java日期转换

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import java.text.*;
import java.util.*;

1.-----------------------------------------
得到系统当前时间：

java.util.Date dt=newjava.util.Date();
System.out.print(dt); //输出结果是：Wed Aug 10 11:29:11 CST 2005

SimpleDateFormat sdf=newSimpleDateFormat("yyyy-MM-dd");
System.out.print(sdf.format(dt)); //输出结果是：2005-08-10

2.-----------------------------------------
把字符串转化为java.util.Date
方法一：
SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
java.util.Date dt=sdf.parse("2005-2-19");
System.out.print(sdf.format(dt)); //输出结果是：2005-2-19

方法二：
java.util.Date dt=null;
DateFormat df=DateFormat.getDateInstance();
dt=df.parse("2005-12-19");
System.out.println(dt); //输出结果为：Mon Dec 19 00:00:00 CST 2005
System.out.println(df.format(dt)); //输出结果为：2005-2-19

3.-----------------------------------------
把字符串转化为java.sql.Date
字符串必须是"yyyy-mm-dd"格式，否则会抛出IllegalArgumentException异常
java.sql.Date sdt=java.sql.Date.valueOf("2005-9-6");
System.out.println(sdt); //输出结果为：2005-9-6

4.-----------------------------------------
TestApp.java

public class TestApp {

    publicstatic void main(String[] args) {
       System.out.println("Hello World!");
       Date d=new Date();

       //System.out.println(d.toLocaleString());

       //Calendar cld=Calendar.getInstance();
       System.out.println("Calendar.get(Calendar.DATE)"+(Calendar.getInstance().get(Calendar.DATE)));

       Date dt=new Date();//Date(103,-5,-6);
       System.out.println("getNowYear(Date dt)"+getYear(dt));
       System.out.println("getNowMonth(Date dt)"+getMonth(dt));
       System.out.println("getNowDate(Date dt)"+getDate(dt));
    }

    publicstatic int getNowYear(){
       return Calendar.getInstance().get(Calendar.YEAR);
    }

    publicstatic int getYear(Date dt)throws NullPointerException{
       if(dt==null){
           throw new NullPointerException("日期参数为null");
       }else{
           Calendar cld=Calendar.getInstance();
           cld.setTime(dt);
           return cld.get(Calendar.YEAR);
       }
    }


    publicstatic int getNowMonth(){
       return 1+Calendar.getInstance().get(Calendar.MONTH);
    }


    publicstatic int getMonth(Date dt)throws NullPointerException{
       if(dt==null){
           throw new NullPointerException("日期参数为null");
       }else{
           Calendar cld=Calendar.getInstance();
           cld.setTime(dt);
           return 1+cld.get(Calendar.MONTH);
       }
    }

    publicstatic int getNowDate(){
       return 1+Calendar.getInstance().get(Calendar.DATE);
    }


    publicstatic int getDate(Date dt)throws NullPointerException{
       if(dt==null){
           throw new NullPointerException("日期参数为null");
       }else{
           Calendar cld=Calendar.getInstance();
           cld.setTime(dt);
           return cld.get(Calendar.DATE);
       }
    }
}
//  格式化日期为字符串  "yyyy-MM-dd   hh:mm"
public String formatDateTime(Date basicDate, String strFormat){
   SimpleDateFormat df = new SimpleDateFormat(strFormat);
    returndf.format(basicDate);
}

//  格式化日期为字符串  "yyyy-MM-dd   hh:mm"
public String formatDateTime(String basicDate, String strFormat){
   SimpleDateFormat df = new SimpleDateFormat("yy-MM-ddhh:mm");
   SimpleDateFormat df1 = new SimpleDateFormat(strFormat);
    DateFormatdf3 = DateFormat.getDateInstance(DateFormat.LONG);
    Date tmpDate= null;
    try{
     tmpDate = df1.parse(basicDate);
    }
    catch(Exception e) {
     //   日期型字符串格式错误
     return basicDate;
    }
    returndf.format(tmpDate);
}

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