Working around lack of Optional support in Thymeleaf

user_421049 0
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It's 2020 and Thymeleaf still doesn't support Optional from Java 8, released six year ago. What are the workarounds?

I'm using Spring Boot 2.3.3.RELEASE with Thymeleaf. I have an object of type Foo that the controller provides via the model/session as foo. It has a method findName() that returns Optional<String>. So I can put this in my template:

[[${foo.findName()}]]

Assuming the name is "bar", that shows:

Optional[bar]

That works, but obviously it's not what I want.

So I tried what I would do in Java. The following should print simply the name (e.g. foo), or _____ if the name is missing:

[[${foo.findName().orElse("_____")}]]

Unfortunately that produces an exception:

org.thymeleaf.exceptions.TemplateProcessingException: Could not parse as expression: ""

Trying to use conditions, this will provide the value if it is present:

[[${foo.findName().isPresent()} ? ${foo.findName().get()}]]

But for some reason this throws an exception:

[[${foo.findName().isPresent()} ? ${foo.findName().get()} : '_____']]

First, I'm not sure why the example using orElse() doesn't work, as the Optional instance is an object like any of the others. Secondly, does anyone know a workaround? Thirdly, does anyone know of a workaround that is concise and doesn't take up three times the code?

(What we really need is native support in Thymeleaf so that ${foo.findName()} ?: '_____' will just work naturally.)

thymeleaf spring-boot option-type spring java
2 Answers

Since Thymeleaf uses Spring Epression language when integrated with Spring, then Thymeleaf is not to blame. As of the current version of Spring, the SpEl doesn't support Java 8 Optional yet, here is the GitHub issue #20433.

Possible workarounds require different expressions:

  • When you have a default value (the _ escaping issue is resolved throught a comment) 
    <span th:text="${foo.findName().orElse('---')" />
  • When you don't want to render an enpty (or default) line, you can hide it using th:if: 
    <th:block th:if="${foo.findName().isPresent()}">
    <span th:text="${foo.findName().get()" /> 
</th:block>`
user_37649650

The only thing I can get to work so far is this:

<th:block th:switch="${foo.findName().isPresent()}">
  <th:block th:case="true">[[${foo.findName.get()}]]</th:block>
  <th:block th:case="*">_____</th:block>
</th:block>

Horrors—so verbose! Is that the best that can be done?

user_4210490
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