我正在使用PrimeFace4.0，JSF 2.2，Java和XHTML。我有一个字符串值，我需要从一个bean传递到另一个bean。在一个XHTML页面上选择该值，当用户单击以选择时，将启动新的网页。我可以从我的服务器输出中看到第一个bean（TestSelectBean）成功收集的值，但我似乎无法将它放入下一个bean（TargetBeanFranz）。当String被硬编码到bean中时，它可以正常工作。但是，当我尝试使用托管属性根据用户输入调用它时，我在代码行（85）处得到一个NullPointer，我正在尝试使用它。
第一个HTML： testselect.xhtml
//irrelevant code
<p:layoutUnit position="center">
<h:form>
<p:selectOneRadio id="Test" value="#{testSelectBean.selectedNameOfExperiments}" >
<f:selectItems id="selectedNameOfExperiments" value="#{testSelectBean.nameofexperiments}" var="entry" itemValue="#{entry.key}" itemLabel="#{entry.value}" />
</p:selectOneRadio>
<p:commandLink id="nonAjax" action="open" actionListener="#{testSelectBean.getParameters}" style="margin-right:20px;" ajax="false">
<h:outputText value="Submit" />
</p:commandLink>
</h:form>
</p:layoutUnit>
选择selectedNameOfExperiments的用户被简单地传递给 TestSelectBean ：
@ManagedBean(name = "testSelectBean", eager = true)
@SessionScoped
public class TestSelectBean implements Serializable {
private static final long serialVersionUID = 1L;
protected String selectedNameOfExperiments;
private final Map<String, String> nameofexperiments;
private transient String selected;
public TestSelectBean() throws SQLException {
selected = new String();
nameofexperiments = new HashMap<String, String>();
XYexpdataServiceAdapter xydata = new XYexpdataServiceAdapterImpl();
List<String> dbnameofexperiments = xydata.getNameofexperiments();
for (String ta : dbnameofexperiments) {
nameofexperiments.put(ta, ta);
}
}
public String getSelectedNameOfExperiments() {
return selectedNameOfExperiments;
}
public void setSelectedNameOfExperiments(String selectedNameOfExperiments1) {
this.selectedNameOfExperiments = selectedNameOfExperiments1;
}
public Map<String, String> getNameofexperiments() {
return nameofexperiments;
}
public void getParameters() {
FacesContext.getCurrentInstance().addMessage(null, new FacesMessage("You've selected Experiment:" + selectedNameOfExperiments));
System.out.println("You've selected Experiment:" + selectedNameOfExperiments);
}
}
但是，除非Experiment被硬编码到TargetBeanFranz中，否则XHTML FranzwPopup 将无法启动。
//irrelevant code
<p:layoutUnit position="center">
<p:panelGrid columns="2" style=" font-size: 14">
<h:outputLabel value="Description" style="font-size: 20"/>
<h:outputText value="Neutron-induced production of protons, deuterons and tritons in Copper and Bismuth."/>
<h:outputLabel value="Reference" style="font-size: 20"/>
<h:outputText value="Nuclear Physics A510 (1990) 774-802 (Franz, et. al.)"/>
</p:panelGrid>
<form action="http://localhost:8080/primefaces/faces/handle.xhtml" method="get" name="login" onsubmit="process();
return false;" style="overflow-y: scroll">
Click to display chart data in a table.<br />
<input type="submit" value="Display"/>
</form>
<h:form>
<h:panelGrid columns="4" cellpadding="5">
<p:selectCheckboxMenu id="menu1" value="#{targetBeantFranz.selectedTargets}" label="Targets" filter="true" filterMatchMode="startsWith"
panelStyle="width:220px">
<f:selectItems value="#{targetBeantFranz.targets}" />
</p:selectCheckboxMenu>
<p:selectCheckboxMenu id="menu2" value="#{targetBeantFranz.selectedSecondaries}" label="Secondaries" filter="true" filterMatchMode="startsWith"
panelStyle="width:220px">
<f:selectItems value="#{targetBeantFranz.secondaries}" />
