Er. Ashish Aggarwal

To do this you can use Aspose lib. Aspose cells gives a wide range of api to perform actions on excel sheet. Here is a link where you found how to export excel sheet as png/jpeg images and also how to get the images of excel componnt too.

http://iandjava.blogspot.in/2013/07/convert-excel-document-to-images.html

To convert String to Dom/Document object
Document document = builder.parse(new InputSource(new StringReader(inputString)));

and if you have input stream that you can directly transform stram to document object
Document document = builder.parse(new InputSource(inputStream));

for futher transformation of string to dom and dom to String object please refer this link.
http://iandjava.blogspot.com/2013/06/java-string-to-document-and-document-to.html

To Convert String from input Stream simple way is

InputStream is = new ByteArrayInputStream(inputString.getBytes());
and to convert string into a specified format so we can provide the charset as

InputStream in = new ByteArrayInputStream(inputString.getBytes("UTF-8"));
for futher reference to convert string from input stream and input stream to string refer link.
http://iandjava.blogspot.in/2013/06/package-com.html