java - How to return a file with Google Cloud Endpoints? -

i have method generate csv file db records

    public static void generatecsvforattendees( list<attendee> attendeelist ) throws filenotfoundexception     {         printwriter pw = new printwriter(new file("test.csv"));          stringbuilder sb = new stringbuilder();          //header         sb.append( "id" );         sb.append( ',' );         sb.append( "name" );         sb.append( ',' );         sb.append( "lastname" );         sb.append('\n');          //content         for( attendee attendee: attendeelist )         {             sb.append( attendee.getid() );             sb.append( ',' );             sb.append( attendee.getuser().getname() );             sb.append( ',' );             sb.append( attendee.getuser().getlastname() );             sb.append( '\n' );          }          pw.write(sb.tostring());         pw.close();     } 

i method endpoint in order invoke kind of client (web or mobile) download it. in google cloud endpoint documentation there isn't file valid return type. how create , endpoint return file?

here how save file endpoint cloud storage , return url downloading it.

1/ activate google cloud storage in project console

2/ create bucket in cloud storage instance, name bucketname. optional: can set access rights on bucket.

3/ in endpoint class, create gcsservice folllow:

private final gcsservice gcsservice = gcsservicefactory.creategcsservice(new retryparams.builder()         .initialretrydelaymillis(10)         .retrymaxattempts(10)         .totalretryperiodmillis(15000)         .build()); 

4/ in method, create bytearrayoutputstream:

bytearrayoutputstream os = new bytearrayoutputstream(); 

5/ create printer bytearrayoutputstream

6/ following:

bytebuffer buf = bytebuffer.wrap(os.tobytearray()); gcsfilename gcsfilename = new gcsfilename(bucketname, bucketfilename); //bucketfilename =  file name gcsfileoptions options = new gcsfileoptions.builder().mimetype("text/plain").build(); gcsoutputchannel outputchannel = gcsservice.createorreplace(gcsfilename, options); outputchannel.write(buf); outputchannel.close(); 

7/ file should saved cloud storage: have return in string wrapper url open it. following documentation decide url use (depending on whether user shall authenticated or not, see section "a user granted read access object") https://cloud.google.com/storage/docs/cloud-console#_accessing