通过Spring-mvc的@InitBinder注释的方法可以对WebDataBinder做一些初始化操作。
比如设置Validator。 
我一直在想能不能为每个Request或者每个Action方法单独设置Validator。
也就是说Controller里有多个被@InitBinder标注的方法。 在不同的Action时被分别调用。

我注意到了@InitBinder的value参数，

api docs里是这样描述的：
The names of command/form attributes and/or request parameters that this init-binder method is supposed to apply to.

Default is to apply to all command/form attributes and all request parameters processed by the annotated handler class. Specifying model attribute names or request parameter names here restricts the init-binder method to those specific attributes/parameters, with different init-binder methods typically applying to different groups of attributes or parameters. 

是乎是可以针对不同的Form对象或命令调用不同的InitBinder方法。

于是我写了下面的Controller试了一下:

@Controller
public class HomeController {
    
    private static final Logger logger = LoggerFactory.getLogger(HomeController.class);
    
    @InitBinder("action1")
    public void initBinder1(WebDataBinder binder){
        logger.info("initBinder1");
    }
    
    @InitBinder("action2")
    public void initBinder2(WebDataBinder binder){
        logger.info("initBinder2");
    }
    
    /**
     * Simply selects the home view to render by returning its name.
     */
    @RequestMapping(value = "/", method = RequestMethod.GET)
    public String home(Model model) {        
        
        Date date = new Date();
        DateFormat dateFormat = DateFormat.getDateTimeInstance(DateFormat.LONG, DateFormat.LONG);
        
        String formattedDate = dateFormat.format(date);
        
        model.addAttribute("serverTime", formattedDate );
        
        return "home";
    }
    
    /**
     * Simply selects the home view to render by returning its name.
     */
    @RequestMapping(value = "/doit", method = RequestMethod.POST, params="action1")
    public String doit1(@RequestParam("value1") int value1,
            @RequestParam("action1") String action, Model model) {        
        logger.info("value1={}",value1);
        
        Date date = new Date();
        DateFormat dateFormat = DateFormat.getDateTimeInstance(DateFormat.LONG, DateFormat.LONG);
        
        String formattedDate = dateFormat.format(date);
        
        model.addAttribute("serverTime", formattedDate );
        
        return "home";
    }
    
    /**
     * Simply selects the home view to render by returning its name.
     */
    @RequestMapping(value = "/doit", method = RequestMethod.POST, params="action2")
    public String doit2(@RequestParam("value1") int value1,
            @RequestParam("action2") String action, Model model) {        
        logger.info("value1={}",value1);
        
        Date date = new Date();
        DateFormat dateFormat = DateFormat.getDateTimeInstance(DateFormat.LONG, DateFormat.LONG);
        
        String formattedDate = dateFormat.format(date);
        
        model.addAttribute("serverTime", formattedDate );
        
        return "home";
    }
}

画面上的Form是这样的

<form action="doit" method="post" enctype="application/x-www-form-urlencoded">
    <input type="text" name="value1" value="100"/>
    <input type="submit" name="action1" value="Action1"/>
    <input type="submit" name="action2" value="Action2"/>
</form>