Pratik Nagelia Pratik Nagelia - 3 months ago 44
JSON Question

Using velocity template and JSON to generate HTML?

I need a direct way to use velocity template and JSON string data to generate HTML data.
For example:

String mergedHtml = Velocity.someMethodToParseTemplate("VelocityTemplate.vm" ,String JsonString");


How can it be done ? Please suggest the code for "someMethodToParseTemplate"?

Answer

You just need to parse the JSON string (for instance using the org.json library) and then to build a VelocityContext out of the parsing result.

Let say you have the following template:

<html>
  <body>
    $name is $age years old and lives $address.streetAddress, ${address.city}.
    <br/>
    $name's friends:
    <ul>
    #foreach($friend in $friends)
      <li>$friend.name, who is $friend.age years old</li>
    #end
    </ul>
  </body>
</html>

You can merge it against a JSON string like this:

import java.io.IOException;
import java.io.StringWriter;
import java.io.Writer;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.VelocityEngine;
import org.json.JSONObject;

public class JsonPublisher
{
  protected VelocityEngine velocity;

  public JsonPublisher()
  {
    // init velocity                                                                                                                                                                                            
    // default resource loader is a file loader on the current directory                                                                                                                                        
    velocity = new VelocityEngine();
    velocity.init();
  }

  public String publish(String templatePath, String jsonString) throws IOException
  {
    // translate json string to velocity context                                                                                                                                                                
    // (we only need to convey the properties of the root object)                                                                                                                                               
    JSONObject jsonObj = new JSONObject(jsonString);
    VelocityContext context = new VelocityContext();
    for(String key : jsonObj.keySet())
    {
      context.put(key, jsonObj.get(key));
    }

    Writer writer = new StringWriter();
    velocity.mergeTemplate(templatePath, "UTF-8", context, writer);
    writer.flush();

    return writer.toString();
  }

  public static void main(String args[])
  {
    try
    {
      String str = "{ \"name\": \"Alice\", \"age\": 20, \"friends\": "+
        "[ { \"name\":\"Bob\", \"age\":21 }, { \"name\":\"Carol\", \"age\":19 } ], " +
        "\"address\": { \"streetAddress\": \"100 Wall Street\", \"city\": \"New York\" } }";
      String result = new JsonPublisher().publish("template.vm", str);
      System.out.println(result);
    }
    catch (Exception e)
    {
      e.printStackTrace();
    }
  }
}

If you want to wrap your JSON object under some root property of the context, let's say $json, then it's even simpler:

....
JSONObject jsonObj = new JSONObject(jsonString);
VelocityContext context = new VelocityContext();
context.put("json", jsonObj);        
....