Java mongodb ISODate 问题
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mongodb ISODate problems
提问by wuchang
I am using java(IDE is eclipse) to query on mongodb. Below is my java code:
我正在使用 java（IDE 是 eclipse）在 mongodb 上进行查询。下面是我的java代码：
DBObject query = new BasicDBObject();
ObjectId id =new ObjectId("529f280b90ee58cb7732c2b8");
query.put("_id", id);
DBCursor cursor = collection.find(query);
while(cursor.hasNext()) {
DBObject object = (DBObject)(cursor.next());
System.out.println(object.get("_id"));
System.out.println(object.get("createDate"));
}
Problems happened in the createDate whose type is ISODate and value is ISODate("2013-10-21T01:34:04.808Z"), but the printlnresult of my code is 'Mon Oct 21 **09**:34:04 CST 2013', the hour has changed from 01 to 09. I don't know what happened!
类型为 ISODate 且值为 的 createDate 出现问题ISODate("2013-10-21T01:34:04.808Z")，但println我的代码的结果是'Mon Oct 21 **09**:34:04 CST 2013'，小时已从 01 更改为 09。我不知道发生了什么！
Can anybody help?
有人可以帮忙吗？
回答by Basil Bourque
The hour did not change. You must be in China, given the "CST" in your example and the 8 hour difference. If you interpret "CST" as "China Standard Time" (rather than Central Standard Timein the US), then you have a time zone that is 8 hours ahead of UTC/GMT. So when ti is 1 AM UTC/GMT, at the vary same moment the clock on the wall in Taipei will read "9 AM".
时间没有改变。鉴于您的示例中的“CST”和 8 小时的差异，您必须在中国。如果您将“CST”解释为“中国标准时间”（而不是美国的中部标准时间），那么您的时区比UTC/GMT早 8 小时。因此，当 ti 是 UTC/GMT 凌晨 1 点时，同一时刻台北墙上的时钟会显示“9 AM”。
Minor point: Those three-letter codes for time zones are obsolete and should be avoided. They are neither standardized nor unique. Use proper time zone names.
小点：时区的那些三字母代码已过时，应避免使用。它们既不标准化也不独特。使用正确的时区名称。
Major point: The problem lies in how you extract a value from MongoDB that represents a date-time.
要点：问题在于如何从 MongoDB 中提取表示日期时间的值。
I don't know MongoDB, and their docis confusing, so I can't help you much further. If you can retrieve an ISO 8601string as seen in your first example, that is much preferable to the format of your second example.
我不知道 MongoDB，而且他们的文档令人困惑，所以我无法进一步帮助您。如果您可以检索第一个示例中看到的ISO 8601字符串，那么这比第二个示例的格式要好得多。
If you want to work with the date-time value in Java, you can feed an ISO 8601 string directly to a DateTimeconstructor in Joda-Time2.3.
如果要使用 Java 中的日期时间值，可以将 ISO 8601 字符串直接提供给Joda-Time2.3 中的DateTime构造函数。
DateTime dateTime = new DateTime( "2013-10-21T01:34:04.808Z" );
Update
更新
This docsays that the Java driver for MongoDB will give you a java.util.Date object. That explains your problem. The java.util.Date & Calendar classes bundled with Java are notoriously bad. One problem is that while a Date instance has no time zone, its toString()method uses the JVM's default time zone to render a string. And Date's toString method uses that terrible ambiguous format.
这个文档说 MongoDB 的 Java 驱动程序会给你一个 java.util.Date 对象。这解释了你的问题。与 Java 捆绑在一起的 java.util.Date 和 Calendar 类是出了名的糟糕。一个问题是，虽然 Date 实例没有时区，但它的toString()方法使用 JVM 的默认时区来呈现字符串。而 Date 的 toString 方法使用了那种可怕的模棱两可的格式。
You should avoid using java.util.Date & Calendar classes. For now use the Joda-Timelibrary. In Java 8, you can use the new java.time.* classes.
您应该避免使用 java.util.Date 和 Calendar 类。现在使用Joda-Time库。在 Java 8 中，您可以使用新的java.time.* classes。
You can convert back and forth between java.util.Date and Joda-Time. Pass a Date instance to Joda-Time constructor. To go back, call Joda-Time toDate()format.
您可以在 java.util.Date 和 Joda-Time 之间来回转换。将 Date 实例传递给 Joda-Time 构造函数。要返回，请调用 Joda-TimetoDate()格式。
Note that while a java.util.Date has no time zone information within it, in contrast a DateTime object does have a time zone assigned. If you want UTC/GMT, specify DateTimeZone.UTC.
请注意，虽然 java.util.Date 中没有时区信息，但相比之下，DateTime 对象确实分配了时区。如果您需要 UTC/GMT，请指定DateTimeZone.UTC.
Your code should look more like:
您的代码应该看起来更像：
java.util.Date date = object.get("createDate");
DateTime createDateTime = new DateTime( date, DateTimeZone.forId( "Asia/Manila" ) );
System.out.println( createDateTime );
… do some work …
java.util.Date dateGoingBackToMongoDB = createDateTime.toDate();
