Spring在应用中获得Bean的方法

矫情吗；* 2022-04-11 12:42 217阅读 0赞

**一.使用ApplicationContext获得Bean**

首先新建一个类，该类必须实现ApplicationContextAware接口，改接口有一个方法，public void setApplicationContext(ApplicationContext applicationContext)throws BeansException，也就是说框架会自动调用这个方法返回一个ApplicationContext对象。具体类如下：

package com.bijian.study.test;
    
    import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.NoSuchBeanDefinitionException;
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.ApplicationContextAware;
    
    public class SpringContextUtils implements ApplicationContextAware {// Spring的工具类，用来获得配置文件中的bean
    
    	private static ApplicationContext applicationContext = null;
    
    	public void setApplicationContext(ApplicationContext applicationContext)
    			throws BeansException {
    		SpringContextUtils.applicationContext = applicationContext;
    	}
    
    	public static ApplicationContext getApplicationContext() {
    		return applicationContext;
    	}
    
    	public static Object getBean(String name) throws BeansException {
    		return applicationContext.getBean(name);
    	}
    
    	public static Object getBean(String name, Class requiredType)
    			throws BeansException {
    		return applicationContext.getBean(name, requiredType);
    	}
    
    	public static boolean containsBean(String name) {
    		return applicationContext.containsBean(name);
    	}
    
    	public static boolean isSingleton(String name)
    			throws NoSuchBeanDefinitionException {
    		return applicationContext.isSingleton(name);
    	}
    
    	public static Class getType(String name)
    			throws NoSuchBeanDefinitionException {
    		return applicationContext.getType(name);
    	}
    
    	public static String[] getAliases(String name)
    			throws NoSuchBeanDefinitionException {
    		return applicationContext.getAliases(name);
    	}
    }

该类中有一个getBean(String name)方法，该方法用applicationContext去获得Bean实例，而applicationContext是由系统启动时自动设置的。

注意，需要把该类在applicationContext.xml配置文件中进行注册。<bean id="springUtil" class="com.bijian.study.test.SpringContextUtils "/>

**二.通过BeanFactory接口获得Bean**

也是新建一个类，不过该类需要实现BeanFactoryAware接口，该接口有一个方法public void setBeanFactory(BeanFactory beanFactory) throws BeansException；该方法是为了设置BeanFactory对象，系统会在启动的时候自动设置BeanFactory。具体代码如下：

package com.bijian.study.test;
    
    import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.BeanFactory;
    import org.springframework.beans.factory.BeanFactoryAware;
    
    public class SpringBeanFactoryUtils implements BeanFactoryAware {
    
    	private static BeanFactory beanFactory = null;
    	private static SpringBeanFactoryUtils factoryUtils = null;
    
    	public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
    		SpringBeanFactoryUtils.beanFactory = beanFactory;
    	}
    
    	public static BeanFactory getBeanFactory() {
    		return beanFactory;
    	}
    
    	public static SpringBeanFactoryUtils getInstance() {
    		if (factoryUtils == null) {
    			// factoryUtils =
    			// (SpringBeanFactoryUtils)beanFactory.getBean("springBeanFactoryUtils");
    			factoryUtils = new SpringBeanFactoryUtils();
    		}
    		return factoryUtils;
    	}
    
    	public static Object getBean(String name) {
    		return beanFactory.getBean(name);
    	}
    }

不过应该注意的是，改类中有一个getInstance方法，由于该代码是网上摘抄的，他提供了这么一个方法，目的是利用单例模式获得该类的一个实例，但由于getBean(String name)方法是静态的，所以用不用单例都无关紧要，经过测试，两种方法都行的通。

另外一点就是必须把该类添加到applicationContext.xml的配置文件中<bean id="springBeanFactoryUtils" class="com.bijian.study.test.SpringBeanFactoryUtils"/>

**三.在servlet中可以用WebApplicationContext类去获取Bean,具体做法是：**

ServletContext context = request.getServletContext();
    //ServletContext context = request.getSession().getServletContext();
    WebApplicationContext webcontext = (WebApplicationContext)context.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
    helloService =  (HelloService) webcontext.getBean("helloService");
    logger.info(helloService.processService("WebApplicationContext test"));

其中context是servlet的上下文，在servlet中可以通过this.getServletContext()或者request.getSession().getServletContext();获得servletContext。但是一点，spring的配置文件必须在WEB-INF下。WebApplicationContext 有一个方法getBean(String name);其实WebApplicationContext 就是ApplicationContext的另一种形式而已。

