Mongodb快速入门之使用Java操作Mongodb
【IT168 专稿】在上一篇文章中，我们学习了Mongodb的安装和初步使用，在本文中，将学习如何使用Java去编程实现对Mongodb的操作。
HelloWorld程序
学习任何程序的第一步，都是编写HelloWorld程序，我们也不例外，看下如何通过Java编写一个HelloWorld的程序。
首先，要通过Java操作Mongodb，必须先下载Mongodb的Java驱动程序，可以在这里下载。
新建立一个Java工程，将下载的驱动程序放在库文件路径下，程序代码如下：
package
com.mkyong.core;
import
java.net.UnknownHostException;
import
com.mongodb.BasicDBObject;
import
com.mongodb.DB;
import
com.mongodb.DBCollection;
import
com.mongodb.DBCursor;
import
com.mongodb.Mongo;
import
com.mongodb.MongoException;
/** * Java + MongoDB Hello world Example * */ public class App { public static void main(String[] args) { try { // 实例化Mongo对象，连接27017端口 Mongo mongo = new Mongo( " localhost " , 27017 ); // 连接名为yourdb的数据库，假如数据库不存在的话，mongodb会自动建立 DB db = mongo.getDB( " yourdb " ); // Get collection from MongoDB, database named "yourDB" // 从Mongodb中获得名为yourColleection的数据集合，如果该数据集合不存在，Mongodb会为其新建立 DBCollection collection = db.getCollection( " yourCollection " ); // 使用BasicDBObject对象创建一个mongodb的document,并给予赋值。 BasicDBObject document = new BasicDBObject(); document.put( " id " , 1001 ); document.put( " msg " , " hello world mongoDB in Java " ); // 将新建立的document保存到collection中去 collection.insert(document); // 创建要查询的document BasicDBObject searchQuery = new BasicDBObject(); searchQuery.put( " id " , 1001 ); // 使用collection的find方法查找document DBCursor cursor = collection.find(searchQuery); // 循环输出结果 while (cursor.hasNext()) { System.out.println(cursor.next()); } System.out.println( " Done " ); } catch (UnknownHostException e) { e.printStackTrace(); } catch (MongoException e) { e.printStackTrace(); } } }
/** * Java + MongoDB Hello world Example * */ public class App { public static void main(String[] args) { try { // 实例化Mongo对象，连接27017端口 Mongo mongo = new Mongo( " localhost " , 27017 ); // 连接名为yourdb的数据库，假如数据库不存在的话，mongodb会自动建立 DB db = mongo.getDB( " yourdb " ); // Get collection from MongoDB, database named "yourDB" // 从Mongodb中获得名为yourColleection的数据集合，如果该数据集合不存在，Mongodb会为其新建立 DBCollection collection = db.getCollection( " yourCollection " ); // 使用BasicDBObject对象创建一个mongodb的document,并给予赋值。 BasicDBObject document = new BasicDBObject(); document.put( " id " , 1001 ); document.put( " msg " , " hello world mongoDB in Java " ); // 将新建立的document保存到collection中去 collection.insert(document); // 创建要查询的document BasicDBObject searchQuery = new BasicDBObject(); searchQuery.put( " id " , 1001 ); // 使用collection的find方法查找document DBCursor cursor = collection.find(searchQuery); // 循环输出结果 while (cursor.hasNext()) { System.out.println(cursor.next()); } System.out.println( " Done " ); } catch (UnknownHostException e) { e.printStackTrace(); } catch (MongoException e) { e.printStackTrace(); } } }
最后，输出的结果为：
{
"
_id
"
: {
"
$oid
"
:
"
4dbe5596dceace565d229dc3
"
} ,
"
id
"
:
1001
,
"
msg
"
:
"
hello world mongoDB in Java
"
} Done
在上面的例子中，演示了使用Java对Mongodb操作的重要方法和步骤，首先通过创建Mongodb对象，传入构造函数的参数是Mongodb的数据库所在地址和端口，然后使用
getDB方法获得要连接的数据库名，使用getCollection获得数据集合的名，然后通过新建立BasicDBObject对象去建立document,最后通过collection的insert方法，将建立的document保存到数据库中去。而collection的find方法，则是用来在数据库中查找document。
从Mongodb中获得collection数据集
在Mongodb中，可以通过如下方法获得数据库中的collection:
DBCollection collection
=
db.getCollection(
"
yourCollection
"
);
如果你不知道collection的名称，可以使用db.getCollectionNames()获得集合，然后再遍历，如下：
DB db
=
mongo.getDB(
"
yourdb
"
); Set collections
=
db.getCollectionNames();
for
(String collectionName : collections){ System.out.println(collectionName); }
完成的一个例子如下：
package
com.mkyong.core;
import
java.net.UnknownHostException;
