Dev Notes

In a previous post (http://www.connorgarvey.com/blog/?p=132), I wrote about how to use Guice injection for Flex services.  I used web.xml to configure the MessageBrokerServlet and configured each Flex service to use Guice as a factory.  Since then, on this project, we’ve had to introduce new servlets.  Rather than continue to use web.xml’s verbose and fully-qualified-path based configuration, we moved to using Guice’s ServletModule class.  Here are the steps we followed.

1. Ensure the guice-servlet.jar is included in your project and is deployed with your build.
2. Add the Guice filter to web.xml.
   

   Code block

   <filter>
     <filter-name>guiceFilter</filter-name>
     <filter-class>com.google.inject.servlet.GuiceFilter</filter-class>
   </filter>
   <filter-mapping>
     <filter-name>guiceFilter</filter-name>
     <url-pattern>/*</url-pattern>
   </filter-mapping>

3. Create a servlet module, a class extending com.google.inject.servlet.ServletModule.
4. Override the configureServlets() method of ServletModule and add the message broker servlet configuration.
   

   Code block

   this.bind(MessageBrokerServlet.class).in(Scopes.SINGLETON);
   final Map<String, String> params = new TreeMap<String, String>();
   params.put("services.configuration.file", this.context
       .getRealPath("WEB-INF/config/flex/services-config.xml"));
   this.serve("/messagebroker/*").with(MessageBrokerServlet.class, params);

   1. Normally, servlets configured in Guice are tagged with @Singleton.  Since the MessageBrokerServlet is third party, it’s marked as a singleton here, in the module.
5. Add the new module to the Guice servlet context listener, which should already be configured in web.xml.
6. Remove the servlet and servlet-mapping from web.xml.

I just finished putting a server together that uses Google’s Guice and Adobe’s BlazeDS.  Here’s how you can quickly get a project working using the same configuration.

* Update: A new post describes using Guice’s ServletModule to configure the MessageBrokerServlet.

Download the libraries

Download Guice and BlazeDS.  Use the project configured in the BlazeDS war to get started.

Create the Guice factory

Since BlazeDS provides the servlet, you won’t be able to configure your classes using Guice unless you have a Flex factory.  This code will inject itself with Guice to get instances of Flex services.

Code block

package com.connorgarvey.guiceblazeds.servlet;
 
import java.util.HashMap;
import java.util.Map;
import com.google.inject.Injector;
import flex.messaging.FactoryInstance;
import flex.messaging.FlexContext;
import flex.messaging.FlexFactory;
import flex.messaging.config.ConfigMap;
import flex.messaging.services.ServiceException;
 
/**
 * <p>A Flex factory that retrieves instances of Flex services from Guice</p>
 * <p>This is based on a similar factory built for Spring by Jeff Vroom</p>
 * @author Connor Garvey
 * @created May 27, 2009 1:09:49 PM
 * @version 1.0.0
 * @since 1.0.0
 */
public class GuiceFactory implements FlexFactory {
  private static final String SOURCE = "source";
 
  /**
   * @see flex.messaging.FlexFactory#createFactoryInstance(java.lang.String, flex.messaging.config.ConfigMap)
   */
  public FactoryInstance createFactoryInstance(final String id, final ConfigMap properties) {
    final GuiceFactoryInstance instance = new GuiceFactoryInstance(this, id, properties);
    instance.setSource(properties.getPropertyAsString(SOURCE, instance.getId()));
    return instance;
  }
 
  /**
   * @see flex.messaging.FlexConfigurable#initialize(java.lang.String, flex.messaging.config.ConfigMap)
   */
  public void initialize(final String id, final ConfigMap configMap) {
  }
 
  /**
   * @see flex.messaging.FlexFactory#lookup(flex.messaging.FactoryInstance)
   */
  public Object lookup(final FactoryInstance inst) {
    return inst.lookup();
  }
 
  static class GuiceFactoryInstance extends FactoryInstance {
    private Map<String, Class<?>> classes = new HashMap<String, Class<?>>();
    GuiceFactoryInstance(final GuiceFactory factory, final String id, final ConfigMap properties) {
      super(factory, id, properties);
    }
 
