关于spring获取webApplication.getBean多种途径和简单解释 _关于Spring

壮心未与年俱老，死去犹能作鬼雄。这篇文章主要讲述关于spring获取webApplication.getBean多种途径和简单解释相关的知识，希望能为你提供帮助。

ApplicationContext ac1 = new FileSystemXmlApplicationContext("com/spark/system/applicationContext.xml"); //如果配置文件放在文件系统的目录下则优先使用该方式 //com/spark/system/applicationContext.xml等价于"file:com/spark/system/applicationContext.xml" ac1.getBean("beanId"); //ApplicationContext ac2=new ClassPathXmlApplicationContext("com/spark/system/applicationContext.xml"); //如果配置文件在类路径下则优先使用该方式 //com/spark/system/applicationContext.xml 等价于"classpath:com/spark/system/applicationContext.xml" ac2.getBean("beanId");

说明：
这种方式适用于采用Spring框架的独立应用程序，需要程序通过配置文件手工初始化Spring的情况。

public void getBean(HttpServletRequest req,HttpSession se) { //se.getServletContext() 也可以 WebApplicationContext wac=(WebApplicationContext)req.getServletContext().getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE); wac.getBean(""); }

说明:此种方式正是我们下面所提到的WebApplicationContextUtils 工具类中getWebApplicationContext(ServletContext sc) 方法的内部实现，以下方式是通过spring 提供的WebApplicationContextUtils 工具类获取WebApplicationContext

方式一:

import org.springframework.web.context.support.WebApplicationContextUtils; ApplicationContext ac1 = WebApplicationContextUtils.getRequiredWebApplicationContext(ServletContext sc) ApplicationContext ac2 = WebApplicationContextUtils.getWebApplicationContext(ServletContext sc) ac1.getBean("beanId"); ac2.getBean("beanId");

说明：
这种方式适合于采用Spring框架的B/S系统，通过ServletContext对象获取ApplicationContext对象，然后在通过它获取需要的类实例。
上面两个工具方式的区别是，前者在获取失败时抛出异常，后者返回null。

方式二:

import org.springframework.web.context.WebApplicationContext; import org.springframework.web.context.support.WebApplicationObjectSupport; public class ApplicationContextUtils extends WebApplicationObjectSupport{ publicWebApplicationContext isgetWebApplicationContext(){ return super.getWebApplicationContext(); } }

继承自抽象类WebApplicationObjectSupport
说明：
抽象类WebApplicationObjectSupport 继承自ApplicationObjectSupport提供getApplicationContext()方法，可以方便的获取到ApplicationContext。Spring初始化时，会通过该ApplicationObjectSupport 的setApplicationContext(ApplicationContext context)方法将ApplicationContext 对象注入。当然直接继承ApplicationObjectSupport自己实现也可以，既然spring 提供了更方便的抽象工具类WebApplicationObjectSupport 建议使用它。以免出现问题
下面看WebApplicationObjectSupport关键源码(红色部分)

/*** Eclipse Class Decompiler, copyright (c) 2012 cnfree ([email protected]) ***/ package org.springframework.web.context.support; import java.io.File; import javax.servlet.ServletContext; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ApplicationObjectSupport; import org.springframework.web.context.ServletContextAware; import org.springframework.web.context.WebApplicationContext; import org.springframework.web.util.WebUtils; public abstract class WebApplicationObjectSupport < span style="color:#FF0000; "> extends ApplicationObjectSupport< /span> implements ServletContextAware{ private ServletContext servletContext; public final void setServletContext(ServletContext servletContext){ if (servletContext != this.servletContext){ this.servletContext = servletContext; if (servletContext != null) initServletContext(servletContext); } } protected boolean isContextRequired(){ return true; } protected void initApplicationContext(ApplicationContext context){ super.initApplicationContext(context); if ((this.servletContext == null) & & (context instanceof WebApplicationContext)){ this.servletContext = ((WebApplicationContext)context) .getServletContext(); if (this.servletContext != null) initServletContext(this.servletContext); } } protected void initServletContext(ServletContext servletContext){} < span style="color:#FF0000; "> protected final WebApplicationContext getWebApplicationContext() throws IllegalStateException{ ApplicationContext ctx = getApplicationContext(); if (ctx instanceof WebApplicationContext){ return ((WebApplicationContext)getApplicationContext()); } if (isContextRequired()){ throw new IllegalStateException( "WebApplicationObjectSupport instance [" + this + "] does not run in a WebApplicationContext but in: " + ctx); } return null; }< /span> protected final ServletContext getServletContext() throws IllegalStateException{ if (this.servletContext != null){ return this.servletContext; } ServletContext servletContext = getWebApplicationContext() .getServletContext(); if ((servletContext == null) & & (isContextRequired())){ throw new IllegalStateException( "WebApplicationObjectSupport instance [" + this + "] does not run within a ServletContext. Make sure the object is fully configured!"); } return servletContext; } protected final File getTempDir() throws IllegalStateException{ return WebUtils.getTempDir(getServletContext()); } }

