注解形式开发Controller方法的返回值类型

下面为方法返回类型的几种形式:

    //形式一:返回值为String,代表要访问的URL地址    @RequestMapping("test1")    public String test1(){        return "index";    }

    //形式二:返回ModelAndView    //构造可以传URL地址,和传入一个Map集合到request域中    //JSP取Map集合时为:${requestScope.admin.username }    //不是:${requestScope.map.admin.username }    @RequestMapping("test2")    public ModelAndView test2(){        Map<String,User> map = new HashMap<String, User>();        map.put("admin",new User("admin","1234"));        ModelAndView mv = new ModelAndView("index",map);        //mv.addObject("map",map);        return mv;    }

    //形式三:返回值为String,但形参为Map集合,键值最好为:String,Object类    //JSP取Map集合时为:${requestScope.admin.username }    //不是:${requestScope.map.admin.username }    @RequestMapping("test3")    public String test3(Map<String,Object> map){        map.put("admin",new User("admin","1234"));        return "index";    }

    //形式四:返回值为String,形参为Model    @RequestMapping("test4")    public String test4(Model model,HttpServletRequest request){        //添加一个List集合        List<User> list = new ArrayList<User>();        list.add(new User("list5","1234"));        model.addAttribute("list",list);        //添加一个Map集合        Map<String,User> map = new HashMap<String, User>();        map.put("user1",new User("map","1234"));        //注意:下面两个方法不同        //addAllAttributes在JSP中取值时为:${requestScope.user1.username }        model.addAllAttributes(map);        //addAttribute在JSP中取值时为:${requestScope.map.user1.username }        model.addAttribute("map",map);        //添加一个对象        model.addAttribute("user",new User("admin","1234"));        return "index";    }

    //形式五:返回值为void,利用Ajax返回,参数为HttpServletResponse    @RequestMapping("test5")    public void test5(HttpServletResponse response) throws IOException{        response.setContentType("application/json");        response.getWriter().write("{\"json\":\"json\"}");    }    //形式六:返回值为void,利用Ajax返回,形参为PrintWriter    @RequestMapping("test6")    public void test6(HttpServletResponse response ,PrintWriter pw){        response.setContentType("application/json");        pw.write("{\"json\":\"json\"}");    }