Android连接服务器Servlet
登陆页面输入用户名和密码，登陆成功后跳转到主页面，失败时显示错误信息。传递参数时用BasicNameValuePair的List以httpPost.setEntity的方式来做，不能用HttpParams。

userName = (EditText) this.findViewById(R.id.editTextUserName);password = (EditText) this.findViewById(R.id.editTextPassword);errorMsg = (TextView) this.findViewById(R.id.textViewLoginMsg);Button loginBtn = (Button) this.findViewById(R.id.btnLogin);loginBtn.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View arg0) {String result;/* 发送部分 */try {HttpClient httpClient = new DefaultHttpClient();String address = strUrl;HttpPost httpPost = new HttpPost(address);List<BasicNameValuePair> params = new LinkedList<BasicNameValuePair>();params.add(new BasicNameValuePair("username", userName.getText().toString()));params.add(new BasicNameValuePair("password", password.getText().toString()));httpPost.setEntity(new UrlEncodedFormEntity(params, "utf-8")); //将参数填入POST Entity中HttpResponse httpResponse = httpClient.execute(httpPost);/* 接收 */if (httpResponse.getStatusLine().getStatusCode() == 200) {result = EntityUtils.toString(httpResponse.getEntity());/* json文本解析 */JSONTokener jsonParser = new JSONTokener(result);JSONObject jsonResult = (JSONObject) jsonParser.nextValue();String status = jsonResult.getString("loginStatus");String outMessage = jsonResult.getString("outMessage");if(status.equals("true")){Intent i = new Intent(LoginActivity.this, MainActivity.class);i.putExtra("username", outMessage);startActivityForResult(i, FIRST_REQUEST_CODE);} else {errorMsg.setVisibility(View.VISIBLE);errorMsg.setText(outMessage);}} else {errorMsg.setVisibility(View.VISIBLE);errorMsg.setText("网络连接问题。CODE:" + httpResponse.getStatusLine().getStatusCode());}} catch (JSONException e) {e.printStackTrace();} catch (UnsupportedEncodingException e) {e.printStackTrace();} catch (ClientProtocolException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}}});