header.addField(Fields.contentType("multipart/form-data; boundary=foo"));
message.setHeader(header);
HttpMultipart multipart = new HttpMultipart("form-data");
multipart.setParent(message);
FormBodyPart p1 = new FormBodyPart(
"field1",
new StringBody("this stuff"));
FormBodyPart p2 = new FormBodyPart(
"field2",
new StringBody("that stuff", Charset.forName("US-ASCII")));
FormBodyPart p3 = new FormBodyPart(
"field3",
new StringBody("all kind of stuff"));
multipart.addBodyPart(p1);
multipart.addBodyPart(p2);