Why do we do this? Why isn't it easier just to create a template in memory and merge it with data in memory?

LearnToMergeAFreemarkerTemplateTest.java

package ca.jbrains.org.freemarker;

import freemarker.template.Configuration;
import freemarker.template.Template;
import freemarker.template.TemplateException;
import io.vavr.collection.HashMap;
import io.vavr.collection.Map;
import org.junit.Assert;
import org.junit.Test;

import java.io.IOException;
import java.io.StringReader;
import java.io.StringWriter;

import static org.hamcrest.CoreMatchers.is;

// CONTRACT
// Merge placeholders with a data-model.
// The data-model is a tree of values with keys. Reach down
// the tree with keys separated by dots: a.b.c means c inside b inside a.
//
// ${key} turns into the value corresponding to the key 'key'.
//
// ${key!"default value"} uses a default value in case the data-model
// contains no value (or a `null` value) for the key 'key'.
//
// We can implement the data-model as a Map or as a hierarchy of Java beans,
// or as a mixture of the two: a Map with a value that's a Java bean, and so on.
//
//
public class LearnToMergeAFreemarkerTemplateTest {
    // The Freemarker documentation tells me to treat this like a Singleton,
    // so I'm doing exactly that by instantiating just one of these and using
    // it for every test.
    public static final Configuration standardConfigurationForTesting = new Configuration(Configuration.VERSION_2_3_28);

    @Test
    public void oneSimplePlaceholder() throws Exception {
        String result = mergeTemplate(
                "Hello, ${name}.",
                HashMap.of("name", "J. B."));

        Assert.assertThat(result, is("Hello, J. B.."));
    }

    private String mergeTemplate(String templateText, Map<String, String> dataModel) throws TemplateException, IOException {
        return mergeTemplateWithDataModel(
                createTemplateInMemory(
                        "anonymous template", templateText),
                dataModel.toJavaMap());
    }

    private static Template createTemplateInMemory(String name, String templateText) throws IOException {
        return new Template(name,
                new StringReader(templateText),
                standardConfigurationForTesting);
    }

    private String mergeTemplateWithDataModel(Template oneSimplePlaceholder, java.util.Map<String, String> dataModel) throws TemplateException, IOException {
        StringWriter canvas = new StringWriter();
        oneSimplePlaceholder.process(dataModel, canvas);
        return canvas.toString();
    }
}