懒惰加载无数据

Question

我试图在primefaces数据表设置中实现延迟加载。目前，在没有延迟加载实现的情况下，这是可行的，但是在实现延迟加载后，我在datatable中没有得到任何数据。但是，我可以在我的LoadData方法中打印我的列表，以验证数据是否正在加载到我的列表中，但一旦返回我的LazyModel并尝试加载datatable，似乎就会出现问题。这可能只是我忽略的一些简单的事情。非常感谢您的帮助！

这是我的屏幕截图列表制作人类代码：

    @ManagedBean
    @RequestScoped
    public class ScreenshotListProducer implements Serializable  {
       private static final long serialVersionUID = 1L;
       @Inject
       private EntityManager em;

       private List<Screenshot> screenshots;

       private LazyDataModel<Screenshot> lazyModel = null;

       private int pageSize = 5;

       public void setPageSize(int pageSize) {
           this.pageSize = pageSize;
       }

       public int getPageSize() {
           return pageSize;
       }

       @Produces
       @Named
       public List<Screenshot> getScreenshots() {
          System.out.println("************* getting screenshots list **************");
          return screenshots;
       }

       @PostConstruct
       public void LoadData() {
            lazyModel = new LazyDataModel<Screenshot>() {
                private static final long serialVersionUID = 1L;

                    @Override
                    public List<Screenshot> load(int first, int pageSize, String sortField, SortOrder sortOrder, Map<String,String> filters) {      
                    int start = first;
                    int end = first + pageSize;

                    try {
                        CriteriaBuilder cb = em.getCriteriaBuilder();
                        CriteriaQuery<Screenshot> criteria = cb.createQuery(Screenshot.class);
                        Root<Screenshot> screenshot = criteria.from(Screenshot.class);
                        criteria.select(screenshot).orderBy(cb.asc(screenshot.get("time")));

                        TypedQuery<Screenshot> s = em.createQuery(criteria);
                        s.setMaxResults(end - start);
                        s.setFirstResult(start);

                        screenshots = s.getResultList();
                        System.out.println("************* lazy screenshot list created **************");
                        for (Screenshot lazylist : screenshots) {
                          System.out.println("id numbers in lazy list: " + lazylist.getId());
                        }
                    } catch (NullPointerException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }

                    return screenshots;
                  }
            };
       }

   public LazyDataModel<Screenshot> getLazyModel() {
        return lazyModel;
    }

这是我的截图课：

@Entity
@XmlRootElement
@Table(name="Test2012", uniqueConstraints = @UniqueConstraint(columnNames = "id"))
public class Screenshot implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue
    @Column(name = "id", columnDefinition="INT")
    private Long id;

    private Timestamp time;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public Timestamp getTime() {
        return time;
    }

    public void setTime(Timestamp time) {
        this.time = time;
    }   
}

这是我的xhtml代码：

    <p:dataTable id="table1" var="scrshot" rowKey="#{scrshot.id}" value="#{screenshotListProducer.lazyModel}" paginator="true" rows="7" paginatorPosition="bottom" 
                 paginatorTemplate="{CurrentPageReport}  {FirstPageLink} {PreviousPageLink} {PageLinks} {NextPageLink} {LastPageLink} {RowsPerPageDropdown}"  
                 rowsPerPageTemplate="7,20,50,100" widgetVar="dataTable" currentPageReportTemplate="(Number of Records: {totalRecords})"
                 emptyMessage="No screenshot data found with given criteria" lazy="true" scrollable="true" draggableColumns="true" scrollHeight="217" style="width: 100%;">  
          <f:facet name="header">  
            <p:outputPanel>  
                <h:outputText value="Search all fields: "/>  
                <p:inputText id="globalFilter" onkeyup="dataTable.filter()"/>  
            </p:outputPanel>  
          </f:facet> 
          <p:column selectionMode="multiple"/>  
          <p:column id="time" headerText="Time" sortBy="#{scrshot.time}" filterBy="#{scrshot.time}" filterMatchMode="startsWith">  
            <h:outputText value="#{scrshot.time}"/>  
          </p:column>   
          <p:column id="id" headerText="ID" sortBy="#{scrshot.id}" filterBy="#{scrshot.id}" filterOptions="#{scrshot.id}" filterMatchMode="exact">  
            <h:outputText value="#{scrshot.id}"/>  
          </p:column>  
    </p:dataTable>

Answer 1

在懒惰加载器的情况下，您必须在加载方法中设置记录的总计数，如this.setRowCount（total_records_that_are_there）；。懒惰加载器需要确定将有多少页，以便可以确定数据表上的下一个和上一个按钮（启用/禁用）。像[0是开始]和[总/rowsize]是总页数，但是你获取使用加载方法（first和page ezie=