如何在Freemarker的list指令中传递字符串变量的值？

问题出在你调用taskHistory.getTaskHistoriesByDefinition时的参数传递方式：你用了字符串插值语法"${currentTaskDefinitionId}"，这会把变量值转成静态字符串字面量传递，而非直接传递变量本身。硬编码能生效是因为直接传入了合法的字符串常量，但动态变量需要直接引用变量名。

修复步骤 #

1. 直接传递变量名：调用Java方法时，不需要用引号和插值包裹变量，直接把currentTaskDefinitionId作为参数传入即可
2. 优化初始变量：将初始定义的空格字符串" "改为空字符串""，避免后续拼接时引入多余空格导致参数无效

修改后的完整代码 #

<#assign currentTaskDefinitionId="">
<#if taskHistory??>
    <#assign currentTaskActivitiId= taskHistory.taskActivitiId?number>
    <#list taskHistory.getAllTaskHistories() as item>
        <#assign taskActivitiIdForApproved = taskHistory.toFMTaskHistory(item).taskActivitiId?number>
        <#if  (taskActivitiIdForApproved <  currentTaskActivitiId)>
            <p> list of all previous taskDefinitionId : ${taskHistory.toFMTaskHistory(item).taskDefinitionId} </p> 

            <#elseif (taskActivitiIdForApproved = currentTaskActivitiId) && taskHistory.toFMTaskHistory(item).decisionType==1>
                <#assign currentTaskDefinitionId += taskHistory.taskDefinitionId>
        </#if> 
    </#list>
</#if> 
<p> Yes I am getting the value for this:  ${currentTaskDefinitionId} </p>

<#if taskHistory??>
    <#list taskHistory.getTaskHistoriesByDefinition(currentTaskDefinitionId)! as newItem>
        <p> User Simple ID: ${taskHistory.toFMTaskHistory(newItem).userSimpleId} </p>
    </#list>
</#if>

额外注意 #

如果currentTaskDefinitionId可能为空字符串，建议在调用方法前增加非空判断，避免传入无效参数：

<#if taskHistory?? && currentTaskDefinitionId?trim != "">
    <#list taskHistory.getTaskHistoriesByDefinition(currentTaskDefinitionId) as newItem>
        <p> User Simple ID: ${taskHistory.toFMTaskHistory(newItem).userSimpleId} </p>
    </#list>
</#if>

内容的提问来源于stack exchange，提问作者Mandeep trekea