初始化失败_Destroying singletons

博客讲述了作者在配置Spring Bean时遇到的问题,由于缺少无参构造函数导致初始化单例失败,浪费了较长时间解决这个问题。异常信息显示在尝试创建'department' bean时,依赖的'employee1' bean无法实例化,原因是找不到类com.gwp.zcc.domain.Employee的默认构造函数。

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这个错误的根源是因为我没有提供无参的构造函数 靠 搞得 浪费了我大概三个多小时的时间。。。。啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊。。。。。。。



信息: Destroying singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@1a42792: defining beans [department,employee1,employee2,employee4]; root of factory hierarchy
Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'department' defined in class path resource [com/gwp/zcc/test/beans.xml]: Cannot resolve reference to bean 'employee1' while setting bean property 'empList' with key [0]; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'employee1' defined in class path resource [com/gwp/zcc/test/beans.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.gwp.zcc.domain.Employee]: No default constructor found; nested exception is java.lang.NoSuchMethodException: com.gwp.zcc.domain.Employee.<init>()
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:275)
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:104)
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveManagedList(BeanDefinitionValueResolver.java:287)
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:126)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1245)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1010)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:472)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409)
    at java.security.AccessController.doPrivileged(Native Method)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:264)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:221)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:429)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:729)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:381)
    at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
    at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
    at com.gwp.zcc.test.TestMain.main(TestMain.java:24)
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'employee1' defined in class path resource [com/gwp/zcc/test/beans.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.gwp.zcc.domain.Employee]: No default constructor found; nested exception is java.lang.NoSuchMethodException: com.gwp.zcc.domain.Employee.<init>()
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:883)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:839)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:440)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409)
    at java.security.AccessController.doPrivileged(Native Method)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:264)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:221)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164)
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:269)
    ... 20 more
Caused by: org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.gwp.zcc.domain.Employee]: No default constructor found; nested exception is java.lang.NoSuchMethodException: com.gwp.zcc.domain.Employee.<init>()
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:58)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:877)
    ... 31 more
Caused by: java.lang.NoSuchMethodException: com.gwp.zcc.domain.Employee.<init>()
    at java.lang.Class.getConstructor0(Class.java:2706)
    at java.lang.Class.getDeclaredConstructor(Class.java:1985)
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:54)
    ... 32 more

### Spring Bean 初始化流程及生命周期详解 #### 1. 实例化 (Instantiation) 当应用程序启动时,Spring 容器会根据配置文件或注解中的定义创建相应的 Bean 对象。这一阶段的主要工作是由容器调用无参构造函数或者工厂方法来生成对象实例[^1]。 #### 2. 属性注入 (Property Population) 在完成实例化之后,Spring 容器会对新创建的对象进行依赖注入操作。这一步骤涉及将其他 Beans 或者基本类型的值赋给当前 Bean 的成员变量。通过 XML 配置、Java 注解(如 `@Autowired` 和 `@Value`),可以实现自动装配功能[^2]。 #### 3. 初始化前回调接口处理 如果某个类实现了特定的接口比如 `BeanNameAware`, `BeanFactoryAware` 等,则在此期间这些方法会被依次触发执行以便让开发者能够获取到更多关于上下文环境的信息并作出相应调整。 #### 4. 自定义初始化逻辑 紧接着上述过程的是允许用户指定自己的初始化动作的时间点。可以通过两种方式达成此目的: - **实现 InitializingBean 接口**: 如果一个 bean 类实现了该接口的话,在其 life cycle 中就会被通知去调用 afterPropertiesSet 方法来进行额外设置。 ```java public class MyBean implements InitializingBean { @Override public void afterPropertiesSet() throws Exception { System.out.println("Custom initialization logic executed."); } } ``` - **声明 init-method 属性**: 可以在 xml 文件里为每一个单独定义好的 bean 设置专属的方法名称作为它的初始入口;或者是利用 Java Config 来标注 @PostConstruct 注解达到同样效果[^3]^。 #### 5. 使用阶段 一旦所有的准备工作都已完成——即完成了前面提到的所有步骤以后,这个 Bean 就处于可用状态了。它可以响应来自客户端的各种请求直到它最终退出服务为止. #### 6. 销毁(仅限单例模式下的非永久存活期beans) 对于那些具有有限生命期限(Scope=prototype除外)的 beans 而言,当它们不再需要继续存在下去的时候,将会经历最后一个环节—销毁。类似于初始化部分也有多种途径可供选择如何优雅地结束资源占用等问题: - **实现 DisposableBean 接口** ```java public class MyDisposableBean implements DisposableBean{ @Override public void destroy()throws Exception{ // Cleanup code here. } } ``` - **配置 destroy-method** 综上所述,Spring Framework 提供了一套完整的机制用于控制 Managed Objects(Like Beans)在整个应用运行周期内的行为表现形式. ```java // Example of using PostConstruct and PreDestroy annotations for custom lifecycle methods. import javax.annotation.PostConstruct; import javax.annotation.PreDestroy; public class LifecycleDemo { private String message; public LifecycleDemo(String msg){ this.message=msg; } @PostConstruct public void init(){ System.out.println("Initializing Bean with Message:"+message); } @PreDestroy public void cleanup(){ System.out.println("Destroying Bean..."); } } ```
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