OSGI企业应用开发（七）细说Blueprint & Gemini Blueprint（二）

一时失言乱红尘 2022-07-13 04:41 204阅读 0赞

上篇文章介绍了标准的Blueprint 规范与 Gemini Blueprint如何自定义Bean配置文件路径，本文接着上篇文章继续介绍Blueprint的使用。

# 一、Bean的配置 #

前面提到过，Gemini Blueprint即实现了Blueprint 规范，又兼容Spring DM风格的配置，本节我们再来了解一下Blueprint与Spring DM在Bean的配置上的差异，具体如下表所示：  
（注意：这两种风格Gemini Blueprint都支持。）  
![这里写图片描述][SouthEast]  
如上图所示，Spring DM风格的Bean配置和Blueprint还是有一些差异的，首先体现在根元素和命名空间声明上，Spring DM根元素为`<beans>`，命名空间声明如下：

而Blueprint根元素为`<blueprint>`，命名空间声明如下：

<?xml version="1.0" encoding="UTF-8"?>
    <blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0" default-activation="lazy">
    
    </blueprint>

相比之下，Blueprint的配置要稍微简单些，除了根元素和命名空间声明外，Bean的配置的主要差异如下：

1、Spring DM使用根元素的default-lazy-init属性指定IoC容器启动时是否立刻实例化所有的Bean，而Blueprint对应的属性为default-activation。

2、Spring DM可以通过default-init-method和default-destroy-method属性指定Bean实例化和销毁时默认的回调方法，还可以通过default-autowire, default-autowire-candidates属性指定Bean的自动装配策略，而这些属性Blueprint是不支持的。

3、Spring DM的Bean支持使用name属性，还支持使用alias属性为Bean指定一个别名，Blueprint是不支持的。

4、Spring DM 配置Bean的scope属性支持singleton, prototype, request, session, bundle等取值，而Blueprint Bean的scope属性仅仅支持singleton, prototype。

5、Spring DM通过Bean的lazy-init属性指定IoC容器启动时是否实例化该Bean，Blueprint对应的属性为activation。

6、Spring DM通过factory-bean属性指定工厂Bean，而Blueprint对应的属性为factory-ref。

7、Spring DM可以使用parent属性继承一个Bean的配置，而Blueprint不支持。

8、Spring DM 通过autowire, autowire-candidate属性指定Bean的自动装配策略，而Blueprint也是不支持的。

9、构造器注入时，Spring DM使用的标签为`<constructor-arg>`，而Blueprint使用的标签为`<argument>`。

Spring DM 和 Blueprint 风格的Bean的配置差异主要体现在上面几个方面，接下来我们开始学习Bean的注册与引用。

# 二、Bundle中Bean的注册与引用 #

前面的文章中有提到过，OSGI应用的每一个Bundle都是使用不同的类加载器加载，OSGI应用并不像普通的Java应用一样，有全局的Classpath的概念，所以如果需要在一个Bundle中使用另外一个Bundle中的类，则需要另外一个Bundle导出这些类，然后在用到这些类的Bundle中导入即可。而OSGI应用对象的共享则是通过服务注册的方式实现。

使用Blueprint將Spring框架整合到OSGI中，ApplicationContext和普通的Java应用也有所差异。一般来说，普通Java应用的ApplicationContext只有一个，而且是全局的，而在OSGI应用中，每个Bundle对应一个单独个ApplicationContext，如下图所示：  
![这里写图片描述][SouthEast 1]

从上图可以清晰的看出，每个Bundle对应的ApplicationContext是不同的，也就是说每个Bundle中配置的Bean是不共享的，例如当我们在A Bundle中定义了一个Bean，然后以属性注入的方式注入到B Bundle中的一个Bean中，这就有问题了，那么如何解决这个问题呢，Spring DM给出的解决方案是將Bean注册为服务，然后在其他Bundle中引用Bean。接下来我们就来学习一下Bean的注册与引用机制。

