public AbstractHttpFileBuilder contentType(CharSequence contentType) {
        requireNonNull(contentType, "contentType");
        autoDetectedContentType(false);
        return setHeader(HttpHeaderNames.CONTENT_TYPE, contentType);
    }
Sets the {@code "content-type"} header. This method is a shortcut for:
<pre>{@code
builder.autoDetectedContentType(false);
builder.setHeader(HttpHeaderNames.CONTENT_TYPE, contentType);
}</pre>
core/src/main/java/com/linecorp/armeria/server/file/AbstractHttpFileBuilder.java