mongodb pagination with aggregate

https://stackoverflow.com/questions/48305624/how-to-use-mongodb-aggregation-for-pagination

http://blog.axant.it/2016/01/20/mongodb-aggregation-pipeline-and-pagination/

db.Order.aggregate([
    { '$match'    : { "company_id" : ObjectId("54c0...") } },
    { '$sort'     : { 'order_number' : -1 } },
    { '$facet'    : {
        metadata: [ { $count: "total" }, { $addFields: { page: NumberInt(3) } } ],
        data: [ { $skip: 20 }, { $limit: 10 } ] // add projection here wish you re-shape the docs
    } }
] )




pipeline = [
    {'$match': {'status': 'done'}},
    {'$group': {'_id': 'results', 'result': {'$push': '$$CURRENT'}}},
    {'$project': {'_id': 0, 'result': 1, 'pages': {'$divide': [{'$size': '$result'}, ITEMS_PER_PAGE]}}},
    {'$unwind': '$result'},
    {'$skip': 1 * ITEMS_PER_PAGE},
    {'$limit': ITEMS_PER_PAGE}
]

pdf to image

import java.awt.image.BufferedImage;

import java.io.File;

import java.io.IOException;

import java.util.List;

import javax.imageio.ImageIO;

import org.apache.pdfbox.pdmodel.PDDocument;

import org.apache.pdfbox.pdmodel.PDPage;

public class Main {

    public static void saveFirstPageThumbnail() throws IOException {

        PDDocument document = PDDocument.load("./sample.pdf");

        List<PDPage> pages = document.getDocumentCatalog().getAllPages();

        PDPage page = pages.get(0); //first one

        BufferedImage bufferedImage = page.convertToImage();

        File outputFile = new File( "./image.jpg");

        ImageIO.write(bufferedImage, "jpg", outputFile);

    }

}

spring boot annotation use

https://howtodoinjava.com/spring-core/stereotype-annotations/

mysql concat two columan

SELECT CONCAT(c.FIRSTNAME, ',', c.LASTNAME) AS FIRSTNAME,
       c.*
FROM   `customer` c;

search on two concat columan

WHERE CONCAT(customers.first_name, ' ', customers.last_name) LIKE '%John Smith%'

WHERE CONCAT(TRIM(customers.first_name), ' ', TRIM(customers.last_name)) LIKE '%John Smith%'

java async

https://www.callicoder.com/java-8-completablefuture-tutorial/

https://github.com/maoyunfei/CompletableFuture-Examples/blob/master/src/main/java/com/maoyunfei/study/CompletableFutureExample7.java

import java.util.Arrays; 

import java.util.List; 

import java.util.concurrent.CompletableFuture;

import java.util.concurrent.*;

class Main {

  public static void main(String[] args) {

    CompletableFuture<Void> completableFuture =

    CompletableFuture.runAsync(()-> {

       TimeUnit.SECONDS.sleep(60);

      System.out.println("hare in the game");

  });

  System.out.println("lower function");

}

}

---------------------------------------------------------------------------------------------

import java.util.Arrays;

import java.util.List;

import java.util.concurrent.CompletableFuture;

import java.util.concurrent.*;

class Main {

  public static void main(String[] args) {

    String name="";

     CompletableFuture<String> completableFuture = new CompletableFuture<String>();

    try {

        completableFuture = CompletableFuture.supplyAsync(() -> {

        try {

        TimeUnit.SECONDS.sleep(60);

        System.out.println("hare in the game");

        return "pawan";

        }catch(Exception e) {

          System.out.println("handle exception");

          throw new IllegalStateException(e);

        }

      });

     CompletableFuture<String> greetingFuture = completableFuture.thenApply(namedata -> {

      return "Hello " + namedata;

    });

     // name=completableFuture.get();

      System.out.println("Name"+greetingFuture.get());

    } catch (Exception e) {

      System.out.println("error");

    }

    System.out.println("lower function"+name);

  }

} ---------------------------------------------------------------------------------

import java.util.Arrays;

import java.util.List;

import java.util.concurrent.CompletableFuture;

import java.util.concurrent.*;

class Main {

  public static void main(String[] args) {

    final String name="pawan";

     CompletableFuture<String> completableFuture = new CompletableFuture<String>();

    try {

        completableFuture = CompletableFuture.supplyAsync(() -> {

        try {

        TimeUnit.SECONDS.sleep(60);

        System.out.println("hare in the game");

        return "pawan";

        }catch(Exception e) {

          System.out.println("handle exception");

          throw new IllegalStateException(e);

        }

      }).thenApply(namedata -> {

      System.out.println("Name"+namedata);

      return namedata;

    });

     // name=completableFuture.get();

    

    } catch (Exception e) {

      System.out.println("error");

    }

    System.out.println("lower function"+name);

  }

}

----------------------------------------------------------------------------------- combine example ----------------------

import java.util.concurrent.CompletableFuture;

import java.util.*;

import java.util.concurrent.*;

class Main {

  public static void main(String[] args) {

    try{

    System.out.println("Hello world!");

    CompletableFuture<Integer> serviceOneValue = CompletableFuture.supplyAsync(() -> {

      System.out.println("pawan");

          try {

        TimeUnit.SECONDS.sleep(1);

    } catch (InterruptedException e) {

       throw new IllegalStateException(e);

    }

      return 10;

    });

    CompletableFuture<Integer> serviceTwoValue = CompletableFuture.supplyAsync(() -> {

          try {

        TimeUnit.SECONDS.sleep(1);

    } catch (InterruptedException e) {

       throw new IllegalStateException(e);

    }

      System.out.println("kumar");

      return 100;

    });

    CompletableFuture<Integer> sumOfTwoService = serviceOneValue.thenCombine(serviceTwoValue, (serviceOneValue1, serviceTwoValue1) -> {

      System.out.println("a+b");

      System.out.println("a+b");

      return serviceOneValue1+serviceTwoValue1;

    });

    System.out.println("result---data");

   

    System.out.println("result---"+sumOfTwoService.get());

    }catch(Exception e) {

      System.out.println(e);

    }

  }

}

completeable feature for comobine multipale async call --------------------------------------------------------------    CompletableFuture<Integer> contestInfromation = CompletableFuture.supplyAsync(() -> {
   return  contestService.getContestInfromationByContest(companyId, contestId);
   });
  
   CompletableFuture<Integer> contestGames = CompletableFuture.supplyAsync(() -> {
    return contestService.getContestGamesInfromationByContest(companyId, contestId);
   });
  
   CompletableFuture<Integer> contestAssignmentInfo = CompletableFuture.supplyAsync(() -> {
    return contestService.getContestAssignmentInfromationByContest(companyId, contestId);
   });
  
   CompletableFuture<Integer> contestTrophies = CompletableFuture.supplyAsync(() -> {
    return contestService.getContestTrophiesInfromationByContest(companyId, contestId);
   });
  
   CompletableFuture<Integer> contestRewards = CompletableFuture.supplyAsync(() -> {
    return contestService.getContestRewardsInfromationByContest(companyId, contestId);
   });
   CompletableFuture.allOf(contestInfromation,contestGames,contestAssignmentInfo,contestTrophies,contestRewards).join();
   System.out.println("contestInfromation"+contestInfromation.get());
   System.out.println("contestGames"+contestGames.get());
   System.out.println("contestAssignmentInfo"+contestAssignmentInfo.get());
   System.out.println("contestTrophies"+contestTrophies.get());
   System.out.println("contestRewards"+contestRewards.get());