条件性胸腺细胞片段

Question

我想使用一个模板片段创建一个最多包含三个项目的列表。无论是否有项目，都将始终显示项目的三个空格，因此看起来是这样的。

<div>
  <div th:if="${#lists.size(block.children) > 0}"
    th:insert="code-block :: block(${block.children[0]})" 
    th:remove="tag">
  </div>
</div>;
<div>
  <div th:if="${#lists.size(block.children) > 1}"
    th:insert="code-block :: block(${block.children[1]})" 
    th:remove="tag">
  </div>
</div>;
<div>
  <div th:if="${#lists.size(block.children) > 2}"
    th:insert="code-block :: block(${block.children[2]})" 
    th:remove="tag">
  </div>
</div>

但是，即使th:if语句的计算结果为false，且列表为空，它仍会尝试执行'th:include语句，从而导致以下错误：

Caused by: org.springframework.expression.spel.SpelEvaluationException:
EL1025E:(pos 14): The collection has '0' elements, index '0' is invalid

如何让if语句优先于片段执行？

Answer 1

是的，不幸的是，由于include优先于if，因此您必须将if向上移动。最简单的方法是将其放入th:block，如下所示：

<div>
  <th:block th:if="${#lists.size(block.children) > 0}">
    <div th:insert="code-block :: block(${block.children[0]})" th:remove="tag" />
  </th:block>
</div>;
<div>
  <th:block th:if="${#lists.size(block.children) > 1}">
    <div th:insert="code-block :: block(${block.children[1]})" th:remove="tag" />
  </th:block>
</div>;
<div>
  <th:block th:if="${#lists.size(block.children) > 2}">
    <div th:insert="code-block :: block(${block.children[2]})" th:remove="tag" />
  </th:block>
</div>

您还可以简化代码，使其看起来更像这样：

<th:block th:each="i: ${#numbers.sequence(0, 2)}">
  <th:block th:if="${#lists.size(block.children) > i}">
    <div th:insert="code-block :: block(${block.children[i]})" th:remove="tag" />
  </th:block>

  <th:block th:unless="${i == 2}">;</th:block>
</th:block>