MongoDB GridFS java存取文件

不念不忘少年蓝@ 2022-08-05 15:06 250阅读 0赞

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]  
[http://www.mongodb.org/display/DOCS/GridFS+Specification][http_www.mongodb.org_display_DOCS_GridFS_Specification]  
[http://api.mongodb.org/java/2.13/][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）][MongoDB_Spring]

[http_www.mongodb.org_display_DOCS_GridFS]: http://www.mongodb.org/display/DOCS/GridFS
[http_www.mongodb.org_display_DOCS_GridFS_Specification]: http://www.mongodb.org/display/DOCS/GridFS+Specification
[http_api.mongodb.org_java_2.13]: http://api.mongodb.org/java/2.13/
[MongoDB_Spring]: http://www.linuxidc.com/Linux/2014-04/99742.htm