So far, Wednesday, February 03, :47 PM. So far,

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1 Binding_and_Refinement Page 1 So far, 3:47 PM So far, We've created a simple persistence project with cloud references. There were lots of relationships between entities that must be fulfilled. How do we keep that straight? How does one efficiently develop a cloud application?

2 Binding_and_Refinement Page 2 Stubbing, Binding, and Refinement 12:14 PM Stubbing, Binding, and Refinement Keys to AppEngine development: stubbing, binding, and refinement Stubbing: creating and naming a placeholder method/object/html item for later control. Binding: insuring that there is an exact match between attributes of several related objects Refinement: Proceeding to develop code from stubs, using full powers of Eclipse to remember bindings where appropriate!

3 Binding_and_Refinement Page 3 Stubbing HTML Sunday, January 30, :44 PM Stubbing HTML Create an HTML page that represents project input/output. Create "stubs" (empty elements) that will contain dynamic content. Name them via the ID field in HTML.

4 Binding_and_Refinement Page 4 Stubbing Widgets Sunday, January 30, :46 PM Second step: Create java describing widgets that appear on the page Bind them to ID's. Fill them with junk (but plausible) data for now. Widget is an implicit binding between HTML and (GWT) Java. Has a java exposure as an instance in the class of page. Has an HTML exposure that is used when stuffing it into an ID'd place.

5 Binding_and_Refinement Page 5 Kinds of widgets Sunday, January 30, :47 PM Some kinds of widgets FlexTable: a table of data, with many formatting options. Button: a pressable button. Label: settable text with no interaction options. Panel: a container for objects.

6 Binding_and_Refinement Page 6 Creating widgets Sunday, January 30, :48 PM Creating widgets: in onmoduleload method: Create a Java object for each HTML object to be managed. Put objects inside one another, as desired. Generate initial callback calls for dynamic content.

7 Binding_and_Refinement Page 7 Important caveats when stubbing Sunday, January 30, :51 PM Important caveats when stubbing Don't try to implement the whole stack at once. Test one stub at a time. Each stub should generate plausible (but not necessarily accurate) depictions. Debug clientside interactions first, then write serverside code.

8 Binding_and_Refinement Page 8 Bindings 12:30 PM Bindings Good news: created by "new project" wizard, maintained by Eclipse (sometimes). Bad news: very hard to rename things! A small suggestion: Save your project under a different name before trying to rename anything!

9 Binding_and_Refinement Page 9 Two binding files 12:16 PM Two key binding files for SimplePersistence project: (src/com.example.example02/)simplepersistence.gwt.xml: Describes bindings between java code and HTML. (war/web-inf/)web.xml: describes mapping between servlets and (server) URLs.

10 Binding_and_Refinement Page 10 HTML/Java binding 12:31 PM HTML/Java binding: SimplePersistence.gwt.xml <module rename-to='simplepersistence'> <!-- Inherit the core Web Toolkit stuff. --> <inherits name='com.google.gwt.user.user'/> <!-- Inherit the default GWT style sheet. You can change --> <!-- the theme of your GWT application by uncommenting --> <!-- any one of the following lines. --> <inherits name='com.google.gwt.user.theme.standard.standard'/> <!-- <inherits name='com.google.gwt.user.theme.chrome.chrome'/> --> <!-- <inherits name='com.google.gwt.user.theme.dark.dark'/> --> <!-- Other module inherits --> <!-- Specify the app entry point class. --> <entry-point class='com.example.example02.client.simplepersistence'/> <!-- Specify the paths for translatable code --> <source path='client'/> </module>

11 Binding_and_Refinement Page 11 Servlet/URL binding 12:33 PM web.xml: describes bindings with web server <web-app> <!-- Servlets: can be more than one --> <!-- the servlet that stores and retrieves persistent data --> <servlet> <servlet-name>thingservlet</servlet-name> <servlet-class> com.example.example02.server.persistentthingserviceimpl </servlet-class> </servlet> <!-- refer to this as --> <servlet-mapping> <servlet-name>thingservlet</servlet-name> <url-pattern>/simplepersistence/thing</url-pattern> </servlet-mapping> <!-- Default page to serve --> <welcome-file-list> <welcome-file>simplepersistence.html</welcome-file> </welcome-file-list> </web-app>

12 Binding_and_Refinement Page 12 Notes on servlet bindings 12:37 PM Notes on servlet bindings: Servlet name is common attribute to class binding and URL binding Can have one class binding known by multiple URLs. Can have a servlet without a URL, which means it can't be called! Cannot have a URL without a bound servlet (will cause application failure).

