Downloading very large results from query via Java Webapp

I have been mulling over a bit of an issue, and I was wondering if anyone had any advice.
I have a web application that I need to add a section for reporting to. It will have a t-sql query constructed based on user gui inputs, execute, and allow the user to download the file to their computer through their browser as a csv. On it's own none of this is overly complicated. I have done these things before. There is one issue I have not grappled with before however. The results may end up as multiple GBs worth of data. What would I do differently (in terms of code) from normal to prevent it from overloading the browser or being tremendously slow? It clearly cannot all be held in memory at once? How do I prevent that from happening?

You can write the csv-data directly to the OutputStream of the incoming request:

package example;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.nio.charset.StandardCharsets;

public class MyServlet extends HttpServlet {

	private final CSVCreator csvCreator;

	private MyServlet(CSVCreator csvCreator) {
		this.csvCreator = csvCreator;
	}

	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		// be nice to your consumer, tell them what they get
		resp.setHeader("Content-Type", "text/comma-separated-values; charset=UTF-8");

		try (Writer writer = new OutputStreamWriter(resp.getOutputStream(), StandardCharsets.UTF_8)) {
			this.csvCreator.createCSV("some params you need to create the correct csv", writer);
		}
	}
}

You will have to change your csv-generation to be able to write to an Writer ... for example:

package example;

import java.io.IOException;

public class CSVCreator {

	public void createCSV(String someParamsYouNeedToCreateTheCSV, Appendable appendable) throws IOException {
		appendable.append("Column1,Column2,Column3\n");
		appendable.append("Row1,Row1,Row1\n");
		appendable.append("Row2,Row2,Row2\n");
	}
}

You could also, for example, use apache-commons-csv to write the csv to the given Appendable (see: https://javadoc.io/doc/org.apache.commons/commons-csv/latest/org/apache/commons/csv/CSVPrinter.html )

package example;

import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVPrinter;

import java.io.IOException;

public class CSVCreator {

	public void createCSV(String someParamsYouNeedToCreateTheCSV, Appendable appendable) throws IOException {
		try (CSVPrinter printer = new CSVPrinter(appendable, CSVFormat.DEFAULT)) {
			printer.printRecord("Column1", "Column2", "Column3");
			printer.printRecord("Row1", "Row1", "Row1");
			printer.printRecord("Row2", "Row2", "Row2");
		}
	}
}

EDIT:

You can create a CSV-File from a ResultSet like this:

package example;

import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVPrinter;

import java.io.IOException;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;

public class ResultSetToCSV {

	public void createCSV(ResultSet rs, Appendable appendable) throws IOException, SQLException {
		final ResultSetMetaData metaData = rs.getMetaData();
		final int columnCount = metaData.getColumnCount();

		try (CSVPrinter printer = new CSVPrinter(appendable, CSVFormat.DEFAULT)) {
			printHeaders(metaData, columnCount, printer);
			printValues(rs, columnCount, printer);
		}
	}

	private void printHeaders(ResultSetMetaData metaData, int columnCount, CSVPrinter printer) throws IOException, SQLException {
		for (int i = 1; i <= columnCount; i++) {
			printer.print(metaData.getColumnLabel(i));
		}
		
		printer.println();
	}

	private void printValues(ResultSet rs, int columnCount, CSVPrinter printer) throws IOException, SQLException {
		while (rs.next()) {
			printValue(rs, columnCount, printer);
		}
	}
	
	private void printValue(ResultSet rs, int columnCount, CSVPrinter printer) throws IOException, SQLException {
		for (int i = 1; i <= columnCount; i++) {
			printer.print(rs.getString(i));
		}
		
		printer.println();
	}
}