JTemplate: Data-Driven Presentation Templates for Java

Templates are documents that describe an output format such as HTML, XML, or CSV. They allow the ultimate representation of a data structure to be specified independently of the data itself, promoting a clear separation of responsibility.

The CTemplate system defines a set of "markers" that are replaced with values supplied by the data structure (which CTemplate calls a "data dictionary") when a template is processed. In JTemplate, the data dictionary is provided by an instance of java.util.Map whose entries represent the values supplied by the dictionary.

For example, the contents of the following map might represent the result of some simple statistical calculations:

{
    "count": 3, 
    "sum": 9.0,
    "average": 3.0
}

A template for transforming this data into HTML is shown below:

<html>
<head>
    <title>Statistics</title>
</head>
<body>
    <p>Count: {{count}}</p>
    <p>Sum: {{sum}}</p>
    <p>Average: {{average}}</p> 
</body>
</html>

At execution time, the "count", "sum", and "average" markers are replaced by their corresponding values from the data dictionary, producing the following markup:

<html>
<head>
    <title>Statistics</title>
</head>
<body>
    <p>Count: 3</p>
    <p>Sum: 9.0</p>
    <p>Average: 3.0</p> 
</body>
</html>

TemplateEncoder Class

JTemplate provides the TemplateEncoder class for merging a template document with a data dictionary. Templates are applied using one of the following TemplateEncoder methods:

public void writeValue(Object value, OutputStream outputStream) { ... }
public void writeValue(Object value, OutputStream outputStream, Locale locale) { ... }
public void writeValue(Object value, Writer writer) { ... }
public void writeValue(Object value, Writer writer, Locale locale) { ... }

The first argument represents the value to write (i.e. the data dictionary), and the second the output destination. The optional third argument represents the locale for which the template will be applied. If unspecified, the default locale is used.

For example, the following code snippet applies a template named map.txt to the contents of a data dictionary whose values are specified by a hash map:

HashMap<String, Object> map = new HashMap<>();

map.put("a", "hello");
map.put("b", 123");
map.put("c", true);

TemplateEncoder encoder = new TemplateEncoder(getClass().getResource("map.txt"), "text/plain");

String result;
try (StringWriter writer = new StringWriter()) {
    encoder.writeValue(map, writer);

    result = writer.toString();
}

System.out.println(result);

If map.txt is defined as follows:

a = {{a}}, b = {{b}}, c = {{c}}

this code would produce the following output:

a = hello, b = 123, c = true

Additional Information

This article introduced the JTemplate framework and provided a brief overview of its key features.

The latest JTemplate release can be downloaded here. For more information, see the project README.

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