13 Binding_and_Refinement Page 13 Structural bindings 5:24 PM Structural bindings Some bindings describe what the compiler will do. Example: "client" code directory gets compiled with GWT. "server" code directory gets compiled with real Java compiler. Watch out: errors in GWT compilation persist until you run the GWT compiler again; other (real Java) errors disappear immediately when repaired.

14 Binding_and_Refinement Page 14 Refinement 12:53 PM Eclipse is particularly suitable to top-down coding via top-down stepwise refinement. Special comment // TODO: Puts a task onto your TODO list. Eclipse sets up bindings, and then tracks their correctness. Example: eclipse knows that every interface that extends RemoteServer needs a corresponding Async interface!

15 Binding_and_Refinement Page 15 Stubbing 12:55 PM Stubbing When programming in eclipse, it often helps to "stub" a function with a // TODO comment. A stub should return a reasonable value and have a reasonable effect, but not necessarily the effect you wanted. The global list of TODO comments forms a "to-do list".

16 Binding_and_Refinement Page 16 How to build a project 3:46 PM How to create a project Start with the sample project. From interface to cloud, top to bottom Add one detail at a time. Respond to issues generated by eclipse. Proceed via a series of refinements: Stub complex regions for later development. Keep a TODO list of things to be done next. Test unrefined code before each next step.

17 Binding_and_Refinement Page 17 Importing and exporting projects 3:55 PM Importing and exporting projects Exporting a project to a folder: File/Export /to filesystem Only files that are subject to change are saved. Importing a project from a folder: File/Import /from folder Project must not exist beforehand. Code for project is /comp/150cpa/examples/simplepersistence Copy onto desktop, "Import ".

18 Binding_and_Refinement Page 18 Refactoring 12:58 PM Refactoring Often during development, you find that you've named something the wrong name or put it in the wrong place. Changing the name or location of a thing is called "refactoring". When you "refactor" a thing, references to it from java are "usually" repaired. But watch out for XML files: their contents are not repaired!

19 Binding_and_Refinement Page 19 Eclipse tricks 3:53 PM A couple of really important eclipse tricks Control-<space>: bring up options for matching entities at your current position in the file. Central error list: points you to each syntax error in the file Syntax errors in server code are detected immediately. Careful: syntax errors in client code are only detected when you compile it.

20 Binding_and_Refinement Page 20 Top-down design 4:17 PM Stubbing goes hand-in-hand with top-down design Decide what the interface looks like. Build the interface in HTML. Decide what it should do. Implement and test one function at a time.

21 Binding_and_Refinement Page 21 Using external services 4:26 PM Using external services So far, we've only studied how to use the distributed datastore service. There are many others, each with its own API. Most important: User service.

22 Binding_and_Refinement Page 22 Using the User service 4:27 PM import com.google.appengine.api.users.user; import com.google.appengine.api.users.userservice; import com.google.appengine.api.users.userservicefactory; // Label userlabel = new Label(""); // <td id="userlabelcontainerid></td> Anchor loginanchor = new Anchor(); //... UserService userservice = UserServiceFactory.getUserService(); User user = userservice.getcurrentuser(); if (user!= null) { userlabel.settext("hello, "+user.getnickname()); loginanchor.sethref(userservice.createlogouturl("/")); loginanchor.settext("logout"); } else { userlabel.settext("hello guest!"); loginanchor.settext("login"); loginanchor.sethref(userservice.createloginurl("/")); } // createloginurl creates a URL with an implicit reference // to *your* page, so that when you login, you get bounced back // via a redirect

23 Binding_and_Refinement Page 23 User service caveats 5:07 PM User identity caveats Cannot store things in the User object but Can store things in the datastore indexed by User. User.getID() field persists over lifetime of account. User.get () field can be changed by user and rendered inoperative! The default is to use the field!

24 Binding_and_Refinement Page 24 Other services 5:04 PM Other services Many APIs for various google entities Calendar Mail Youtube All depend upon identifying the User beforehand

25 Binding_and_Refinement Page 25 Deployment Sunday, January 30, :13 PM Once an application is running, it can be "deployed" Then it runs on google's servers. And acquires an application URL. That I can test! I can't get to your localhost applications! Thus, the first assignment is to create a deployed application! This means that you need a google account, so sign up asap!