import
java.util.Set;
import
com.mongodb.DB;
import
com.mongodb.DBCollection;
import
com.mongodb.Mongo;
import
com.mongodb.MongoException;
/**
* Java : Get collection from MongoDB *
*/
public
class
GetCollectionApp {
public
static
void
main(String[] args) {
try
{ Mongo mongo
=
new
Mongo(
"
localhost
"
,
27017
); DB db
=
mongo.getDB(
"
yourdb
"
); Set
<
String
>
collections
=
db.getCollectionNames();
for
(String collectionName : collections) { System.out.println(collectionName); } DBCollection collection
=
db.getCollection(
"
yourCollection
"
); System.out.println(collection.toString()); System.out.println(
"
Done
"
);
} catch (UnknownHostException e) { e.printStackTrace(); } catch (MongoException e) { e.printStackTrace(); } } }
} catch (UnknownHostException e) { e.printStackTrace(); } catch (MongoException e) { e.printStackTrace(); } } }
Mongodb中如何插入数据
下面，讲解下如何使用4种方式，将JSON数据插入到Mongodb中去。首先我们准备JSON
格式的数据，如下：
{
"
database
"
:
"
mkyongDB
"
,
"
table
"
:
"
hosting
"
,
"
detail
"
: { records :
99
, index :
"
vps_index1
"
, active :
"
true
"
} } }
我们希望用不同的方式，通过JAVA代码向Mongodb插入以上格式的JSON数据
第一种方法，是使用BasicDBObject，方法如下代码所示：
BasicDBObject document
=
new
BasicDBObject(); document.put(
"
database
"
,
"
mkyongDB
"
); document.put(
"
table
"
,
"
hosting
"
); BasicDBObject documentDetail
=
new
BasicDBObject(); documentDetail.put(
"
records
"
,
"
99
"
); documentDetail.put(
"
index
"
,
"
vps_index1
"
); documentDetail.put(
"
active
"
,
"
true
"
); document.put(
"
detail
"
, documentDetail); collection.insert(document);
第二种方法是使用BasicDBObjectBuilder对象，如下代码所示：
BasicDBObjectBuilder documentBuilder
=
BasicDBObjectBuilder.start() .add(
"
database
"
,
"
mkyongDB
"
) .add(
"
table
"
,
"
hosting
"
); BasicDBObjectBuilder documentBuilderDetail
=
BasicDBObjectBuilder.start() .add(
"
records
"
,
"
99
"
) .add(
"
index
"
,
"
vps_index1
"
) .add(
"
active
"
,
"
true
"
); documentBuilder.add(
"
detail
"
, documentBuilderDetail.get()); collection.insert(documentBuilder.get());
第三种方法是使用Map对象，代码如下：
Map documentMap
=
new
HashMap(); documentMap.put(
"
database
"
,
"
mkyongDB
"
); documentMap.put(
"
table
"
,
"
hosting
"
); Map documentMapDetail
=
new
HashMap(); documentMapDetail.put(
"
records
"
,
"
99
"
); documentMapDetail.put(
"
index
"
,
"
vps_index1
"
); documentMapDetail.put(
"
active
"
,
"
true
"
); documentMap.put(
"
detail
"
, documentMapDetail); collection.insert(
new
BasicDBObject(documentMap));
第四种方法，也就是最简单的，即直接插入JSON格式数据
String json
=
"
{'database' : 'mkyongDB','table' : 'hosting',
"
+
"
'detail' : {'records' : 99, 'index' : 'vps_index1', 'active' : 'true'}}}
"
; DBObject dbObject
=
(DBObject)JSON.parse(json); collection.insert(dbObject);
这里使用了JSON的parse方法，将解析后的JSON字符串转变为DBObject对象后再直接插入到collection中去。
完整的代码如下所示：
packagecom.mkyong.core; importjava.net.UnknownHostException; importjava.util.HashMap; importjava.util.Map; importcom.mongodb.BasicDBObject; importcom.mongodb.BasicDBObjectBuilder; importcom.mongodb.DB; importcom.mongodb.DBCollection; importcom.mongodb.DBCursor; importcom.mongodb.DBObject; importcom.mongodb.Mongo; importcom.mongodb.MongoException; importcom.mongodb.util.JSON;
/**
* Java MongoDB : Insert a Document *
*/
publicclass InsertDocumentApp { publicstaticvoid main(String[] args){
try
{ Mongo mongo
=
new
Mongo(
"
localhost
"
,
27017
); DB db
=
mongo.getDB(
"
yourdb
"
);
//
get a single collection
DBCollection collection
=
db.getCollection(
"
dummyColl
"
);
//
BasicDBObject example
System.out.println(
"
BasicDBObject example...
"
); BasicDBObject document
=
new
BasicDBObject(); document.put(
"
database
"
,
"
mkyongDB
"
); document.put(
"
table
"
,
"
hosting
"
); BasicDBObject documentDetail
=
new
BasicDBObject(); documentDetail.put(
"
records
"
,
"
99
"
); documentDetail.put(
"
index
"
,
"
vps_index1
"
); documentDetail.put(
"
active
"
,
"
true
"
); document.put(
"
detail
"
, documentDetail); collection.insert(document); DBCursor cursorDoc
=
collection.find();
while
(cursorDoc.hasNext()){ System.out.println(cursorDoc.next()); } collection.remove(
new
BasicDBObject());
//
BasicDBObjectBuilder example
System.out.println(
"
BasicDBObjectBuilder example...
"
); BasicDBObjectBuilder documentBuilder
=
BasicDBObjectBuilder.start() .add(
"
database
"
,
"
mkyongDB
"
) .add(
"
table
"
,
"
hosting
"
); BasicDBObjectBuilder documentBuilderDetail
=
BasicDBObjectBuilder.start() .add(
"
records
"
,
"
99
"
) .add(
"
index
"
,
"
vps_index1
"
) .add(
"
active
"
,
"
true
"
); documentBuilder.add(
"
detail
"
, documentBuilderDetail.get()); collection.insert(documentBuilder.get()); DBCursor cursorDocBuilder
=
collection.find();
while
(cursorDocBuilder.hasNext()){ System.out.println(cursorDocBuilder.next()); } collection.remove(
new
BasicDBObject());
//
Map example
System.out.println(
"
Map example...
"
); Map documentMap
=
new
HashMap(); documentMap.put(
"
database
"
,
"
mkyongDB
"
); documentMap.put(
"
table
"
,
"
hosting
"
); Map documentMapDetail
=
new
HashMap(); documentMapDetail.put(
"
records
"
,
"
99
"
); documentMapDetail.put(
"
index
"
,
"
vps_index1
"
); documentMapDetail.put(
"
active
"
,
"
true
"
); documentMap.put(
"
detail
"
, documentMapDetail); collection.insert(
new
BasicDBObject(documentMap)); DBCursor cursorDocMap
=
collection.find();
while
(cursorDocMap.hasNext()){ System.out.println(cursorDocMap.next()); } collection.remove(
new
BasicDBObject());
//
JSON parse example
System.out.println(
"
JSON parse example...