    @Override
    public Object lookup() {
      final Injector injector = (Injector)FlexContext.getServletContext().getAttribute(
          GuiceServletContextListener.KEY);
      injector.injectMembers(this);
      String className = this.getSource();
      Class<?> clazz = this.classes.get(className);
      if (clazz == null) {
        try {
          clazz = Class.forName(this.getSource());
          this.classes.put(className, clazz);
        }
        catch (ClassNotFoundException ex) {
          ServiceException throwing = new ServiceException();
          throwing.setMessage("Could not find remote service class '" + this.getSource() + "'");
          throwing.setRootCause(ex);
          throwing.setCode("Server.Processing");
          throw throwing;
        }
      }
      return injector.getInstance(clazz);
    }
 
    @Override
    public String toString() {
      return "Guice factory <id='" + this.getId() + "',source='" + this.getSource() +
          "',scope='" + this.getScope() + "'>";
    }
  }
}

Create a context listener

The Guice servlet jar contains a ServletContextListener, but I haven’t taken the time to integrate it into this solution.  For simplicity, you can use this one, which works with the factory above.

Code block

package com.connorgarvey.guiceblazeds.servlet;
 
import java.util.List;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import com.google.inject.Guice;
import com.google.inject.Injector;
import com.google.inject.Module;
 
/**
 * Prepares Guice on application startup
 * @author Connor Garvey
 * @created May 27, 2009 8:37:26 AM
 * @version 1.0.0
 * @since 1.0.0
 */
public abstract class GuiceServletContextListener implements ServletContextListener {
  /**
   * The key of the servlet context attribute holding the injector
   */
  public static final String KEY = Injector.class.getName();
 
  /**
   * @see javax.servlet.ServletContextListener#contextDestroyed(javax.servlet.ServletContextEvent)
   */
  public void contextDestroyed(final ServletContextEvent servletContextEvent) {
    servletContextEvent.getServletContext().removeAttribute(KEY);
  }
 
  /**
   * @see javax.servlet.ServletContextListener#contextInitialized(javax.servlet.ServletContextEvent)
   */
  public void contextInitialized(final ServletContextEvent servletContextEvent) {
    servletContextEvent.getServletContext().setAttribute(KEY,
        this.getInjector(servletContextEvent.getServletContext()));
  }
 
  private Injector getInjector(final ServletContext servletContext) {
    return Guice.createInjector(this.getModules());
  }
 
  /**
   * Gets the modules used by the application
   * @return the modules
   */
  protected abstract List<? extends Module> getModules();
}

Extend GuiceContextListener

Create a concret version of the class above.  It should return all modules needed for the application.

Modify web.xml

Now, prepare web.xml with the normal BlazeDS settings plus some extras for Guice.

Code block

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd">
<web-app>
  <display-name>Guice BlazeDS</display-name>
  <description>Guice BlazeDS</description>
  <listener>
    <listener-class>flex.messaging.HttpFlexSession</listener-class>
  </listener>
  <listener>
    <listener-class>com.connorgarvey.guiceblazeds.servlet.MyCustomGuiceServletContextListener</listener-class>
  </listener>
  <servlet>
    <servlet-name>MessageBrokerServlet</servlet-name>
    <display-name>MessageBrokerServlet</display-name>
    <servlet-class>flex.messaging.MessageBrokerServlet</servlet-class>
    <init-param>
      <param-name>services.configuration.file</param-name>
      <param-value>/WEB-INF/config/flex/services-config.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>MessageBrokerServlet</servlet-name>
    <url-pattern>/messagebroker/*</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
  </welcome-file-list>
</web-app>

This way, BlazeDS will start at server startup, followed by Guice.

Modify BlazeDS config

Open services-config.xml and add this at the top of the file.  Point it to the Guice factory.

Code block

<?xml version="1.0" encoding="UTF-8"?>
<services-config>
  <factories>
    <factory id="guice" class="com.connorgarvey.guiceblazeds.servlet.GuiceFactory" />
  </factories>

Set the factory of all remoting destinations

In remoting-config.xml, be sure to set the factory of all destinations to the name specified in services-config.xml above.

