Parser JSoup change the tags to lower case letter

Unfortunately not, the constructor of Tag class changes the name to lower case:

private Tag(String tagName) {
    this.tagName = tagName.toLowerCase();
}

But there are two ways to change this behavour:

1. If you want a clean solution, you can clone / download the JSoup Git and change this line.
2. If you want a dirty solution, you can use reflection.

Example for #2:

Field tagName = Tag.class.getDeclaredField("tagName"); // Get the field which contains the tagname
tagName.setAccessible(true); // Set accessible to allow changes

for( Element element : doc.select("*") ) // Iterate over all tags
{
    Tag tag = element.tag(); // Get the tag of the element
    String value = tagName.get(tag).toString(); // Get the value (= name) of the tag

    if( !value.startsWith("#") ) // You can ignore all tags starting with a '#'
    {
        tagName.set(tag, value.toUpperCase()); // Set the tagname to the uppercase
    }
}

tagName.setAccessible(false); // Revert to false

Here is a code sample (version >= 1.11.x):

Parser parser = Parser.htmlParser();
parser.settings(new ParseSettings(true, true));
Document doc = parser.parseInput(html, baseUrl);

There is ParseSettings class introduced in version 1.9.3. It comes with options to preserve case for tags and attributes.