Spring在应用中获得Bean的方法

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。

 

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》。