java - Autowiring 字段为空，但在构造函数 Autowiring 时不是-6ren

java - Autowiring 字段为空，但在构造函数 Autowiring 时不是

转载作者：塔克拉玛干更新时间：2023-11-02 19:22:33

我有一个 Autowiring 其他 bean 的组件:

@Component
public class MyComponent {
    @Autowired
    private Environment env; // null

    @Autowired
    public MyComponent(ConfigurationUtils configUtils /* not null */) {
    }
}

当添加 Environment env 作为构造函数参数时，它也不是 null。

但为什么呢？

更新

@Component
public class MyComponent implements InitializingBean {
    private final Logger log = LoggerFactory.getLogger(getClass());

    @Autowired
    private Environment env; // TODO: null

    @Autowired
    public MyComponent(ConfigurationUtils configUtils) {
        log.debug("configUtils == null: " + (configUtils == null));
        log.debug("env == null: " + (env == null));
        log.debug(env.getProperty("foo")); // to trigger NPE
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        log.debug("Initialized environment: " + env);
    }
}

控制台输出:

DEBUG c.e.MyComponent - configUtils == null: false
DEBUG c.e.MyComponent - env == null: true
WARN  o.s.w.c.s.AnnotationConfigWebApplicationContext - Exception encountered during context initialization - cancelling refresh attempt
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'myComponent' defined in URL [jar:file:/var/lib/tomcat7/webapps/site/WEB-INF/lib/site-0.0.1-SNAPSHOT.jar!/com/example/MyComponent.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.example.MyComponent]: Constructor threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:278) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1133) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1036) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:505) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:302) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:229) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:298) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:725) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757) ~[spring-context-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480) ~[spring-context-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:403) [spring-web-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:306) [spring-web-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:106) [spring-web-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4971) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5467) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:901) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:877) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:632) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:1073) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:553) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.startup.HostConfig.check(HostConfig.java:1648) [tomcat-catalina-7.0.52.jar:7.0.52]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.7.0_65]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) ~[na:1.7.0_65]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.7.0_65]
    at java.lang.reflect.Method.invoke(Method.java:606) ~[na:1.7.0_65]
    at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:301) [tomcat-coyote-7.0.52.jar:7.0.52]
    at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819) [na:1.7.0_65]
    at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801) [na:1.7.0_65]
    at org.apache.catalina.manager.ManagerServlet.check(ManagerServlet.java:1445) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.manager.ManagerServlet.deploy(ManagerServlet.java:677) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.manager.ManagerServlet.doPut(ManagerServlet.java:435) [tomcat-catalina-7.0.52.jar:7.0.52]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:649) [servlet-api-3.0.jar:na]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727) [servlet-api-3.0.jar:na]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:108) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:610) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040) [tomcat-coyote-7.0.52.jar:7.0.52]
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607) [tomcat-coyote-7.0.52.jar:7.0.52]
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:313) [tomcat-coyote-7.0.52.jar:7.0.52]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [na:1.7.0_65]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [na:1.7.0_65]
    at java.lang.Thread.run(Thread.java:745) [na:1.7.0_65]
Caused by: org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.example.MyComponent]: Constructor threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:163) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:125) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:270) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    ... 54 common frames omitted
Caused by: java.lang.NullPointerException: null
    at com.example.MyComponent.<init>(MyComponent.java:23) ~[site-0.0.1-SNAPSHOT.jar:na]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.7.0_65]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57) ~[na:1.7.0_65]
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.7.0_65]
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526) ~[na:1.7.0_65]
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:147) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    ... 56 common frames omitted
ERROR o.s.web.context.ContextLoader - Context initialization failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'myComponent' defined in URL [jar:file:/var/lib/tomcat7/webapps/site/WEB-INF/lib/site-0.0.1-SNAPSHOT.jar!/com/example/MyComponent.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.example.MyComponent]: Constructor threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:278) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1133) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1036) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:505) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:302) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:229) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:298) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:725) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757) ~[spring-context-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480) ~[spring-context-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:403) ~[spring-web-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:306) ~[spring-web-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:106) [spring-web-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4971) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5467) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:901) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:877) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:632) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:1073) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:553) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.startup.HostConfig.check(HostConfig.java:1648) [tomcat-catalina-7.0.52.jar:7.0.52]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.7.0_65]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) ~[na:1.7.0_65]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.7.0_65]
    at java.lang.reflect.Method.invoke(Method.java:606) ~[na:1.7.0_65]
    at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:301) [tomcat-coyote-7.0.52.jar:7.0.52]
    at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819) [na:1.7.0_65]
    at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801) [na:1.7.0_65]
    at org.apache.catalina.manager.ManagerServlet.check(ManagerServlet.java:1445) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.manager.ManagerServlet.deploy(ManagerServlet.java:677) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.manager.ManagerServlet.doPut(ManagerServlet.java:435) [tomcat-catalina-7.0.52.jar:7.0.52]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:649) [servlet-api-3.0.jar:na]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727) [servlet-api-3.0.jar:na]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:108) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:610) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408) [tomcat-catalina-7.0.52.jar:7.0.52]
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040) [tomcat-coyote-7.0.52.jar:7.0.52]
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607) [tomcat-coyote-7.0.52.jar:7.0.52]
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:313) [tomcat-coyote-7.0.52.jar:7.0.52]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [na:1.7.0_65]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [na:1.7.0_65]
    at java.lang.Thread.run(Thread.java:745) [na:1.7.0_65]
Caused by: org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.example.MyComponent]: Constructor threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:163) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:125) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:270) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    ... 54 common frames omitted
Caused by: java.lang.NullPointerException: null
    at com.example.MyComponent.<init>(MyComponent.java:23) ~[site-0.0.1-SNAPSHOT.jar:na]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.7.0_65]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57) ~[na:1.7.0_65]
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.7.0_65]
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526) ~[na:1.7.0_65]
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:147) ~[spring-beans-4.1.1.RELEASE.jar:4.1.1.RELEASE]
    ... 56 common frames omitted

