阅读 springdm in action 笔记--Spring DM extenders

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本文适合对OSGI有一定了解和基础的研发人员，最初的想法是记录在学习过程中的知识点，以备将来查询。由于我e文水平实在有限，很多地方是直译或者凭着自己的理解来翻译，如果大家发现有不对的地方请指正。另外提供spingdm in action 英文版的下载地址：http://download.csdn.net/source/3002996

META-INF/MANIFEST.MF

Manifest-Version: 1.0#标记受保护的地址，该地址只能被程序本身访问到Private-Package: .,WEB-INFBundle-Version: 1.0.0Build-Jdk: 1.6.0_22Built-By: johnTool: Bnd-0.0.311Bnd-LastModified: 1296090877032Bundle-Name: springdm-web-sampleBundle-ManifestVersion: 2Created-By: Apache Maven Bundle Plugin#标记web程序的根目录Web-ContextPath: springdm-web-sampleBundle-SymbolicName: com.manning.sdmia.springdm-web-sample

通过Spring-Context可以改变spring配置文件的默认路径，多个文件以逗号分隔

Spring-Context: config/application-context.xml, config/app-context-2.xmlSpring-Context: config/*.xml Spring-Context: config/**/*.xml可以递归cofig下所有目录中的xml文件

通过osgi:service可以发布一个osgi服务，注册到osgi registry中

通过osgi:reference可以引用一个osgi服务到本地bundle中

<osgi:reference id="myService" interface="com.manning.sdmia.MyService"/> <bean id="webController" class="com.manning.sdmia.web.MyController"> <property name="service" ref="myService"/> </bean>

Spring DM中OSGi 资源定位策略

OSGi search strategyPrefixesDescriptionClass spaceclasspath: classpath*:Search is delegated to the bundle classloader. The bundle itself, imported packages, and required bundles are then scanned usingthe same semantics as the Bundle.getResource method. JAR fileosgibundlejar:Only the bundle itself is scanned, using the same semantics as the Bundle.getEntry method.Bundle spaceosgibundle:The bundle and its fragments (if any) are scanned. Delegates internally to the Bundle.findEntries method. This is Spring DM’s default resource-loading strategy.

例子：

Spring-Context: osgibundle:config/application-context.xml<bean id="someBean" class="com.manning.sdmia.SomeBean"> <property name="resource" value="classpath:help/section1.html" /> </bean>

wait-for-dependencies:=false 延迟创建application context 知道他依赖的服务都是有效状态

Spring-Context: config/application-context.xml;wait-for-dependencies:=false

TIMEOUT

如果一个dependency（暂时翻译为依赖）丢失，可能严重危机application context创建，可以通过设置timeout指令来避免application context创建过程被长期挂起，通过下面的设置，application context在尝试创建失败之前，等待他的强制依赖（ mandatory dependencies）120秒。timeout仅仅对 mandatory dependencies有效，当设置wait-for-dependencies：false时该指令将被忽略

Spring-Context: config/application-context.xml;timeout:=120

SPRING DM 事件机制

Application context events inSpring DM

Event class Description OsgiBundleContextRefreshedEvent;Published when an application context is successfully started or refreshedOsgiBundleContextFailedEventPublished when the creation of an application context failsOsgiBundleContextClosedEventPublished when an application context is closed, usu-ally when a Spring-powered bundle is stopped

一个简单的办法是实现一个implements OsgiBundleApplicationContextListener 的bean并且发布成OSGI service，Spring

DM 将自动发现它并增加到被管理的监听列表中.见如下代码

package com.manning.sdmia.ch04;import org.springframework.osgi.context.event.OsgiBundleApplicationContextEvent; import org.springframework.osgi.context.event.OsgiBundleApplicationContextListener; import org.springframework.osgi.context.event.OsgiBundleContextClosedEvent; import org.springframework.osgi.context.event.OsgiBundleContextRefreshedEvent;public class ApplicationContextObserver implements OsgiBundleApplicationContextListener<OsgiBundleApplicationContextEvent> { private transient int countRefreshed = 0; private transient int countClosed = 0; public void onOsgiApplicationEvent(OsgiBundleApplicationContextEvent evt) { if(evt instanceof OsgiBundleContextRefreshedEvent) { countRefreshed++; } else if(evt instanceof OsgiBundleContextClosedEvent) { countClosed++; } } public int getCountRefreshed() { return countRefreshed; } public int getCountClosed() { return countClosed; } }

在spring配置文件声明该监听

<?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.springframework.org/schema/osgi" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/osgi http://www.springframework.org/schema/osgi/spring-osgi.xsd"> <bean id="observer" class="com.manning.sdmia.ch04.ApplicationContextObserver" /><osgi:service ref="observer" interface="org.springframework.osgi.context.event.OsgiBundleApplicationContextListener"/></beans>

在spring bean中使用OSGI BUNDLE CONTEXT

方法一：实现一个 implementing BundleContextAware的bean并实现setBundleContext方法

import org.osgi.framework.BundleContext; import org.springframework.osgi.context.BundleContextAware;public class OsgiAddict implements BundleContextAware { public void setBundleContext(BundleContext bundleContext) { ... } }

方法二：

import org.osgi.framework.BundleContext;public class PojoOsgiAddict { private BundleContext bundleContext; public void setBundleContext(BundleContext bundleContext) { this.bundleContext = bundleContext; } }

必须明确的注入bundleContext

简单的web程序结构：

my-web-bundle META-INF/ MANIFEST.MF spring/ application.xml WEB-INF/ web.xml

web bundle中类加载机制：

■ Its bundle space (classes in the JAR or WAR and classes from all the associated bundle fragments)

■ Classes from the packages imported with the Import-Package header

■ All the exported classes from bundles appearing in the Require-Bundle header

■ Bundle-Classpath: .,WEB-INF/classes,WEB-INF/lib/libA.jar, WEB-INF/lib/libB.jar

web.xml配置spring环境：

<context-param><param-name>contextClass</param-name><param-value>org.springframework.osgi.web.context.support.OsgiBundleXmlWebApplicationContext</param-value></context-param><context-param><param-name>contextConfigLocation</param-name><param-value>WEB-INF/applicationContext.xml,WEB-INF/applicationContext-osgi.xml</param-value></context-param><listener><listener-class>org.springframework.web.context.ContextLoaderListener</listener-class></listener>