.domain.ValidatorHolder">
<property name="myValidator" ref="validator"/>
</bean>
<bean id="validator" scope="prototype" class="com.example.domain.MyValidator">
<!-- This instructs the container to proxy the current bean-->
<aop:scoped-proxy/>
</bean>
在main方法内部,我编写了以下代码:
ApplicationContext xmlContext = new FileSystemXmlApplicationContext("classpath:applicationContext.xml");
ValidatorHolder validatorHolder21 = (ValidatorHolder) xmlContext.getBean("validatorHolder");
ValidatorHolder validatorHolder22 = (ValidatorHolder) xmlContext.getBean("validatorHolder");
System.out.println("=====================================");
System.out.println(validatorHolder21.getMyValidator() == validatorHolder22.getMyValidator());
System.out.println("=====================================");
无论如何我都认为是true
让我们重新研究Sean Patrick Floyd的答案(范围代理,b))
我使用以下主要方法类:
@SpringBootApplication
@ComponentScan("com.example.domain")
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
ApplicationContext context = new AnnotationConfigApplicationContext(DemoApplication.class);
ValidatorHolder validatorHolder1 = (ValidatorHolder) context.getBean("validatorHolder");
ValidatorHolder validatorHolder2 = (ValidatorHolder) context.getBean("validatorHolder");
System.out.println("=====================================");
System.out.println(validatorHolder1.getMyValidator() == validatorHolder2.getMyValidator());
System.out.println("=====================================");
}
当我运行应用程序时-我看到了
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'validatorHolder' defined in file [D:\freelance\demo\target\classes\com\example\domain\ValidatorHolder.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.example.domain.ValidatorHolder]: No default constructor found; nested exception is java.lang.NoSuchMethodException: com.example.domain.ValidatorHolder.<init>()
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1099)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1044)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:504)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:755)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:759)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:689)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:321)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:969)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:958)
at com.example.DemoApplication.main(DemoApplication.java:20)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.example.domain.ValidatorHolder]: No default constructor found; nested exception is java.lang.NoSuchMethodException: com.example.domain.ValidatorHolder.<init>()
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:85)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1092)
... 20 common frames omitted
Caused by: java.lang.NoSuchMethodException: com.example.domain.ValidatorHolder.<init>()
at java.lang.Class.getConstructor0(Class.java:3074)
at java.lang.Class.getDeclaredConstructor(Class.java:2170)
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:80)
... 21 common frames omitted
PS2问题与构造函数上缺少@Autowired
有关
解决此问题后
System.out.println(validatorHolder1.getMyValidator() == validatorHolder2.getMyValidator());
返回true
但是如果稍微替换一下MyValidator代码:
@Service
@Scope(value="prototype", proxyMode=ScopedProxyMode.TARGET_CLASS)
public class MyValidator {
Object object = new Object();
public Object getObject() {
return object;
}
public void setObject(Object object) {
this.object = object;
}
}
System.out.println(validatorHolder1.getMyValidator() == validatorHolder2.getMyValidator());
真正
System.out.println(validatorHolder1.getMyValidator().getObject() == validatorHolder2.getMyValidator().getObject());
假
乃至
System.out.println(validatorHolder1.getMyValidator().getObject() == validatorHolder1.getMyValidator().getObject());
假
您误解了方法注入技术。 您需要使bean抽象才能工作:
public class MyValidator {}
public abstract class ValidatorHolder {
public abstract MyValidator getMyValidator();
}
现在,您可以按以下方式在XML中定义bean:
<bean class="com.somepackage.MyValidator" scope="prototype" />
<bean class="com.somepackage.ValidatorHolder">
<lookup-method name="getMyValidator" bean="myValidator" />
</bean>
在这种情况下,Spring将创建ValidatorHolder
的匿名子类,该子类将在每次调用它的类型时返回原型bean(新副本)。
使用带注释的服务类,无法进行查找方法注入,但这是使用@Configuration
类的方法:
@Configuration
public class MyConfiguration{
@Bean
@Scope("prototype")
public MyValidator myValidator(){
return new MyValidator();
}
@Bean
public ValidatorHolder validatorHolder(){
return new ValidatorHolder(){
@Override public MyValidator getMyValidator(){
return myValidator();
}
};
}
}
在这种情况下,您将自己创建ValidatorHolder
的子类,并且可以清楚地看到会发生什么。
但是只有当您使bean和提供者方法成为抽象时,这两个版本才有效。
最后,定义弹跳豆有三种不同的方法:
@Service
@Component
, @Component
Component) @Bean
方法的@Configuration
类。 在示例代码中,您将这三种样式混合在一起,这几乎从来不是一个好主意。 选择一种技术并坚持下去。
关于作用域代理,这可以通过所有三种bean注册技术来实现。
a)XML
public class MyValidator {}
public class ValidatorHolder {
private MyValidator myValidator;
public void setMyValidator(MyValidator myValidator){
this.myValidator = myValidator;}
public MyValidator getMyValidator();
}
<bean class="com.somepackage.MyValidator" scope="prototype" />
<bean class="com.somepackage.ValidatorHolder">
<aop:scoped-proxy />
</bean>
b)带注释的服务等级
@Service @Scope(value="prototype", proxyMode=ScopedProxyMode.TARGET_CLASS)
public class MyValidator {}
@Service
public class ValidatorHolder {
@Autowired
public ValidatorHolder(MyValidator myValidator){
this.myValidator=myValidator;
}
private final MyValidator myValidator;
public MyValidator getMyValidator(){ return myValidator; };
}
c) @Configuration
类,类似于XML版本的Bean类
@Configuration
public class MyConfiguration{
@Bean
@Scope("prototype")
public MyValidator myValidator(){
return new MyValidator();
}
@Bean
public ValidatorHolder validatorHolder(){
return new ValidatorHolder(myValidator());
}
}
请注意,所有代理解决方案将始终返回相同的对象即代理。 但是底层功能将委托给不同的对象。 通过将以下代码添加到MyValidator来进行尝试:
private int counter = 1;
public int counter(){
return counter ++;
}
现在,与调用此代码的频率无关:
validatorHolder.getMyValidator().counter();
它将始终返回1
。
@Service
public class ValidatorHolder {
@Autowired
ApplicatioContext context;
public MyValidator getMyValidator() {
return context.getBean(MyValidator.class);
}
}
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