Servlet对“空”值参数的处理

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletExcept    ion, IOException {
		String id=request.getParameter("id");
		if(id==null){
			System.out.println("id==null");
		}
		if("".equals(id)){
			System.out.println("id=[]");
		}
		if(" ".equals(id)){
			System.out.println("id=[ ]");
		}
		if(StringUtils.isEmpty(id)){
			System.out.println("id is empty");
		}
	}

思考：在传递什么样的参数的情况下返回那些值。

<form action="${ctx }/servlet/ts" method="post">
    	<input type="text" name="id" value=" "/>
    	<input type="submit" value="提交"/>
    </form>
    <a href="${ctx }/servlet/ts?id= ">点击我</a>
    <a href="${ctx }/servlet/ts">点击我</a>
    <a href="${ctx }/servlet/ts?id=">点击我</a>