How to edit tags in html String in Java

I have a html string:

<p>1</p> <p><img src="/filename.jpg" /></p> 
<p>2</p> <p><img src="/filename.jpg" alt="1324" width="600" height="180" /></p>
<p>3</p> <p><img style="border-width: 1px;" src=/filename.jpg" alt="" width="1000" height="300" /></p>
<p>4</p> <p><img style="border-width: 1px; max-width:100%" src=/filename.jpg" alt="" width="1000" height="300" /></p>

I need to search for all img tags in this string. If it doesn't have that property, insert style="max-width:100%" as an attribute to them. If that img tag already has the style attribute, then I need to add property "max-width:100%". I use Java.

How to accomplish this?

Solution

Use the Jsoup lib.
Download Jar or using mvn.

import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.select.Elements;

/**
 * Created by hwding on 3/8/17.
 */
public class Bar {
    public static void main(String[] args) {
        String string = "<p>1</p> <p><img src=\"/filename.jpg\" /></p> <p>2</p> <p><img src=\"/filename.jpg\" alt=\"1324\" width=\"600\" height=\"180\" /></p> <p>3</p> <p><img style=\"border-width: 1px;\" src=/filename.jpg\" alt=\"\" width=\"1000\" height=\"300\" /></p> <p>4</p> <p><img style=\"border-width: 1px; max-width:100%\" src=/filename.jpg\" alt=\"\" width=\"1000\" height=\"300\" /></p>";

        Document document = Jsoup.parse(string);
        Elements elements = document.select("img");

        elements.forEach(e -> {
            if(!e.hasAttr("style"))
                e.attr("style", "max-width:100%");
            System.out.println(e.toString());
        });
    }
}

Output:

<img src="/filename.jpg" style="max-width:100%">
<img src="/filename.jpg" alt="1324" width="600" height="180" style="max-width:100%">
<img style="border-width: 1px;" src="/filename.jpg&quot;" alt="" width="1000" height="300">
<img style="border-width: 1px; max-width:100%" src="/filename.jpg&quot;" alt="" width="1000" height="300">