how to get param in method post spring mvc?

I'm using spring mvc. And I can't get param from url when method = post. But when I change method to GET, so I can get all param.

This is my form:

<form method="POST" action="http://localhost:8080/cms/customer/create_customer" id="frmRegister" name ="frmRegister" enctype="multipart/form-data">
    <input class ="iptRegister" type="text" id="txtEmail" name="txtEmail" value="" />
    <input class ="iptRegister" type="password" id="txtPassword" name="txtPassword" value="" />
    <input class ="iptRegister" type="text" id="txtPhone" name="txtPhone" value="" />

    <input type="button" id="btnRegister" name="btnRegister" value="Register" onclick="" style="cursor:pointer"/>
</form>

This is my controller:

@RequestMapping(value= "/create_customer", method = RequestMethod.POST)
@ResponseBody
public String createCustomer(HttpServletRequest request, 
        @RequestParam(value="txtEmail", required=false) String email, 
        @RequestParam(value="txtPassword", required=false) String password, 
        @RequestParam(value="txtPhone", required=false) String phone){

    ResultDTO<String> rs = new ResultDTO<String>();
    rs.setStatus(IConfig.SHOW_RESULT_SUCCESS_ON_MAIN_SCREEN);
    try{
        Customer c = new Customer();
        c.setEmail(email);
        c.setPassword(password);
        c.setPhone(phone);
        customerService.insert(c);
        rs.setData("Insert success");
    }catch(Exception ex){
        log.error(ex);
        rs.setStatus(IConfig.SHOW_RESULT_ERROR_ON_MAIN_SCREEN);
        rs.setData("Insert failure");
    }
    return rs.toString();
}

How can I resolved this?