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![JSON { "employees": [ { "firstname":"John" , "lastname":"Doe" }, { "firstname":"Anna" , "lastname":"Smith" }, { "firstname":"Peter" , “lastname":"Jones" } ] }](https://image.slidesharecdn.com/androiddev3-150925070518-lva1-app6891/75/Android-dev-3-16-2048.jpg)
![JSON • Name/Value Pairs: “name” : “value” – "firstname":"John" • JSON Objects: , … - – { "firstname":"John" , "lastname":"Doe" } • JSON Arrays: * …, …, … + [ { "firstname":"John" , "lastname":"Doe" }, { "firstname":"Anna" , "lastname":"Smith" }, … ]](https://image.slidesharecdn.com/androiddev3-150925070518-lva1-app6891/75/Android-dev-3-17-2048.jpg)
Uploaded byAravindharamanan S
Android dev 3
This document discusses using web services in Android development. It covers making HTTP requests to web services, parsing the response, and creating your own basic web service using PHP. Key points include constructing the URL, executing asynchronous HTTP requests, checking response codes, and parsing XML or JSON responses. The document provides code samples for making a request and handling the response. It also discusses possible issues like blocking the UI thread during the request and suggests using threads to avoid this. Finally, it proposes an exercise to build an accessible application using a web service and GPS.
Android dev 3
- 1. Intro to Android Development3 Accessibility Capstone Nov 29, 2011
- 2. Outline • Web Services •XML vs. JSON • Your Own Web Service
- 3. Hello, Android The keyto the capstone… (sort of)
- 4. Using Web Services HTTPRequest HTTP Response
- 5. Using Web Services HTTPRequest HTTP Response
- 6. Using Web Services HTTPRequest HTTP Response webserver some program
- 7. Why use aweb service?
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- 11. An HTTP Request http://www.google.com http://www.geonames.org/ http://ws.geonames.org/wikipediaSearch?q=l ondon&maxRows=10 Addingparameters: ?param1=val1¶m2=val2
- 12. An HTTP Response •Response code 2xx = success! 4xx = client error 5xx = server error
- 13. An HTTP Response •Response code 2xx = success! 4xx = client error 5xx = server error • Response body (XML, JSON) <geonames> <entry> <lang>en</lang> <title>London</title> <summary> London (; and largest urban area of England and the United Kingdom. At its core, the ancient City of London, to which the name historically belongs, still retains its limited mediaeval boundaries; but since at least the 19th century the name "London" has also referred to the whole metropolis which has developed around
- 14. XML and JSON •Parsers – XML: Different traversals include SAX, DOM, etc. – JSON: Look at JSONObject/JSONArray classes • Overviews – http://www.w3schools.com/json/ – http://www.w3schools.com/xml/ • Recommend using JSON: small, easy to parse, fast
- 15. XML <?xml version="1.0"?> <note> <to>Tove</to> <from>Jani</from> <heading>Reminder</heading> <body>Don't forgetme this weekend!</body> </note>
- 16. JSON { "employees": [ { "firstname":"John", "lastname":"Doe" }, { "firstname":"Anna" , "lastname":"Smith" }, { "firstname":"Peter" , “lastname":"Jones" } ] }
- 17. JSON • Name/Value Pairs:“name” : “value” – "firstname":"John" • JSON Objects: , … - – { "firstname":"John" , "lastname":"Doe" } • JSON Arrays: * …, …, … + [ { "firstname":"John" , "lastname":"Doe" }, { "firstname":"Anna" , "lastname":"Smith" }, … ]
- 18. How to Usea Webservice • Find a webservice or write your own example: www.geonames.org • Construct the URL add parameters, extra headers (if needed • Execute the request asynchronously • Check the response code 200 = success, 4xx = client error, 5xx = server error • Parse the response body
- 19. Construct the URL finalstatic String PLACE_NAME = "Seattle"; final static String URL = “http://ws.geonames.org/” + “wikipediaSearch?q=" + PLACE_NAME + "&maxRows=4";
- 20. Execute the Request publicString callWebService(){ HttpClient httpclient = new DefaultHttpClient(); HttpGet request = new HttpGet(URL); String result = ""; ResponseHandler<String> handler = new BasicResponseHandler(); try { result = httpclient.execute(request, handler); } catch (ClientProtocolException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } httpclient.getConnectionManager().shutdown(); return result; }