Spring DM Bean的注册与引用机制实际上有个缺点，它要求被注册的Bean必须实现了某个接口，为了方便说明问题，笔者在前面文章中搭建好的环境中进行演示，首先我们可以在com.csdn.osgi.common工程中新建一个com.csdn.osgi.domain.Employee接口，表示员工的信息，内容如下：

package com.csdn.osgi.domain;
    
    public interface Employee {
    
        public String getName();
    
        public int getAge();
    
        public String getAddress();
    
    }

然后定义一个具体的类来实现Employee 接口，比如我们有实现类com.csdn.osgi.domain.Programmer，如下：

package com.csdn.osgi.domain;
    
    public class Programmer implements Employee{ 
    
        private String name; // 员工姓名
    
        private int age; // 员工年龄
    
        private String address; // 居住地址
    
        private double salary; // 员工薪资
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public int getAge() {
            return age;
        }
    
        public void setAge(int age) {
            this.age = age;
        }
    
        public String getAddress() {
            return address;
        }
    
        public void setAddress(String address) {
            this.address = address;
        }
    
        public double getSalary() {
            return salary;
        }
    
        public void setSalary(double salary) {
            this.salary = salary;
        }
    
    }

接着在com.csdn.osgi.common工程中，新建 META-INF/spring/employee.xml文件，在新建的文件中，配置一个Programmer类的实例，如下：

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd" default-lazy-init="false">
    
       <bean id="programmer" class="com.csdn.osgi.domain.Programmer">
            <property name="name" value="Smith"/>
            <property name="age" value="25"/>
            <property name="address" value="Nanjin"/>
            <property name="salary" value="2000"/>
       </bean>
    
    </beans>

如上面代码所示，我们在com.csdn.osgi.common这个Bundle中通过Spring实例化了一个Programmer对象，其他Bundle中如果需要注入这个实例，该怎样做呢？

接下来我们在com.csdn.osgi.helloworld工程中，新建一个Company类，表示公司信息，例如：

package com.csdn.osgi.domain;
    
    public class Company {
    
        private String name; // 公司名称
    
        private Employee emp; // 假设只有一个员工
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public Employee getEmp() {
            return emp;
        }
    
        public void setEmp(Employee emp) {
            this.emp = emp;
        }
    }

项目结构如下图所示：  
![这里写图片描述][SouthEast 2]  
需要注意的是，Company类在com.csdn.osgi.helloworld这个Bundle中，而Programmer类在com.csdn.osgi.common中，我们需要在com.csdn.osgi.common这个Bundle中导出com.csdn.osgi.domain这个包，具体做法很简单，可以將com.csdn.osgi.common工程中的MANIFEST.MF文件，修改成如下内容：

Manifest-Version: 1.0
    Bundle-ManifestVersion: 2
    Bundle-Name: Common
    Bundle-SymbolicName: com.csdn.osgi.common
    Bundle-Version: 1.0.0.qualifier
    Bundle-Activator: com.csdn.osgi.common.Activator
    Bundle-Vendor: CSDN
    Bundle-RequiredExecutionEnvironment: JavaSE-1.8
    Import-Package: org.osgi.framework;version="1.3.0"
    Export-Package: com.csdn.osgi.domain

其中`Export-Package: com.csdn.osgi.domain`为新增内容，解决依赖问题后，我们可以在com.csdn.osgi.helloworld工程中，新建一个config/company.xml文件(**注意：前面我们通过Spring-Context头自定义了Bean配置文件路径为config/\*.xml**)，然后配置一个Company实例，内容如下：

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd" default-lazy-init="false">
    
       <bean id="company" class="com.csdn.osgi.domain.Company">
            <property name="name" value="CSDN"/>
            <property name="emp" ref="programmer"/>
       </bean>
    
