结果集。next()未迭代

我的代码:

public class DisplayImage extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String connectionURL = "jdbc:mysql://localhost:3306/ycards";
        java.sql.Connection con = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            con = DriverManager.getConnection(connectionURL, "root", "letmein");
            PreparedStatement st1 = con.prepareStatement("select image from pictures");
            ResultSet rs1 = st1.executeQuery();
            String imgLen = "";
            while (rs1.next()) {
                imgLen = rs1.getString(1);
                int len = imgLen.length();
                byte[] rb = new byte[len];
                InputStream readImg = rs1.getBinaryStream(1);
                readImg.read(rb, 0, len);
                response.setContentType("image/png");
                response.getOutputStream().write(rb, 0, len);
                response.getOutputStream().flush();
            }
            st1.close();
        } catch (Exception e) {
            e.printStackTrace();
        }

    }
}

输出:

它只显示第一行,不显示其余的,为什么要这样做?注意:在本例中,密码和用户名不是真实的。