java Freemarker：在哈希中迭代嵌套列表
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原文地址: http://stackoverflow.com/questions/27264613/
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Freemarker: iterating nested list in hash
提问by pat.inside
I want to iterate a List nested in a Map, the data structure is like:
我想迭代一个嵌套在 Map 中的 List，数据结构如下：
Map<Integer, List<Integer>> groups = new TreeMap<>()
// Some code else to put values into groups ...
Freemarker template:
自由标记模板：
<#list groups?keys as groupKey>
${groupKey} // It's OK here.
<#list groups[groupKey] as item> // Exception threw here, detail message is pasted below
${item}
</#list>
</#list>
Detail exception message:
详细异常信息：
FreeMarker template error: For "...[...]" left-hand operand: Expected a sequence or string or something automatically convertible to string (number, date or boolean), but this evaluated to an extended_hash (wrapper: f.t.SimpleHash): ==> groups
FreeMarker 模板错误：对于“...[...]”左手操作数：需要一个序列或字符串或自动转换为字符串（数字、日期或布尔值）的东西，但这被评估为extended_hash（包装器：ftSimpleHash） : ==> 组
So, what is the problem?
那么，问题是什么？
P.S.
聚苯乙烯
I have tried groups.get(groupKey)instead of groups[groupKey], it throws a new Exception stack:
我尝试过，groups.get(groupKey)而不是groups[groupKey]，它抛出一个新的异常堆栈：
java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.String
java.lang.String.compareTo(String.java:108)
java.util.TreeMap.getEntry(TreeMap.java:346)
java.util.TreeMap.get(TreeMap.java:273)
freemarker.template.SimpleHash.get(SimpleHash.java:160)
freemarker.core.Dot._eval(Dot.java:40)
freemarker.core.Expression.eval(Expression.java:76)
采纳答案by ddekany
The problem in the original question is that FTL's hash type is not like Map. It's a collection of "variables", that is, the keys must be String-s. (Even that ?keysworks is a glitch in BeansWrapper... though now it comes handy.) Since the key is a number, FTL assumes that you want to get an item from a sequence (a Listor array), or that you want to get a character from a string, hence the original error message.
原题的问题是FTL的hash类型不像Map. 它是“变量”的集合，即键必须是String-s。（即使这样?keys工作也是一个小问题BeansWrapper......尽管现在它很方便。）由于键是一个数字，FTL 假设您想从序列（aList或数组）中获取一个项目，或者您想获取一个字符串中的字符，因此是原始错误消息。
The solution is using the Java API-s, like getin Dev-an's answer. (On the long term FTL meant to introduce the map type, so all this problems with non-string keys will end, but who knows when that will be...)
解决方案是使用 Java API-s，就像get在 Dev-an 的回答中一样。（从长远来看，FTL 意味着引入地图类型，所以所有这些非字符串键的问题都会结束，但谁知道那会是什么时候......）
Update:Since 2.3.22 there's ?apito access the Java API of objects, like myMap?api.get(nonStringKey). However, it's by default not allowed (see the api_builtin_enabledconfiguration setting and more in the Manual: http://freemarker.org/docs/ref_builtins_expert.html#ref_buitin_api_and_has_api). Also note that as Java maps are particular about the numerical type, if the key is not an Integercoming from a Java, you have to use myMap?api.get(myNumericalKey?int).
更新：从 2.3.22 开始，?api可以访问对象的 Java API，例如myMap?api.get(nonStringKey). 但是，默认情况下是不允许的（请参阅api_builtin_enabled手册中的配置设置和更多内容：http: //freemarker.org/docs/ref_builtins_expert.html#ref_buitin_api_and_has_api）。另请注意，由于 Java 映射特别关注数字类型，如果键不是Integer来自 Java，则必须使用myMap?api.get(myNumericalKey?int).
回答by Dev-an
Try the following:
请尝试以下操作：
<#list groups?keys as groupKey>
${groupKey}
<#list groups.get(groupKey) as item>
${item}
</#list>
</#list>
