List：

List<String> clientSourceData=new ArrayList<String>();
clientSourceData.add("field字段");
clientSourceData.add("title标题");

ftl：

<#if clientSourceData?exists>
    <#list clientSourceData as key> 
        <tr>
            <td>${key}</td>
        </tr>
    </#list>
</#if>

Map：

Map<String,String> clientSourceData=new HashMap<String,String>();
clientSourceData.put("field", "字段");
clientSourceData.put("title", "标题");

ftl：

<#if clientSourceData?exists>
    <#list clientSourceData?keys as key> 
        <tr>
             <td>${key}</td>
             <td>${clientSourceData[key]}</td>
         </tr>
    </#list>
</#if>

List<Map>：

List<Map<String,String>> columns=new ArrayList<Map<String,String>>();
for(int i=0;i<10;i++){
    Map<String,String> col=new HashMap<>();
    col.put("field", "字段"+i);
    col.put("title", "标题"+i);
    columns.add(col);
}

ftl：

<#list columns as col>
    {
        field : ${col["field"]},
        halign:'center',
        title : ${col["title"]},
    }
</#list>