曜日を求める関数

APEXには日本語表記などに変換する仕組みは無いので、
以下のコードを共通処理として登録
public String getYobi(Date vdDate){
datetime tDate = datetime.newInstance(vdDate.year(), vdDate.month(), vdDate.day());
String week = tDate.format('E');
if(week == 'Sun'){
return '日';
}else if(week =='Mon'){
return '月';
}else if(week =='Tue'){
return '火';
}else if(week =='Wed'){
return '水';
}else if(week =='Thu'){
return '木';
}else if(week =='Fri'){
return '金';
}else if(week =='Sat'){
return '土';
}
return null;
}