1. 建立java项目
2. 新建lib包，导入jar包

3.链接mongdo数据库代码

    /**

     * 1.获取连接

     * 2.上传文件

     * 3.下载文件

     * 4.删除文件

     *

     */

   

       public static GridFS GetMongoGridFS(){

              List<ServerAddress> adds = new ArrayList<>();

              ServerAddress serverAddress = new ServerAddress("192.168.1.100", 27017);

              adds.add(serverAddress);

               

              List<MongoCredential> credentials = new ArrayList<>();

              //MongoCredential.createScramSha1Credential()三个参数分别为 用户名 数据库名称 密码

              MongoCredential mongoCredential = MongoCredential.createScramSha1Credential("uname", "mg", "pw".toCharArray());

              credentials.add(mongoCredential);

               

              //通过连接认证获取MongoDB连接

              MongoClient mongoClient = new MongoClient(adds,credentials);

              //连接到数据库

              DB mongoDatabase = mongoClient.getDB("testdb");

              GridFS myFS = new GridFS(mongoDatabase);

              return myFS;

       }

上传文件

     /**

      * @return

      * 上传文件

      * @Title: UploadFile  

      * @Description: TODO(这里用一句话描述这个方法的作用)  

      * @param: @param file     

      * @return: void     

      * @throws

      */

     public String UploadFile(File file) {

         try {

              GridFS gridFS = GetMongoGridFS();

             GridFSFile mgupfile = gridFS.createFile(file); 

             mgupfile.save(); 

             return mgupfile.getId().toString();

         } catch (Exception e) {

              return null;

         }

}

下载文件

    /**

     * 下载文件

     * @Title: DownloadFile  

     * @Description: TODO(这里用一句话描述这个方法的作用)  

     * @param: @param objectid

     * @param: @return     

     * @return: String     

     * @throws

     */

    public String DownloadFile(String  objectid) {

         try {

              GridFS gridFS = GetMongoGridFS();

              GridFSDBFile file2 =gridFS.findOne(new ObjectId(objectid));

              String filename="D:/tmp/5"+file2.getFilename();

              long writeTo = file2.writeTo(new File(filename));

              if(writeTo>=0){

                   return  filename;

              }else{

                   return null;

              }

         } catch (Exception e) {

              return null;

         }

}

删除文件

    /**

     * 删除文件

     * @Title: DeleteFile  

     * @Description: TODO(这里用一句话描述这个方法的作用)  

     * @param: @param objectid

     * @param: @return     

     * @return: String     

     * @throws

      */

     public void DeleteFile(String  objectid) {

         GridFS gridFS = GetMongoGridFS();

         GridFSDBFile file =gridFS.findOne(new ObjectId("5c4fed8064873a4a68427f93"));

         gridFS.remove((ObjectId) file.getId());

}