response.body().string()获取的中文乱码怎么解决？

FormBody requestBody = new FormBody.Builder()
        .add("username",user.getUserName())
        .add("password",user.getPassWord())
        .build();
Request.Builder builder = new Request.Builder();
final Request request = builder
        .url(BaseUrl + "login")
        .post(requestBody)
        .build();
Call call = okHttpClient.newCall(request);
Response response = call.execute();
response.body().contentType();
String res = response.body().string();