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

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{





 





	public  WebApplicationContext 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 (cnfree2000@hotmail.com) ***/





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 (cnfree2000@hotmail.com) ***/





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

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