Java—日期处理

java.sql.Timestamp;
java.sql.Time;
java.sql.Date;
用于数据库
 
使用 SimpleDateFormat 将数据库中的时间格式化

// 使用 SimpleDateFormat 将数据库中的时间格式化
public class TestDate {

	public static void main(String[] args) {
		Connection conn = null;
		Statement stmt = null;
		ResultSet rs = null;
		try {
			Class.forName("com.mysql.jdbc.Driver");
			conn = DriverManager.getConnection(
					"jdbc:mysql://localhost:3306/testjdbc?useUnicode=true&characterEncoding=UTF-8", "root", "root");
			stmt = conn.createStatement();
			rs = stmt.executeQuery("select lastLoginTime from t_user1");
			while (rs.next()) {
				java.sql.Date d = rs.getDate("lastLoginTime");
				SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日");
				System.out.println(sdf.format(d));
			}
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		} catch (SQLException e) {
			e.printStackTrace();
		}
		try {
			if (rs != null) {
				rs.close();
			}
		} catch (SQLException e) {
			e.printStackTrace();
		}
		try {
			if (stmt != null) {
				stmt.close();
			}
		} catch (SQLException e) {
			e.printStackTrace();
		}
		try {
			if (conn != null) {
				conn.close();
			}
		} catch (SQLException e) {
			e.printStackTrace();
		}
	}
}

使用 Calendar 将月份提取出来

// 使用 Calendar 将月份提取出来
public class TestDate1 {

	public static void main(String[] args) {
		Connection conn = null;
		Statement stmt = null;
		ResultSet rs = null;
		try {
			Class.forName("com.mysql.jdbc.Driver");
			conn = DriverManager.getConnection(
					"jdbc:mysql://localhost:3306/testjdbc?useUnicode=true&characterEncoding=UTF-8", "root", "root");
			stmt = conn.createStatement();
			rs = stmt.executeQuery("select lastLoginTime from t_user1");
			while (rs.next()) {
				Date d = rs.getDate("lastLoginTime");
//				SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日");
				// 初始化
				Calendar c = Calendar.getInstance();
				// c拿到了Date的时间了
				c.setTime(d);
				System.out.println(c.get(Calendar.MONTH));
			}
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		} catch (SQLException e) {
			e.printStackTrace();
		}
		try {
			if (rs != null) {
				rs.close();
			}
		} catch (SQLException e) {
			e.printStackTrace();
		}
		try {
			if (stmt != null) {
				stmt.close();
			}
		} catch (SQLException e) {
			e.printStackTrace();
		}
		try {
			if (conn != null) {
				conn.close();
			}
		} catch (SQLException e) {
			e.printStackTrace();
		}
	}
}

打印出来为 00:00:00 ,因为Date类型没有保存时间,它保存的是日期,所以打印出来为00:00:00

// 使用 Calendar 将月份提取出来
public class TestDate2 {

	public static void main(String[] args) {
		Connection conn = null;
		Statement stmt = null;
		ResultSet rs = null;
		try {
			Class.forName("com.mysql.jdbc.Driver");
			conn = DriverManager.getConnection(
					"jdbc:mysql://localhost:3306/testjdbc?useUnicode=true&characterEncoding=UTF-8", "root", "root");
			stmt = conn.createStatement();
			rs = stmt.executeQuery("select lastLoginTime from t_user1");
			while (rs.next()) {
//				Date d = rs.getDate("lastLoginTime");
//				SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");
//				// 打印出来为 00:00:00 ,因为Date类型没有保存时间,它保存的是日期,所以打印出来为00:00:00 
//				System.out.println(sdf.format(d));
				
				// 打印时间
				Timestamp ts = rs.getTimestamp("lastLoginTime");
				SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");
				System.out.println(sdf.format(ts));
			}
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		} catch (SQLException e) {
			e.printStackTrace();
		}
		try {
			if (rs != null) {
				rs.close();
			}
		} catch (SQLException e) {
			e.printStackTrace();
		}
		try {
			if (stmt != null) {
				stmt.close();
			}
		} catch (SQLException e) {
			e.printStackTrace();
		}
		try {
			if (conn != null) {
				conn.close();
			}
		} catch (SQLException e) {
			e.printStackTrace();
		}
	}
}

拿到当前系统的时间

public class TestDateAndTime {

	public static void main(String[] args) {
		// 拿到当前系统的时间
		// 可以用于程序的耗时计算(在程序执行的时候写一次，在程序结束的时候写一次，在两者相减)
		System.out.println(System.currentTimeMillis());
		Date d = new Date();
		System.out.println("Date："+d);
		Calendar c = Calendar.getInstance();
		System.out.println("当前年为："+c.get(Calendar.YEAR));
		
		// 将字符串转化成Date或者Time,使用Timestamp的valueOf()方法
		String s = "1970-12-30 08:24:37.0";
		Timestamp ts = Timestamp.valueOf(s);
		System.out.println(ts);
		
		
	}

}

获取日本当前的时间：TimeZone.getTimeZone(“Japan”)

//获取日本当前的时间：TimeZone.getTimeZone("Japan")
public class TestDateAndTime1 {

	public static void main(String[] args) {
		Calendar cJapan = new GregorianCalendar(TimeZone.getTimeZone("Japan"));
		// HOUR_OF_DAY：24小时制的
		System.out.println("日本当前的小时为："+cJapan.get(Calendar.HOUR_OF_DAY));
		
		// 获取打印 TimeZone下的ID
		for(String id:TimeZone.getAvailableIDs()) {
			System.out.println(id);
		}
	}

}