Freemarker 无法从列表中获取对象值

Posted 2023-02-22

【中文标题】Freemarker 无法从列表中获取对象值

【英文标题】：Freemarker cannot get object value from the list

【发布时间】：2016-04-02 21:59:50

【问题描述】：

我使用最新的 freemarker 版本 2.3.23 我有包含用户对象的列表，用户对象很简单，只包含名称属性。我的 ftl 文件如下所示：

<#list userlist>
<#items as item>
    $item.name
</#items>

我的 Java 代码如下所示：

public static void main(String[] args) throws Exception 
    List<User> user = new ArrayList<User>();
    User user1 = new User();
    User user2 = new User();
    user1.setName("jason");
    user2.setName("tony");
    user.add(user1);
    user.add(user2);
    Map<String, Object> params = new HashMap<String, Object>();
    params.put("userlist", user);
    Template template = FreemarkerUtil.getTemplate(FreemarkerUtil.TEMPLATE_PATH, "test.ftl");
    FileWriter fw = null;
    try 
        fw = new FileWriter(new File(FreemarkerUtil.getProjOutputDomainPath() + "test.txt"));
        template.process(params, fw);
     catch (Exception e) 
        e.printStackTrace();
     finally 
        if (fw != null) 
            fw.close();
        
    
 
class User 
    private String name;

    public String getName() 
        return name;
    

    public void setName(String name) 
        this.name = name;
    

错误显示如下：

The following has evaluated to null or missing:
    ==> item.name  [in template "test.ftl" at line 3, column 19]`enter code here`
    Tip: It's the step after the last dot that caused this error, not those before it.
    Tip: If the failing expression is known to be 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)??

    FTL stack trace ("~" means nesting-related):
    - Failed at: $item.name  [in template "test.ftl" at line 3, column 17]

    Java stack trace (for programmers):
    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$IterationContext.loopForItemsElement(IteratorBlock.java:207)
    at freemarker.core.Items.accept(Items.java:43)
    at freemarker.core.Environment.visitByHiddingParent(Environment.java:345)
    at freemarker.core.IteratorBlock$IterationContext.executeNestedBlockInner(IteratorBlock.java:276)
    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.Environment.process(Environment.java:302)
    at freemarker.template.Template.process(Template.java:325)
    at auto.freemarker.template.mysqlGenerator.main(MySQLGenerator.java:61)

【参考方案1】：

仅公开公共类的方法/属性，因此User 类必须是公共的（或者getName() 必须继承自公共类/接口）。

【讨论】：

我已经将用户类解压为公共类，现在可以了。谢谢。

嵌套类也可以是公共的，所以不需要提取。

【参考方案2】：

尝试如下替换您的 ftl 文件。

<#list userlist as item>
    $item.name
</#list>

希望这能解决您的问题。祝你有美好的一天:-)