How to convert an InputStream to a DataHandler?

Question

I\'m working on a java web application in which files will be stored in a database. Originally we retrieved files already in the DB by simply calling getBytes o

Answer 1

Here is an answer for specifically working with the Spring Boot org.springframework.core.io.Resource object which is I think how a lot of us are getting here. Note that you might need to modify the content type in the code below as I'm inserting a png file into an html formatted email.

Note: As others have mentioned, merely attaching an InputStream isn't enough as it gets used multiple times, just mapping through to Resource.getInputStream() does the trick.

public class SpringResourceDataSource implements DataSource {
    private Resource resource;

    public SpringResourceDataSource(Resource resource) {
        this.resource = resource;
    }

    @Override
    public InputStream getInputStream() throws IOException {
        return resource.getInputStream();
    }

    @Override
    public OutputStream getOutputStream() throws IOException {
        throw new UnsupportedOperationException("Not implemented");
    }

    @Override
    public String getContentType() {
        return "image/png";
    }

    @Override
    public String getName() {
        return "SpringResourceDataSource";
    }
}   

Usage of the class looks like this:

    PathMatchingResourcePatternResolver pathMatchingResourcePatternResolver = new PathMatchingResourcePatternResolver();
    Resource logoImage = pathMatchingResourcePatternResolver.getResource("/static/images/logo.png");
    MimeBodyPart logoBodyPart = new MimeBodyPart();
    DataSource logoFileDataSource = new SpringResourceDataSource(logoImage);


    logoBodyPart.setDataHandler(new DataHandler(logoFileDataSource));