GridFS首先会在当前数据库创建两个集合:"fs.files"和"fs.chunks"集合,前者记录了文件名,文件创建时间,文件类型等基本信息;后者分块存储了文件的二进制数据(并支持加密这些二进制数据)。分块的意思是把文件按照指定大小分割,然后存入多个文档中。"fs.files"怎么知道它对应的文件二进制数据在哪些块呢?那是因为在"fs.chunks"中有个"files_id"键,它对应"fs.files"的"_id"。"fs.chunks"还有一个键(int型)"n",它表明这些块的先后顺序。这两个集合名中的"fs"也是可以通过参数自定义的。
官方文档
http://www.mongodb.org/display/DOCS/GridFS
http://www.mongodb.org/display/DOCS/GridFS+Specification
http://api.mongodb.org/java/2.13/
下面我们用mongo-java-driver来实现文件的读取。
MongoGridFSTest.java
package cn.slimsmart.mongodb.demo.crud; import java.io.File; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.InputStream; import java.net.UnknownHostException; import com.mongodb.BasicDBObject; import com.mongodb.DB; import com.mongodb.DBObject; import com.mongodb.MongoClient; import com.mongodb.gridfs.GridFS; import com.mongodb.gridfs.GridFSDBFile; import com.mongodb.gridfs.GridFSInputFile; public class MongoGridFSTest { private static MongoClient mongoClient = null; private static DB db = null; private static GridFS gridFS = null; private static String dbName = "gridfs"; public static void main(String[] args) throws UnknownHostException, Exception { mongoClient = new MongoClient("192.168.36.61", 23000); db = mongoClient.getDB(dbName); gridFS = new GridFS(db); String file = "src/main/resources/20150315172324.png"; if(!new File(file).exists()){ System.out.println("file is not exists."); } String fileName = "20150315172324.png"; //把文件保存到gridfs中,并以文件的md5值为id save(new FileInputStream(file), fileName,fileName); //据文件名从gridfs中读取到文件 GridFSDBFile gridFSDBFile = getByFileName(fileName); if(gridFSDBFile != null){ System.out.println("filename:" + gridFSDBFile.getFilename()); System.out.println("md5:" + gridFSDBFile.getMD5()); System.out.println("length:" + gridFSDBFile.getLength()); System.out.println("uploadDate:" + gridFSDBFile.getUploadDate()); System.out.println("--------------------------------------"); gridFSDBFile.writeTo(new FileOutputStream("src/main/resources/20150315172324_out.png")); }else{ System.out.println("can not get file by name:" + fileName); } } /** * 用给出的id,保存文件,透明处理已存在的情况 * id 可以是string,long,int,org.bson.types.ObjectId 类型 * @param in * @param id */ public static void save(InputStream in, Object id,String fileName){ DBObject query = new BasicDBObject("_id", id); GridFSDBFile gridFSDBFile = gridFS.findOne(query); if(gridFSDBFile == null){ GridFSInputFile gridFSInputFile = gridFS.createFile(in); gridFSInputFile.setId(id); gridFSInputFile.setFilename(fileName); //gridFSInputFile.setChunkSize(); //gridFSInputFile.setContentType(); //gridFSInputFile.setMetaData(); gridFSInputFile.save(); } } /** * 据id返回文件 * @param id * @return */ public static GridFSDBFile getById(Object id){ DBObject query = new BasicDBObject("_id", id); GridFSDBFile gridFSDBFile = gridFS.findOne(query); return gridFSDBFile; } /** * 据文件名返回文件,只返回第一个 * @param fileName * @return */ public static GridFSDBFile getByFileName(String fileName){ DBObject query = new BasicDBObject("filename", fileName); GridFSDBFile gridFSDBFile = gridFS.findOne(query); return gridFSDBFile; } }
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