<destination id="SomeService">
  <properties>
    <factory>guice</factory>
    <source>com.connorgarvey.guiceblazeds.service.flex.SomeFlexService</source>
  </properties>
</destination>

How this all works

1. When the server starts, BlazeDS and Guice are initialized by the servlet listeners.
2. When BlazeDS receives a request, to a service, it’ll see that it’s supposed to retrieve it from the “guice” factory.
3. The Guice factory will return an instance of the class specified in the source of the service configuration from Guice to BlazeDS for use in completing the request.

As described in an earlier post, Android is not friendly to mocking frameworks or mock-style testing.  If you want to test any class in your application that deals with the Android API, it’s best to run your tests through the emulator, accessing real Android classes.  It’s unfortunate because you’re not just testing your application.  You’re also testing Android.  Anyway, here’s a way to mock a UI component.

If you’re just starting, here are a couple notes to keep you on the right track.

• Android is bundled with JUnit 3.  Don’t try using an updated JUnit library or another testing framework.  The Android jar doesn’t contain any functional code, so all test cases have to be run in the emulator, which uses JUnit 3.  The test framework that will work best is in the Android API.
• If you need basic implementations of Android classes, try to avoid mocking them.

“Mock”ing

In my latest test, I needed a TextView so that I could call the simplest method, setText(String).  I’ll describe how I got one.

Don’t bother with the android.test.mock package.  It just contains implementations of classes that throw UnsupportedOperationExceptions.  There isn’t anything there that I have yet found useful.

1. In the test case, instead of extending TestCase, extend at InstrumentationTestCase or, if necessary, one of its subclasses.  It’ll set up most of the stuff that’s available in an Activity and make it available to your test case.

   Code block

   public class AnAndroidTest extends InstrumentationTestCase {

2. Create a mock implementation of TextView or the class you need.

   Code block

   public class MockTextView extends TextView {
     public MockTextView(final Context context) {
       super(context);
     }
   }

3. The TextView constructor needs a real Context object because it will call methods on it.  The context is difficult to mock because parts of it are private to Android.  Since the Android JAR is just an API and doesn’t have any functional code, you couldn’t even see the methods if you tried.  They only exist in the VM in the emulator.  AFAIK, if you can’t see a method, you can’t mock it.  That’s why your test case extends InstrumentationTestCase.  Put this in it.

   Code block

   final TextView textView = new MockTextView(this.getInstrumentation().getContext());

Now write the test case.  The text view is real and has a fully functional context, so the emulator will have everything it needs to support your test case.

Green Mileage is now an open source application at Google Code.  You can find the full source for most of the Android posts on this site in it at http://code.google.com/p/greenmileage/.  Just click the Source tab, then the Browse link.

The code needs a lot of cleanup, but is still probably worth a look if you’re new to Android.

Scroll down for the full source.  Today, to execute code asynchronously in JavaFX, the background code must be written in Java.  Ideally, your Java code will return JavaFX data types, keeping your FX code clean and helping you be prepared for the day when you won’t need Java.

This is how you can create and return JavaFX sequences from your Java code.

Set the return type of your method to com.sun.javafx.runtime.sequence.Sequence.  Many of the com.sun.javafx classes seem to have been created for use in Java code.

Code block

@Override
public Sequence<String> call() throws Exception {

In your code, use any type of collection class you like.  It’s easiest to use List classes, though, because they can be directly converted.

Code block

List<String> names = Arrays.asList("Arthur", "Trillian", "Zaphod");

Then, convert the list to a sequence using com.sun.javafx.runtime.sequence.Sequences and return it.

Code block

return Sequences.make(TypeInfo.getTypeInfo(String.class), names);

Here it is all together for impatient people like me.

Code block

@Override
public Sequence<String> call() {
  List names = Arrays.asList("Arthur", "Trillian", "Zaphod");
  return Sequences.make(TypeInfo.getTypeInfo(String.class), names);
}

Spring’s architecture isn’t very friendly to static classes and methods.  It doesn’t have any way of injecting static properties of classes because it doesn’t have any way to discover them.  Spring’s designers have acknowledged that it’s a shortcoming of the framework and suggest the use of this solution.

