Question

我目前正在使用vaadin处理一个小的addresstable，只是为了了解一下vaadin。我遇到了一个问题，我想手动对表格的条目进行排序。问题是，当我尝试这样做时，我得到一个NullPointerException：

item.getItemProperty(Columns.NAME).getValue()

我在这里试了几件事。我检查了项目和项目是否为空，item.getItemProperty（Columns.NAME）为null。所以，当我尝试制作一个如果我仍然得到一个NullPointerException

if(item.getItemProperty(Columns.NAME).getValue() == null){}

该值为null，我理解，但我想将此值赋给其他项目，我不知道如何。

SEVERE: Servlet.service() for servlet [com.example.addresstable.AddresstableUI$Servlet] in context with path [/Addresstable] threw exception [com.vaadin.server.ServiceException: java.lang.NullPointerException] with root cause
java.lang.NullPointerException
  at com.vaadin.data.util.IndexedContainer$IndexedContainerProperty.getValue(IndexedContainer.java:898)
  at com.example.addresstable.AddressTable.addAddressToTable(AddressTable.java:114)
  at com.example.addresstable.AddresstableUI.init(AddresstableUI.java:26)
  at com.vaadin.ui.UI.doInit(UI.java:639)
  at com.vaadin.server.communication.UIInitHandler.getBrowserDetailsUI(UIInitHandler.java:222)
  at com.vaadin.server.communication.UIInitHandler.synchronizedHandleRequest(UIInitHandler.java:74)
  at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:41)
  at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1402)
  at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:305)
  at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
  at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
  at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
  at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
  at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
  at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
  at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
  at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
  at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
  at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
  at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
  at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
  at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
  at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
  at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070)
  at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
  at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
  at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
  at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
  at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
  at java.lang.Thread.run(Unknown Source)

Answer 1

IndexedContainer＆＃39; Item是IndexedContainerItem 当调用它getItemProperty时，结果永远不会为空：

@Override
public Property getItemProperty(Object id) {
    return new IndexedContainerProperty(itemId, id);
}

但是当你致电Property＆＃39; getValue时，如果没有itemId或propertyId，它可能为null：

@Override
public T getValue() {
    return (T) items.get(itemId).get(propertyId);
}

可能是Vaadin错误：link

修改

如果要检查容器是否包含该项目，可以执行以下操作：

public class MyIndexedContainer extends IndexedContainer { @Override public Item getUnfilteredItem(Object itemId) { // make it public return super.getUnfilteredItem(itemId); } }

然后

Table table = new Table(); MyIndexedContainer mic = new MyIndexedContainer(); table.setContainerDataSource(mic); //... // check that the container contains the item if (mic.getUnfilteredItem(item) != null) { //... }

NullPointerException不可阻挡

1 个答案: