如何处理 FTL 模板中未定义的表达式？

Question

我有一个 ftl 模板，我在其中创建了一个文本区域，每当该文本区域内的值在 java 中获取为 null 时，ftl 模板发生错误，请查找堆栈跟踪：

Java backtrace for programmers:
----------
freemarker.core.InvalidReferenceException: Expression shopparam is undefined on line 267, column 76 in epd/Shops_edit.ftl.
    at freemarker.core.TemplateObject.assertNonNull(TemplateObject.java:124)
    at freemarker.core.TemplateObject.invalidTypeException(TemplateObject.java:134)
    at freemarker.core.Dot._getAsTemplateModel(Dot.java:78)
at freemarker.core.Expression.getAsTemplateModel(Expression.java:89)
    at freemarker.core.Expression.getStringValue(Expression.java:93)
    at freemarker.core.DollarVariable.accept(DollarVariable.java:76)
    at freemarker.core.Environment.visit(Environment.java:208)
    at freemarker.core.MixedContent.accept(MixedContent.java:92)
    at freemarker.core.Environment.visit(Environment.java:208)
    at freemarker.core.Environment.process(Environment.java:188)
    at freemarker.template.Template.process(Template.java:237)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:502)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1148)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:387)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:417)
    at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:230)
    at org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:534)
    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:879)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:747)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
    at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:520)

FTL 模板代码在这里：

<td colspan="2">
    <textarea name="shop_param_value" rows=4>
        ${shopparam.value}
    </textarea>

Answer 1

在您的具体情况下：${(shopparam.value)!}

您使用的是一些非常旧的 FreeMarker 版本（绝对应该升级），当您收到此错误消息时（并查看其中的建议）：

The following has evaluated to null or missing:
==> shopparam  [in nameless template at line 1, column 3]

----
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)??
----

另请参阅文档：https://freemarker.apache.org/docs/dgui_template_exp.html#dgui_template_exp_missing

如何处理 FTL 模板中未定义的表达式？

how to handle undefind expression in FTL templates?

freemarker