Introduction to FTL
Freemarker template Language is an engine built using Java language. You can use FTL to generate any kind of files for example - you can generate HTML, Javascripts, Java (yes you can generate java programs as well), PDF etc., (sky is the limit here).
There are multiple template engines available in the market. This blog doesn't give any comparison of the template languages, rather it focuses mainly on the FTL.
How does FTL work?
Its simple, the below diagram is an self explanatory of how the FTL works.
How do I implement a Hello World example?
Step 1 : Download the latest freemarker jar here
Step 2 : Create java project and add this jar in the build path
Step 3 : Write a template file
Step 4 : Write Java program to process the template file
<!-- HelloWorld.ftl -->
<html>
<h1>${welcomeMsg}</h1>
</html>
// Java Program
public class FreemarkerHelloWorld {
public static void main(String[] args) {
Configuration config = new Configuration(Configuration.VERSION_2_3_25);
try {
config.setDirectoryForTemplateLoading(new File("./src/templates/"));
Template template = config.getTemplate("HelloWorld.ftl");
Writer file = new FileWriter(new File("HelloWorld.html"));
Map<String, String> model = new HashMap<String, String>();
model.put("welcomeMsg", "Hello World !!");
template.process(model, file);
file.flush();
file.close();
System.out.println("File generated");
} catch (Exception e) {
// Handling the exceptions generically. Should be handled as per the
// actual exceptions
e.printStackTrace();
}
}
}
on executing the above code html file gets generated as below. Bingo !!!!
<html>
<h1>Hello World !!</h1>
</html>
Well, How do I display list of data?
Its simple again, we need to enhance our model to hold list data. Let's take an example and see how we can do this.
<!-- ListDemo.ftl -->
<html>
<h1> ${welcomeMsg} </h1>
<body>
<p>Names are : </p>
<ul>
<#list names as name>
<li>${name}</li>
</#list>
</ul>
</body>
</html>
public class FreemarkerListDemo {
public static void main(String[] args) {
Configuration config = new Configuration(Configuration.VERSION_2_3_25);
try {
config.setDirectoryForTemplateLoading(new File("./src/templates/"));
Template template = config.getTemplate("ListDemo.ftl");
Writer file = new FileWriter(new File("ListDemo.html"));
Map<String, Object> model = new HashMap<String, Object>();
model.put("welcomeMsg", "Hello World !!");
List<String> names = new ArrayList<>();
names.add("Steve");
names.add("John");
names.add("Adam");
model.put("names", names);
template.process(model, file);
file.flush();
file.close();
System.out.println("File generated");
} catch (Exception e) {
// Handling the exceptions generically. Should be handled as per the
// actual exceptions
e.printStackTrace();
}
}
}
Generated File :
<!-- ListDemo.ftl -->
<html>
<h1> Hello World !! </h1>
<body>
<p>Names are : </p>
<ul>
<li>Steve</li>
<li>John</li>
<li>Adam</li>
</ul>
</body>
</html>
Can I conditionally display data?
Yes, off-course. The below example displays name which contains Adam in it.
<!-- ListDemoWithConditions.ftl -->
<html>
<h1> ${welcomeMsg} </h1>
<body>
<p>Names are : </p>
<ul>
<#list names as name>
<!-- Check if name contains Adam-->
<#if name?contains("Adam")>
<li>${name}</li>
</#if>
</#list>
</ul>
</body>
</html>
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