异常-----freemarker.core.ParseException: Encountered "string"

1、错误描述

 freemarker.core.ParseException: Encountered "string" at line 21, column 21 in type.ftl.
 Was expecting one of:
     "}" ...
     "." ...
     "[" ...
     "(" ...
     "?" ...
     "!" ...
     <TERMINATING_EXCLAM> ...
     "??" ...
     "+" ...
     "-" ...
     "*" ...
     "/" ...
     "%" ...
     "!=" ...
     "=" ...
     "==" ...
     ">=" ...
     <ESCAPED_GTE> ...
     ">" ...
     <ESCAPED_GT> ...
     <LESS_THAN_EQUALS> ...
     <LESS_THAN> ...
     ".." ...
     <AND> ...
     <OR> ...

     at freemarker.core.FMParser.generateParseException(FMParser.java:4702)
     at freemarker.core.FMParser.jj_consume_token(FMParser.java:4573)
     at freemarker.core.FMParser.StringOutput(FMParser.java:1070)
     at freemarker.core.FMParser.Content(FMParser.java:2580)
     at freemarker.core.FMParser.OptionalBlock(FMParser.java:2791)
     at freemarker.core.FMParser.Root(FMParser.java:2963)
     at freemarker.template.Template.<init>(Template.java:171)
     at freemarker.cache.TemplateCache.loadTemplate(TemplateCache.java:447)
     at freemarker.cache.TemplateCache.getTemplate(TemplateCache.java:360)
     at freemarker.cache.TemplateCache.getTemplate(TemplateCache.java:235)
     at freemarker.template.Configuration.getTemplate(Configuration.java:578)
     at freemarker.template.Configuration.getTemplate(Configuration.java:543)
     at com.you.freemarker.FreemarkerTemplate.getTemplate(FreemarkerTemplate.java:52)
     at com.you.freemarker.FreemarkerTemplate.printFtl(FreemarkerTemplate.java:76)
     at com.you.test.freemarker.FreemarkerTest.studentPrint(FreemarkerTest.java:172)
     at com.you.test.freemarker.FreemarkerTest.testDataType(FreemarkerTest.java:159)
     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
     at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
     at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
     at java.lang.reflect.Method.invoke(Unknown Source)
     at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)
     at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
     at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42)
     at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
     at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
     at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
     at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:68)
     at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47)
     at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
     at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
     at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
     at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
     at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
     at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
     at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
     at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

2、错误原因

  ${(num.color)??string}

“？？”出现错误，不符合freemarker中的语法规定

3、解决办法

将“？？”修改成符合freemarker语法的“？？？”

 ${(num.color)???string}

结果：false

4，原因

前连个问号是判断是否存在，后面一个问号是让它以String的类型输出