1. Create the static property of the class without any annotations
2. Mark the class to have static properties injected with @Component so that the properties will be injected on Spring startup
3. Create a non-static setter method that sets the static property
4. Mark the setter method with @Autowired(required = true)

Code block

@Component
public class UserUtils
{
  private static UserAccessor userAccessor;
 
  /**
   * Sets the user DAO. This method should never be called except by Spring
   * @param userAccessor The user accessor to set
   */
  @Autowired(required = true)
  public void setUserAccessor(userAccessor UserAccessor) {
    UserUtils.userAccessor = userAccessor;
  }
}

Using this technique, you can have all of the advantages of Spring injection without the headaches of Spring injection!  Avoid using this technique whenever possible.  It should only be used to support legacy applications.  With a lot of statically stored values, your application will not scale well.

A lot of people have found this site by searching for an Android button tutorial, so here it is.

1. This tutorial assumes that you already have an activity and are using an XML layout.
2. Open the layout XML and add the button element.  Assign an ID with the “@+id” operator.  The + tells Android to generate an ID for this element so that you can reference it in your Java files.
   1. This is an example. Your layout and text elements will probably be very different. In this example case, the ID of the button is “close”.

      <Button android:id="@+id/close"
          android:layout_width="fill_parent"
          android:layout_height="wrap_content"
          android:layout_alignParentBottom="true"
          android:text="@string/title_close" />

3. Open the activity class.  Add a class property to hold a reference to the button.

   Code block

   private Button closeButton;

4. If you haven’t already, override the onCreate method.

   Code block

   @Override
   protected void onCreate(Bundle savedInstanceState) {
   }

   1. For this example, we don’t need the saved instance state, so ignore it.
5. Now, in the onCreate method, attach a listener to the click event for the button.  This example will call “finish()” on the activity, the Android analog of clicking the close button on a window.

Code block

protected void onCreate(Bundle savedInstanceState) {
  this.setContentView(R.layout.layoutxml);
  this.closeButton = (Button)this.findViewById(R.id.close);
  this.closeButton.setOnClickListener(new OnClickListener() {
    @Override
    public void onClick(View v) {
      finish();
    }
  });
}

1. Here’s a short description of what’s happening.
   1. First, get the button ID.  The ID created earlier in the layout, “close”, is compiled by Android and assigned a unique integer ID which is available to the application through the “R” class, which I assume is short for “Resources”.
   2. Request a reference to the button from the activity by calling “findViewById”.  The button has to be retrieved from the activity because while an ID is unique in an activity, it is not unique among all activities.
   3. Assign the retrieved button to an instance variable so that if you need it later, you can easily find it without having to query for it again.
   4. Create a class implementing “OnClickListener” and set it as the on click listener for the button.

As UI elements go, buttons are some of the simplest.  Later, I’ll write about menus and dialogs, which aren’t so easy.

While working on a project that uses Hibernate, my team was getting a little frustrated while trying to interrogate a tree structure in our data model since all collections are mapped as java.util.HashSets.  We wanted a simple function that could print the tree to the log, so I took a free hour and wrote this.  It was a little more complicated than I anticipated because it had to handle situations like these.

root
   |
   |- child
   |
   |- child

root
   |
   |- child
      |
      |- child

and the infamous (to me) …

root
   |
   |- child
   |   |
   |   |- child
   |       |
   |       |- child
   |
   |- child

There’s a subtle difference.  Notice that in the middle one, the line for the first child stops because there aren’t any more children, but in the last one, the line continues?  I could have created some kind of 2D text buffer and gone back to draw the line, but that would be boring.  Here’s what I came up with. I don’t know whether it’s pretty, but it works!

