我试图用我从 DynamoDB 表（Amazon NoSQL DB）中检索的数据填充 JSF 数据表。目前一切正常，直到对 scanResults 的迭代。调试器显示我的 scanResult 有一个所有帐户的列表，但是当我尝试迭代这些结果以构建我的列表时，似乎没有任何内容添加到 allUserSummary 列表中，并且最终出现空指针异常。
基本用户 POJO：
public class User {
private String uuid;
public User(String uuid) {
this.uuid = uuid;
}
}
托管bean：
private List<User> allUserSummary;
private List<String> uuid;
private User selectedUser;
public List<User> getAllUserSummary() throws Exception {
populateData();
return allUserSummary;
}
private void populateData() throws Exception {
// Create a new AmazonDynamoDBClient and mapper
AmazonDynamoDBClient client = dynamoClient.getDynamoClient();
DynamoDBMapper mapper = new DynamoDBMapper(client);
try {
// Create a new scan expression and filter to find the required data from the db
DynamoDBScanExpression scanExpression = new DynamoDBScanExpression();
Map<String, Condition> scanFilter = new HashMap<String, Condition>();
Condition scanCondition = new Condition().withComparisonOperator(ComparisonOperator.NOT_NULL);
scanFilter.put("uuid", scanCondition);
scanExpression.setScanFilter(scanFilter);
// Run the scan
List scanResults = mapper.scan(UserAccounts.class, scanExpression);
// Iterate over the scanned results and add the required data to a new User
for (Iterator it = scanResults.iterator(); it.hasNext();) {
allUserSummary.add(new User(scanResults.get(1).toString()));
}
} catch (Exception e) {
// TODO
}
}
数据表（我使用 primefaces，但问题与标准 JSF DT 相同）：
<h:form>
<pou:dataTable id="users"
var="user"
value="#{accountManager.allUserSummary}"
paginator="true"
rows="10"
selection="#{accountManager.selectedUser}">
<f:facet name="header">
UUID
</f:facet>
<pou:column selectionMode="multiple" />
<pou:column headerText="Uuid">
#{user.uuid}
</pou:column>
<f:facet name="footer">
<pou:commandButton id="multiViewButton"
value="View"
icon="ui-icon-search"
update=""
oncomplete=""/>
</f:facet>
</pou:dataTable>
</h:form>
堆栈跟踪：
java.lang.IllegalArgumentException: ""
at javax.faces.component.UIComponentBase.findComponent(UIComponentBase.java:570)
at org.primefaces.util.ComponentUtils.findClientIds(ComponentUtils.java:244)
at org.primefaces.renderkit.CoreRenderer.buildAjaxRequest(CoreRenderer.java:222)
at org.primefaces.component.commandbutton.CommandButtonRenderer.encodeMarkup(CommandButtonRenderer.java:81)
at org.primefaces.component.commandbutton.CommandButtonRenderer.encodeEnd(CommandButtonRenderer.java:53)
at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:875)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1764)
at org.primefaces.component.datatable.DataTableRenderer.encodeFacet(DataTableRenderer.java:839)
at org.primefaces.component.datatable.DataTableRenderer.encodeTFoot(DataTableRenderer.java:823)
at org.primefaces.component.datatable.DataTableRenderer.encodeRegularTable(DataTableRenderer.java:247)
at org.primefaces.component.datatable.DataTableRenderer.encodeMarkup(DataTableRenderer.java:224)
at org.primefaces.component.datatable.DataTableRenderer.encodeEnd(DataTableRenderer.java:108)
at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:875)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1764)
at javax.faces.render.Renderer.encodeChildren(Renderer.java:168)
at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:845)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1757)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1760)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1760)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:402)
at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:131)
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:288)
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:121)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:594)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1542)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:343)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
at org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:61)
at org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108)
at org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:137)
at org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)
at org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:66)
at org.apache.shiro.web.servlet.AdviceFilter.executeChain(AdviceFilter.java:108)
at org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:137)
at org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)
at org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:66)
at org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:449)
at org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:365)
at org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90)
at org.apache.shiro.subject.support.SubjectCallable.call(SubjectCallable.java:83)
at org.apache.shiro.subject.support.DelegatingSubject.execute(DelegatingSubject.java:380)
at org.apache.shiro.web.servlet.AbstractShiroFilter.doFilterInternal(AbstractShiroFilter.java:362)
at org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:279)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:161)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:331)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231)
at com.sun.enterprise.v3.services.impl.ContainerMapper$AdapterCallable.call(ContainerMapper.java:317)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:195)
at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:849)
at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:746)
at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1045)
at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:228)
at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
at java.lang.Thread.run(Thread.java:680)