GridFS是MongoDB為存取大型文檔（超過4mb）准備的。首先是關於GridFS原理性的介紹。
一、GridFS原理
This filesystem within MongoDB was designed for … well, holding files, especially files over 4MB … why 4MB?
Well BSON objects are limited to 4MB in size (BSON is the format that MongoDB uses to store it’s database information) so GridFS helps store files across multiple chunks.
As Kristina Chodorow of 10Gen puts it …
GridFS breaks large files into manageable chunks. It saves the chunks to one collection (fs.chunks) and then metadata about the file to another collection (fs.files). When you query for the file, GridFS queries the chunks collection and returns the file one piece at a time.
Why would you want to break large files in to “chunks”? A lot of of comes down to efficient memory & disk usage.
Say you want to store larger files (maybe a 2GB video) when you preform a query on that file all 2GB needs to be loaded into memory … say you have a bigger file, 10GB, 25GB etc … it’s quite likely you’d run out of usable RAM or not have that much RAM available at all!
So, GridFS solves this problem by streaming the data back (in chunks) to the client … this way you’d never need to use more than 4MB of RAM.
二、命令行方式操作
在MongoDB的安裝目錄下有個mongoFiles.exe這就是用來存取文件的。
存儲之后，發現這個文件被存在了testDatabase的fs.files集合下。利用testDatabase.fs.files.find("mylove.wma")可以查詢到此文檔。
三、java方式存儲
View Code
1 import java.io.File;
2 import java.net.UnknownHostException;
3 import java.util.Date;
4 import java.util.List;
5 import com.mongodb.BasicDBObject;
6 import com.mongodb.DB;
7 import com.mongodb.DBCollection;
8 import com.mongodb.DBCursor;
9 import com.mongodb.DBObject;
10 import com.mongodb.Mongo;
11 import com.mongodb.MongoException;
12 import com.mongodb.gridfs.GridFS;
13 import com.mongodb.gridfs.GridFSInputFile;
14
15 public class MongoDBClientTest {
16
17 public static void main(String[] args) {
18 // initData();
19 // query();
20 initData4GridFS();
21 }
22
23
24 private static void initData4GridFS() {
25 long start = new Date().getTime();
26 try {
27 Mongo db = new Mongo("127.0.0.1", 50000);
28 DB mydb = db.getDB("wlb");
29 File f = new File("D://study//document//MySQL5.1參考手冊.chm");
30 GridFS myFS = new GridFS(mydb);
31 GridFSInputFile inputFile = myFS.createFile(f);
32 inputFile.save();
33
34 DBCursor cursor = myFS.getFileList();
35 while(cursor.hasNext()){
36 System.out.println(cursor.next());
37 }
38 db.close();
39 long endTime = new Date().getTime();
40 System.out.println(endTime - start);
41 System.out.println((endTime - start) / 10000000);
42 }catch (Exception e) {
43 e.printStackTrace();
44 }
45 }
46 }
四、參考博客
1、http://learnmongo.com/posts/getting-started-with-mongodb-gridfs/
2、http://blog.csdn.net/zhangzhaokun/article/details/6287309
