尝试添加具有指定排序属性的列时，我得到了 NPE。关于我做错了什么的任何想法？
这是课程：
@Entity
@Table(name="checklist_template")
public class CheckListTemplate extends DomainObject implements Comparable<CheckListTemplate>, Serializable {
private static final long serialVersionUID = 2959377496669050427L;
@Id
@GeneratedValue
private Long id;
@Column(nullable=false)
private String name;
public CheckListTemplate() {}
public CheckListTemplate(String name) {
this.name = name;
}
//some other attributes, getters, setters etc
}
这是代码：
public class CheckListTemplateDataPanel extends Panel {
@SpringBean
public ChecklistTemplateService checklistTemplateService;
DataTable<CheckListTemplate> table;
NavigationToolbar navigationToolbar;
ChecklistTemplateProvider checklistTemplateProvider;
public CheckListTemplateDataPanel(String id) {
super(id);
IColumn[] columns = new IColumn[1];
columns[0] = new PropertyColumn<CheckListTemplate>(Model.of("Name"), "name", "name"); //this is what generates the exception. if i ignore the third argument, the code works but i get no link to click for sorting
table = new DataTable<CheckListTemplate>("datatable", columns, checklistTemplateProvider = new ChecklistTemplateProvider(), 10);
table.setOutputMarkupId(true);
table.addBottomToolbar(navigationToolbar = new NavigationToolbar(table));
table.addTopToolbar(new HeadersToolbar(table, null));
add(table);
}
private class ChecklistTemplateProvider extends SortableDataProvider<CheckListTemplate> {
public ChecklistTemplateProvider() {
setSort("name", true);
}
@Override
public Iterator<? extends CheckListTemplate> iterator(int first, int count) {
return checklistTemplateService.findAll(new PageRequest(table.getCurrentPage(), count)).iterator();
}
@Override
public int size() {
return safeLongToInt(checklistTemplateService.count());
}
@Override
public IModel<CheckListTemplate> model(CheckListTemplate object) {
return Model.of(object);
}
public void setFilterString(String filterString){
this.filterString = filterString;
}
}
public static int safeLongToInt(long l) {
if (l < Integer.MIN_VALUE || l > Integer.MAX_VALUE) {
throw new IllegalArgumentException
(l + " cannot be cast to int without changing its value.");
}
return (int) l;
}
}
这是一个例外：
2012 May 03 13:58:58,480[ERROR] - RequestCycle - Exception in rendering component: [MarkupContainer [Component id = header]]
org.apache.wicket.WicketRuntimeException: Exception in rendering component: [MarkupContainer [Component id = header]]
at org.apache.wicket.Component.renderComponent(Component.java:2729)
at org.apache.wicket.MarkupContainer.onRender(MarkupContainer.java:1539)
at org.apache.wicket.Component.render(Component.java:2521)
at org.apache.wicket.MarkupContainer.renderNext(MarkupContainer.java:1441)
at org.apache.wicket.MarkupContainer.renderComponentTagBody(MarkupContainer.java:1604)
at org.apache.wicket.MarkupContainer.onComponentTagBody(MarkupContainer.java:1528)
at org.apache.wicket.Component.renderComponent(Component.java:2690)
at org.apache.wicket.MarkupContainer.onRender(MarkupContainer.java:1539)
at org.apache.wicket.Component.render(Component.java:2521)
at org.apache.wicket.markup.repeater.AbstractRepeater.renderChild(AbstractRepeater.java:122)
at org.apache.wicket.markup.repeater.AbstractRepeater.onRender(AbstractRepeater.java:103)
at org.apache.wicket.Component.render(Component.java:2521)
at org.apache.wicket.MarkupContainer.renderNext(MarkupContainer.java:1441)
at org.apache.wicket.MarkupContainer.renderComponentTagBody(MarkupContainer.java:1604)
at org.apache.wicket.MarkupContainer.renderAssociatedMarkup(MarkupContainer.java:697)
at org.apache.wicket.markup.html.panel.Panel.onComponentTagBody(Panel.java:114)
at org.apache.wicket.Component.renderComponent(Component.java:2690)