下面是ApplicationObjectSupport源码

/*** Eclipse Class Decompiler, copyright (c) 2012 cnfree ([email protected]) ***/ package org.springframework.context.support; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.springframework.beans.BeansException; import org.springframework.context.ApplicationContext; import org.springframework.context.ApplicationContextAware; import org.springframework.context.ApplicationContextException; public abstract class ApplicationObjectSupport implements ApplicationContextAware{ protected final Log logger; private ApplicationContext applicationContext; private MessageSourceAccessor messageSourceAccessor; public ApplicationObjectSupport(){ this.logger = LogFactory.getLog(super.getClass()); } public final void setApplicationContext(ApplicationContext context) throws BeansException{ if ((context == null) & & (!(isContextRequired()))){ this.applicationContext = null; this.messageSourceAccessor = null; } else if (this.applicationContext == null){ if (!(requiredContextClass().isInstance(context))){ throw new ApplicationContextException( "Invalid application context: needs to be of type [" + requiredContextClass().getName() + "]"); } this.applicationContext = context; this.messageSourceAccessor = new MessageSourceAccessor(context); initApplicationContext(context); } else if (this.applicationContext != context){ throw new ApplicationContextException( "Cannot reinitialize with different application context: current one is [" + this.applicationContext + "], passed-in one is [" + context + "]"); } } protected boolean isContextRequired(){ return false; } protected Class requiredContextClass(){ return ApplicationContext.class; } protected void initApplicationContext(ApplicationContext context) throws BeansException{ initApplicationContext(); } protected void initApplicationContext() throws BeansException{} public final ApplicationContext getApplicationContext() throws IllegalStateException{ if ((this.applicationContext == null) & & (isContextRequired())){ throw new IllegalStateException( "ApplicationObjectSupport instance [" + this + "] does not run in an ApplicationContext"); } return this.applicationContext; } protected final MessageSourceAccessor getMessageSourceAccessor() throws IllegalStateException{ if ((this.messageSourceAccessor == null) & & (isContextRequired())){ throw new IllegalStateException( "ApplicationObjectSupport instance [" + this + "] does not run in an ApplicationContext"); } return this.messageSourceAccessor; } }

通过源码很容易看得出spring做的这两次封装是如何获取到WebApplicationContext的当然自己也可以实现底层接口自己封装。比如:继承自抽象类ApplicationObjectSupport,抽象类ApplicationObjectSupport提供getApplicationContext()方法，可以方便的获取到ApplicationContext。Spring初始化时，会通过该抽象类的setApplicationContext(ApplicationContext context)方法将ApplicationContext 对象注入。

再比如:实现接口ApplicationContextAware,实现该接口的setApplicationContext(ApplicationContext context)方法，并保存ApplicationContext 对象。Spring初始化时，会通过该方法将ApplicationContext 对象注入。
以上方法适合不同的情况，请根据具体情况选用相应的方法。
这里值得提一点的是，系统中用到上述方法的类实际上就于Spring框架紧密耦合在一起了，因为这些类是知道它们是运行在Spring框架上的，因此，系统中，应该尽量的减少这类应用，使系统尽可能的独立于当前运行环境，尽量通过DI的方式获取需要的服务提供者。

PS:除了通过applicationContext来手动获取getBean("beanId")之外，还可以通过beanfactory工厂的.getBean("beanId")获取Bean 实例
例如:

ResourcePatternResolver resolver=new PathMatchingResourcePatternResolver(); Resource resource=resolver.getResource("classpath:com/**/beans.xml"); BeanFactory bf=new XmlBeanFactory(resource); bf.getBean("beanId");

有待研究通过BeanFactory.getBean和ApplicationContext.getBean 的异同解释，和利弊以及使用情况。志同道合的同志可随时留言讨论，小弟欢迎大家一起学习本文属于原创，请勿抄袭，谢谢！

【关于spring获取webApplication.getBean多种途径和简单解释】