Code block

/**
 * Creates a tree representation of the node
 * @param node The node, which may not be null
 * @return A string containing the formatted tree
 */
public static String toStringTree(Node node) {
  final StringBuilder buffer = new StringBuilder();
  return toStringTreeHelper(node, buffer, new LinkedList<Iterator<Node>>()).toString();
}
 
private static void toStringTreeDrawLines(List<Iterator<Node>> parentIterators, boolean amLast) {
  StringBuilder result = new StringBuilder();
  Iterator<Iterator<Node>> it = parentIterators.iterator();
  while (it.hasNext()) {
    Iterator<Node> anIt = it.next();
    if (anIt.hasNext() || (!it.hasNext() && amLast)) {
      result.append("   |");
    }
    else {
      result.append("    ");
    }
  }
  return result.toString();
}
 
private static StringBuilder toStringTreeHelper(Node node, StringBuilder buffer, List<Iterator<Node>>
    parentIterators) {
  if (!parentIterators.isEmpty()) {
    boolean amLast = !parentIterators.get(parentIterators.size() - 1).hasNext();
    buffer.append("\n");
    String lines = toStringTreeDrawLines(parentIterators, amLast);
    buffer.append(lines);
    buffer.append("\n");
    buffer.append(lines);
    buffer.append("- ");
  }
  buffer.append(node.toString());
  if (node.hasChildren()) {
    Iterator<Node> it = node.getChildNodes().iterator();
    parentIterators.add(it);
    while (it.hasNext()) {
      Node child = it.next();
      toStringTreeHelper(child, buffer, parentIterators);
    }
    parentIterators.remove(it);
  }
  return buffer;
}

I just started using Terracotta for the first time.  This is how I put it in my project and configured Ant tasks to start and stop the server. The client is using Windows, so the Ant tasks work in Windows.

1. Create tc-config.xml in the root of the project.

   Code block

   <?xml version="1.0" encoding="UTF-8"?>
   <con:tc-config xmlns:con="http://www.terracotta.org/config">
     <servers>
       <server host="%i" name="localhost">
         <dso-port>9510</dso-port>
         <jmx-port>9520</jmx-port>
         <data>bin/terracotta/server-data</data>
         <logs>bin/terracotta/server-logs</logs>
         <statistics>bin/terracotta/cluster-statistics</statistics>
       </server>
       <update-check>
         <enabled>true</enabled>
       </update-check>
     </servers>
     <clients>
       <logs>bin/terracotta/client-logs</logs>
       <statistics>bin/terracotta/client-statistics/%D</statistics>
       <modules>
         <module name="tim-hibernate-3.2.5" version="1.2.2"/>
         <module name="tim-ehcache-1.3" version="1.2.2"/>
         <module name="tim-cglib-2.1.3" version="1.2.2"/>
         <module name="tim-ehcache-commons" version="1.2.2"/>
       </modules>
     </clients>
   </con:tc-config>

2. Put Terracotta into your library directory.  You’ll need bin, docs, lib and schema directories and the license files.
   1. You don’t need the licenses for the software to work, but it’s always a good idea to include them, especially if your app is not open source
3. Create the Ant targets.

   <target name="start.terracotta.windows">
     <exec executable="cmd">
       <arg value="/c"/>
       <arg value="lib\terracotta-2.7.2\bin\start-tc-server.bat"/>
     </exec>
   </target>
   
   <target name="stop.terracotta.windows">
     <exec executable="cmd">
       <arg value="/c"/>
       <arg value="lib\terracotta-2.7.2\bin\stop-tc-server.bat"/>
     </exec>
   </target>

   1. Notice the backslashes there.  Normally, Ant will convert forward slashes to backslashes in Windows.  Since this is a command line argument, though, it doesn’t.  If you’re running on both *nix and Windows, you’ll have to have two versions of the paths, one with forward and one with back slashes.
4. That’s it. Run the start task to start and the stop task to stop.

Many of Android’s screens use attractive dividers with gradients that fade from black to white to black.  Here’s how to create one of your own.

1. Create a file called “black_white_gradient.xml” in /res/drawable. Paste this into it.

Code block

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
  <gradient
      android:startColor="#00000000"
      android:centerColor="#FFFFFFFF"
      android:endColor="#00000000"
      android:angle="0" />
</shape>

2. Create a view in the target layout and apply the gradient as the background.  The “black_white_gradient” in “@drawable/black_white_gradient” refers to the file name of the shape above.

<View android:id="@+id/divider"
    android:background="@drawable/black_white_gradient"
    android:layout_width="fill_parent"
    android:layout_height="1dp"
    android:layout_below="@id/someOtherThing" />