- 21. Execute the Request publicString callWebService(){ HttpClient httpclient = new DefaultHttpClient(); HttpGet request = new HttpGet(URL); String result = ""; ResponseHandler<String> handler = new BasicResponseHandler(); try { result = httpclient.execute(request, handler); } catch (ClientProtocolException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } httpclient.getConnectionManager().shutdown(); return result; } the client will open a connection and executes the request
- 22. Execute the Request publicString callWebService(){ HttpClient httpclient = new DefaultHttpClient(); HttpGet request = new HttpGet(URL); String result = ""; ResponseHandler<String> handler = new BasicResponseHandler(); try { result = httpclient.execute(request, handler); } catch (ClientProtocolException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } httpclient.getConnectionManager().shutdown(); return result; } request object contains URL
- 23. Execute the Request publicString callWebService(){ HttpClient httpclient = new DefaultHttpClient(); HttpGet request = new HttpGet(URL); String result = ""; ResponseHandler<String> handler = new BasicResponseHandler(); try { result = httpclient.execute(request, handler); } catch (ClientProtocolException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } httpclient.getConnectionManager().shutdown(); return result; } this kind of response handler will return the response body as a string if the request was successful
- 24. Execute the Request publicString callWebService(){ HttpClient httpclient = new DefaultHttpClient(); HttpGet request = new HttpGet(URL); String result = ""; ResponseHandler<String> handler = new BasicResponseHandler(); try { result = httpclient.execute(request, handler); } catch (ClientProtocolException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } httpclient.getConnectionManager().shutdown(); return result; } executes the request and processes the response using the handler
- 25. Execute the Request publicString callWebService(){ HttpClient httpclient = new DefaultHttpClient(); HttpGet request = new HttpGet(URL); String result = ""; ResponseHandler<String> handler = new BasicResponseHandler(); try { result = httpclient.execute(request, handler); } catch (ClientProtocolException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } httpclient.getConnectionManager().shutdown(); return result; } generated by the handler
- 26. Calling on callWebService()and Displaying the Results public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); TextView tv = (TextView) findViewById(R.id.resultTV); String result = callWebService(); tv.setText(result); }
- 27. What’s wrong withthe example?
- 28. What’s wrong withthe example? • result = httpclient.execute(request, handler); blocks and waits for entire page to download! • Solution: threads – You may have to use another thread in your application! – java.util.concurrent package – Good example in Hello, Android (web services chapter) – Keeping it all simple is key, then program away
- 29. Your Own WebService • May need if… – You need additional processing power – You want to tie phone app into a web product – Etc… • If you create your own web service… – Server Side Scripting (PHP, Ruby on Rails, etc.) – Web server (abstract.cs, etc.)
- 30. Your Own WebService • Very Basic PHP Overview: 1. Create .php page (http://foo.com/service.php) 2. Use $_GET*‘param’+ (http://foo.com/service.php?param=helloworld 3. Do stuff with the parameters ($bar = $_GET*‘param’+ ) 4. Format output into XML or JSON or whatever you need (echo $bar) • Phone app will visit php page and get its result
- 31. Other Topics • GPSand Sensors – LocationManager • SQL Database – SQLiteDatabase • Camera • Multitouch
- 32. Exercise Develop an applicationthat uses a web service that is accessible to a blind person. For extra brownie points: use the GPS! -Use TTS to make the application accessible. -Find a web service (you can start from Geonames) -Find and use a Java XML parser to parse the response body (you can try SAX) Note: many web services use JSON, not XML.