最佳答案

添加InitializingBean接口(interface)到您的 bean 并检查其中的属性:

@Component
public class MyComponent implements InitializingBean {
    @Autowired
    private Environment env; // null

    @Autowired
    public MyComponent(ConfigurationUtils configUtils /* not null */) {
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("Initialized environment: " + env);
    }
}

默认的 Spring bean 生命周期:

使用( Autowiring ？)参数创建对象/调用构造函数
填充( Autowiring ？)bean 属性(字段和 setter )
调用 afterPropertiesSet(如果 bean 实现了 InitializingBean)
在 bean 上发布引用
...
删除 bean 的引用
调用销毁(如果 bean 实现 DisposableBean)

关于java - Autowiring 字段为空，但在构造函数 Autowiring 时不是，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/27172323/

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问题: 是否有可能有一个字段被 JPA 保留但被序列化跳过？可以实现相反的效果(JPA 跳过字段而序列化则不会)，如果使用此功能，那么相反的操作肯定会很有用。类似这样的事情: @Entity cl
php - 无重复(分组依据)字段 1 循环，字段 2 位于水平线
假设我有一个名为“dp”的表 Year | Month | Payment| Payer_ID | Payment_Recipient | 2008/2009 | July
c - 我在 IP header 中找不到 DSCP 字段，只有已弃用的 TOS 字段
我将尝试通过我的 Raspberry Pi 接入点保证一些 QoS。开始之前，我先动手:我阅读了有关 tcp、udp 和 ip header 的内容。在IP header description我看
dart - 什么时候应该在 dart 中使用 final 字段、工厂构造函数或带有 getter 的私有(private)字段？
如果你能弄清楚如何重命名这个问题，我愿意接受建议。在 Dart 语言中，可以编写一个带有 final 字段的类。这些是只能设置的字段构造函数前 body 跑。这可以在声明中(通常用于类中的静态常量)
javascript - jquery:使用两个带有两个字段(字段 1、字段 2 + 1 天)的日期选择器，例如 booking.com
你怎么样？我有两个带有两个字段的日期选择器我希望当用户选择 (From) 时，第二个字段 (TO) 将是 next day 。比如 booking.com 例如:当用户选择From 01-01-2
mysql - 将字段从 T1 字段 A 复制到 T2 字段 A where(if or when) T1 field B = T2 field B (mysql)
我想我已经看到了这个问题的一些答案，这些答案可能与我需要的相差不远，但我对 mysql 的了解还不够确定，所以我会根据我的具体情况提出问题。我有一个包含多个表的数据库，为此，如果“image”表上的
mySQL在单个查询中多次使用相同的表/字段
我在 mySQL 数据库中有 2 个表: customers ============ customer_id (1, 2 ) customer_name (john, mark) orders ==
数据库归档与基于时间段的表/字段
我正在开发一个员工目标 Web 应用程序。领导/经理在与团队成员讨论后为他们设定目标。这是一年/半年/季度，具体取决于组织遵循的评估周期。现在的问题是添加基于时间段的字段或存档上一季度/年度数据的
Sitecore 字段，用于从媒体库中选择多个文件并能够上传文件
我正在寻找允许内容编辑器从媒体库中选择多个文件的东西，这些文件将在渲染中列出。他们还需要能够上传文件和搜索。它必须在页面编辑器(版本 8 中称为体验编辑器)中工作。到目前为止我所考虑的: 一堆文件字
r - 创建 "other"字段
现在，我有以下由 original.df %.% group_by(Category) %.% tally() %.% arrange(desc(n)) 创建的 data.frame。 DF 5),
潘塔霍。将登录的错误消息放入字符串/字段
我想知道是否有一些步骤/解决方案可以处理错误消息并将它们放入 Pentaho 工具中的某个字符串或字段中？例如，如果连接到数据库时发生某些错误，则将该消息从登录到字符串/字段。最佳答案我们在作业的
iPhone如何制作 "To"字段，如短信应用程序
如何制作像短信应用程序一样的“收件人”字段？例如，右侧有一个“+”按钮，当添加某人时，名称将突出显示并可单击，如圆角矩形等。有没有内置的框架？最佳答案不，但请参阅 Three20 的 TTMess
delphi - 列出记录的元素\字段
是否可以获取记录的元素或字段的列表通过类型信息类似于类的已发布属性的列表吗？谢谢！最佳答案取决于您的delphi版本，如果您使用的是delphi 2010或更高版本，则可以使用“新rtti”
带有外键列表的 SQLite 字段
我正在构建一个 SQLite 数据库来保存我的房地产经纪人的列表。我已经能够使用外键来识别每个代理的列表，但我想在每个代理的记录中创建一个列表；从代理商和列表之间的一对一关系转变为一对多关系。看这里

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