1.在javax.servlet.Filter中直接获取

ServletContext context = config.getServletContext();

2.在HttpServlet中直接获取

this.getServletContext()

3.在其他方法中，通过HttpRequest获得

request.getSession().getServletContext();

4.在struts2中还有常见的两种方法获得

获取HttpServletRequest / HttpSession / ServletContext / HttpServletResponse对象

方法一，通过ServletActionContext.类直接获取：

HttpServletRequest request = ServletActionContext.getRequest();

request.getSession();

ServletContext servletContext = ServletActionContext.getServletContext();

HttpServletResponse response = ServletActionContext.getResponse();

方法二，实现指定接口，由struts框架运行时注入：

public class HelloWorldAction implements ServletRequestAware, ServletResponseAware, ServletContextAware{

private HttpServletRequest request;

private ServletContext servletContext;

private HttpServletResponse response;

public void setServletRequest(HttpServletRequest req) {

this.request=req;

}

public void setServletResponse(HttpServletResponse res) {

this.response=res;

}

public void setServletContext(ServletContext ser) {

this.servletContext=ser;

}

}