"
); String json
=
"
{'database' : 'mkyongDB','table' : 'hosting',
"
+
"
'detail' : {'records' : 99, 'index' : 'vps_index1', 'active' : 'true'}}}
"
; DBObject dbObject
=
(DBObject)JSON.parse(json); collection.insert(dbObject); DBCursor cursorDocJSON
=
collection.find();
while
(cursorDocJSON.hasNext()){ System.out.println(cursorDocJSON.next()); } collection.remove(
new
BasicDBObject()); }
catch
(UnknownHostException e){ e.printStackTrace(); }
catch
(MongoException e){ e.printStackTrace(); } } }
更新Document
假设如下的JSON格式的数据已经保存到Mongodb中去了，现在要更新相关的数据。
{
"
_id
"
: {
"
$oid
"
:
"
x
"
} ,
"
hosting
"
:
"
hostA
"
,
"
type
"
:
"
vps
"
,
"
clients
"
:
1000
} {
"
_id
"
: {
"
$oid
"
:
"
x
"
} ,
"
hosting
"
:
"
hostB
"
,
"
type
"
:
"
dedicated server
"
,
"
clients
"
:
100
} {
"
_id
"
: {
"
$oid
"
:
"
x
"
} ,
"
hosting
"
:
"
hostC
"
,
"
type
"
:
"
vps
"
,
"
clients
"
:
900
}
假设现在要将hosting中值为hostB的进行更新，则可以使用如下的方法：
BasicDBObject newDocument
=
new
BasicDBObject(); newDocument.put(
"
hosting
"
,
"
hostB
"
); newDocument.put(
"
type
"
,
"
shared host
"
); newDocument.put(
"
clients
"
,
111
); collection.update(
new
BasicDBObject().append(
"
hosting
"
,
"
hostB
"
), newDocument);
可以看到，这里依然使用了BasicDBObject对象，并为其赋值了新的值后，然后使用collection的update方法，即可更新该对象。
更新后的输出如下：
{
"
_id
"
: {
"
$oid
"
:
"
x
"
} ,
"
hosting
"
:
"
hostA
"
,
"
type
"
:
"
vps
"
,
"
clients
"
:
1000
} {
"
_id
"
: {
"
$oid
"
:
"
x
"
} ,
"
hosting
"
:
"
hostB
"
,
"
type
"
:
"
shared host
"
,
"
clients
"
:
111
} {
"
_id
"
: {
"
$oid
"
:
"
x
"
} ,
"
hosting
"
:
"
hostC
"
,
"
type
"
:
"
vps
"
,
"
clients
"
:
900
}
另外，还可以使用mongodb中的$inc修饰符号去对某个值进行更新，比如，要将hosting值为hostB的document的clients的值得更新为199(即100+99=199)，可以这样：
BasicDBObject newDocument
=
new
BasicDBObject().append(
"
$inc
"
,
new
BasicDBObject().append(
"
clients
"
,
99
)); collection.update(
new
BasicDBObject().append(
"
hosting
"
,
"
hostB
"
), newDocument);
则输出如下：
{
"
_id
"
: {
"
$oid
"
:
"
x
"
} ,
"
hosting
"
:
"
hostA
"
,
"
type
"
:
"
vps
"
,
"
clients
"
:
1000
} {
"
_id
"
: {
"
$oid
"
:
"
x
"
} ,
"
hosting
"
:
"
hostB
"
,
"
type
"
:
"
dedicated server
"
,
"
clients
"
:
199
} {
"
_id
"
: {
"
$oid
"
:
"
x
"
} ,
"
hosting
"
:
"
hostC
"
,
"
type
"
:
"
vps
"
,
"
clients
"
:
900
}
接下来，讲解$set修饰符的使用。比如要把hosting中值为hostA的document中的
type的值进行修改，则可以如下实现：
BasicDBObject newDocument3
=
new
BasicDBObject().append(
"
$set
"
,
new
BasicDBObject().append(
"
type
"
,
"
dedicated server
"
)); collection.update(
new
BasicDBObject().append(
"
hosting
"
,
"
hostA
"
), newDocument3);
则输出如下，把type的值从vps改为dedicated server:
{
"
_id
"
: {
"
$oid
"
:
"
x
"
} ,
"
hosting
"
:
"
hostB
"
,
"
type
"
:
"
dedicated server
"
,
"
clients
"
:
100
} {
"
_id
"
: {
"
$oid
"
:
"
x
"
} ,
"
hosting
"
:
"
hostC
"
,
"
type
"
:
"
vps
"
,
"
clients
"
:
900
} {
"
_id
"
: {
"
$oid
"
:
"
x
"
} ,
"
hosting
"
:
"
hostA
"
,
"
clients
"
:
1000
,
"
type
"
:
"
dedicated server
"
}
要注意的是，如果不使用$set的修饰符，而只是如下代码：
BasicDBObject newDocument3
=
new
BasicDBObject().append(
"
type
"
,
"
dedicated server
"
); collection.update(
new
BasicDBObject().append(
"
hosting
"
,
"
hostA
"
), newDocument3);
则会将所有的三个document的type类型都改为dedicated server了，因此要使用$set以更新特定的document的特定的值。
如果要更新多个document中相同的值，可以使用$multi，比如，要把所有vps为type的document,将它们的clients的值更新为888，可以如下实现：
BasicDBObject updateQuery
=
new
BasicDBObject().append(
"
$set
"
,
new
BasicDBObject().append(
"
clients
"
,
"
888
"
)); collection.update(
new
BasicDBObject().append(
"
type
"
,
"
vps
"
), updateQuery,
false
,
true
);
输出如下：
{
"
_id
"
: {
"
$oid
"
:
"
x
"
} ,
"
hosting
"
:
"
hostA
"
,
"
clients
"
:
"
888
"
,
"
type
"
:
"
vps
"
} {
"
_id
"
: {
"
$oid
"
:
"
x
"
} ,
"
hosting
"
:
"
hostB
"
,
"
type
"
:
"
dedicated server
"
,
"
clients
"
:
100
} {
"
_id
"
: {
"
$oid
"
:
"
x
"
} ,
"
hosting
"
:
"
hostC
"
,
"
clients
"
:
"
888
"
,
"
type
"
:
"
vps
"
}
最后，还是给出更新document的完整例子：
package
com.liao;
import
java.net.UnknownHostException;
import
com.mongodb.BasicDBObject;
import
com.mongodb.DB;
import
com.mongodb.DBCollection;
import
com.mongodb.DBCursor;
import
com.mongodb.Mongo;
import
com.mongodb.MongoException; publicclass UpdateDocumentApp { publicstaticvoid printAllDocuments(DBCollection collection){ DBCursor cursor
=
collection.find();
while
(cursor.hasNext()) { System.out.println(cursor.next()); } } publicstaticvoid removeAllDocuments(DBCollection collection){ collection.remove(
new
BasicDBObject()); } publicstaticvoid insertDummyDocuments(DBCollection collection){ BasicDBObject document
=
new
BasicDBObject(); document.put(
"
hosting
"
,
"
hostA
"
); document.put(
"
type
"
,
"
vps
"
); document.put(
"
clients
"
,
1000
); BasicDBObject document2
=
new
BasicDBObject(); document2.put(
"
hosting
"
,
"
hostB
"
); document2.put(
"
type
"
,
"
dedicated server
"
); document2.put(
"
clients
"
,
100
); BasicDBObject document3
=
new
BasicDBObject(); document3.put(
"
hosting
"
,
"
hostC
"
); document3.put(
"
type
"
,
"
vps
"
); document3.put(
"
clients
"
,
900
); collection.insert(document); collection.insert(document2); collection.insert(document3); } publicstaticvoid main(String[] args) {
try
{ Mongo mongo
=
new
Mongo(
"
localhost
"
,
27017
); DB db
=
mongo.getDB(
"
yourdb
"
); DBCollection collection
=
db.getCollection(
"
dummyColl
"
); System.out.println(
"
Testing 1...
"
); insertDummyDocuments(collection);
//
find hosting = hostB, and update it with new document
BasicDBObject newDocument
=
new
BasicDBObject(); newDocument.put(
"
hosting
"
,
"
hostB
"
); newDocument.put(
"
type
"
,
"
shared host
"
); newDocument.put(
"
clients
"
,
111
); collection.update(
new
BasicDBObject().append(
"
hosting
"
,
"
hostB
"
), newDocument); printAllDocuments(collection); removeAllDocuments(collection); System.out.println(
"
Testing 2...
