SpringMVC_day02_3（Spring作用域传值）

                                                                        SpringMVC作用域传值.
1. 把作用域对象当作方法参数
2. request作用域传值的三种方式（在JSP 页面中可以通过 Request作用域获得值）
    2.1 Map当作参数(解耦)
        2.1.1 Spring会给Map接口注入BindingAwareModelMap

    @Controller
    public class DemoController {
	    @RequestMapping("scope")
	    public String scope(Map<String,Object> map){
    //		    Map的本质也是   req.setAttribute("msg", "消息");
		    map.put("msg", "map方式的参数");
		    return "index.jsp"; // 默认的方式的是请求转发
	    }
    }

2.2 Model 当作参数(解耦:解除和原生Servlet的耦合)
2.2.1 Spring会给Model接口注入BindingAwareModelMap

    @Controller
    public class DemoController {
	    @RequestMapping("scope")
	    public String scope(Model model){
		    model.addAttribute("msg", "Model消息");// 还是存放在 Request里面
		    return "index.jsp";
	    }
    }

2.3 request当作参数(原生Servlet API)
index.jsp
<body>

msg:${msg}<br/>
session:${sessionScope.msg}<br/>
application:${applicationScope.msg}
</body>

DemoController.java

@Controller
public class DemoController {
	// 如何向JSP页面传递值呢？
	@RequestMapping("scope")
	public String scope(HttpServletRequest req){
		req.setAttribute("msg", "消息");
		req.getSession().setAttribute("msg", "session的消息");
		req.getServletContext().setAttribute("msg", "application的消息");
		return "index.jsp";
        }
}

3. session两种方式
3.1 通过request对象获取

	@RequestMapping("scope")
	public String scope(HttpServletRequest req){
		HttpSession session = req.getSession();
		session.setAttribute("", "");
		return "index.jsp";
	}

3.2 直接把Session当作方法参数

	@RequestMapping("scope")
	public String scope(HttpSession session){
		session.setAttribute("", "");
		return "index.jsp";
	}

4. application作用域
4.1 不能把application当作方法参数,通过request获取

	    @RequestMapping("scope")
	    public String scope(HttpServletRequest req){
		    ServletContext application = req.getServletContext();
		    application.setAttribute("", "");
		    return "index.jsp";
	    }

SpringMVC_day02_3（Spring作用域传值）

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