[Q#40281030][A#40293024] How to export queried data from Google Cloud Datastore to csv using Java?

https://stackoverflow.com/q/40281030

I have a use case where I need to perform the querying operation on the data stored in Google Cloud Datastore and display the results and provide a download link to the csv file of the same data. I had gone through different documentations, but it dealt mostly with python whereas my implementation is in Java. Please guide.

Answer

https://stackoverflow.com/a/40293024

Here is one possible way: you build your csv file in memory in a Cloud Endpoint by querying the Cloud datastore and print to a ByteArrayOutputStream, as shown hereafter: Then you save the csv file to Cloud Storage and return the URL for downloading it, as I explained in the following answer: https://stackoverflow.com/a/37603225/3371862 An other possibility would be to stream the result through a Google App Engine servlet (i.e. you don't go through Cloud Endpoints). Have a look at how to write csv file in google app by using java

APIzation

ByteArrayOutputStream csvOS = new ByteArrayOutputStream();
PrintStream printer = new PrintStream(csvOS);
printer.println("L1C1;L1C2;L1C3");
printer.println("L2C1;L2C2;L2C3");
printer.close();

package com.stackoverflow.api;

import java.io.ByteArrayOutputStream;
import java.io.PrintStream;

public class Human40293024 {

  public static void exportToCSV() {
    ByteArrayOutputStream csvOS = new ByteArrayOutputStream();
    PrintStream printer = new PrintStream(csvOS);
    printer.println("L1C1;L1C2;L1C3");
    printer.println("L2C1;L2C2;L2C3");
    printer.close();
  }
}

package com.stackoverflow.api;

import java.io.ByteArrayOutputStream;
import java.io.PrintStream;

/**
 * How to export queried data from Google Cloud Datastore to csv using Java?
 *
 * @author APIzator
 * @see <a href="https://stackoverflow.com/a/40293024">https://stackoverflow.com/a/40293024</a>
 */
public class APIzator40293024 {

  public static void exportDatum() throws Exception {
    ByteArrayOutputStream csvOS = new ByteArrayOutputStream();
    PrintStream printer = new PrintStream(csvOS);
    printer.println("L1C1;L1C2;L1C3");
    printer.println("L2C1;L2C2;L2C3");
    printer.close();
  }
}