Is there a way to programmatically handle missing/misspelled template parameters in Thymeleaf?

I've read How to throw exception is template variable not found in Context?. The answer proposes adding validation inside the template. I already have a lot of templates, so changing them would be a lot of work. Plus: If someone fets/typos a variable, they are just as likely is fet adding the validation as well.

To be more specific: I have a class like this

class TemplateRenderer {
    private final TemplateEngine templateEngine;

    public TemplateRenderer() {
        this.templateEngine = new TemplateEngine();
        templateEngine.setTemplateResolver(new StringTemplateResolver());
    }

    public String render(String template, Map<String, Object> variables) {
        IContext context = new Context(Locale.GERMAN, variables);

        return templateEngine.process(template, context);
    }
}

That is used like this:

public class Main {
    public static void main(String[] args) {
        TemplateRenderer renderer = new TemplateRenderer();

        System.out.println(renderer.render("<span th:text=${key} />", Map.of("key", "value")));
        System.out.println(renderer.render("<span th:text=${misspelled_key} />", Map.of("key", "value")));
        System.out.println(renderer.render("<span th:text=${key} />", Map.of("misspelled_key", "value")));
        System.out.println(renderer.render("<span th:text=${key} />", Map.of()));
    }
}

The first println outputs <span >value</span> as expected, the last three output <span ></span>.

Is there a way I can cause the last three to log a warning or throw an exception? Is there some custom hook I can implement inside my TemplateRenderer class?

Is there a way to programmatically handle missing/misspelled template parameters in Thymeleaf?

I've read How to throw exception is template variable not found in Context?. The answer proposes adding validation inside the template. I already have a lot of templates, so changing them would be a lot of work. Plus: If someone fets/typos a variable, they are just as likely is fet adding the validation as well.

To be more specific: I have a class like this

class TemplateRenderer {
    private final TemplateEngine templateEngine;

    public TemplateRenderer() {
        this.templateEngine = new TemplateEngine();
        templateEngine.setTemplateResolver(new StringTemplateResolver());
    }

    public String render(String template, Map<String, Object> variables) {
        IContext context = new Context(Locale.GERMAN, variables);

        return templateEngine.process(template, context);
    }
}

That is used like this:

public class Main {
    public static void main(String[] args) {
        TemplateRenderer renderer = new TemplateRenderer();

        System.out.println(renderer.render("<span th:text=${key} />", Map.of("key", "value")));
        System.out.println(renderer.render("<span th:text=${misspelled_key} />", Map.of("key", "value")));
        System.out.println(renderer.render("<span th:text=${key} />", Map.of("misspelled_key", "value")));
        System.out.println(renderer.render("<span th:text=${key} />", Map.of()));
    }
}

The first println outputs <span >value</span> as expected, the last three output <span ></span>.

Is there a way I can cause the last three to log a warning or throw an exception? Is there some custom hook I can implement inside my TemplateRenderer class?

• java
• error-handling
• thymeleaf

1 Answer 1

I'm guessing you could do something like

    public String render(String template, Map<String, Object> variables) {
        final Set<String> badVariables = new LinkedHashSet<>();
        IContext context = new IContext() {
            public boolean containsVariable(String name) {
                boolean result = variables.containsKey(name);
                if (!result) badVariables.add(name);
                return result;
            }
            public Object getVariable(String name) {
                Object result = variables.get(name);
                if (result == null && !variables.containsKey(name)) {
                    badVariables.add(name);
                }
                return result;
            }
            public Set<String> getVariableNames() {
                return variables.keySet();
            }
            public Locale getLocale() {
                return Locale.GERMAN;
            }
        };

        String result = templateEngine.process(template, context);
        if (!badVariables.isEmpty()) {
           throw new RuntimeException("Bad variables " + badVariables);
        }
        return result;
    }