<g:form controller="post" action="save" enctype="multipart/form-data">
      My picture  <input type="file" name="myPicture" />
    <g:submitButton name="submit" value="Save"/>
</g:form>

class Post {

byte[] myPicture

static mapping = {
    myPicture type:  "blob"
}

static constraints = {
    myPicture(nullable:false)
}

}

def save = {
    def post = loadPost(params.id)

    post.properties = params

    if(post.save()) {
        print "hallo world"
        redirect(action:'list', params:params)
    } else {
        render(view:'edit', model:[post:post])
    }
}

2009-04-27 18:16:07,319 [20806951@qtp0-0] ERROR errors.GrailsExceptionResolver  - java.lang.ClassCastException: [B cannot be cast to java.sql.Blob

def save = {

    def post = loadPost(params.id)

    def f = request.getFile('myPicture')

    post.myPicture = f.getBytes()
    post.pictureType = f.getContentType()


    if(post.save()) {

def upload = {
    def f = request.getFile('myFile')
    if(!f.empty) {
      f.transferTo( new File('/some/local/dir/myfile.txt') )
      response.sendError(200,'Done');
    }
    else {
       flash.message = 'file cannot be empty'
       render(view:'uploadForm')
    }
}