</p:selectCheckboxMenu>
<p:selectCheckboxMenu id="menu3" value="#{targetBeantFranz.selectedReactions}" label="Reactions" filter="true" filterMatchMode="startsWith"
panelStyle="width:220px">
<f:selectItems value="#{targetBeantFranz.reactions}" />
</p:selectCheckboxMenu>
<p:selectCheckboxMenu id="menu4" value="#{targetBeantFranz.selectedBeamEnergies}" label="Beam Energy" filter="true" filterMatchMode="startsWith"
panelStyle="width:220px">
<f:selectItems value="#{targetBeantFranz.beamenergies}" />
</p:selectCheckboxMenu>
</h:panelGrid>
<p:panel header="Resulting Plots">
<p:commandLink id="nonAjax" actionListener="#{targetBeantFranz.getParameters}" style="margin-right:20px;" ajax="false">
<button id="change">Submit Query</button>
</p:commandLink>
<div id="container" style="min-width: 310px; margin: 0 auto"></div>
</p:panel>
</h:form>
</p:layoutUnit>
//more irrelevant
相反，我在 TargetBeanFranz 的第85行获得了一个NPE，我尝试初始化Experiment。
//stuff
@ManagedBean(name = "targetBeantFranz", eager = true)
@SessionScoped
public class TargetBeanFranz implements Serializable {
@ManagedProperty(value="#{testSelectBean}")
private TestSelectBean testSelectBean;
public TestSelectBean getTestSelectBean(){
return testSelectBean;
}
public void setTestSelectBean (TestSelectBean testSelectBean) {
this.testSelectBean = testSelectBean;
}
private static final long serialVersionUID = 1L;
private String Experiment;
//more stuff
public TargetBeanFranz() throws SQLException {
targets = new HashMap<String, String>();
selectedTargets = new ArrayList<String>();
secondaries = new HashMap<String, String>();
selectedSecondaries = new ArrayList<String>();
reactions = new HashMap<String, String>();
selectedReactions = new ArrayList<String>();
beamenergies = new HashMap<String, String>();
selectedBeamEnergies = new ArrayList<String>();
seriesDataArray = new ArrayList<String>();
seriesDataArArray = new ArrayList<ArrayList<String>>();
seriesNameArray = new ArrayList<String>();
seriesToolTipArray = new ArrayList<String>();
seriesErrorArray = new ArrayList<String>();
seriesErrorArArray = new ArrayList<ArrayList<String>>();
allselected = new ArrayList<XYexpdata>();
Experiment = testSelectBean.getSelectedNameOfExperiments(); //This is line 85 and where I'm getting the NPE.
XYexpdataServiceAdapter xydata = new XYexpdataServiceAdapterImpl();
List<String> dbtargets = xydata.getTargetNamesbyExperiment(Experiment);
for (String ta : dbtargets) {
targets.put(ta, ta);
}
List<String> dbsecondaries = xydata.getSecondaryNamesbyExperiment(Experiment);
for (String ta : dbsecondaries) {
secondaries.put(ta, ta);
}
List<String> dbreactions = xydata.getReactionNamesbyExperiment(Experiment);
for (String ta : dbreactions) {
reactions.put(ta, ta);
}
List<String> dbbeamenergies = xydata.getBeamEnergybyExperiment(Experiment);
for (String ta : dbbeamenergies) {
beamenergies.put(ta, ta);
}
}
//more code
答案 0 :(得分：0)
我认为您的问题的原因是，您的命令链接中的动作侦听器的签名不匹配。
bean中的方法必须是以下类型：
public void getParameters(javax.faces.ActionEvent event) {
.....
}
如果您使用的是Java EE 7，则还应避免使用javax.faces.bean包中的注释，因为它们已被放弃。使用CDI bean，它可以让生活更轻松：
@Named
@SessionScoped
public class TestSelectBean {
...
}
@Named
@SessionScoped
public class TargetBeanFranz {
@Inject
private TestSelectBean testSelectBean;
....
}
在此处查看有关CDI主题的更多信息：Backing beans (@ManagedBean) or CDI Beans (@Named)?