at org.apache.wicket.MarkupContainer.onRender(MarkupContainer.java:1539)
at org.apache.wicket.Component.render(Component.java:2521)
at org.apache.wicket.extensions.markup.html.repeater.data.table.DataTable$ToolbarContainer.onRender(DataTable.java:429)
at org.apache.wicket.Component.render(Component.java:2521)
at org.apache.wicket.markup.repeater.AbstractRepeater.renderChild(AbstractRepeater.java:122)
at org.apache.wicket.markup.repeater.AbstractRepeater.onRender(AbstractRepeater.java:103)
at org.apache.wicket.Component.render(Component.java:2521)
at org.apache.wicket.MarkupContainer.renderNext(MarkupContainer.java:1441)
at org.apache.wicket.MarkupContainer.renderComponentTagBody(MarkupContainer.java:1604)
at org.apache.wicket.MarkupContainer.renderAssociatedMarkup(MarkupContainer.java:697)
at org.apache.wicket.markup.html.panel.Panel.onComponentTagBody(Panel.java:114)
at org.apache.wicket.Component.renderComponent(Component.java:2690)
at org.apache.wicket.MarkupContainer.onRender(MarkupContainer.java:1539)
at org.apache.wicket.Component.render(Component.java:2521)
at org.apache.wicket.MarkupContainer.renderNext(MarkupContainer.java:1441)
at org.apache.wicket.MarkupContainer.renderComponentTagBody(MarkupContainer.java:1604)
at org.apache.wicket.MarkupContainer.renderAssociatedMarkup(MarkupContainer.java:697)
at org.apache.wicket.markup.html.panel.Panel.onComponentTagBody(Panel.java:114)
at org.apache.wicket.Component.renderComponent(Component.java:2690)
at org.apache.wicket.MarkupContainer.onRender(MarkupContainer.java:1539)
at org.apache.wicket.Component.render(Component.java:2521)
at org.apache.wicket.MarkupContainer.renderNext(MarkupContainer.java:1441)
at org.apache.wicket.MarkupContainer.renderComponentTagBody(MarkupContainer.java:1604)
at org.apache.wicket.MarkupContainer.onComponentTagBody(MarkupContainer.java:1528)
at org.apache.wicket.Component.renderComponent(Component.java:2690)
at org.apache.wicket.MarkupContainer.onRender(MarkupContainer.java:1539)
at org.apache.wicket.Component.render(Component.java:2521)
at org.apache.wicket.MarkupContainer.autoAdd(MarkupContainer.java:229)
at org.apache.wicket.markup.resolver.MarkupInheritanceResolver.resolve(MarkupInheritanceResolver.java:66)
at org.apache.wicket.markup.resolver.ComponentResolvers.resolve(ComponentResolvers.java:81)
at org.apache.wicket.MarkupContainer.renderNext(MarkupContainer.java:1445)
at org.apache.wicket.MarkupContainer.renderComponentTagBody(MarkupContainer.java:1604)
at org.apache.wicket.MarkupContainer.onComponentTagBody(MarkupContainer.java:1528)
at org.apache.wicket.Component.renderComponent(Component.java:2690)
at org.apache.wicket.MarkupContainer.onRender(MarkupContainer.java:1539)
at org.apache.wicket.Component.render(Component.java:2521)
at org.apache.wicket.MarkupContainer.autoAdd(MarkupContainer.java:229)
at org.apache.wicket.markup.resolver.MarkupInheritanceResolver.resolve(MarkupInheritanceResolver.java:73)
at org.apache.wicket.markup.resolver.ComponentResolvers.resolve(ComponentResolvers.java:81)
at org.apache.wicket.MarkupContainer.renderNext(MarkupContainer.java:1445)
at org.apache.wicket.MarkupContainer.renderComponentTagBody(MarkupContainer.java:1604)
at org.apache.wicket.MarkupContainer.onComponentTagBody(MarkupContainer.java:1528)
at org.apache.wicket.Component.renderComponent(Component.java:2690)
at org.apache.wicket.MarkupContainer.onRender(MarkupContainer.java:1539)
at org.apache.wicket.Component.render(Component.java:2521)
at org.apache.wicket.MarkupContainer.autoAdd(MarkupContainer.java:229)
at org.apache.wicket.markup.resolver.MarkupInheritanceResolver.resolve(MarkupInheritanceResolver.java:66)
