FreeMarker: Logical Operators

Logical or: ||

Logical and: &&

Logical not: !

 

Below table summarizes the behaviour of logical operators.

a	b	a && b	a || b	!a
false	false	false	false	true
false	true	false	true	true
true	false	false	true	false
true	true	true	true	false

 

Find the below working application.

 

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

 

logicalOperators.ftl

<#assign a=true, b=false >

${b?string} && ${b?string} : ${(b && b)?string}
${b?string} && ${a?string} : ${(b && a)?string}
${a?string} && ${b?string} : ${(a && b)?string}
${a?string} && ${a?string} : ${(a && a)?string}

${b?string} || ${b?string} : ${(b || b)?string}
${b?string} || ${a?string} : ${(b || a)?string}
${a?string} || ${b?string} : ${(a || b)?string}
${a?string} || ${a?string} : ${(a || a)?string}

!true = ${(!a)?string}
!false = ${(!b)?string}

Step 2: Define ‘FreeMarkerUtil’ class that takes model object 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 LogicalOperatorsPopulator.

 

LogicalOperatorsPopulator.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 LogicalOperatorsPopulator {
  public static void main(String args[]) throws Exception {

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

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

  }
}

Output

false && false : false
false && true : false
true && false : false
true && true : true

false || false : false
false || true : true
true || false : true
true || true : true

!true = false
!false = true

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