Passing a value to a custom tag

2019-08-15 03:15发布

站内文章 / Java
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问题:

I have a custom tag that I'm trying to pass a String to. It was giving me a NullPointerException. After making some edits suggested below, I am getting ${note} instead of the processed output I had intended. Can anyone help me with this? Here is the relevant code from the JSP. I'm using Struts 2 in my form, and I've marked the line where I'm calling my custom tag.

<s:iterator value="bulletins">
    <s:if test="approved == false">
        <s:form action="ApproveBulletin" method="post">
            <table border="2" width="100%">
                <tr>
                    <td colspan="2"><b>From:</b> <s:property value="name" /></td>
                </tr>
                <tr>
                    <td colspan="2"><b>Subject:</b> <s:property value="subject" /></td>
                </tr>
                <tr>
                    <td colspan="2"><b>Date:</b> <s:property value="date" /> <br>
                    </td>
                </tr>
                <tr>
                        <!-- Custom tag is here -- my variable is note -->
                    <td colspan="2"><t:notePrint note="%{note}" /> <s:hidden
                    name="id" value="%{id}" /></td><s:hidden
                        name="id" value="%{id}" /></td>
                </tr>
                <tr>
                    <td><s:submit type="button" name="approve" value="Approve" /></td>
                    <td><s:submit type="button" name="deny" value="Deny" /></td>
                </tr>
            </table>
            <br />
        </s:form>
    </s:if>
</s:iterator>

Here is my tld.

<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag 
Library 1.2//EN"
"http://java.sun.com/j2ee/dtd/web-jsptaglibrary_1_2.dtd">
<taglib>
    <tlib-version>1.0</tlib-version>
    <jsp-version>1.1</jsp-version>
    <short-name>NotePrintTag</short-name>
    <uri>notePrintTag</uri>
    <tag>
        <name>notePrint</name>
        <tag-class>tags.NotePrint</tag-class>
        <body-content>scriptless</body-content>
        <attribute>
            <name>note</name>
        </attribute>
    </tag>
</taglib>

Here is my tag. The NullPointerException actually shows up here, and I've marked the line.

public class NotePrint extends SimpleTagSupport {
    private String note;

    public void setNote(String note) {
        this.note = note;
    }

    public String getNote() {
        return note;
    }

    public void doTag() throws JspException, IOException {
        PageContext pageContext = (PageContext) getJspContext();
        JspWriter out = pageContext.getOut();
        ActionContext.getContext().getValueStack().findValue(note);
        String[] noteArray = note.split("\n");

        for (int i = 0; i < noteArray.length; i++) {
            out.println(noteArray[i] + "<br /><br />");
        }
    }
}

Here is my exception report.

java.lang.NullPointerException
    tags.NotePrint.doTag(NotePrint.java:24)
    org.apache.jsp.BulletinApproval_jsp._jspx_meth_t_005fnotePrint_005f0(BulletinApproval_jsp.java:396)
    org.apache.jsp.BulletinApproval_jsp._jspx_meth_s_005fform_005f0(BulletinApproval_jsp.java:293)
    org.apache.jsp.BulletinApproval_jsp._jspx_meth_s_005fif_005f0(BulletinApproval_jsp.java:229)
    org.apache.jsp.BulletinApproval_jsp._jspx_meth_s_005fiterator_005f0(BulletinApproval_jsp.java:189)
    org.apache.jsp.BulletinApproval_jsp._jspService(BulletinApproval_jsp.java:109)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
    org.apache.struts2.dispatcher.ServletDispatcherResult.doExecute(ServletDispatcherResult.java:159)
    org.apache.struts2.dispatcher.StrutsResultSupport.execute(StrutsResultSupport.java:186)
    com.opensymphony.xwork2.DefaultActionInvocation.executeResult(DefaultActionInvocation.java:361)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:265)
    com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:163)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:251)
    org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:122)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:148)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:94)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:243)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:89)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:128)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:267)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:126)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:138)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:164)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:128)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:176)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)
    com.opensymphony.xwork2.ActionChainResult.execute(ActionChainResult.java:222)
    com.opensymphony.xwork2.DefaultActionInvocation.executeResult(DefaultActionInvocation.java:361)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:265)
    com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:163)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:251)
    org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:122)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:148)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:94)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:243)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:89)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:128)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:267)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:126)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:138)
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:164)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:128)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:176)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:236)
    org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)
    org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:485)
    org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:395)

回答1:

You aren't passing %{note} as the note attribute, you are passing it as the body. Change your tag to:

<t:notePrint note="%{note}"/>

Note that the string literal %{note} will be passed to your tag and you will need to explicitly parse it as an OGNL expression if you want that support. You should be able to parse the expression by calling:

ActionContext.getContext().getValueStack().findValue(note);


回答2:

<attribute><!--  TLD declaration appears amiss  -->
<name>note</name>
<required>true</required><!--  REQUIRED TO BE PRESENT true or false on the start element  -->
<rtexprvalue>true</rtexprvalue><!--  whether the attribute in the tag must look for EL expressions in it before passing it to the tag handler class  -->
</attribute>


回答3:

To demonstrate the solution of this problem lets take an analogy . Suppose we have "userName" and "password" which is retrieved from index.jsp and we have to pass our data in custom tag attribute. In my case its working

<body>

<%
String name=request.getParameter("name");
String password=request.getParameter("password");
%>

<%@ taglib prefix="c" uri="/WEB-INF/mytag.tld" %>

<c:logintag name="<%=namee%>" password="<%=password %>"/>



标签： java java-ee struts2 custom-tag
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