    </beans>

这里我们直接將com.csdn.osgi.common Bundle中配置的employee对象注入，然后启动OSGI容器，看看会有什么问题，控制台输出日志如下：

十二月 25, 2016 9:08:05 下午 org.eclipse.gemini.blueprint.extender.internal.boot.ChainActivator <init>
    信息: Blueprint API detected; enabling Blueprint Container functionality
    十二月 25, 2016 9:08:05 下午 org.eclipse.gemini.blueprint.extender.internal.activator.LoggingActivator start
    信息: Starting [org.eclipse.gemini.blueprint.extender] bundle v.[2.0.0.M02]
    osgi> 十二月 25, 2016 9:08:05 下午 org.eclipse.gemini.blueprint.extender.internal.support.ExtenderConfiguration start
    信息: No custom extender configuration detected; using defaults...
    十二月 25, 2016 9:08:05 下午 org.springframework.scheduling.timer.TimerTaskExecutor afterPropertiesSet
    信息: Initializing Timer
    hello world!
    十二月 25, 2016 9:08:06 下午 org.eclipse.gemini.blueprint.extender.support.DefaultOsgiApplicationContextCreator createApplicationContext
    信息: Discovered configurations {osgibundle:/META-INF/spring/*.xml} in bundle [Common (com.csdn.osgi.common)]
    Hello World!!
    十二月 25, 2016 9:08:06 下午 org.eclipse.gemini.blueprint.extender.support.DefaultOsgiApplicationContextCreator createApplicationContext
    信息: Discovered configurations {config/*.xml} in bundle [Helloworld (com.csdn.osgi.helloworld)]
    十二月 25, 2016 9:08:06 下午 org.eclipse.gemini.blueprint.extender.internal.blueprint.activator.support.BlueprintContainerCreator createApplicationContext
    信息: Discovered configurations {bundleentry://43.fwk1878169648/OSGI-INF/blueprint/beans.xml} in bundle [Helloworld (com.csdn.osgi.helloworld)]
    十二月 25, 2016 9:08:06 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
    信息: Refreshing OsgiBundleXmlApplicationContext(bundle=com.csdn.osgi.common, config=osgibundle:/META-INF/spring/*.xml): startup date [Sun Dec 25 21:08:06 CST 2016]; root of context hierarchy
    十二月 25, 2016 9:08:06 下午 org.eclipse.gemini.blueprint.context.support.AbstractOsgiBundleApplicationContext unpublishContextAsOsgiService
    信息: Application Context service already unpublished
    十二月 25, 2016 9:08:06 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
    信息: Refreshing OsgiBundleXmlApplicationContext(bundle=com.csdn.osgi.helloworld, config=config/*.xml): startup date [Sun Dec 25 21:08:06 CST 2016]; root of context hierarchy
    十二月 25, 2016 9:08:06 下午 org.eclipse.gemini.blueprint.context.support.AbstractOsgiBundleApplicationContext unpublishContextAsOsgiService
    信息: Application Context service already unpublished
    十二月 25, 2016 9:08:06 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
    信息: Refreshing OsgiBundleXmlApplicationContext(bundle=com.csdn.osgi.helloworld, config=bundleentry://43.fwk1878169648/OSGI-INF/blueprint/beans.xml): startup date [Sun Dec 25 21:08:06 CST 2016]; root of context hierarchy
    十二月 25, 2016 9:08:06 下午 org.eclipse.gemini.blueprint.context.support.AbstractOsgiBundleApplicationContext unpublishContextAsOsgiService
    信息: Application Context service already unpublished
    十二月 25, 2016 9:08:06 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
    信息: Loading XML bean definitions from OSGi resource[bundleentry://43.fwk1878169648/OSGI-INF/blueprint/beans.xml|bnd.id=43|bnd.sym=com.csdn.osgi.helloworld]
    十二月 25, 2016 9:08:06 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
    信息: Loading XML bean definitions from URL [bundleentry://43.fwk1878169648/config/beans.xml]
    十二月 25, 2016 9:08:06 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
    信息: Loading XML bean definitions from URL [bundleentry://37.fwk1878169648/META-INF/spring/beans.xml]
    十二月 25, 2016 9:08:06 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
    信息: Loading XML bean definitions from URL [bundleentry://43.fwk1878169648/config/company.xml]
    十二月 25, 2016 9:08:06 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
    信息: Loading XML bean definitions from URL [bundleentry://37.fwk1878169648/META-INF/spring/dmconfig.xml]
    十二月 25, 2016 9:08:06 下午 org.eclipse.gemini.blueprint.extender.internal.dependencies.startup.DependencyWaiterApplicationContextExecutor stageOne
    信息: No outstanding OSGi service dependencies, completing initialization for OsgiBundleXmlApplicationContext(bundle=com.csdn.osgi.helloworld, config=bundleentry://43.fwk1878169648/OSGI-INF/blueprint/beans.xml)
    十二月 25, 2016 9:08:06 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
    信息: Loading XML bean definitions from URL [bundleentry://43.fwk1878169648/config/dmconfig.xml]
    十二月 25, 2016 9:08:06 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
