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

2022-10-17 09:40:38




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

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

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