Java FreeMarker 模板错误：以下已评估为空或缺失 | 但不是真的

FreeMarker template error: The following has evaluated to null or missing | BUT NOT TRUE

提问by Aziz

The error I'm facing is so weird. Everything looks fine, but I get this error when the browser sends the GET request to the server. What I'm trying to do is actually catching the HTTP parameters, save them in an object saved in an ArrayList sending to a Freemarker template.

我面临的错误太奇怪了。一切看起来都很好，但是当浏览器向服务器发送 GET 请求时我收到了这个错误。我想要做的实际上是捕获 HTTP 参数，将它们保存在保存在 ArrayList 中的对象中，然后发送到 Freemarker 模板。

Could you please help me? Thanks a lot.

请你帮助我好吗？非常感谢。

The error:

错误：

freemarker.log._JULLoggerFactory$JULLogger error SEVERE: Error executing FreeMarker template FreeMarker template error: The following has evaluated to null or missing: ==> item.lat1 [in template "view/result.ftl" at line 18, column 15]

freemarker.core.InvalidReferenceException: [... Exception message was already printed; see it above ...] at freemarker.core.InvalidReferenceException.getInstance(InvalidReferenceException.java:131) at freemarker.core.EvalUtil.coerceModelToString(EvalUtil.java:355) at freemarker.core.Expression.evalAndCoerceToString(Expression.java:82) at freemarker.core.DollarVariable.accept(DollarVariable.java:41) at freemarker.core.Environment.visit(Environment.java:324) at freemarker.core.MixedContent.accept(MixedContent.java:54) at freemarker.core.Environment.visitByHiddingParent(Environment.java:345) at freemarker.core.IteratorBlock$IterationContext.executeNestedBlockInner(IteratorBlock.java:268) at freemarker.core.IteratorBlock$IterationContext.executeNestedBlock(IteratorBlock.java:220) at freemarker.core.IteratorBlock$IterationContext.accept(IteratorBlock.java:194) at freemarker.core.Environment.visitIteratorBlock(Environment.java:572) at freemarker.core.IteratorBlock.acceptWithResult(IteratorBlock.java:78) at freemarker.core.IteratorBlock.accept(IteratorBlock.java:64) at freemarker.core.Environment.visit(Environment.java:324) at freemarker.core.MixedContent.accept(MixedContent.java:54) at freemarker.core.Environment.visit(Environment.java:324) at freemarker.core.Environment.process(Environment.java:302) at freemarker.template.Template.process(Template.java:325) at spark.template.freemarker.FreeMarkerEngine.render(FreeMarkerEngine.java:71) at controller.App.lambda$main$1(App.java:57) at spark.RouteImpl$1.handle(RouteImpl.java:58) at spark.webserver.MatcherFilter.doFilter(MatcherFilter.java:162) at spark.webserver.JettyHandler.doHandle(JettyHandler.java:61) at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:189) at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141) at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:119) at org.eclipse.jetty.server.Server.handle(Server.java:517) at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:302) at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:242) at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:245) at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:95) at org.eclipse.jetty.io.SelectChannelEndPoint$2.run(SelectChannelEndPoint.java:75) at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.produceAndRun(ExecuteProduceConsume.java:213) at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.run(ExecuteProduceConsume.java:147) at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:654) at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:572) at java.lang.Thread.run(Thread.java:745)

[qtp285763673-17] ERROR spark.webserver.MatcherFilter - java.lang.IllegalArgumentException: freemarker.core.InvalidReferenceException: The following has evaluated to null or missing: ==> item.lat1 [in template "view/result.ftl" at line 18, column 15]

freemarker.log._JULLoggerFactory$JULLogger 错误 严重：执行 FreeMarker 模板时出错 FreeMarker 模板错误：以下已评估为 null 或缺失：==> item.lat1 [in template "view/result.ftl" at line 18, column 15]

freemarker.core.InvalidReferenceException: [... 异常消息已打印；见上面...] 在 freemarker.core.InvalidReferenceException.getInstance(InvalidReferenceException.java:131) 在 freemarker.core.EvalUtil.coerceModelToString(EvalUtil.java:355) 在 freemarker.core.Expression.evalAndCoerceToString(Expression.java: 82) at freemarker.core.DollarVariable.accept(DollarVariable.java:41) at freemarker.core.Environment.visit(Environment.java:324) at freemarker.core.MixedContent.accept(MixedContent.java:54) at freemarker。 core.Environment.visitByHiddingParent(Environment.java:345) at freemarker.core.IteratorBlock$IterationContext.executeNestedBlockInner(IteratorBlock.java:268) at freemarker.core.IteratorBlock$IterationContext.executeNestedBlock(IteratorBlock.java:220) at freemarker。 .

