【发布时间】：2014-09-16 18:58:33
【问题描述】：
我正在使用 freemarker 生成 xml 输出并且在访问嵌套对象的属性时遇到问题我在"Stack Overflow" 上看到了这篇文章，但我仍然无法获取属性并获得无效的引用表达式。
代码示例
public class Inc {
private String id;
private List<BusinessAddress> businessAddress;
....
//get and setters for properties
....
}
//------------------------------
public class BusinessAddress{
private String id;
private Address details;
....
//get and setters for properties
....
}
//------------------------------
public class Address {
private String id;
//get and setters for properties
....
}
//--------------------------------------
public class FreemarkerTest {
public static void main(String[] args) {
try
{
Inc inc = ......;
Template freemarkerTemplate = null;
Configuration configuration = new Configuration();
configuration.setClassForTemplateLoading(FreemarkerTest.class, "/");
String templateFile = "freemarker/template.ftl";
StringWriter out = new StringWriter();
freemarkerTemplate = configuration.getTemplate(templateFile);
Map<String,Object> contextPropsExpressioned = new HashMap<String,Object>();
contextPropsExpressioned.put("payload", inc);
freemarkerTemplate.process(contextPropsExpressioned, out);
System.out.println(out);
out.flush();
out.close();
}
catch(Exception ex)
{
System.out.println(ex.getMessage());
}
}
而freemarker模板是
<#list payload.businessAddress as businessAddress>
<EntityLocation>
<nc:Location id="${businessAddress}Sub${details.id}" dataid="${businessAddress.id}">
</nc:Location>
</EntityLocation>
</#list>
偶数
<#list payload.businessAddress as businessAddress>
<EntityLocation>
<nc:Location id="${businessAddress}Sub${getDetails().id}" dataid="${businessAddress.id}">
</nc:Location>
</EntityLocation>
</#list
我收到的异常是
FreeMarker template error:
The failing instruction (FTL stack trace):
----------
==> ${details.id} [in template "freemarker/template.ftl" at line 172, column 97]
----------
Tip: If the failing expression is known to be legally null/missing, either specify a default value.....
Java stack trace (for programmers):
----------
freemarker.core.InvalidReferenceException: [... Exception message was already printed; see it above ...]...
任何帮助将不胜感激。 谢谢
【问题讨论】：
-
你试过
${businessAddress.details.id}吗？ -
是的，这是我尝试的第一个版本，我也遇到了同样的错误：“以下已评估为 null 或缺失：==> businessAddress.detail”
-
因此，您可能在该列表或
Address字段中的某处有空值。 -
我浏览了所有测试用例，才意识到其中一个地址没有通过 json 转换进行初始化。我确实恢复到 ${businessAddress.details.id}，现在它的格式正确。在模板中添加了一些额外的检查以及空值，即使这种情况永远不会发生。感谢亚历山大的帮助
-
您可以回答自己的问题，这将对未来的访问者有所帮助。
标签： freemarker