使用ssh框架，批量插入数据时报如下错误：

java.lang.RuntimeException: Could not execute JDBC batch update; nested exception is org.hibernate.exception.DataException: Could not execute JDBC batch update

com.renren.web.action.AlbumAction.addPhotos(AlbumAction.java:137)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:497)
org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:269)
org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:170)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:425)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:228)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:462)
javax.servlet.http.HttpServlet.service(HttpServlet.java:661)
javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:198)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)

批量保存的action:
AlbumForm af = (AlbumForm) form;

    
    Users u= (Users)request.getSession().getAttribute("loginInfo");
    String userId =u.getId().toString();
    String albumId = request.getParameter("albumId");
    Album  album = (Album) photoServiceImp.findById(Album.class, Integer.valueOf(albumId));
    
    String webSavePath = "/images/upload/"+u.getId()+"/album/"+albumId;        
    String upPath = request.getSession().getServletContext().getRealPath(webSavePath);
    System.out.println(albumId+"--"+userId+"\r\n"+upPath+"\r\n");
    System.out.println("文件个数："+af.getAllPhoto().size());
    //循环上传照片
    for (int i = 0; i < af.getAllPhoto().size(); i++) {
        Photo p = new Photo();
        FormFile photo = af.getPhotos(i);
        System.out.println(photo.getFileName());
        try {
            String saveName = MyFileStream.uploadFile(photo, upPath);                 
            p.setAddTime(new Date());
            p.setAlbum(album);
            p.setPhoto(webSavePath+"/"+saveName); 
            System.out.println(webSavePath+"/"+saveName);
            photoServiceImp.save(p);
            System.out.println("添加的信息"+p.getId()+"--"+p.getAddTime());
            System.out.println("Hashcode"+p.hashCode());
             
        } catch (Exception e) {
            // TODO: handle exception
            throw new RuntimeException(e.getMessage());
        }
    }
    //清空form中的photos数组列表
    //af.clearPhotos();
    return mapping.findForward("goOneAlbumUI");

photo表的主键生成策略是increment；实体类的配置文件，使用反向工程生成的。

为啥报批量更新失败，需要强制flush么？？？困扰许久