Java <；中的NullPointerException；p:ajax>；侦听器函数：Primefaces5

我有Primefaces“selectCheckboxMenu”，希望在表中动态显示选中的复选框

我的xhtml文件内容是：

        <p:selectCheckboxMenu id="formRole"
            value="#{formSecurityBean.roleMulti}" filter="true"
            filterMatchMode="contains" label="Select"
            rendered="#{formSecurityBean.renderFormRoleGrid}">
            <f:selectItems value="#{formSecurityBean.formRoleList}" var="role"
                itemValue="#{role.roleID}" itemLabel="#{role.roleName}" />
            <p:ajax listener="#{formSecurityAction.testing}" update="roleAction"></p:ajax>
        </p:selectCheckboxMenu>
        <p:dataTable id="roleAction" var="selectedFormRole"
            value="#{formSecurityBean.selectedRoleList}">
            <p:column>
                <h:outputLabel value="#{selectedFormRole.roleName}" />
            </p:column>
        </p:dataTable>

selectedRoleList.add（formSecurityBean.getFormRoleMap（）.get（i））；

上述代码行中似乎存在问题。
您添加了两次空值

---

大小变为2，但它仍然为Null，当您对其调用toString（）时，NPE将出现。

在`p:ajax中没有NPE。Afaics在您的系统中有一个NPEcode@Kukeltje，我认为这个NPE与jsf的生命周期（类似于列表的并发访问/修改）有关，这就是原因。否则，如果代码进入方法，并且有一个NPE，那么在代码中仍然存在，代码执行将不会进入循环。可能与生命周期相关，但仍然是您的代码。创建mcve并精确定位NPE的确切位置。在所有这些分析之后（这就是复制件所解释的），带着一个特定的问题回到这里。你是对的。这就是当你在同一行代码上坐上几个小时，思考所有可能的事情，而忘记基本的东西时会发生的事情。我想删除这个问题。如果我认为这是毫无价值的，那么这是正确的政策吗？它确实没有任何价值（我的复制建议是正确的），不接受答案，并把它标记为复制品，我想会更好。还有自动删除它们的服务。不确定接受后是否会发生这种情况

public void testing() {

    List<RoleResponseTO> selectedRoleList = new ArrayList<RoleResponseTO>();
    if (formSecurityBean.getRoleMulti() != null
            && formSecurityBean.getRoleMulti().length > 0) {
        for (int i = 0; i < formSecurityBean.getRoleMulti().length; i++) {
            selectedRoleList.add(formSecurityBean.getFormRoleMap().get(i));
        }
        formSecurityBean.setSelectedRoleList(selectedRoleList);
    }

    if (formSecurityBean.getSelectedRoleList() != null) {
        System.out.println(formSecurityBean.getSelectedRoleList().size());
        Iterator<RoleResponseTO> it = formSecurityBean
                .getSelectedRoleList().iterator();
        while (it.hasNext()) {
            RoleResponseTO tmp = it.next();
            System.out.println(tmp.getRoleName());      //HERE NullPointerException
        }
    }
}

20:26:25,505 INFO  [stdout] (http-0.0.0.0-0.0.0.0-8080-1) 2

20:26:44,192 WARNING [javax.enterprise.resource.webcontainer.jsf.lifecycle] (http-0.0.0.0-0.0.0.0-8080-1) /security/formSecurity.xhtml @75,75 listener="#{formSecurityAction.testing}": java.lang.NullPointerException: javax.el.ELException: /security/formSecurity.xhtml @75,75 listener="#{formSecurityAction.testing}": java.lang.NullPointerException
    at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:111) [jsf-impl-2.1.7-jbossorg-2.jar:]
    at org.primefaces.behavior.ajax.AjaxBehaviorListenerImpl.processAjaxBehavior(AjaxBehaviorListenerImpl.java:53) [primefaces-5.1.jar:5.1]
    at javax.faces.event.AjaxBehaviorEvent.processListener(AjaxBehaviorEvent.java:113) [jboss-jsf-api_2.1_spec-2.0.1.Final.jar:2.0.1.Final]
    at javax.faces.component.behavior.BehaviorBase.broadcast(BehaviorBase.java:106) [jboss-jsf-api_2.1_spec-2.0.1.Final.jar:2.0.1.Final]
    at javax.faces.component.UIComponentBase.broadcast(UIComponentBase.java:760) [jboss-jsf-api_2.1_spec-2.0.1.Final.jar:2.0.1.Final]
    at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:794) [jboss-jsf-api_2.1_spec-2.0.1.Final.jar:2.0.1.Final]
    at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1259) [jboss-jsf-api_2.1_spec-2.0.1.Final.jar:2.0.1.Final]
    at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:81) [jsf-impl-2.1.7-jbossorg-2.jar:]
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101) [jsf-impl-2.1.7-jbossorg-2.jar:]
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118) [jsf-impl-2.1.7-jbossorg-2.jar:]
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:593) [jboss-jsf-api_2.1_spec-2.0.1.Final.jar:2.0.1.Final]
.
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Caused by: java.lang.NullPointerException
    at com.alt.security.controller.FormSecurityAction.testing(FormSecurityAction.java:352) [classes:]
    at com.alt.security.controller.FormSecurityAction$Proxy$_$$_WeldClientProxy.testing(FormSecurityAction$Proxy$_$$_WeldClientProxy.java) [classes:]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) [rt.jar:1.7.0_51]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) [rt.jar:1.7.0_51]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) [rt.jar:1.7.0_51]
    at java.lang.reflect.Method.invoke(Method.java:606) [rt.jar:1.7.0_51]
.
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