How-To: Android Client – Server designs

Applications are usually designed so that a Server provides a service to a Client. Choosing an implementation depends on the requirements. Inside this article I will be explaining three implementation types:

• SOAP
• Servlet
• JSON

I will use the Android application which was developed inside my previous post.

SOAP

Simple Object Access Protocol is basically designed to provide a lightweight mechanism to exchange data in a XML format. Setting up a SOAP web service isn’t al that difficult. There is a disadvantage of using SOAP, and that’s overhead. Because there is no default SOAP support inside the Android library, I will be using kSOAP.

So lets set-up an implementation.

1. Create a server implementation
     public class Hello {
     
          public String sayHello(String name) {
               return "Hello " + name;
          }
     }
2. Create an Android implementation
3. Create a call to the server
     private void callService(SoapSerializationEnvelope envelope) {
          HttpTransportSE androidHttpTransport = new HttpTransportSE(URL);

          // Call the URL
          try {
               androidHttpTransport.call(SOAP_ACTION, envelope);
          } catch (IOException e) {
               display("Error:" + e.getClass().getName() + ": " + e.getMessage());
          } catch (XmlPullParserException e) {
               display("Error:" + e.getClass().getName() + ": " + e.getMessage());
          }
     }
4. Handle the response
     private SoapPrimitive getResultFromService(String text) {
          SoapObject request = new SoapObject(NAMESPACE, METHOD_NAME);
          SoapSerializationEnvelope envelope = new SoapSerializationEnvelope(SoapEnvelope.VER11);

          request.addProperty("name", text);

          envelope.setOutputSoapObject(request);

          callService(envelope);

          SoapPrimitive result = null;
          try {
               result = (SoapPrimitive) envelope.getResponse();
          } catch (SoapFault e) {
               display("Error:" + e.getClass().getName() + ": " + e.getMessage());
          }
          return result;
     }

Download source code BackEndWSDL [5kB] and FrondEndWSDL [114kB]

Servlet

The most simple form of exchanging data is by way of HTTP(s) with the use of Java Servlets. There’s no need to serialize to/from XML, so it can be a real time saver.

So lets set-up an implementation.

1. Create a server implementation
     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
          String text = "";
          StringBuffer sb = new StringBuffer();
          try {
               BufferedReader reader = new BufferedReader(new InputStreamReader(request.getInputStream()));
               String line = reader.readLine();
               while (line != null) {
                    sb.append(line);
                    line = reader.readLine();
               }
               if (sb.length() != 0) {
                    text = sb.toString();
               }
          } catch (Exception e) {
          }

          response.setContentType("text/plain");
          response.setHeader("Cache-Control", "no-cache");

          if (StringUtils.isNotEmpty(text)) {
               response.getWriter().write(HELLO_STRING + text);
          } else {
               response.getWriter().write(HELLO_STRING);
          }

     }
2. Create an Android implementation
3. Create a call to the server
     private InputStream callService(String text) {
          InputStream in = null;
         
          try {
               URL url = new URL(SERVLET_URL);
               URLConnection conn = url.openConnection();

               
               HttpURLConnection httpConn = (HttpURLConnection) conn;
               httpConn.setRequestMethod("POST");
               httpConn.setDoInput(true);
               httpConn.setDoOutput(true);
               httpConn.connect();
               
               DataOutputStream dataStream = new DataOutputStream(conn.getOutputStream());
               
               dataStream.writeBytes(text);
               dataStream.flush();
            dataStream.close();

            int responseCode = httpConn.getResponseCode();
               if (responseCode == HttpURLConnection.HTTP_OK) {
                    in = httpConn.getInputStream();
               }
          } catch (Exception ex) {
               display("Error: Not not connect");
          }
          return in;
     }
4. Handle the response
     private String getResultFromServlet(String text) {
          String result = "";
          InputStream in = callService(text);
          if(in!=null) {
               result= convertStreamToString(in);
          } else {
               result = "Error: Service not returning result";
          }
          return result;
     }
     private static String convertStreamToString(InputStream is) {
          BufferedReader reader = new BufferedReader(new InputStreamReader(is));
          StringBuilder sb = new StringBuilder();

          String line = null;
          try {
               while ((line = reader.readLine()) != null) {
                    sb.append(line + "\n");
               }
          } catch (IOException e) {
               e.printStackTrace();
          } finally {
               try {
                    is.close();
               } catch (IOException e) {
                    e.printStackTrace();
               }
          }
          return sb.toString();
     }

Download source code BackEndServlet [242kB] and FrondEndServlet [16kB]

JSON

So SOAP has the advantage of using a model, and HTTP(s) has the advantage of being simple. There is an implementation that uses both. JavaScript Object Notation is a light-weight data-interchange format, think of it as XML on a diet

So lets set-up an implementation.

1. Create a server implementation
     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
          String text = "";
          StringBuffer sb = new StringBuffer();
          try {
               BufferedReader reader = new BufferedReader(new InputStreamReader(request.getInputStream()));
               String line = reader.readLine();
               while (line != null) {
                    sb.append(line);
                    line = reader.readLine();
               }
               if (sb.length() != 0) {
                    text = sb.toString();
               }
          } catch (Exception e) {
               System.out.println(e);
          }

          response.setContentType("text/plain");
          response.setHeader("Cache-Control", "no-cache");
         
          JsonObject jsonObj=new JsonObject();
         
          if (StringUtils.isNotEmpty(text)) {
               jsonObj.addProperty(JSON_KEY, HELLO_STRING + text);
          } else {
               jsonObj.addProperty(JSON_KEY, HELLO_STRING);
          }
          PrintWriter out = response.getWriter();
          out.println(jsonObj);
     }
2. Create an Android implementation
3. Create a call to the server
     private InputStream callService(String text) {
          InputStream in = null;

          try {
               URL url = new URL(SERVLET_URL);
               URLConnection conn = url.openConnection();

               HttpURLConnection httpConn = (HttpURLConnection) conn;
               httpConn.setRequestMethod("POST");
               httpConn.setDoInput(true);
               httpConn.setDoOutput(true);
               httpConn.connect();

               DataOutputStream dataStream = new DataOutputStream(conn
                         .getOutputStream());

               dataStream.writeBytes(text);
               dataStream.flush();
               dataStream.close();

               int responseCode = httpConn.getResponseCode();
               if (responseCode == HttpURLConnection.HTTP_OK) {
                    in = httpConn.getInputStream();
               }
          } catch (Exception ex) {
               display("Error: Not not connect");
          }
          return in;
     }
4. Handle the response
     private String getResultFromServlet(String text) {
          String result = "";

          InputStream in = callService(text);
          if (in != null) {
               JSONObject jsonResponse;
               try {
                    jsonResponse = new JSONObject(convertStreamToString(in));
                    result = jsonResponse.getString("output");
               } catch (JSONException e) {
                    result = "Error: JSON Object couldn't be made";
               }
          } else {
               result = "Error: Service not returning result";
          }
          return result;
     }
          private static String convertStreamToString(InputStream is) {
          BufferedReader reader = new BufferedReader(new InputStreamReader(is));
          StringBuilder sb = new StringBuilder();

          String line = null;
          try {
               while ((line = reader.readLine()) != null) {
                    sb.append(line + "\n");
               }
          } catch (IOException e) {
          } finally {
               try {
                    is.close();
               } catch (IOException e) {
                    e.printStackTrace();
               }
          }
          return sb.toString();
     }

Download source code BackEndJSON [399kB] and FrondEndJSON [15kB]