Replace Email Template Using Java Pattern and Matcher Class

• Let's say you have some simple email template that contains details like email address, phone/mobile or activation link, etc and you want to generate an email template without any free marker dependency using Java Pattern and Matcher class. So let's try to make that and also download a link is given bottom side.

Step 1:  

• Here I created one email template which HTML code looks below.

Hi {{user.first_name}} {{user.last_name}},
Welcome and thank you for subscribing.
    
Now that you’ve subscribed, you’ll be receiving our emails {{freq.duration}}.
        These emails will contain our most recent article or news. You will also receive exclusive offers, promotions,
        and information on events.

        Our team is happy to have you on board. If you have any questions or comments,
        please don’t hesitate to contact us. You can simply reply to our emails or contact me directly using the contact information below.
Thanks again!

Step 2: 

• As you can see above the HTML body contains  some regex pattern like {{user.first_name}}, {{user.last_name}} etc. 
• There are identifiers where we will replace with JSON values

Step 3: Sample input JSON

{
 "user": {
  "first_name": "Joseph",
  "last_name": "Miller"
 },
 "freq": {
  "duration": "2 Days of a Week"
 }
}

Step 4: 

• Let's create a Java file and write logic to replace the HTML body.

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.apache.commons.io.FileUtils;

import java.io.File;
import java.io.IOException;
import java.net.URISyntaxException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class App {
    private static final String INPUT_HTML_FILE = "welcome_email_template.html";
    private static final String OUTPUT_HTML_FILE = "welcome_output.html";
    private static ObjectMapper mapper = new ObjectMapper();

    public static void main(String[] args) throws IOException, URISyntaxException {
        JsonNode jsonNode = getSampleJson();
        String fileContent = getFileContent();
        Pattern patter = Pattern.compile("\\{\\{(user|freq)\\.([a-zA-Z_]+)\\}\\}", Pattern.CASE_INSENSITIVE);
        Matcher matcher = patter.matcher(fileContent);
        StringBuffer replaceEmailBody = new StringBuffer();
        while (matcher.find()) {
            String keyName = matcher.group(1); // Get keyName like User, Freq etc
            String attribute = matcher.group(2); // Get Attribute like first name, last name etc
            Object replaceString = replaceEmailBodyFromJsNode(keyName, attribute, jsonNode);
            matcher.appendReplacement(replaceEmailBody, String.valueOf(replaceString));
        }
        matcher.appendTail(replaceEmailBody);
        createOutPutHtmlFile(replaceEmailBody.toString());
    }


    private static JsonNode getSampleJson() throws IOException {
        String strJson = "{\"user\": {\"first_name\": \"Joseph\",\"last_name\": \"Miller\"},\"freq\": {\"duration\": \"2 Days of a Week\"}}";
        JsonNode jsonNode = mapper.readValue(strJson, JsonNode.class);
        return jsonNode;
    }

    private static String getFileContent() throws IOException {
        File file = getFile();
        return new String(Files.readAllBytes(file.toPath()));
    }

    private static Object replaceEmailBodyFromJsNode(String keyName, String attribute, JsonNode inputJs) {
        Object newValue = "";
        if (keyName.equals("user")) {
            if (inputJs.has(attribute)) {
                newValue = inputJs.path(keyName).path(attribute).asText();
            }
        } else if (keyName.equals("freq")) {
            if (inputJs.has(attribute)) {
                newValue = inputJs.path(keyName).path(attribute).asText();
            }
        }
        return newValue;
    }

    private static void createOutPutHtmlFile(String replaceEmailBody) throws IOException {
        File file = new File(getFile().getParent() + "/" + OUTPUT_HTML_FILE);
        file.createNewFile();
        FileUtils.writeStringToFile(file, replaceEmailBody, StandardCharsets.UTF_8);
    }

    private static File getFile() {
        ClassLoader classLoader = ClassLoader.getSystemClassLoader();
        File file = new File(classLoader.getResource(INPUT_HTML_FILE).getFile());
        return file;
    }
}

Step 5: Once you run the above Java code, you will get below the HTML output file.

Hi Joseph Miller,

Welcome and thank you for subscribing.

Now that you’ve subscribed, you’ll be receiving our emails 2 Days of a Week. These emails will contain our most recent article or news.You will also receive exclusive offers, promotions, and information on events. Our team is happy to have you on board. If you have any questions or comments, please don’t hesitate to contact us. You can simply reply to our emails or contact me directly using the contact information below.

Thanks again!

Download Zip File: Click Here 

Thanks