一键选取所有复选框

<input type="checkbox" onclick="checkAll_box();"/>//一键选择所有复选框
<input type="checkbox" name="announcementIDs" value="${acm.userCertId}" />//各复选框
function checkAll_box(){
    var str = "";
    $("[name='announcementIDs']").each(function () {
        if($(this).is(':checked')){
            $("[name='announcementIDs']").attr('checked',false);
        }else{
            $("[name='announcementIDs']").attr('checked',true);
		}
    })
}