1.Calendar 转化 String

//获取当前时间的具体情况,如年,月,日,week,date,分,秒等
        Calendar calendat = Calendar.getInstance();

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
String dateStr = sdf.format(calendar.getTime());

2.String 转化Calendar

String str="2010-5-27";
SimpleDateFormat sdf= new SimpleDateFormat("yyyy-MM-dd");

Date date =sdf.parse(str);

Calendar calendar = Calendar.getInstance();

calendar.setTime(date);

3.Date 转化String

SimpleDateFormat sdf= new SimpleDateFormat("yyyy-MM-dd");

String dateStr=sdf.format(new Date());

4.String 转化Date

String str="2010-5-27";

SimpleDateFormat sdf= new SimpleDateFormat("yyyy-MM-dd");

Date birthday = sdf.parse(str);

5.Date 转化Calendar

Calendar calendar = Calendar.getInstance();
calendar.setTime(new java.util.Date());

6.Calendar转化Date

Calendar calendar = Calendar.getInstance();
java.util.Date date =calendar.getTime();

下面有个例子，插入oralce表类型为DATE的数据

SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd HHmmss");
    String date = sdf.format(new Date()); 

    -----------------------------------------

     String sql = "Insert into SM_SEND (*****************) " +
                  "values (*******************************

                   "',1," + "to_date('" +date+ "','YYYY-MM-DD HH24:MI:SS')" +
                   "," + "to_date('" +date+ "','YYYY-MM-DD HH24:MI:SS')" +
                   ",0,null,null,null,null,null,null,null)";