at org.apache.wicket.markup.resolver.ComponentResolvers.resolve(ComponentResolvers.java:81)
at org.apache.wicket.MarkupContainer.renderNext(MarkupContainer.java:1445)
at org.apache.wicket.MarkupContainer.renderComponentTagBody(MarkupContainer.java:1604)
at org.apache.wicket.MarkupContainer.onComponentTagBody(MarkupContainer.java:1528)
at org.apache.wicket.Component.renderComponent(Component.java:2690)
at org.apache.wicket.MarkupContainer.onRender(MarkupContainer.java:1539)
at org.apache.wicket.Component.render(Component.java:2521)
at org.apache.wicket.MarkupContainer.autoAdd(MarkupContainer.java:229)
at org.apache.wicket.markup.resolver.MarkupInheritanceResolver.resolve(MarkupInheritanceResolver.java:73)
at org.apache.wicket.markup.resolver.ComponentResolvers.resolve(ComponentResolvers.java:81)
at org.apache.wicket.MarkupContainer.renderNext(MarkupContainer.java:1445)
at org.apache.wicket.MarkupContainer.renderComponentTagBody(MarkupContainer.java:1604)
at org.apache.wicket.MarkupContainer.onComponentTagBody(MarkupContainer.java:1528)
at org.apache.wicket.Component.renderComponent(Component.java:2690)
at org.apache.wicket.MarkupContainer.onRender(MarkupContainer.java:1539)
at org.apache.wicket.Component.render(Component.java:2521)
at org.apache.wicket.MarkupContainer.autoAdd(MarkupContainer.java:229)
at org.apache.wicket.markup.resolver.MarkupInheritanceResolver.resolve(MarkupInheritanceResolver.java:66)
at org.apache.wicket.markup.resolver.ComponentResolvers.resolve(ComponentResolvers.java:81)
at org.apache.wicket.MarkupContainer.renderNext(MarkupContainer.java:1445)
at org.apache.wicket.MarkupContainer.renderComponentTagBody(MarkupContainer.java:1604)
at org.apache.wicket.MarkupContainer.onComponentTagBody(MarkupContainer.java:1528)
at org.apache.wicket.Component.renderComponent(Component.java:2690)
at org.apache.wicket.MarkupContainer.onRender(MarkupContainer.java:1539)
at org.apache.wicket.Component.render(Component.java:2521)
at org.apache.wicket.MarkupContainer.autoAdd(MarkupContainer.java:229)
at org.apache.wicket.markup.resolver.MarkupInheritanceResolver.resolve(MarkupInheritanceResolver.java:73)
at org.apache.wicket.markup.resolver.ComponentResolvers.resolve(ComponentResolvers.java:81)
at org.apache.wicket.MarkupContainer.renderNext(MarkupContainer.java:1445)
at org.apache.wicket.MarkupContainer.renderAll(MarkupContainer.java:1555)
at org.apache.wicket.Page.onRender(Page.java:1594)
at org.apache.wicket.Component.render(Component.java:2521)
at org.apache.wicket.Page.renderPage(Page.java:932)
at org.apache.wicket.request.target.component.BookmarkablePageRequestTarget.respond(BookmarkablePageRequestTarget.java:261)
at org.apache.wicket.request.AbstractRequestCycleProcessor.respond(AbstractRequestCycleProcessor.java:105)
at org.apache.wicket.RequestCycle.processEventsAndRespond(RequestCycle.java:1258)
at org.apache.wicket.RequestCycle.step(RequestCycle.java:1329)
at org.apache.wicket.RequestCycle.steps(RequestCycle.java:1436)
at org.apache.wicket.RequestCycle.request(RequestCycle.java:545)
at org.apache.wicket.protocol.http.WicketFilter.doGet(WicketFilter.java:486)
at org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:319)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter.doFilterInternal(OpenEntityManagerInViewFilter.java:113)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.__invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.NullPointerException
at org.apache.wicket.extensions.markup.html.repeater.data.sort.OrderByLink$CssModifier.onComponentTag(OrderByLink.java:208)
at org.apache.wicket.Component.renderComponentTag(Component.java:4270)
at org.apache.wicket.Component.renderComponent(Component.java:2681)
... 125 more