java - 为什么我收到HTTP 400错误请求

我正在使用HTTP客户端（从http://www.mkyong.com/java/apache-httpclient-examples/复制的代码）发送发布请求。我一直在尝试将它与http://postcodes.io一起使用以查找大量邮政编码，但是失败了。根据http://postcodes.io，我应该以以下JSON格式向http://api.postcodes.io/postcodes发送发帖请求：{"postcodes" : ["OX49 5NU", "M32 0JG", "NE30 1DP"]}，但是我总是收到HTTP响应代码400。
我在下面包含了我的代码。请告诉我我做错了什么？
谢谢

private void sendPost() throws Exception {

    String url = "http://api.postcodes.io/postcodes";
    HttpClient client = HttpClientBuilder.create().build();
    HttpPost post = new HttpPost(url);

    List<NameValuePair> urlParameters = new ArrayList<NameValuePair>();
    urlParameters.add(new BasicNameValuePair("postcodes", "[\"OX49 5NU\", \"M32 0JG\", \"NE30 1DP\"]"));
    post.setEntity(new UrlEncodedFormEntity(urlParameters));
    HttpResponse response = client.execute(post);

    System.out.println("Response Code : "
                + response.getStatusLine().getStatusCode());
    System.out.println("Reason : "
            + response.getStatusLine().getReasonPhrase());
    BufferedReader br = new BufferedReader(
            new InputStreamReader(response.getEntity().getContent()));
    StringBuffer result = new StringBuffer();
    String line = "";
    while ((line = br.readLine()) != null) {
        result.append(line);
    }
    br.close();
    System.out.println(result.toString());
}

最佳答案

这有效，不建议使用HTTP.UTF_8：

String url = "http://api.postcodes.io/postcodes";
HttpClient client = HttpClientBuilder.create().build();
HttpPost post = new HttpPost(url);

StringEntity params =new StringEntity("{\"postcodes\" : [\"OX49 5NU\", \"M32 0JG\", \"NE30 1DP\"]}");
post.addHeader("Content-Type", "application/json");
post.setEntity(params);