    信息: Loading XML bean definitions from URL [bundleentry://37.fwk1878169648/META-INF/spring/employee.xml]
    十二月 25, 2016 9:08:06 下午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
    信息: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@48766948: defining beans [helloWorld,blueprintBundle,blueprintBundleContext,blueprintContainer,blueprintConverter]; root of factory hierarchy
    ================Hello World================
    十二月 25, 2016 9:08:06 下午 org.eclipse.gemini.blueprint.extender.internal.dependencies.startup.DependencyWaiterApplicationContextExecutor stageOne
    信息: No outstanding OSGi service dependencies, completing initialization for OsgiBundleXmlApplicationContext(bundle=com.csdn.osgi.helloworld, config=config/*.xml)
    十二月 25, 2016 9:08:06 下午 org.eclipse.gemini.blueprint.extender.internal.dependencies.startup.DependencyWaiterApplicationContextExecutor stageOne
    信息: No outstanding OSGi service dependencies, completing initialization for OsgiBundleXmlApplicationContext(bundle=com.csdn.osgi.common, config=osgibundle:/META-INF/spring/*.xml)
    十二月 25, 2016 9:08:06 下午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
    信息: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@6ec2b45d: defining beans [object,length,buffer,current-time,list,programmer]; root of factory hierarchy
    十二月 25, 2016 9:08:06 下午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
    信息: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@30a0eb63: defining beans [helloWorld1,helloWorld2,company]; root of factory hierarchy
    ================Hello World================
    ================Hello World================
    =========Company=========
    十二月 25, 2016 9:08:06 下午 org.springframework.beans.factory.support.DefaultSingletonBeanRegistry destroySingletons
    信息: Destroying singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@30a0eb63: defining beans [helloWorld1,helloWorld2,company]; root of factory hierarchy
    十二月 25, 2016 9:08:06 下午 org.eclipse.gemini.blueprint.extender.internal.support.DefaultOsgiBundleApplicationContextListener onOsgiApplicationEvent
    严重: Application context refresh failed (OsgiBundleXmlApplicationContext(bundle=com.csdn.osgi.helloworld, config=config/*.xml))
    org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'company' defined in URL [bundleentry://43.fwk1878169648/config/company.xml]: Cannot resolve reference to bean 'programmer' while setting bean property 'emp'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'programmer' is defined
        at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:328)
        at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:106)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1305)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1067)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:511)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:450)
        at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:290)
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:287)
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:189)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:557)
        at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:842)
        at org.eclipse.gemini.blueprint.context.support.AbstractDelegatedExecutionApplicationContext.access$1600(AbstractDelegatedExecutionApplicationContext.java:60)
        at org.eclipse.gemini.blueprint.context.support.AbstractDelegatedExecutionApplicationContext$4.run(AbstractDelegatedExecutionApplicationContext.java:325)
        at org.eclipse.gemini.blueprint.util.internal.PrivilegedUtils.executeWithCustomTCCL(PrivilegedUtils.java:85)
        at org.eclipse.gemini.blueprint.context.support.AbstractDelegatedExecutionApplicationContext.completeRefresh(AbstractDelegatedExecutionApplicationContext.java:290)
        at org.eclipse.gemini.blueprint.extender.internal.dependencies.startup.DependencyWaiterApplicationContextExecutor$CompleteRefreshTask.run(DependencyWaiterApplicationContextExecutor.java:137)
        at java.lang.Thread.run(Thread.java:745)
    Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'programmer' is defined
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanDefinition(DefaultListableBeanFactory.java:504)
        at org.springframework.beans.factory.support.AbstractBeanFactory.getMergedLocalBeanDefinition(AbstractBeanFactory.java:1041)
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:273)
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:189)
        at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:322)
        ... 17 more
    
