MongoDB GridFS java存取文件

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;
    }
}

参考文章：

1.MongoDB结合Spring存储文件（图片、音频等等）