struts2 获取前台名称相同时，会出现空格字符串加上值的怪事

<tr>
                    <td class="data_td_left">教师：</td>
                    <td class="data_td_right">
                     <s:iterator value="teacherList" status="sta">
                    	<input type="checkbox" class="teacher" name="item.teacherIds" value="${id}" ${fn:contains(item.teacherIds,id)?"checked":"" }  />${teacherName}   
                    	<s:if test="#sta.count%10==0">
                    		<br/>
                    	</s:if>
                    </s:iterator>
                    </td>
                  </tr>

后台要把获取的ID trim()一下，否则获取不到

public static String getTeachersName(String ids){
		String names = "";
		List<Teacher>  list =  DevCache.getTeacherList();
		Map<String,String> map = new HashMap<String, String>();
		for(Teacher t : list){
			map.put(t.getId()+"", t.getTeacherName());
		}
		String[] strs = ids.split(",");
		System.out.println(map.keySet());
		for(String id : strs){
			if(map.keySet().contains(id.trim())){
				names += map.get(id.trim())+",";
			}
		}

		if(names.length() > 0)
			names = names.substring(0, names.length() -1);
		return names;
	}