"
); insertDummyDocuments(collection); BasicDBObject newDocument2
=
new
BasicDBObject().append(
"
$inc
"
,
new
BasicDBObject().append(
"
clients
"
,
99
)); collection.update(
new
BasicDBObject().append(
"
hosting
"
,
"
hostB
"
), newDocument2); printAllDocuments(collection); removeAllDocuments(collection); System.out.println(
"
Testing 3...
"
); insertDummyDocuments(collection); BasicDBObject newDocument3
=
new
BasicDBObject().append(
"
$set
"
,
new
BasicDBObject().append(
"
type
"
,
"
dedicated server
"
)); collection.update(
new
BasicDBObject().append(
"
hosting
"
,
"
hostA
"
), newDocument3); printAllDocuments(collection); removeAllDocuments(collection); System.out.println(
"
Testing 4...
"
); insertDummyDocuments(collection); BasicDBObject updateQuery
=
new
BasicDBObject().append(
"
$set
"
,
new
BasicDBObject().append(
"
clients
"
,
"
888
"
)); collection.update(
new
BasicDBObject().append(
"
type
"
,
"
vps
"
), updateQuery,
false
,
true
); printAllDocuments(collection); removeAllDocuments(collection); System.out.println(
"
Done
"
); }
catch
(UnknownHostException e) { e.printStackTrace(); }
catch
(MongoException e) { e.printStackTrace(); } } }
查询Document
下面学习如何查询document,先用下面的代码往数据库中插入1-10数字：
for
(
int
i
=
1
; i
<=
10
; i
++
){ collection.insert(
new
BasicDBObject().append(
"
number
"
, i));
}
}
接下来，看下如下的例子：
1) 获得数据库中的第一个document:
DBObject doc
=
collection.findOne(); System.out.println(dbObject);
输出为：
{
"
_id
"
: {
"
$oid
"
:
"
4dc7f7b7bd0fb9a86c6c80bd
"
} ,
"
number
"
:
1
}
2)获得document的集合
DBCursor cursor
=
collection.find();
while
(cursor.hasNext()){ System.out.println(cursor.next()); }
这里，使用collection.find()方法，获得当前数据库中所有的documents对象集合
然后通过对DBCursor对象集合的遍历，即可输出当前所有documents。输出如下：
{
"
_id
"
: {
"
$oid
"
:
"
4dc7f7b7bd0fb9a86c6c80bd
"
} ,
"
number
"
:
1
}
//
..........中间部分省略，为2到9的输出
{
"
_id
"
: {
"
$oid
"
:
"
4dc7f7b7bd0fb9a86c6c80c6
"
} ,
"
number
"
:
10
}
3) 获取指定的document
比如要获得number=5的document对象内容，可以使用collection的find方法即可，如下：
BasicDBObject query
=
new
BasicDBObject(); query.put(
"
number
"
,
5
); DBCursor cursor
=
collection.find(query);
while
(cursor.hasNext()){ System.out.println(cursor.next()); }
即输出：
{
"
_id
"
: {
"
$oid
"
:
"
4dc7f7b7bd0fb9a86c6c80c1
"
} ,
"
number
"
:
5
}
4) 使用in操作符号
在mongodb中，也可以使用in操作符，比如要获得number=9和number=10的document对象，可以如下操作：
BasicDBObject query
=
new
BasicDBObject(); List list
=
new
ArrayList(); list.add(
9
); list.add(
10
); query.put(
"
number
"
,
new
BasicDBObject(
"
$in
"
, list)); DBCursor cursor
=
collection.find(query);
while
(cursor.hasNext()){ System.out.println(cursor.next()); }
这里使用了一个List，并将list传入到BasicDBObject的构造函数中，并使用了in操作符号，输出如下：
{
"
_id
"
: {
"
$oid
"
:
"
4dc7f7b7bd0fb9a86c6c80c5
"
} ,
"
number
"
:
9
} {
"
_id
