SpringBoot 获取上下文，获取bean的几种中方式

传统Spring项目

在写传统的spring项目中，一般通过初始化抽象类AbstractXmlApplicationContext 的实现类，并传入spring.xml，来获取应用上下文，最终通过getBean方法获取bean，如下：

	ApplicationContext app1 = new FileSystemXmlApplicationContext("applicationContext.xml"); app1.getBean("beanName"); ApplicationContext app2 = new ClassPathXmlApplicationContext("applicationContext.xml"); app2.getBean("beanName"); 

SpringBoot项目获取bean的几种方式

1. 通过启动类中返回的上下文获取

	ConfigurableApplicationContext app = SpringApplication.run(BeanDemoApplication.class, args); SpringUtil.setAppContext(app); 

public class SpringUtil { private static ApplicationContext appContext; public static void setAppContext(ApplicationContext appContext) { SpringUtil.appContext = appContext; } public static ApplicationContext getAppContext() { return appContext; } } 

在第三方类中使用：

	ApplicationContext appContext = SpringUtil.getAppContext(); appContext.getBean("beanName"); 

2. 通过工具类获取

RequestContextUtils.findWebApplicationContext(HttpServletRequest request),WebApplicationContextUtils.getWebApplicationContext(ServletContext sc)
a. 在controller中传入request，例如：

    public String test(HttpServletRequest request,HttpServletRequest response) { WebApplicationContext wc = RequestContextUtils.findWebApplicationContext(request); wc.getBean("beanName"); WebApplicationContext wc2 = WebApplicationContextUtils.getWebApplicationContext(request.getServletContext()); wc2.getBean("beanName"); } 

b. 在service中或者其他后端服务中获取：

HttpServletRequest request = ((ServletRequestAttributes)RequestContextHolder.getRequestAttributes()).getRequest(); WebApplicationContext wc = RequestContextUtils.findWebApplicationContext(request); WebApplicationContext wc2 = WebApplicationContextUtils.getWebApplicationContext(request.getServletContext()); wc.getBean("beanName"); wc2.getBean("beanName"); 

3. 通过实现接口ApplicationContextAware

@Component public class TestApplicationContextAware implements ApplicationContextAware { private ApplicationContext applicationContext; @Override public void setApplicationContext(ApplicationContext applicationContext) throws BeansException { this.applicationContext = applicationContext; } public Object getBean(String beanName) { return applicationContext.getBean(beanName); } public ApplicationContext getApplicationContext() { return applicationContext; } } 

在其他类中调用

	@Autowired private TestApplicationContextAware app; public void testMethod() { app.getBean("beanName"); } 

4. 通过继承抽象类：ApplicationObjectSupport，WebApplicationObjectSupport

原理参考第3点

5. 其他方式

在网上看，发现也可以直接调用：ContextLoader.getCurrentWebApplicationContext()，或者 ContextLoaderListener.getCurrentWebApplicationContext() 其实都是调用同一段代码，如下：

	@Nullable
	public static WebApplicationContext getCurrentWebApplicationContext() { ClassLoader ccl = Thread.currentThread().getContextClassLoader(); if (ccl != null) { WebApplicationContext ccpt = currentContextPerThread.get(ccl); if (ccpt != null) { return ccpt; } } return currentContext; } 

说明：目前通过这种方式获取上下文为null，从代码可以看出，上下文是通过currentContextPerThread.get(ccl) 来获取的，而currentContextPerThread缓存是通过方法contextInitialized(ServletContextEvent event) 来初始化的，至于为何获取为空