在android上发送带有身份验证的json对象时出现错误请求

Question

当我尝试发送带有身份验证的json对象时，我收到错误bad request。我看了How to send a JSON object over HttpClient Request with Android?，但它没有解决我的问题。

public void getServerData() throws JSONException, ClientProtocolException, IOException {

    ArrayList<String> stringData = new ArrayList<String>();
    DefaultHttpClient httpClient = new DefaultHttpClient();
    ResponseHandler <String> resonseHandler = new BasicResponseHandler();

    byte[] data = "myusername:mypassword".getBytes("UTF-8");
    String encoding = Base64.encodeToString(data, Base64.DEFAULT);

    HttpPost postMethod = new HttpPost("http://url/email_check.json");
    postMethod.setHeader(HTTP.CONTENT_TYPE, "application/json");

    postMethod.setHeader("Authorization", "Basic " + encoding);

    JSONObject json = new JSONObject();
    json.put("email","somebody@email.com");


    postMethod.setEntity(new ByteArrayEntity(json.toString().getBytes("UTF8")));
    String response = httpClient.execute(postMethod,resonseHandler);
    Log.e("response :", response);
    }

行String response = httpClient.execute(postMethod,resonseHandler);导致ClientProtocolException如下：

cause: org.apache.http.client.HttpResponseException: Bad Request
detailMessage: Bad Request
stackState: (id=830103290336)
stackTrace: null
statusCode: 400

知道出了什么问题吗？