public ContentPreviewerFactoryBuilder defaultCharset(Charset defaultCharset) {
        this.defaultCharset = requireNonNull(defaultCharset, "defaultCharset");
        return this;
    }
Sets the default {@link Charset} used to produce the text preview when a charset is not specified in the
{@code "content-type"} header. {@link StandardCharsets#UTF_8} is used by default.

<p>Note that this charset is only for the text preview, not for the binary preview.</p>
core/src/main/java/com/linecorp/armeria/common/logging/ContentPreviewerFactoryBuilder.java