Java如何从spring容器中获取注入的bean对象

import org.apache.struts2.ServletActionContext;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

/**
 * 从spring容器中获取注入的bean对象
 * @explain 必须获取到ServletContext对象，Controller层以struts2为例
 * @author Marydon
 * @creationTime 2018年6月1日上午10:06:49
 * @version 1.0
 * @since
 * @email marydon20170307@163.com
 */
public final class BeansUtils {
  private static final Logger logger = LoggerFactory.getLogger(BeansUtils.class);
  private static ApplicationContext ctx;
  private static WebApplicationContext webCtx;
  // 静态代码块：加载该类时会被运行的代码
  static {

    if (ctx == null) {
      try {
        // 入参需要拿到ServletContext对象
        webCtx = WebApplicationContextUtils
            .getRequiredWebApplicationContext(ServletActionContext.getServletContext());
        logger.info("从web.xml容器中加载spring-config.xml");
      } catch (Exception e) {
        logger.info("直接加载spring-config.xml");
      }
      if (webCtx == null)
        // 你可以自定义spring配置文件的文件名
        ctx = new ClassPathXmlApplicationContext("spring-config.xml");
    }
  }

  /**
   * 通过beanID获取bean实例
   * 
   * @param beanID
   *      bean的代码
   * @return 返回对应的实例
   * @throws RuntimeException
   *       bean没有定义
   */
  public static Object getBeanInstance(String beanID) throws RuntimeException {
    logger.info("在spring容器中获取Bean对象 ID=" + beanID);
    Object obj;
    if (BeansUtils.ctx == null) {
      if (BeansUtils.webCtx.containsBeanDefinition(beanID)) {
        obj = BeansUtils.webCtx.getBean(beanID);
      } else {
        logger.info("beanID=" + beanID + "没有定义");
        throw new RuntimeException(beanID + "没有定义!");
      }
    } else {
      if (BeansUtils.ctx.containsBeanDefinition(beanID)) {
        obj = BeansUtils.ctx.getBean(beanID);
      } else {
        logger.info("beanID=" + beanID + "没有定义");
        throw new RuntimeException(beanID + "没有定义!");
      }
    }
    return obj;
  }
}