原来部分代码如下:
CloseableHttpClient client = HttpClients.createDefault();
HttpPost post = new HttpPost(url);
try {
    StringEntity s = new StringEntity(jsonStr);
    s.setContentEncoding("UTF-8");
    s.setContentType("application/json");//发送json数据需要设置contentType
    post.setEntity(s);
    CloseableHttpResponse res = client.execute(post);
修改如下,在初始化StringEntity时指定UTF-8:
CloseableHttpClient client = HttpClients.createDefault();
HttpPost post = new HttpPost(url);
try {
    StringEntity s = new StringEntity(jsonStr,"UTF-8");
    s.setContentEncoding("UTF-8");
    s.setContentType("application/json");//发送json数据需要设置contentType
    post.setEntity(s);
    CloseableHttpResponse res = client.execute(post);