<form id="registForm"> 
 <input type="text" id="username" name="username"> 
</form> 

// 导入jquery、validte库略
$(function() {
	$.validator.setDefaults({
		submitHandler: function(form) {
			// 验证通过处理
			...
		}
	});
				
	$("#registForm").validate({
		rules: {
			username: {
				required: true,
				remote: "checkUsername.do"
			},			
		},
		messages: {
			username: {
				required: "用户名不能为空",
				remote: "用户名已经存在"
			}
		}
	});
});

@RequestMapping("/checkUsername")
public @ResponseBody boolean checkUsername(@RequestParam String username) {
	// 测试
	return !"test".equals(username);
}

@RequestMapping("/checkUsername")
public @ResponseBody String checkUsername(@RequestParam String username) {
	// 测试
	return !"test".equals(username) "true" : "false";
}

....
username: {
	required: true,
	remote: {
		url: "checkUsername.do",
		type: "post",    //数据发送方式
		dataType: "json",   //接受数据格式 
		data: {      //要传递的数据
			username: function() {
				return $("#username").val();
			},
			extra: function() {
				return "额外信息";
			}
		 }
	}
}

@RequestMapping(value = "/checkUsername", method = RequestMethod.POST)
public @ResponseBody boolean checkUsername(User user, @RequestParam String extra) {
	// 测试
	System.out.println(extra);
	return !"test".equals(user.getUsername());
}