How to send data(table) from database via email in java?

I can send regular emails (not from database), but how could I send full table in an email?
This is my code:

private static Message preparedMessage(Session session, String myAccountEmail,
        String recepient) {
    try {
        Message message = new MimeMessage(session);
        message.setFrom(new InternetAddress(myAccountEmail));
        message.setRecipient(Message.RecipientType.TO, new InternetAddress(recepient));
        message.setSubject("Email using Java");
        String htmlTest="<h2> i'm sending an email!</h2>";
        message.setContent(htmlTest, "text/html"); 
       }
        return message;
    } catch (Exception ex) {
        Logger.getLogger(JavaMailUtil.class.getName()).log(Level.SEVERE, null, ex);
    }
    return null;
}

I tried something simple like this:

     List <PetrolData> petrolList = MP_RacunDAO.select("03.08.2020", "11.08.2020"); //This is data that i want to put in table
       for(PetrolData pd : petrolList){
        String htmlTable = "<table border='1'> <tr> "
                + "<th>Column 1</td>"
                + "<th>Column 2</td>"
                + "<th>Column 3</td>"
                + "</tr>"
                + "<tr>"
                + "<td>"+pd.getTitle()+"</td>"
                + "<td>"+pd.getSum1()+"</td>"
                + "<td>"+pd.getSum2()+"</td>"                   
                + "</tr>"
                + "</table>";
            }

Obviously, It is not working for me, what can I do?

If you want to create an HMTL table in a row without using any external library, you can use a StringBuilder for that.

You would basically have to add the opening tag of the table and the header row before you loop through the data, then add a row for each PetrolData and after the loop you add the closing tag of the table.

See this example (which uses potentially unnecessary linebreaks and tabs, but they are useful for example output, because I won't send an email here):

public static void main(String[] args) {
	// sample data
	List<PetrolData> petrolDataList = new ArrayList<>();
	petrolDataList.add(new PetrolData("Petrol 1", 4.1f, 8.2f, 12.4f));
	petrolDataList.add(new PetrolData("Petrol 2", 5.3f, 9.2f, 13.24f));
	petrolDataList.add(new PetrolData("Petrol 3", 6.0f, 10.1f, 14.312f));
	petrolDataList.add(new PetrolData("Petrol 4", 7.7f, 11.9f, 15.15f));
	petrolDataList.add(new PetrolData("Petrol 5", 8.45f, 12.0f, 16.936f));
	petrolDataList.add(new PetrolData("Petrol 6", 9.67f, 13.2f, 17.777f));
	
	StringBuilder htmlTableBuilder = new StringBuilder();
	// open the table
	htmlTableBuilder.append("<table border=\"1\">").append(System.lineSeparator());
	// open a rown, header row here
	htmlTableBuilder.append("\t").append("<tr>").append(System.lineSeparator());
	// add the headers to the header row
	htmlTableBuilder.append("\t").append("\t").append("<th>").append("Title").append("</th>").append(System.lineSeparator());
	htmlTableBuilder.append("\t").append("\t").append("<th>").append("Sum 1").append("</th>").append(System.lineSeparator());
	htmlTableBuilder.append("\t").append("\t").append("<th>").append("Sum 2").append("</th>").append(System.lineSeparator());
	htmlTableBuilder.append("\t").append("\t").append("<th>").append("Sum 3").append("</th>").append(System.lineSeparator());
	// close the header row
	htmlTableBuilder.append("\t").append("</tr>").append(System.lineSeparator());
	
	// add a data row for each PetrolData
	for (PetrolData pd : petrolDataList) {
		// open a row again
		htmlTableBuilder.append("\t").append("<tr>").append(System.lineSeparator());
		// add the data
		htmlTableBuilder.append("\t").append("\t").append("<td>").append(pd.getTitle()).append("</td>").append(System.lineSeparator());
		htmlTableBuilder.append("\t").append("\t").append("<td>").append(pd.getSum1()).append("</td>").append(System.lineSeparator());
		htmlTableBuilder.append("\t").append("\t").append("<td>").append(pd.getSum2()).append("</td>").append(System.lineSeparator());
		htmlTableBuilder.append("\t").append("\t").append("<td>").append(pd.getSum3()).append("</td>").append(System.lineSeparator());
		// close the row
		htmlTableBuilder.append("\t").append("</tr>").append(System.lineSeparator());
	}
	// and close the table
	htmlTableBuilder.append("</table>");
	
	// then print the result
	System.out.println(htmlTableBuilder.toString());
}

The output of this is the following, which you could easily embed in a valid HTML mail:

<table border="1">
<tr>
<th>Title</th>
<th>Sum 1</th>
<th>Sum 2</th>
<th>Sum 3</th>
</tr>
<tr>
<td>Petrol 1</td>
<td>4.099999904632568</td>
<td>8.199999809265137</td>
<td>12.399999618530273</td>
</tr>
<tr>
<td>Petrol 2</td>
<td>5.300000190734863</td>
<td>9.199999809265137</td>
<td>13.239999771118164</td>
</tr>
<tr>
<td>Petrol 3</td>
<td>6.0</td>
<td>10.100000381469727</td>
<td>14.312000274658203</td>
</tr>
<tr>
<td>Petrol 4</td>
<td>7.699999809265137</td>
<td>11.899999618530273</td>
<td>15.149999618530273</td>
</tr>
<tr>
<td>Petrol 5</td>
<td>8.449999809265137</td>
<td>12.0</td>
<td>16.93600082397461</td>
</tr>
<tr>
<td>Petrol 6</td>
<td>9.670000076293945</td>
<td>13.199999809265137</td>
<td>17.777000427246094</td>
</tr>
</table>

Pay attention to the format of doubles, you might have to apply a DecimalFormat or anything similar for correct values to be shown.