您的问题类似于this question（您显然使用了embed.setThumbnail而不是embed.setImage）

* Sets the Thumbnail of the embed.
 * MessageChannel channel; // = reference of a MessageChannel
 * EmbedBuilder embed = new EmbedBuilder();
 * InputStream file = new URL("https://http.cat/500").openStream();
 * embed.setThumbnail("attachment://cat.png") // we specify this in sendFile as "cat.png"
 *      .setDescription("This is a cute cat :3");
 * channel.sendFiles(FileUpload.fromData(file, "cat.png")).setEmbeds(embed.build()).queue();