"
: {
"
$oid
"
:
"
4dc7f7b7bd0fb9a86c6c80c6
"
} ,
"
number
"
:
10
}
5) 使用>,<等比较符号
在mongodb中，也可以使用比如>,<等数量比较符号，比如要输出number>5的document集合，则使用“$gt”即可，同理，小于关系则使用$lt，例子如下：
BasicDBObject query
=
new
BasicDBObject(); query.put(
"
number
"
,
new
BasicDBObject(
"
$gt
"
,
5
)); DBCursor cursor
=
collection.find(query);
while
(cursor.hasNext()){ System.out.println(cursor.next()); }
输出如下：
{
"
_id
"
: {
"
$oid
"
:
"
4dc7f7b7bd0fb9a86c6c80c2
"
} ,
"
number
"
:
6
} {
"
_id
"
: {
"
$oid
"
:
"
4dc7f7b7bd0fb9a86c6c80c3
"
} ,
"
number
"
:
7
} {
"
_id
"
: {
"
$oid
"
:
"
4dc7f7b7bd0fb9a86c6c80c4
"
} ,
"
number
"
:
8
} {
"
_id
"
: {
"
$oid
"
:
"
4dc7f7b7bd0fb9a86c6c80c5
"
} ,
"
number
"
:
9
} {
"
_id
"
: {
"
$oid
"
:
"
4dc7f7b7bd0fb9a86c6c80c6
"
} ,
"
number
"
:
10
} 也可以多个比较符号一起使用，比如要输出number
>
5和number
<
8的document,则如下： BasicDBObject query
=
new
BasicDBObject(); query.put(
"
number
"
,
new
BasicDBObject(
"
$gt
"
,
5
).append(
"
$lt
"
,
8
)); DBCursor cursor
=
collection.find(query);
while
(cursor.hasNext()){ System.out.println(cursor.next()); }
同样，如果是不等于的关系的话，可以使用$ne操作符，如下：
BasicDBObject query5
=
new
BasicDBObject(); query5.put(
"
number
"
,
new
BasicDBObject(
"
$ne
"
,
8
)); DBCursor cursor6
=
collection.find(query5);
while
(cursor6.hasNext()){ System.out.println(cursor6.next()); }
以上输出number=8之外的所有document。
删除document
下面我们学习如何删除document，依然以上面的已插入的1-10的documents集合为例说明：
1) 删除第一个document
DBObject doc
=
collection.findOne(); collection.remove(doc);
2) 删除指定的document
比如删除number=2的document,如下方法：
BasicDBObject document
=
new
BasicDBObject(); document.put(
"
number
"
,
2
); collection.remove(document);
要注意的是，如下的方法将只会删除number=3的document。
BasicDBObject document
=
new
BasicDBObject(); document.put(
"
number
"
,
2
); document.put(
"
number
"
,
3
); collection.remove(document);
3) 使用in 操作符号指定删除document
下面的例子将同时删除number=4和number=5的document，使用的是in操作符
BasicDBObject query2
=
new
BasicDBObject(); List list
=
new
ArrayList(); list.add(
4
); list.add(
5
); query2.put(
"
number
"
,
new
BasicDBObject(
"
$in
"
, list)); collection.remove(query2);
4) 使用“$gt”删除大于某个值的document
BasicDBObject query
=
new
BasicDBObject(); query.put(
"
number
"
,
new
BasicDBObject(
"
$gt
"
,
9
)); collection.remove(query);
以上会删除number=10的document。
5) 删除所有的document
DBCursor cursor
=
collection.find();
while
(cursor.hasNext()){ collection.remove(cursor.next()); }
保存图片到Mongodb
下面将讲解如何使用Java MongoDB GridFS API去保存图片等二进制文件到Monodb，关于Java MongoDB GridFS API的详细论述，请参考http://www.mongodb.org/display/DOCS/GridFS+Specification
1)保存图片
代码段如下：
String newFileName
=
"
mkyong-java-image
"
; File imageFile
=
newFile(
"
c:\\JavaWebHosting.png
"
); GridFS gfsPhoto
=
new
GridFS(db,
"
photo
"
); GridFSInputFile gfsFile
=
