SpringBoot获取上下文，获取bean的几种中方式

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;
}。