Overview

Using YearMonth as a sample, I will summarize how to create your own Utility. Finally, make it available in $ {# yearmonths.format (hogeYm,'yyyy-MM')}.

Supplement (additional note)

Since Thymeleaf does not have a Utility to operate the date and time API by default, YearMonth is used for the sample. However, there seems to be an official additional module (thymeleaf-extras-java8time), and it seems better to use this for the date and time API. Thymeleaf and Date and Time API

Premise

thymeleaf3
spring-boot 1.4

Creating the Utility body

The implementation was based on Thymeleaf's Dates.

public final class YearMonths {
    public String format(final YearMonth target, final String pattern) {
        if (target == null) {
            return null;
        }
        try {
            // org.thymeleaf.util.Use Validate
            Validate.notEmpty(pattern, "Pattern cannot be null or empty");
            return target.format(DateTimeFormatter.ofPattern(pattern));
        } catch (final Exception e) {
            throw new TemplateProcessingException(
                    "Error formatting date with format pattern \"" + pattern + "\"", e);
        }
    }
}

Create your own Dialect

Create a Dialect to manage the date and time Utility

public class YearMonthDialect implements IExpressionObjectDialect {
    //The name you want to use in Thymeleaf
    private static final String YEAR_MONTH_EXPRESSION_NAME = "yearmonths";

    //Name management Set
    private static final Set<String> ALL_EXPRESSION_NAMES = new HashSet<String>(){
                {add(YEAR_MONTH_EXPRESSION_NAME);}
            };

    @Override
    public IExpressionObjectFactory getExpressionObjectFactory() {
        return new IExpressionObjectFactory() {
            @Override
            public Set<String> getAllExpressionObjectNames() {
                return ALL_EXPRESSION_NAMES;
            }

            @Override
            public Object buildObject(IExpressionContext context, String expressionObjectName) {
                //Associate the name with the instance of your own Utility
                if(expressionObjectName.equals(YEAR_MONTH_EXPRESSION_NAME)){
                    return new YearMonths();
                }
                return null;
            }

            @Override
            public boolean isCacheable(String expressionObjectName) {
                //Implemented as needed
                return false;
            }
        };
    }

    @Override
    public String getName() {
        return "YearMonth";
    }
}

Registration to DI container

Dialect must be registered in the DI container to be available in SpringBoot. I will write an example of creating and registering a dedicated Configuration.

@Configuration
public class ThymeleafConfiguration {
    @Bean
    public DateTimeDialect DateTimeDialect() {
        return new DateTimeDialect();
    }
}

Call in template

You will be able to call it as follows.

${#yearmonths.format(hogeYm,'yyyy-MM')}

Summary

Create a Utility
Create a Dialect to manage the Utility
Register Dialect in DI container

reference

-Try Thymeleaf 3.0 Part 3 Make a utility -Create a Utility Object (original View Helper in Rails) with thymeleaf

Create your own Utility with Thymeleaf with Spring Boot