gfsPhoto.createFile(imageFile); gfsFile.setFilename(newFileName); gfsFile.save();
这里，将c盘下的JavaWebHosting.png保存到mongodb中去，并命名为mkyong-java-image。
2) 读取图片信息
代码段如下
String newFileName
=
"
mkyong-java-image
"
; GridFS gfsPhoto
=
new
GridFS(db,
"
photo
"
); GridFSDBFile imageForOutput
=
gfsPhoto.findOne(newFileName); System.out.println(imageForOutput);
将会输出JSON格式的结果;
{
"
_id
"
: {
"
$oid
"
:
"
4dc9511a14a7d017fee35746
"
} ,
"
chunkSize
"
:
262144
,
"
length
"
:
22672
,
"
md5
"
:
"
1462a6cfa27669af1d8d21c2d7dd1f8b
"
,
"
filename
"
:
"
mkyong-java-image
"
,
"
contentType
"
:
null
,
"
uploadDate
"
: {
"
$date
"
:
"
2011-05-10T14:52:10Z
"
} ,
"
aliases
"
:
null
}
可以看到，输出的是文件的属性相关信息。
3) 输出已保存的所有图片
下面代码段，输出所有保存在photo命名空间下的图片信息：
GridFS gfsPhoto
=
new
GridFS(db,
"
photo
"
); DBCursor cursor
=
gfsPhoto.getFileList();
while
(cursor.hasNext()){ System.out.println(cursor.next()); }
4) 从数据库中读取一张图片并另存
下面的代码段，从数据库中读取一张图片并另存为另外一张图片到磁盘中
String newFileName
=
"
mkyong-java-image
"
; GridFS gfsPhoto
=
new
GridFS(db,
"
photo
"
); GridFSDBFile imageForOutput
=
gfsPhoto.findOne(newFileName); imageForOutput.writeTo(
"
c:\\JavaWebHostingNew.png
"
);
5) 删除图片
String newFileName
=
"
mkyong-java-image
"
; GridFS gfsPhoto
=
new
GridFS(db,
"
photo
"
); gfsPhoto.remove(gfsPhoto.findOne(newFileName));
如何将JSON数据格式转化为DBObject格式
在mongodb中，可以使用com.mongodb.util.JSON类，将JSON格式的字符串转变为DBObject对象。MongoDB for JAVA驱动中提供了用于向数据库中存储普通对象的接口DBObject，当一个文档从MongoDB中取出时，它会自动把文档转换成DBObject接口类型，要将它实例化为需要的对象。比如：
{
'
name
'
:
'
mkyong
'
,
'
age
'
:
30
}
这样的JSON格式字符串，转换方法为：
DBObject dbObject
=
(DBObject) JSON.parse(
"
{'name':'mkyong', 'age':30}
"
);
完整的代码如下：
packagecom.mkyong.core; importjava.net.UnknownHostException; importcom.mongodb.DB; importcom.mongodb.DBCollection; importcom.mongodb.DBCursor; importcom.mongodb.DBObject; importcom.mongodb.Mongo; importcom.mongodb.MongoException; importcom.mongodb.util.JSON;
/**
* Java MongoDB : Convert JSON data to DBObject *
*/
publicclass App { publicstaticvoid main(String[] args){
try
{ Mongo mongo
=
new
Mongo(
"
localhost
"
,
27017
); DB db
=
mongo.getDB(
"
yourdb
"
); DBCollection collection
=
db.getCollection(
"
dummyColl
"
); DBObject dbObject
=
(DBObject) JSON .parse(
"
{'name':'mkyong', 'age':30}
"
); collection.insert(dbObject); DBCursor cursorDoc
=
collection.find();
while
(cursorDoc.hasNext()){ System.out.println(cursorDoc.next()); } System.out.println(
"
Done
"
); }
catch
(UnknownHostException e){ e.printStackTrace(); }
catch
(MongoException e){ e.printStackTrace(); } } }
则输出为：
{
"
_id
"
: {
"
$oid
"
:
"
4dc9ebb5237f275c2fe4959f
"
} ,
"
name
"
:
"
mkyong
"
,
"
age
"
:
30
}
Done
可以看到，将JSON格式的数据类型直接转换为mongodb中的文档类型并输出。
小结：
本文学习了如何使用Mongodb for JAVA驱动，对mongodb进行日常的数据库操作，比如增加，删除和修改，下一篇教程中，将指导学习Spring对mongodb的操作