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Struts2 list couldn't be resolved

2019-01-19 09:00发布

站内文章 / 前沿技术
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问题:

please help me. I am facing this error for 3 days. I have searched all the examples on the web, but I couldn't figured it out.

These are my files:

struts.xml

...
<action name="menu"  class="com.struts.actions.MenuAction" method="asdf">
<result name="success" type="tiles">struts2tiles.home</result>
</action>
...

menu2.jsp

....
<body>
<s:form action="menu">
    <s:checkboxlist label="What's your favor color" list="colors" name="colors" />

<s:submit value="submit" name="submit" />

</s:form>
</body>

MenuAction

public class MenuAction extends ActionSupport {
    private ArrayList<String> colors;
    private String yourColor;

    public ArrayList<String> getColors() {
        return colors;
    }

    public void setColors(ArrayList<String> colors) {
        this.colors = colors;
    }

    public String getYourColor() {
        return yourColor;
    }

    public void setYourColor(String yourColor) {
        this.yourColor = yourColor;
    }

    public String asdf() {
        colors = new ArrayList<String>();
        colors.add("red");
        colors.add("yellow");
        colors.add("blue");
        colors.add("green");

        return SUCCESS;
    }

    @Override
    public String execute() {
        System.out.println("execute menu action");
        colors = new ArrayList<String>();
        colors.add("red");
        colors.add("yellow");
        colors.add("blue");
        colors.add("green");

        return SUCCESS;
    }

}

Anything I did, still the same error persists:

Dec 22, 2011 10:56:44 PM org.apache.catalina.core.ApplicationDispatcher invoke
SEVERE: Servlet.service() for servlet jsp threw exception
tag 'checkboxlist', field 'list', name 'colors': The requested list key 'colors' could not be resolved as a collection/array/map/enumeration/iterator type. Example: people or people.{name} - [unknown location]
    at org.apache.struts2.components.Component.fieldError(Component.java:237)
    at org.apache.struts2.components.Component.findValue(Component.java:358)
    at org.apache.struts2.components.ListUIBean.evaluateExtraParams(ListUIBean.java:80)
    at org.apache.struts2.components.UIBean.evaluateParams(UIBean.java:856)
    at org.apache.struts2.components.UIBean.end(UIBean.java:510)
    at org.apache.struts2.views.jsp.ComponentTagSupport.doEndTag(ComponentTagSupport.java:42)
    at org.apache.jsp.jsp.common.menu2_jsp._jspx_meth_s_005fcheckboxlist_005f0(menu2_jsp.java:166)
    at org.apache.jsp.jsp.common.menu2_jsp._jspx_meth_s_005fform_005f0(menu2_jsp.java:122)
    at org.apache.jsp.jsp.common.menu2_jsp._jspService(menu2_jsp.java:84)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:433)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:389)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:333)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:684)
    at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:593)
    at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:530)
    at org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:927)
    at org.apache.jasper.runtime.PageContextImpl.doInclude(PageContextImpl.java:684)
    at org.apache.jasper.runtime.PageContextImpl.include(PageContextImpl.java:678)
    at org.apache.tiles.jsp.context.JspTilesRequestContext.include(JspTilesRequestContext.java:80)
    at org.apache.tiles.jsp.context.JspTilesRequestContext.dispatch(JspTilesRequestContext.java:73)
    at org.apache.tiles.context.TilesRequestContextWrapper.dispatch(TilesRequestContextWrapper.java:72)
    at org.apache.struts2.tiles.StrutsTilesRequestContext.dispatch(StrutsTilesRequestContext.java:88)
    at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:283)
    at org.apache.tiles.jsp.taglib.InsertAttributeTag.render(InsertAttributeTag.java:140)
    at org.apache.tiles.jsp.taglib.InsertAttributeTag.render(InsertAttributeTag.java:117)
    at org.apache.tiles.jsp.taglib.RenderTagSupport.execute(RenderTagSupport.java:154)
    at org.apache.tiles.jsp.taglib.RoleSecurityTagSupport.doEndTag(RoleSecurityTagSupport.java:75)
    at org.apache.tiles.jsp.taglib.ContainerTagSupport.doEndTag(ContainerTagSupport.java:80)
    at org.apache.jsp.jsp.common.mainLayout_jsp._jspx_meth_tiles_005finsertAttribute_005f2(mainLayout_jsp.java:181)
    at org.apache.jsp.jsp.common.mainLayout_jsp._jspService(mainLayout_jsp.java:94)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:433)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:389)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:333)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:684)
    at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:593)
    at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:530)
    at org.apache.tiles.servlet.context.ServletTilesRequestContext.include(ServletTilesRequestContext.java:217)
    at org.apache.tiles.servlet.context.ServletTilesRequestContext.dispatch(ServletTilesRequestContext.java:177)
    at org.apache.tiles.context.TilesRequestContextWrapper.dispatch(TilesRequestContextWrapper.java:72)
    at org.apache.struts2.tiles.StrutsTilesRequestContext.dispatch(StrutsTilesRequestContext.java:88)
    at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:606)
    at org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:246)
    at org.apache.struts2.views.tiles.TilesResult.doExecute(TilesResult.java:105)
    at org.apache.struts2.dispatcher.StrutsResultSupport.execute(StrutsResultSupport.java:186)
    at com.opensymphony.xwork2.DefaultActionInvocation.executeResult(DefaultActionInvocation.java:373)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:277)
    at com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:176)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:263)
    at org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:138)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:207)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:207)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:190)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:94)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:243)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:270)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:145)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:171)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:176)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:190)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:187)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
    at org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)
    at org.apache.struts2.components.ActionComponent.executeAction(ActionComponent.java:291)
    at org.apache.struts2.components.ActionComponent.end(ActionComponent.java:173)
    at org.apache.struts2.views.jsp.ComponentTagSupport.doEndTag(ComponentTagSupport.java:42)
    at org.apache.jsp.index_jsp._jspx_meth_s_005faction_005f0(index_jsp.java:108)
    at org.apache.jsp.index_jsp._jspService(index_jsp.java:76)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:433)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:389)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:333)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:88)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:224)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:405)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:964)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:515)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:302)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

