rest-assured/src/main/java/io/restassured/config/DecoderConfig.java
public DecoderConfig defaultCharsetForContentType(String charset, String contentType) {
        notNull(charset, "Charset");
        notNull(contentType, "ContentType");
        Map<String, String> map = new HashMap<String, String>(contentTypeToDefaultCharset);
        map.put(trim(contentType).toLowerCase(), trim(charset));
        return new DecoderConfig(charset, useNoWrapForInflateDecoding, true, contentDecoders, map);
    }
public DecoderConfig defaultCharsetForContentType(String charset, String contentType) {
        notNull(charset, "Charset");
        notNull(contentType, "ContentType");
        Map<String, String> map = new HashMap<String, String>(contentTypeToDefaultCharset);
        map.put(trim(contentType).toLowerCase(), trim(charset));
        return new DecoderConfig(charset, useNoWrapForInflateDecoding, true, contentDecoders, map);
    }
Specify the default charset to use for the specific content-type if it's not specified in the content-type header explicitly

@param charset     The charset to use as default (unless specified explicitly)
@param contentType The content-type
@return A new instance of {@link DecoderConfig}