FreeMarker: Concatenate maps or hashes

Using ‘+’ operator, you can concatenate maps or hashes.

 

What if hashes contain the same key?

The hash on the right-hand side of the + takes precedence.

 

Example

<#assign countryCapitals = {"India":"New Delhi", "Nepal":"Khatmandu"} + {"Armenia":"Yerevan", "Brazil":"Brasilia"}>

 

- Capital of India is ${countryCapitals.India}

- Capital of Brazil is ${countryCapitals.Brazil}

 

Find the below working application.

 

Step 1: Create hashConcatenation.ftl file under src/main/resources/templates folder.

 

hashConcatenation.ftl

<#assign countryCapitals = {"India":"New Delhi", "Nepal":"Khatmandu"} + {"Armenia":"Yerevan", "Brazil":"Brasilia"}>

- Capital of India is ${countryCapitals.India}
- Capital of Brazil is ${countryCapitals.Brazil}

Step 2: Define ‘FreeMarkerUtil’ class that take model class and template file as input and merge them.

 

FreeMarkerUtil.java

package com.sample.app.util;

import java.io.StringWriter;
import java.util.Locale;

import freemarker.template.Configuration;
import freemarker.template.Template;
import freemarker.template.TemplateExceptionHandler;

public class FreeMarkerUtil {

	private static final Configuration FREE_MARKER_CONFIGURATION = new Configuration(Configuration.VERSION_2_3_30);

	static {
		FREE_MARKER_CONFIGURATION.setClassForTemplateLoading(FreeMarkerUtil.class, "/templates/");
		FREE_MARKER_CONFIGURATION.setDefaultEncoding("UTF-8");
		FREE_MARKER_CONFIGURATION.setLocale(Locale.US);
		FREE_MARKER_CONFIGURATION.setTemplateExceptionHandler(TemplateExceptionHandler.RETHROW_HANDLER);
		FREE_MARKER_CONFIGURATION.setFallbackOnNullLoopVariable(false);
	}

	public static StringWriter mergeModelAndTemplate(Object modelObject, String ftlFile) throws Exception {
		StringWriter stringWriter = new StringWriter();

		Template template = FREE_MARKER_CONFIGURATION.getTemplate(ftlFile);

		template.process(modelObject, stringWriter);

		return stringWriter;
	}

}

Step 3: Define HashConcatenationPopulator.

 

HashConcatenationPopulator.java

package com.sample.app;

import java.io.StringWriter;
import java.util.HashMap;
import java.util.Map;

import com.sample.app.util.FreeMarkerUtil;

public class HashConcatenationPopulator {
	public static void main(String args[]) throws Exception {

		Map<String, Object> modelObject = new HashMap<String, Object>();

		StringWriter stringWriter = FreeMarkerUtil.mergeModelAndTemplate(modelObject, "hashConcatenation.ftl");
		System.out.println(stringWriter.toString().trim());

	}
}

Output

- Capital of India is New Delhi

- Capital of Brazil is Brasilia

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