SpringBoot 獲取上下文，獲取bean的幾種中方式

傳統Spring項目

在寫傳統的spring項目中，一般通過初始化抽象類AbstractXmlApplicationContext 的實現類，並傳入spring.xml，來獲取應用上下文，最終通過getBean方法獲取bean，如下：

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

SpringBoot項目獲取bean的幾種方式

1. 通過啟動類中返回的上下文獲取

	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; } } 

在第三方類中使用：

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

2. 通過工具類獲取

RequestContextUtils.findWebApplicationContext(HttpServletRequest request),WebApplicationContextUtils.getWebApplicationContext(ServletContext sc)
a. 在controller中傳入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中或者其他后端服務中獲取：

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

3. 通過實現接口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; } } 

在其他類中調用

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

4. 通過繼承抽象類：ApplicationObjectSupport，WebApplicationObjectSupport

原理參考第3點

5. 其他方式

在網上看，發現也可以直接調用：ContextLoader.getCurrentWebApplicationContext()，或者 ContextLoaderListener.getCurrentWebApplicationContext() 其實都是調用同一段代碼，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; } 

說明：目前通過這種方式獲取上下文為null，從代碼可以看出，上下文是通過currentContextPerThread.get(ccl) 來獲取的，而currentContextPerThread緩存是通過方法contextInitialized(ServletContextEvent event) 來初始化的，至於為何獲取為空