Anyone has an idea?

回答1:

The requested list key 'colors' could not be resolved as a collection/array/map/enumeration/iterator type

This error occurs when you try to access a list/collection which haven't been created.

May be you are calling action directly i.e. loacalhost:8080/youraction.action.

Please ensure that you access list after the action class is instantiated i.e. corresponding action is called.

If you want to directly access it before calling action make it static and access it inside jsp.



回答2:

In simple words you are accessing the page i.e menu2.jsp directly without processing any action and hence no initialization of the list. go through an action and initialize the list on the way to menu2.jsp that what the error says

The requested list key 'colors' could not be resolved as a collection/array/map/enumeration/iterator type

Hope this helps



回答3:

There are three ways to do it.

  1. If we initialize all collection objects at class level then this problem doesn't occur, As per my understanding, when particular action is triggered at that time, JSP page is not knowing the the type of field. in this case, when you write "private ArrayList<String> colors;" instead of this, make it

    private ArrayList colors= new ArrayList();

  2. And using prepare like Tomasz Gutkowski said before, also works.

  3. By using interceptor tag also we can tell the same like this (include within action tag)

    interceptor-ref name="params"
    interceptor-ref name="prepare"
    interceptor-ref name="basicStack"



回答4:

You need to add implement Preparable and method prepare() and in this method prepare colors list.

It should be like this:

public class MenuAction extends ActionSupport implements Preparable{
    private ArrayList<String> colors;
    private String yourColor;

    public ArrayList<String> getColors() {
        return colors;
    }

    public void setColors(ArrayList<String> colors) {
        this.colors = colors;
    }

    public String getYourColor() {
        return yourColor;
    }

    public void setYourColor(String yourColor) {
        this.yourColor = yourColor;
    }

    public String asdf() {
        colors = new ArrayList<String>();
        colors.add("red");
        colors.add("yellow");
        colors.add("blue");
        colors.add("green");

        return SUCCESS;
    }

    @Override
    public String execute() {
        System.out.println("execute menu action");


        return SUCCESS;
    }
    public void prepare() throws Exception {
        colors = new ArrayList<String>();
        colors.add("red");
        colors.add("yellow");
        colors.add("blue");
        colors.add("green");

    }
}


回答5:

I had the same problem; and i removed the struts xml validation and it worked fine



回答6:

Before accessing any field from action class in jsp file, you need to make sure that action class object gets created and field being accessed is initialized properly.

In your struts.xml, for action 'menu' you have configured to call method 'asdf'. So first thing to note is that execute method won't be called by struts framework to execute your action 'menu' but instead method 'asdf' would be invoked.

In form present in menu2.jsp, in tag you are trying to access variable named colors present in your action class. So when menu2.jsp is invoked, corresponding action is not invoked and hence field colors is not initialized.

So how do you invoke MenuAction class before menu2.jsp? Here's one attempt to achieve this:

struts.xml

<!-- Define one extra action in struts.xml which redirects-->
<action name="invokeMenuActionFirst" class="com.struts.actions.MenuAction" method="input">
    <result name="input">/menu2.jsp</result>
</action>

Whereever you are invoking menu2.jsp directly, you need to invoke action 'invokeMenuActionFirst' instead. For example consider sample other.jsp as follows.

other.jsp

<a href="menu2.jsp">Link </a>
<%-- Replace links similar to above created using plain html markup with following struts2 markup. --%>
<a href="<s:url action='invokeMenuActionFirst'/>">Link </a>

Here input method is provided by ActionSupport class whose default implementation returns String "input". You should also move initialization code of colors to MenuAction default constructor.

I got this idea from https://struts.apache.org/docs/message-resource-files.html.



回答7:

struts.xml file has to be configure for the action method, which populate the list/map/set as mentioned below.
<action name="selectAction" class="<full class name>" method="display"> <result name="none">pages/<file name>.jsp</result> </action

At the browser put the url as mentioned below :
http://hostname:port/context/selectAction.action
Now the collection will be populated and the struts select will display the content of the collection



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