How can I get data from my controller?

Question

I have two controllers (classes). In one of them I'am making a request and the result data of it I want to transfer to another controller. But somehow it returns only an empty list. First controller that makes a request and sends data:

package controllers;

import com.querydsl.core.Tuple;
import com.querydsl.jpa.impl.JPAQueryFactory;
import models.*;
import play.db.jpa.JPAApi;
import play.db.jpa.Transactional;
import play.mvc.Controller;
import play.mvc.Result;

import javax.inject.Inject;
import javax.persistence.EntityManager;
import java.time.LocalDate;
import java.util.ArrayList;
import java.util.List;

import static java.util.Collections.addAll;

public class TestingController extends Controller {



    private JPAApi jpaApi;
    @Inject
    public TestingController(JPAApi jpaApi) {
        this.jpaApi = jpaApi;
    }

    private static ArrayList<ArrayList<Object>> listOfLists = new ArrayList<>();

    @Transactional
    public Result resolving_requests() {
        QClaim claim = QClaim.claim;
        QFinancialClaimData financialClaimData = QFinancialClaimData.financialClaimData;
        QDate_diff date_diff=QDate_diff.date_diff;
        EntityManager em=jpaApi.em();
        JPAQueryFactory queryFactory = new JPAQueryFactory(em);

        //QUERY1: Costs and amounts of different claims for the last year
        String columns[] = {"Month, Year", "Type of risk", "Risks count", "Risks amount"};
        List<Tuple> q1=queryFactory.select(claim.typeOfRisk, financialClaimData.overAllAmount.sum(), claim.claimDate_finish.count(), claim.claimDate_start.month(), claim.claimDate_start.year())
                .from(claim)
                .where(claim.claimDate_start.year().gt(LocalDate.now().getYear()-2).and(claim.claimDate_start.month().gt(LocalDate.now().getMonthValue())).or(claim.claimDate_start.year().eq(LocalDate.now().getYear())))
                .groupBy(claim.typeOfRisk, claim.claimDate_start.month(), claim.claimDate_start.year())
                .orderBy(claim.claimDate_start.year().asc(), claim.claimDate_start.month().asc(), claim.typeOfRisk.asc())
                .fetch( );
        ArrayList<Object> singleList = new ArrayList<>();
        addAll(singleList, columns); //Adding all columns' names to the first row, simailar to foreach
        this.listOfLists.add(singleList);
        for (Tuple l: q1){
            singleList = new ArrayList<>();
            singleList.add(l.get(claim.claimDate_start.month()).toString() + "/" + l.get(claim.claimDate_start.year()).toString());
            singleList.add(l.get(claim.typeOfRisk));
            singleList.add(l.get(claim.claimDate_finish.count()));
            singleList.add(l.get(financialClaimData.overAllAmount.sum()));
            this.listOfLists.add(singleList);
        }

        System.out.println(listOfLists);
        for (List i: listOfLists){
            for (Object i_inner: i){
                System.out.print(i_inner+"|"); //That works fine and I see a result
            }
            System.out.print("\n");
        }
        return ok("Your new application is ready.");
    }

    public static ArrayList<ArrayList<Object>> get_arr_list() {
        return listOfLists; //Probably that returns empty list
    }
}

The second controller, that should receive ArrayList: package controllers;

import com.fasterxml.jackson.databind.JsonNode;
import play.mvc.*;
import java.util.ArrayList;


public class ReportsController extends Controller {

    public Result generating_reports(){
                ArrayList<ArrayList<Object>> listOfLists = TestingController.get_arr_list();
                System.out.println("Here should be a list: "+listOfLists); //This returns an empty list []

        return  ok("All is ready!");
    }
}

How can I fix it?

Answer 1

First it is vital to post a minimal runnable code that demonstrates the problem. This means removeing ALL that is not essential, and INCLUDING everything that is needed for the code to be compiled and run. Here is an example (See comments for explanations):

import static java.util.Collections.addAll;
import java.util.ArrayList;

public class TestingController {

    private static ArrayList<ArrayList<Object>> listOfLists = new ArrayList<>();

    //in the code you posted this method never gets executed
    public void resolving_requests() {

        String columns[] = {"Month, Year", "Type of risk", "Risks count", "Risks amount"};

        ArrayList<Object> singleList = new ArrayList<>();
        addAll(singleList, columns); //Adding all columns' names to the first row, simailar to foreach

        listOfLists.add(singleList);
    }

    public static ArrayList<ArrayList<Object>> get_arr_list() {
        return listOfLists; //Probably that returns empty list
    }

    public static void main(String args[]) {

        //this will print an empty list because resolving_requests was not executed
        System.out.println("listOfLists "+ TestingController.get_arr_list()) ;

        //execute resolving_requests
        new TestingController().resolving_requests();

        //now array list is not empty 
        System.out.println("listOfLists "+ TestingController.get_arr_list()) ;
    }
}