java.sql.Date与java.util.Date相互转换

爱被打了一巴掌 2022-09-19 12:14 190阅读 0赞

数据库操作时，遇到时间类型，经常会涉及到 java.sql.Date与java.util.Date 之间的转换。

在此，总结一个简单的转换方法。

查看java.util.Date类的源码

/**
         * Allocates a <code>Date</code> object and initializes it so that
         * it represents the time at which it was allocated, measured to the
         * nearest millisecond.
         *
         * @see     java.lang.System#currentTimeMillis()
         */
        public Date() {
            this(System.currentTimeMillis());
        }
    
        /**
         * Allocates a <code>Date</code> object and initializes it to
         * represent the specified number of milliseconds since the
         * standard base time known as "the epoch", namely January 1,
         * 1970, 00:00:00 GMT.
         *
         * @param   date   the milliseconds since January 1, 1970, 00:00:00 GMT.
         * @see     java.lang.System#currentTimeMillis()
         */
        public Date(long date) {
            fastTime = date;
        }

可以得知，java 中的Date 取得就是系统的当前时间距1970年的毫秒数。

而 java.sql.Date 继承了java.util.Date

/*
     * Copyright (c) 1996, 2010, Oracle and/or its affiliates. All rights reserved.
     * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
     */
    
    package java.sql;
    
    /**
     * <P>A thin wrapper around a millisecond value that allows
     * JDBC to identify this as an SQL <code>DATE</code> value.  A
     * milliseconds value represents the number of milliseconds that
     * have passed since January 1, 1970 00:00:00.000 GMT.
     * <p>
     * To conform with the definition of SQL <code>DATE</code>, the
     * millisecond values wrapped by a <code>java.sql.Date</code> instance
     * must be 'normalized' by setting the
     * hours, minutes, seconds, and milliseconds to zero in the particular
     * time zone with which the instance is associated.
     */
    public class Date extends java.util.Date {
    
        /**
         * Constructs a <code>Date</code> object initialized with the given
         * year, month, and day.
         * <P>
         * The result is undefined if a given argument is out of bounds.
         *
         * @param year the year minus 1900; must be 0 to 8099. (Note that
         *        8099 is 9999 minus 1900.)
         * @param month 0 to 11
         * @param day 1 to 31
         * @deprecated instead use the constructor <code>Date(long date)</code>
         */
        public Date(int year, int month, int day) {
            super(year, month, day);
        }
    
        /**
         * Constructs a <code>Date</code> object using the given milliseconds
         * time value.  If the given milliseconds value contains time
         * information, the driver will set the time components to the
         * time in the default time zone (the time zone of the Java virtual
         * machine running the application) that corresponds to zero GMT.
         *
         * @param date milliseconds since January 1, 1970, 00:00:00 GMT not
         *        to exceed the milliseconds representation for the year 8099.
         *        A negative number indicates the number of milliseconds
         *        before January 1, 1970, 00:00:00 GMT.
         */
        public Date(long date) {
            // If the millisecond date value contains time info, mask it out.
            super(date);
    
        }
    
        /**
         * Sets an existing <code>Date</code> object
         * using the given milliseconds time value.
         * If the given milliseconds value contains time information,
         * the driver will set the time components to the
         * time in the default time zone (the time zone of the Java virtual
         * machine running the application) that corresponds to zero GMT.
         *
         * @param date milliseconds since January 1, 1970, 00:00:00 GMT not
         *        to exceed the milliseconds representation for the year 8099.
         *        A negative number indicates the number of milliseconds
         *        before January 1, 1970, 00:00:00 GMT.
         */
        public void setTime(long date) {
            // If the millisecond date value contains time info, mask it out.
            super.setTime(date);
        }
    
       /**
        * Private serial version unique ID to ensure serialization
        * compatibility.
        */
        static final long serialVersionUID = 1511598038487230103L;
    }

由于 java.sql.Date 继承自 java.util.Date，那么两种Date类型有个共同的方法，就是getTime()。

利用getTime进行格式的转换时，时间不会有精度的丢失。

public class DateTest {
    	public static void main(String args[]) {
    		// 定义当前时间
    		java.util.Date now = new java.util.Date();
    		
    		// 将java.util.sql 转为 java.sql.date
    		java.sql.Date sqlNow = new java.sql.Date(now.getTime());
    		
    		// 将java.sql.date 转为 java.util.date
    		java.util.Date utilNow = new java.util.Date(sqlNow.getTime());
    		
    		DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    		System.out.println(now);
    		System.out.println(df.format(sqlNow));
    		System.out.println(utilNow);
    	}
    }

控制台输出

Wed Dec 25 17:27:33 GMT+08:00 2013
    2013-12-25 17:27:33
    Wed Dec 25 17:27:33 GMT+08:00 2013