Thymeleaf [# th:each] is not getting parsed - spring-boot

Question

I have a thymeleaf (3.0.11.RELEASE) TEXT template with iteration as follows:
[# th:each="sei : ${specificInfoElements}"]
[(${sei?.elementLabel})] ： [(${sei?.elementValues})]
[/]
The above is not getting evaluated by template engine and its coming as follows in output:
[# th:each="sei : ${specificInfoElements}"]
:
[/]
Can anybody help me understand what I am doing wrong?
Note: I am using spring boot.
#Autowired
private SpringTemplateEngine thymeleafTemplateEngine;
Context thymeleafContext = new Context();
thymeleafContext.setVariables(templateModel);
String outputText = thymeleafTemplateEngine.process(emailTemplateString,
thymeleafContext);

Answer 1

I just tested this with Spring Boot and it works fine. What I did exactly:
Create a new project via start.spring.io using Spring Boot 2.5.1 with Java 11
Update application.properties with:
spring.thymeleaf.mode=TEXT
spring.thymeleaf.suffix=.txt
Create a file src/main/resources/templates/test.txt containing the template:
[# th:each="sei : ${specificInfoElements}"]
[(${sei?.elementLabel})] ： [(${sei?.elementValues})]
[/]
Create a test class that extends from CommandLineRunner so I can just start the app and see some output:
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;
import org.thymeleaf.context.Context;
import org.thymeleaf.spring5.SpringTemplateEngine;
import java.util.List;
#Component
public class Test implements CommandLineRunner {
#Autowired
private SpringTemplateEngine templateEngine;
#Override
public void run(String... args) throws Exception {
Context context = new Context();
context.setVariable("specificInfoElements", List.of(new SpecificInfoElement("first label", "first value"),
new SpecificInfoElement("second label", "second element")));
String result = templateEngine.process("test", context);
System.out.println("result = " + result);
}
private static class SpecificInfoElement {
private String elementLabel;
private String elementValues;
public SpecificInfoElement(String elementLabel, String elementValues) {
this.elementLabel = elementLabel;
this.elementValues = elementValues;
}
public String getElementLabel() {
return elementLabel;
}
public String getElementValues() {
return elementValues;
}
}
}
Running this outputs:
2021-06-22 08:22:39.229 INFO 13464 --- [ main] com.example.demo.DemoApplication : Started DemoApplication in 1.119 seconds (JVM running for 2.828)
result =
first label ： first value
second label ： second element
I hope this can help you figure out what you are doing differently.

Answer 2

Since I am storing templates in DB, thymeleaf is using StringTemplateResolver by default. StringTemplateResolver is added to the SpringTemplateEngine upon calling process method for the first time as shown in the code snippet taken from org.thymeleaf.TemplateEngine:
if (this.templateResolvers.isEmpty()) {
this.templateResolvers.add(new StringTemplateResolver());
}
I changed the template mode of StringTemplateResolver before calling the process method as follows:
if (CollectionUtils.isEmpty(springTemplateEngine.getTemplateResolvers())) {
// calling process method will initialize SpringTemplateEngine with StringTemplateResolver.
springTemplateEngine.process("template contents", context);
Set<ITemplateResolver> templateResolvers =
springTemplateEngine.getTemplateResolvers();
StringTemplateResolver stringTemplateResolver = (StringTemplateResolver) templateResolvers.iterator().next();
stringTemplateResolver.setTemplateMode(TemplateMode.TEXT);
}