java 用 _id 查找 MongoDB 下的数据

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找网上的资料看了下增删改查，等日后补上。

已经实现了数据的插入，现在想通过 _id属性来查找数据。一开始看到类似 55b321df715cc162076eb466 这么一长串的内容觉得是string类型。但是发现并不能搜索到结果，在网上搜到了解决方案：

String sid = "55b321df715cc162076eb466";sitem.put("_id", new ObjectId(sid));cursor = collection.find(sitem);

通过ObjectId类型就可以查找数据了。

demo源代码:

package persistence;import java.net.UnknownHostException;import java.util.Date;import org.bson.types.ObjectId;import net.sf.json.JSONObject;import com.mongodb.BasicDBObject;import com.mongodb.DB;import com.mongodb.DBCollection;import com.mongodb.DBCursor;import com.mongodb.DBObject;import com.mongodb.Mongo;import domain.Article;public class TestMongo {public static void main(String[] args) {Mongo mongo = null;try {// 8908 mongo.duapp.com smbWruErqVUXLgjDDSEGmongo = new Mongo("localhost", 27017);System.out.println("connection success");DB db = mongo.getDB("myblog");DBCollection collection = db.getCollection("article");BasicDBObject item = new BasicDBObject();item.put("title", "Rectangle Area");item.put("date", new Date());item.put("extract","Find the total area covered by two rectilinear rectangles in a 2D plane. Each rectangle is defined by its bottom left corner and top right corner as shown in the figure.");String content = "Assume that the total area is never beyond the maximum possible value of int.这道题求得是两个举行覆盖的面积。如果两个矩形没有相交的话直接返回两个矩形面积之和就可以了，如果有重合，那么再减去重合的面积即可。在如何计算重合面积上花费了一些时间，感觉思维还是有待加强。代码：";item.put("content", content);collection.insert(item);String sid = "55b321df715cc162076eb466";Object sido = new Object();DBCursor cursor = collection.find();while (cursor.hasNext()) {// System.out.println("result:"+cursor.next());DBObject o = cursor.next();/* * String id =(String) o.get("_id").toString(); sido = * o.get("_id"); System.out.println(id); sid = id; String title * =(String) o.get("title"); System.out.println(title); *  * Date date =(Date) o.get("date"); * System.out.println(date.getDate()); *  * String extract =(String) o.get("extract"); * System.out.println(extract); */System.out.println("search for id:" + sid);BasicDBObject sitem = new BasicDBObject();sitem.put("_id", new ObjectId(sid));cursor = collection.find(sitem);while (cursor.hasNext()) {System.out.println("found result:");System.out.println(cursor.next().get("date").toString());}}} catch (Exception e) {e.printStackTrace();}}}

结果：

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