Add a form data part to the body.
Add a form data part to the body.
Add a part to the body.
Add a part to the body.
Add a part to the body.
Assemble the specified parts into a request body.
Set the MIME type. Expected values for {@code type} are {@link #FORM} (the default), {@link #ALTERNATIVE}, {@link #DIGEST}, {@link #PARALLEL} and {@link #MIXED}.