Java reads mongo database data and downloads it directly, omitting intermediate files

Insert test data:

package com.haiyoung.biz;

import org.bson.Document;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.stereotype.Service;

import java.util.ArrayList;
import java.util.List;

/**
 * Created by Haiyoung on 2018/4/1.
 */
@Service
public class MongoTest {

    @Autowired
    private MongoTemplate mongoTemplate;

    /**
     * add test data
     */
    public void addData(){
        List<Document> list = new ArrayList<>();
        int count = 0;
        for(int i=0;i<10000;i++){
            Document doc = new Document();
            doc.append("key","key"+i);
            list.add(doc);
            count++;
            if(count % 300 == 0){//Insert data every 300 bars
                mongoTemplate.insert(list, "collection_test");
                list.clear();
            }
        }
        if(!list.isEmpty()){
            mongoTemplate.insert(list, "collection_test");
        }
    }
}

import com.haiyoung.biz.MongoTest;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class DatabaseDownloadApplicationTests {

	@Autowired
	private MongoTest mongoTest;

	@Test
	public void insertData(){
		mongoTest.addData();
	}

}

Download service class:

package com.haiyoung.biz.db_download;

import com.google.gson.Gson;
import com.mongodb.DBObject;
import com.mongodb.MongoException;
import org.bson.Document;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.dao.DataAccessException;
import org.springframework.data.mongodb.core.DocumentCallbackHandler;
import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.data.mongodb.core.query.Query;
import org.springframework.stereotype.Service;

import java.util.ArrayList;
import java.util.List;

@Service
public class MongoDownloadService {

    @Autowired
    private MongoTemplate mongoTemplate;

    public interface MongoCollectionPrinter{
        void print(List<Object> returnList);

        void close();
    }

    /**
     * How to export and download data
     *
     * @param collectionName The name of the collection to export the data from
     * @param batchNum batch write
     * @param printer implement download
     */
    public void export(String collectionName, int batchNum, MongoCollectionPrinter printer){

        List<Object> returnList = new ArrayList<>();
        Query query = new Query();
        mongoTemplate.executeQuery(query, collectionName, new DocumentCallbackHandler() {

            @Override
            public void processDocument(Document document) throws MongoException, DataAccessException {
                returnList.add(document);
                if(returnList.size() % batchNum == 0){
                    printer.print(returnList);
                    returnList.clear();
                }
            }
        });
        if(!returnList.isEmpty()){
            printer.print(returnList);
            returnList.clear();
        }
    }

}

Service implementation and web mapping

package com.haiyoung.biz.db_download;

import com.google.gson.Gson;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.OutputStream;
import java.net.URLEncoder;
import java.util.List;

@Controller
@RequestMapping(value = "/page")
public class MongoDownloadController {

    @Autowired
    private MongoDownloadService mongoDownloadService;

    private static String[] IEBrowserSignals = {"MSIE", "Trident", "Edge"};

    /**
     * Determine the browser type
     *
     * @param request
     * @return
     */
    private static boolean isMSBrowser(HttpServletRequest request){
        String userAgent = request.getHeader("User-Agent");
        for(String signal : IEBrowserSignals){
            if(userAgent.contains(signal)){
                return true;
            }
        }
        return false;
    }

    /**
     * Implement the MongoCollectionPrinter interface
     * Override print and close methods
     */
    public static class DownloadPrinter implements MongoDownloadService.MongoCollectionPrinter {

        private OutputStream output = null;

        private DownloadPrinter(HttpServletResponse response, String fileName) {
            response.reset();// Clear the status code and headers in the response
            response.setContentType("application/x-msdownload");//Set the file type
            response.setHeader("Content-Disposition",
                    "attachment; filename=\""+fileName+"\"");// set the file name

            try {
                output = response.getOutputStream();// Get the output stream
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }

        @Override
        public void print(List<Object> returnList) {
            try {
                output.write(new Gson().toJson(returnList).getBytes("UTF-8"));
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }

        @Override
        public void close() {
            try {
                output.flush();
                output.close();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }finally {
                if (output !=null){
                    try {
                        output.close();
                    } catch (IOException e) {
                        throw new RuntimeException(e);
                    }
                }
            }
        }
    }

    @RequestMapping(value = "/download")
    public void export(HttpServletRequest request, HttpServletResponse response,
                       @RequestParam(value = "collectionName") String collectionName){
        try {
            String fileName = collectionName+".txt";
            if(isMSBrowser(request)){
                fileName = URLEncoder.encode(fileName, "UTF-8");
            }else{
                fileName = new String(fileName.getBytes("UTF-8"),"ISO-8859-1");
            }

            DownloadPrinter printer = new DownloadPrinter(response, fileName);
            mongoDownloadService.export(collectionName, 300, printer);
            printer.close();
        }catch (Exception e){
            throw new RuntimeException(e);
        }
    }
}

Source code link: https://github.com/Haiyoung/HyProject/tree/master/database-download