另外，在普通的java类中，即不是在servlet中可以用ContextLoader获得。ContextLoader是org.springframework.web.context包当中的一个类。

WebApplicationContext webApplication = ContextLoader.getCurrentWebApplicationContext(); 
    helloService = (HelloService) webApplication.getBean("helloService");
    logger.info(helloService.processService("ContextLoader.getCurrentWebApplicationContext() test"));

用这种方法就能获取一个WebApplicationContext 的对象。

最后经过测试，在重复100000次的基础上，第一二中方法只用了16毫秒，而第三种方法消耗了62毫秒，所以推荐使用第一二种方法。

**四.非WEB项目**

即在java main函数中执行spring的代码，如下有四种方式。

package com.bijian.study.test;
    
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.support.FileSystemXmlApplicationContext;
    import org.springframework.context.support.GenericXmlApplicationContext;
    
    import com.bijian.study.service.HelloService;
      
    public class Main {  
      
        public static void main(String[] args) throws Exception {
        	
        	String[] path1 = {"WebContent/WEB-INF/springMVC-servlet.xml"};  
            ApplicationContext context1 = new FileSystemXmlApplicationContext(path1);  
            HelloService helloService1 = context1.getBean(HelloService.class);  
            System.out.println(helloService1.processService("bijian"));  
              
            String path2="WebContent/WEB-INF/springMVC-servlet.xml";  
            ApplicationContext context2 = new FileSystemXmlApplicationContext(path2);  
            HelloService helloService2 = context2.getBean(HelloService.class);  
            System.out.println(helloService2.processService("bijian"));  
              
            ApplicationContext context = new FileSystemXmlApplicationContext("/WebContent/WEB-INF/springMVC-servlet.xml");  
            //HelloService helloService = context.getBean(HelloService.class);  
            HelloService helloService = (HelloService) context.getBean("helloService");  
            System.out.println(helloService.processService("bijian"));  
            
            GenericXmlApplicationContext context4 = new GenericXmlApplicationContext();  
            context4.setValidating(false);  
            context4.load("classpath:springMVC-servlet.xml");  
            context4.refresh();  
            HelloService helloService4 = context4.getBean(HelloService.class);
            System.out.println(helloService4.processService("bijian"));
        }  
    }

特别说明：context4.load("classpath:springMVC-servlet.xml");方式，需将springMVC-servlet.xml拷贝一份到src目录下，否则执行会报“class path resource \[springMVC-servlet.xml\] cannot be opened because it does not exist”，如下所示。

![117dcf7d-619a-303c-8ba5-d08729415b61.png][]

**附：Web工程中验证的代码**

@RequestMapping("/greeting")
    public ModelAndView greeting(@RequestParam(value = "name", defaultValue = "World") String name, HttpServletRequest request) {
    
            Map<String, Object> map = new HashMap<String, Object>();
            try {
                //由于浏览器会把中文直接换成ISO-8859-1编码格式,如果用户在地址打入中文,需要进行如下转换处理
                String tempName = new String(name.getBytes("ISO-8859-1"), "utf-8");
    
                logger.trace("tempName:" + tempName);
                logger.info(tempName);
    
                String userName = helloService.processService(tempName);
    
                map.put("userName", userName);
                
                logger.trace("运行结果:" + map);
                
                helloService = (HelloService) SpringContextUtils.getBean("helloService");
                logger.info(helloService.processService("SpringContextUtils test"));
                
                helloService = (HelloService) SpringBeanFactoryUtils.getBean("helloService");
                logger.info(helloService.processService("SpringBeanFactoryUtils test"));
                
                ServletContext context = request.getServletContext();
                //ServletContext context = request.getSession().getServletContext();
                WebApplicationContext webcontext = (WebApplicationContext)context.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
                helloService =  (HelloService) webcontext.getBean("helloService");
                logger.info(helloService.processService("WebApplicationContext test"));
                
                WebApplicationContext webApplication = ContextLoader.getCurrentWebApplicationContext(); 
                helloService = (HelloService) webApplication.getBean("helloService");
                logger.info(helloService.processService("ContextLoader.getCurrentWebApplicationContext() test"));
            } catch (UnsupportedEncodingException e) {
                logger.error("HelloController greeting方法发生UnsupportedEncodingException异常:" + e);
            } catch (Exception e) {
                logger.error("HelloController greeting方法发生Exception异常:" + e);
            }
            return new ModelAndView("/hello", map);
    }

工程完整代码见附件《SpringMVC.zip》。

[117dcf7d-619a-303c-8ba5-d08729415b61.png]: /images/20220411/9819ee5607344457a0a906ead1b59972.png