function checktype(obj) {
var str=$(obj).val();
var index=str.lastIndexOf('.');
var len=str.length;
var suffix=str.substring(index+1,len);
alert(suffix);
// /*
// ExpertsMntnEntity expertsMntnEntity=new ExpertsMntnEntity(); */
// expertsMntnEntity.photosuffix=suffix;
}
<input id="photosuffix" name="photosuffix" value="${expertsMntnEntity.photosuffix}" style="width: 100px;height:20px;line-height:30px;>“
<input type="file" id="content" name="content" value="${expertsMntnEntity.content}" style="width:148px;height:18px;" onchange="checktype(this)">