    十二月 25, 2016 9:08:06 下午 org.eclipse.gemini.blueprint.context.support.AbstractOsgiBundleApplicationContext unpublishContextAsOsgiService
    信息: Application Context service already unpublished
    十二月 25, 2016 9:08:06 下午 org.eclipse.gemini.blueprint.blueprint.container.support.BlueprintContainerServicePublisher registerService
    信息: Publishing BlueprintContainer as OSGi service with properties {Bundle-SymbolicName=com.csdn.osgi.helloworld, Bundle-Version=1.0.0.qualifier, osgi.blueprint.container.version=1.0.0.qualifier, osgi.blueprint.container.symbolicname=com.csdn.osgi.helloworld}
    十二月 25, 2016 9:08:06 下午 org.eclipse.gemini.blueprint.extender.internal.support.DefaultOsgiBundleApplicationContextListener onOsgiApplicationEvent
    信息: Application context succesfully closed (OsgiBundleXmlApplicationContext(bundle=com.csdn.osgi.helloworld, config=config/*.xml))
    十二月 25, 2016 9:08:06 下午 org.eclipse.gemini.blueprint.extender.internal.dependencies.startup.DependencyWaiterApplicationContextExecutor fail
    严重: Unable to create application context for [com.csdn.osgi.helloworld], unsatisfied dependencies: none
    org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'company' defined in URL [bundleentry://43.fwk1878169648/config/company.xml]: Cannot resolve reference to bean 'programmer' while setting bean property 'emp'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'programmer' is defined
        at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:328)
        at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:106)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1305)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1067)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:511)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:450)
        at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:290)
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:287)
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:189)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:557)
        at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:842)
        at org.eclipse.gemini.blueprint.context.support.AbstractDelegatedExecutionApplicationContext.access$1600(AbstractDelegatedExecutionApplicationContext.java:60)
        at org.eclipse.gemini.blueprint.context.support.AbstractDelegatedExecutionApplicationContext$4.run(AbstractDelegatedExecutionApplicationContext.java:325)
        at org.eclipse.gemini.blueprint.util.internal.PrivilegedUtils.executeWithCustomTCCL(PrivilegedUtils.java:85)
        at org.eclipse.gemini.blueprint.context.support.AbstractDelegatedExecutionApplicationContext.completeRefresh(AbstractDelegatedExecutionApplicationContext.java:290)
        at org.eclipse.gemini.blueprint.extender.internal.dependencies.startup.DependencyWaiterApplicationContextExecutor$CompleteRefreshTask.run(DependencyWaiterApplicationContextExecutor.java:137)
        at java.lang.Thread.run(Thread.java:745)
    Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'programmer' is defined
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanDefinition(DefaultListableBeanFactory.java:504)
        at org.springframework.beans.factory.support.AbstractBeanFactory.getMergedLocalBeanDefinition(AbstractBeanFactory.java:1041)
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:273)
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:189)
        at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:322)
        ... 17 more
    