[qtp285763673-17] 错误 spark.webserver.MatcherFilter - java.lang.IllegalArgumentException：freemarker.core.InvalidReferenceException：以下已评估为 null 或缺失：==> item.lat1 [在模板“view/result.ftl”中第 18 行，第 15 列]

.. But true, because I do print the Array and it works fine!

.. 但确实如此，因为我确实打印了 Array 并且它工作正常！

  final FreeMarkerEngine freeMarkerEngine = new FreeMarkerEngine();
    final Configuration freeMarkerConfiguration = new Configuration();
    freeMarkerConfiguration.setTemplateLoader(new ClassTemplateLoader(App.class, "/"));
    freeMarkerEngine.setConfiguration(freeMarkerConfiguration);

    get("/rest", (request, response) -> {
        Double lat1 = Double.parseDouble(request.queryParams("lat1") != null ? request.queryParams("lat1") : "anonymous");
        Double lon1 = Double.parseDouble(request.queryParams("lon1") != null ? request.queryParams("lon1") : "anonymous");
        Double lat2 = Double.parseDouble(request.queryParams("lat2") != null ? request.queryParams("lat2") : "anonymous");
        Double lon2 = Double.parseDouble(request.queryParams("lon2") != null ? request.queryParams("lon2") : "anonymous");

        if (shouldReturnHtml(request)) {
            response.status(200);
            response.type("text/html");
            Map<String, Object> attributes = new HashMap<>();
            attributes.put("list",loadTheList(lat1,lon1,lat2,lon2));
            return freeMarkerEngine.render(new ModelAndView(attributes, "/view/result.ftl"));
        }
        else {
            response.status(200);
            response.type("application/json");
            return null;
        }
    });


}

private static boolean shouldReturnHtml(Request request) {
    String accept = request.headers("Accept");
    return accept != null && accept.contains("text/html");
}
public static ArrayList<Bereken> loadTheList(double lat1, double lon1, double lat2, double lon2) {
    ArrayList<Bereken> list = new ArrayList<>();
    list.add(new Bereken(lat1,lon1,lat2,lon2));
    return list;
}

And result.ftl:

结果.ftl：

      <#list list as item>
        <h2>${item.lat1}</h2>
        <h2>${item.lon1}</h2>
        <h2>${item.lat2}</h2>
        <h2>${item.lon2}</h2>
    </#list>

采纳答案by J.K.Lauren

You are adding 1 instance of the Bereken class to the "list". So i would assume the Bereken class does not provide public properties lat1, lat2, lon1, lon2 or coresponding getter methods.

您将 Bereken 类的 1 个实例添加到“列表”中。所以我假设 Bereken 类不提供公共属性 lat1、lat2、lon1、lon2 或相应的 getter 方法。

回答by bsmither

I just ran across this yesterday. I was working through a tutorial and one of the steps did not include the code for a getter method in a class that created an object. I guess the author just assumed the reader knew that should have happened already.

我昨天刚遇到这个。我正在完成一个教程，其中一个步骤不包括创建对象的类中的 getter 方法的代码。我猜作者只是假设读者知道这应该已经发生了。

So, wherever this 'Bereken' thing is (I just learned it is a JavaBean class), be sure to add the setter and getter methods for the properties associated with each element in the 'list'.

因此，无论“Bereken”这个东西在哪里（我刚刚了解到它是一个 JavaBean 类），请务必为与“列表”中的每个元素关联的属性添加 setter 和 getter 方法。

回答by Alan47

I know this is an old question, but I just bumped into this. Freemarker will also complain that the value "is null or missing" if you pass it an instance of a private class (which I just tried). If you pass in a Java Bean class, it needsto be public. The error message is very misleading in this case.

我知道这是一个老问题，但我刚刚遇到了这个问题。如果您将私有类的实例（我刚刚尝试过）传递给它，Freemarker 还会抱怨该值“为空或丢失”。如果你在一个Java Bean类通过，它需要是public。在这种情况下，错误消息非常具有误导性。