MongoDB的java驱动提供了查询的功能，查询条件也是bson对象，这篇就看下怎么进行简单的数据查询
1、数据结构
集合：firstCollection
数据内容：
{ “_id” : ObjectId(“55adba52fa1f3cf038c2aea6”), “name” : “user0”, “age” : 22, “sex” : 0 }
{ “_id” : ObjectId(“55adba52fa1f3cf038c2aea7”), “name” : “user1”, “age” : 23, “sex” : 1 }
{ “_id” : ObjectId(“55adba52fa1f3cf038c2aea8”), “name” : “user2”, “age” : 24, “sex” : 0 }
{ “_id” : ObjectId(“55adba52fa1f3cf038c2aea9”), “name” : “user3”, “age” : 25, “sex” : 1 }
{ “_id” : ObjectId(“55adba52fa1f3cf038c2aeaa”), “name” : “user4”, “age” : 26, “sex” : 0 }
{ “_id” : ObjectId(“55adba52fa1f3cf038c2aeab”), “name” : “user5”, “age” : 27, “sex” : 1 }
2、连接数据库，拿到集合firstCollection
MongoClient mClient = new MongoClient(“10.211.55.8”);
DB db = mClient.getDB(“test”);
DBCollection collection = db.getCollection(“firstCollection”);
3、查询name为user1的对象
查询条件Json内容：
{“name”: “user1”}
查询条件Java内容：
BasicDBObject queryObject = new BasicDBObject(“name”,”user1″);
执行过程：
DBObject obj = collection.findOne(queryObject);
这样就拿到了name为user1的对象了
4、查询name包含user的对象
这样模糊查询，也就类似于like查询是通过正则表达式来完成的
查询条件Json内容：
{“name”:/user/}
查询条件Java内容：
Pattern queryPattern = Pattern.compile(“user”, Pattern.CASE_INSENSITIVE);
BasicDBObject queryObject = new BasicDBObject(“name”,queryPattern);
执行过程：
Pattern queryPattern = Pattern.compile(“user”, Pattern.CASE_INSENSITIVE);
BasicDBObject queryObject = new BasicDBObject(“name”,queryPattern);
Cursor cursor = collection.find(queryObject);
while(cursor.hasNext()){
DBObject obj = cursor.next();
System.out.println(obj.toString());
5、查询年龄大于24的对象
查询条件Json内容：
{“age”:{“$gt”:24}}
查询条件Java内容:
两个Bson对象嵌套
BasicDBObject gt = new BasicDBObject(“$gt”,24);
BasicDBObject queryObject = new BasicDBObject(“age”,gt);
执行过程：
BasicDBObject gt = new BasicDBObject(“$gt”,24);
BasicDBObject queryObject = new BasicDBObject(“age”,gt);
Cursor cursor = collection.find(queryObject);
while(cursor.hasNext()){
DBObject obj = cursor.next();
System.out.println(obj.toString());
备注：
$gt：>
$gte：>=
$eq: =
$ne: !=
$lt: <
$lte:
Original: https://www.cnblogs.com/luoaz/p/4691639.html
Author: 小爱博客
Title: java MongoDB查询（一）简单查询
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