    十二月 25, 2016 9:08:06 下午 org.eclipse.gemini.blueprint.context.support.AbstractOsgiBundleApplicationContext publishContextAsOsgiServiceIfNecessary
    信息: Publishing application context as OSGi service with properties {org.eclipse.gemini.blueprint.context.service.name=com.csdn.osgi.helloworld, org.springframework.context.service.name=com.csdn.osgi.helloworld, Bundle-SymbolicName=com.csdn.osgi.helloworld, Bundle-Version=1.0.0.qualifier}
    十二月 25, 2016 9:08:06 下午 org.eclipse.gemini.blueprint.extender.internal.support.DefaultOsgiBundleApplicationContextListener onOsgiApplicationEvent
    信息: Application context successfully refreshed (OsgiBundleXmlApplicationContext(bundle=com.csdn.osgi.helloworld, config=bundleentry://43.fwk1878169648/OSGI-INF/blueprint/beans.xml))
    十二月 25, 2016 9:08:06 下午 org.eclipse.gemini.blueprint.context.support.AbstractOsgiBundleApplicationContext publishContextAsOsgiServiceIfNecessary
    信息: Publishing application context as OSGi service with properties {org.eclipse.gemini.blueprint.context.service.name=com.csdn.osgi.common, org.springframework.context.service.name=com.csdn.osgi.common, Bundle-SymbolicName=com.csdn.osgi.common, Bundle-Version=1.0.0.qualifier}
    十二月 25, 2016 9:08:06 下午 org.eclipse.gemini.blueprint.extender.internal.support.DefaultOsgiBundleApplicationContextListener onOsgiApplicationEvent
    信息: Application context successfully refreshed (OsgiBundleXmlApplicationContext(bundle=com.csdn.osgi.common, config=osgibundle:/META-INF/spring/*.xml))

错误信息意思很明显，名称为programmer这个Bean未定义，原因是该Bean定义在com.csdn.osgi.common这个Bundle中，在com.csdn.osgi.helloworld Bundle中无法直接访问，接下来我们通过Bean的注册和引用来解决该问题。

在com.csdn.osgi.common工程中，新建一个META-INF/spring/dmconfig.xml文件，用来注册Bean，内容如下：

<?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:osgi="http://www.eclipse.org/gemini/blueprint/schema/blueprint" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.eclipse.org/gemini/blueprint/schema/blueprint http://www.eclipse.org/gemini/blueprint/schema/blueprint/gemini-blueprint.xsd">
    
        <osgi:service id="employee" ref="programmer" interface="com.csdn.osgi.domain.Employee" />
    
    </beans>

然后在com.csdn.osgi.helloworld Bundle中，新建config/dmconfig.xml文件，我们在该文件中引入其他Bundle中注册的Bean，内容如下：

<?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:osgi="http://www.eclipse.org/gemini/blueprint/schema/blueprint" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.eclipse.org/gemini/blueprint/schema/blueprint http://www.eclipse.org/gemini/blueprint/schema/blueprint/gemini-blueprint.xsd">
    
        <osgi:reference id="employee" interface="com.csdn.osgi.domain.Employee" />
    
        <alias name="employee" alias="programmer"/>
    
    </beans>

需要注意的是，`<osgi:service/>`标签的id属性值不能和Bean的id相同。上面的配置中我们使用`<alias/>`标签为employee指定别名为programmer，然后重启OSGI容器，会发现com.csdn.osgi.common Bundle中定义的名称为programmer的Bean成功注入到Company类中。

Bean的注册与引用机制对项目开发非常重要，在后面整合Mybatis时，我们可以將用于操作数据库的SqlSessionTemplate注册为服务，然后在其他Bundle就可以引用该服务操作数据库了。

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