在freemarker中使用if条件时出错

Question

我正在使用 if 条件

<#if searchForm.frm_searchType == "Non-Member">
  <#assign isMember = true>
  <#assign isNonMember = false>
<#else>
  <#assign isMember = false>
  <#assign isNonMember = true>
</#if>

它给出了以下错误

 ERROR [freemarker.runtime] (default task-1) Error executing FreeMarker template: freemarker.core.InvalidReferenceException: The following has evaluated to null or missing:
==> searchForm.frm_searchType  [in template "memberSearch.ftl" at line 83, column 6]


Tip: It's the step after the last dot that caused this error, not those before it.

Tip: If the failing expression is known to legally refer to something that's sometimes null or missing, either specify a default value like myOptionalVar!myDefault, or use <#if myOptionalVar??>when-present<#else>when-missing</#if>. (These only cover the last step of the expression; to cover the whole expression, use parenthesis: (myOptionalVar.foo)!myDefault, (myOptionalVar.foo)??



FTL stack trace ("~" means nesting-related):
    - Failed at: #if searchForm.frm_searchType == "Non...  [in template "memberSearch.ftl" at line 83, column 1]

    at freemarker.core.InvalidReferenceException.getInstance(InvalidReferenceException.java:134)
    at freemarker.core.EvalUtil.compare(EvalUtil.java:198)
    at freemarker.core.EvalUtil.compare(EvalUtil.java:115)
    at freemarker.core.ComparisonExpression.evalToBoolean(ComparisonExpression.java:78)
    at freemarker.core.IfBlock.accept(IfBlock.java:49)
    at freemarker.core.Environment.visit(Environment.java:347)
    at freemarker.core.Environment.visit(Environment.java:353)
    at freemarker.core.Environment.process(Environment.java:326)
    at freemarker.template.Template.process(Template.java:383)
    at org.springframework.web.servlet.view.freemarker.FreeMarkerView.processTemplate(FreeMarkerView.java:367)
    at org.springframework.web.servlet.view.freemarker.FreeMarkerView.doRender(FreeMarkerView.java:284)
    at org.springframework.web.servlet.view.freemarker.FreeMarkerView.renderMergedTemplateModel(FreeMarkerView.java:234)
    at org.springframework.web.servlet.view.AbstractTemplateView.renderMergedOutputModel(AbstractTemplateView.java:167)
    at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)
    at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1244)
    at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1027)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:971)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:686)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:791)
    at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:74)
    at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:129)
    at com.cgi.kym.web.filter.ZipFilter.doFilter(ZipFilter.java:45)
    at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)
    at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)
    at com.cgi.kym.web.filter.SecurityFilter.doFilter(SecurityFilter.java:169)
    at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)
    at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)
    at io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:84)
    at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
    at io.undertow.servlet.handlers.ServletChain$1.handleRequest(ServletChain.java:68)
    at 
    

基本上我正在将速度模板转换为 freemarker 模板。 searchForm 是另一个文件，我正在尝试从该文件中获取数据并在模板中使用。 如果条件，它在速度模板中有效，但在 freemarker 中无效。

Answer 1

我们可以处理 null 或缺失值，如下所示

<#if (searchForm.frm_searchType)!"Non-Member" == "Non-Member">
  <#assign isMember = true>
  <#assign isNonMember = false>
<#else>
  <#assign isMember = false>
  <#assign isNonMember = true>
</#if>

在这里，我将默认值设置为“非会员”。 因此，当值为 null 或缺失时，它采用默认值。 还有一些其他方法也可以处理 null 或缺失值，例如

<#if (searchForm.frm_searchType)?default('') == "Non-Member">

或者

<#if (searchForm.frm_searchType)! == "Non-Member">

我尝试了所有方法，它们都有效。 我从 freemarker 文档“处理缺失值”中尝试了这个