使用MongoDB Java驱动程序的3.11.0JAR包使用账户密码连接mongodb下载图片

这里提供一个使用MongoDB Java驱动程序的3.11.0版本，使用账户密码连接MongoDB，然后从GridFS中下载图片的示例代码：

import com.mongodb.MongoClient;
import com.mongodb.MongoCredential;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import com.mongodb.client.gridfs.GridFSBucket;
import com.mongodb.client.gridfs.GridFSBuckets;
import com.mongodb.client.gridfs.GridFSDownloadStream;
import com.mongodb.client.gridfs.model.GridFSFile;
import org.bson.types.ObjectId;

import java.io.FileOutputStream;
import java.io.IOException;

public class DownloadImage {
    public static void main(String[] args) {
        String dbName = "your_db_name";
        String username = "your_username";
        String password = "your_password";

        // 创建MongoDB凭证
        MongoCredential credential = MongoCredential.createCredential(username, dbName, password.toCharArray());

        // 创建MongoDB客户端
        MongoClient mongoClient = new MongoClient(new ServerAddress("your_server_address"), credential, MongoClientOptions.builder().build());

        // 连接到数据库
        MongoDatabase database = mongoClient.getDatabase(dbName);

        // 获取GridFSBucket对象
        GridFSBucket gridFSBucket = GridFSBuckets.create(database);

        String filename = "your_image_filename"; // 图片的文件名
        ObjectId fileId = null;

        // 根据文件名查找文件
        GridFSFile gridFSFile = gridFSBucket.find().filter(Filters.eq("filename", filename)).first();
        if (gridFSFile != null) {
            fileId = gridFSFile.getObjectId();
        }

        if (fileId != null) {
            // 打开下载流
            GridFSDownloadStream downloadStream = gridFSBucket.openDownloadStream(fileId);

            // 创建输出流
            FileOutputStream outputStream = null;
            try {
                outputStream = new FileOutputStream("your_image_save_path");

                // 下载文件
                int fileLength = downloadStream.getGridFSFile().getLength();
                byte[] buffer = new byte[fileLength];
                int len;
                while ((len = downloadStream.read(buffer)) != -1) {
                    outputStream.write(buffer, 0, len);
                }
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    downloadStream.close();
                    outputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

        // 关闭MongoDB客户端
        mongoClient.close();
    }
}

在这个示例中，我们首先创建了MongoDB凭证，然后使用凭证创建了MongoDB客户端。接着，我们连接到指定的数据库，获取GridFSBucket对象。然后，我们根据文件名查找文件，并获取文件的ObjectId。最后，我们打开下载流，创建输出流，下载文件并保存到本地。