public void saveToFile (String fileName) {

    	ZipOutputStream zipOut = null;
    	// create new ZIP file
        try {
			zipOut = new ZipOutputStream(new FileOutputStream(fileName));
		} catch (FileNotFoundException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
			return;
		}
        // enable compression
        zipOut.setMethod(ZipOutputStream.DEFLATED);
        // set compression level to max.
        zipOut.setLevel (9);

        // save trips
        try {
			tripDB.write(zipOut);
		} catch (Exception e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		}
        
        // save rosters
        try {
			rosterDB.write(zipOut);
		} catch (Exception e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		}

        // save rivers
        try {
			riverDB.write(zipOut);
		} catch (Exception e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		}
        
        try {
			zipOut.close();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

    }