public void listFilesInDirectory(File dir) {
  File[] files = dir.listFiles();
  if (files != null) {
    for  (File f : files) {
      if (f.isDirectory()) {
        listFilesInDirectory(f);
      } else {
        System.out.println(f.getName());
      }
    }
  }
}

… which in real projects often grows to a larger block of code. The web is full of code blocks like this for walking a directory tree. The best version I came across is this object oriented one by Torsten Curdt. Since you usually don’t want to write this yourself, I suggested in my talk to use FileUtils which makes recursive iteration much easier:

Collection jspFiles = FileUtils.listFiles(rootDirName,
                        new String[] { "jsp" }, true);

This looks concise and useful but as I tried to use it, I wasn’t too pleased with the FileUtils’ solution. Here is why:

• The recursion is processed in one go, i.e. all results are written to a List even when using the iterateFiles method. The recursion is not processed iteratively.
• You can not influence the directories that are searched.
• Only files are returned, you can not search for directories.
• The API is not very expressive (e.g. what does the “true” mean).
• No generics (raw collection types are returned).

A Better API

Not being satisfied with the solutions I found, I “dreamed up” my own API for listing and finding files. I don’t consider it complete but for the most part I am pleased with the ease of use that the builder pattern provides. The code for this can currently be found in an unrelated goole code project. The rest of this article shows the functions that are currently supported.

Find files two ways

There are generally two ways to use the result – as interator or as list:

1. Iterate over all files in the windows directory:

for (File f : Files.find(”c:\\windows”)) {

}

2. Get all the files in a directory as a list of files:

List<File> allFiles = Files.find(somedir).list();

Except from the return type the second version does the same as the JDK command listFiles:

File[]  allFiles = (new File(somedir)).listFiles()

Easy recursive listing

To iterate all the files in the C:\Windows directory, you would use:

for (File f : Files.find(”c:\\windows”).recursive()) {

}

Note: This actually works iteratively, i.e. the recursion happens as you fetch files from the iterator. The result is not fetched into a huge list.

With a Predicate you can limit the recursion to specific directories. In this example all .svn directories within a source tree are skipped:

Predicate<File> noSvnDirs = new Predicate<File>() {
boolean apply(File file) {
return !file.getName().equals(”.svn”);
}
}

for (File f : Files.find(”src/java/”).recursive(noSvnDir)) {

}

Want Files, Directories or both?

Define if you want only files, only directories or both in your result with yield*()-Methods.

Files.find(someBaseDir).recursive().yieldFiles()  // this is the default
Files.find(someBaseDir).recursive().yieldDirectories()
Files.find(someBaseDir).recursive().yieldFilesAndDirectories()

Filtering the results

To get all textfiles within a dir use:

Files.find(dir).withExtension("txt").list();
Files.find(dir).ignoreCase().withExtension("txt").list();

You can also filter by Name, e.g. to find README files:

Files.find(dir).withName("README").list();
Files.find(dir).ignoreCase().withName("readme").list();

Note that the default matching is case sensitive. The commands caseSensitive() and ignoreCase() can be used to toggle the matching behaviour.

For special needs you can also specify a Predicate<File> to filter the resulting files.

Files.find(dir).recursive().withFilter(somePredicate).list();

Finding Directories

When looking for directories there are some special usecases that are supported, e.g. looking for directories that contain a specific file:

Files.find(dir).recursive().yieldDirectories()
               .containingFile("Thumbs.db");

• A tutorial for creating a Preferences Activity got me started – unfortunaltely the xml preferences definition it uses is incorrect. The tags are names of Classes which have to be capitalized.
• The open the preferences activity I added a Option Menu.
• I wanted to add some kind of progress indicator. I ended up using the ProgressDialog and the AsyncTask to run the downloading and xml parsing in the background. To fix issues with device rotation I might have a look at the BetterAsyncTask in the Droid-FU library later.
• I also ran into DateFormat and Date issues with the UTC formated Date in the XML file. I Thought about using  joda-time at least twice but then stuck to the JDK implementation for smaller app size. The fact that android brings it’s own class named DateFormat which just provides a localized JDK-DateFormat object doesn’t help either.

• The Android Tutorials are a great starting point, though i only followed through with the HelloWorld Tutorial. In retrospect I should have looked at the Notepad Tutorial a little closer because it explains important concepts (namely activities/intents).
• http://www.anddev.org/ is a useful source for tutorials and code snippets
• It’s still java but a completely different API, so you often have to look for classes and methods via code completion oder in examples to get things done.
• Downloading: Can be done with the included HTTP Client library. Unfortuantely Android still uses an old version of the HTTP Client though, which made it hard to find documentation (e.g. how to set authentication credentials). Additionally you shoudn’t forget to declare the INTERNET-permissions in your application manifest.
• Storing and retrieving Files looks fairly easy (getDir(), getCacheDir()-Methods are there) at first sight but you have to unerstand the Android filesystem security model if you don’t want to spend hours with debugging. The before mentoined methods use internal storage where each application stores it’s data independently. Public read/write (e.g. file exchange with other applications) is only possible when you store your content with the specific method openFileOutput(). The external SD card on the other hand can be openly accessed with the regular Java File API.
• XML Parsing: I started out with the sax parser but since my XML file was pretty complex I ditched it and downloaded dom4j which has a really easy to use API. Unfortunately it adds at least 200KB of final app size. I now realized I could have gone with the regular DOM parser which has a decent API. I’ll have to reevaluate this later – maybe the end user responsiveness does require the faster streaming parser approach (sax).
• UI design: Declarative XML based looks powerful and well thought out but I mostly stuck to tutorial layout for now. This is an area I still have to get into.

Ok, that’s it for now. Android is turning out to be a great plattform – exciting times.

install.bat:

@SET mvn=d:\java\maven\bin\mvn
@%mvn% install:install-file -DgroupId=com.google.gdata
       -DartifactId=%1 -Dversion=%2 -Dfile=%3 -Dpackaging=jar
       -DgeneratePom=true

installall.bat:

call install.bat gdata-analytics 2.0 gdata-analytics-2.0.jar
call install.bat gdata-appsforyourdomain 1.0 gdata-appsforyourdomain-1.0.jar
call install.bat gdata-base 1.0 gdata-base-1.0.jar
call install.bat gdata-blogger 2.0 gdata-blogger-2.0.jar
call install.bat gdata-books 1.0 gdata-books-1.0.jar
call install.bat gdata-calendar 1.0 gdata-calendar-2.0.jar
call install.bat gdata-client 1.0 gdata-client-1.0.jar
call install.bat gdata-codesearch 2.0 gdata-codesearch-2.0.jar
call install.bat gdata-contacts 3.0 gdata-contacts-3.0.jar
call install.bat gdata-core 1.0 gdata-core-1.0.jar
call install.bat gdata-docs 2.0 gdata-docs-2.0.jar
call install.bat gdata-finance 2.0 gdata-finance-2.0.jar
call install.bat gdata-health 2.0 gdata-health-2.0.jar
call install.bat gdata-maps 2.0 gdata-maps-2.0.jar
call install.bat gdata-media 1.0 gdata-media-1.0.jar
call install.bat gdata-photos 2.0 gdata-photos-2.0.jar
call install.bat gdata-spreadsheet 3.0 gdata-spreadsheet-3.0.jar
call install.bat gdata-webmastertools 2.0 gdata-webmastertools-2.0.jar
call install.bat gdata-youtube 2.0 gdata-youtube-2.0.jar

You surely could get fancy and automate the splitting between artifact-name and version number, but hey, I needed those JARs installed quickly and that’s what it does.

When you later like to split thes MP3/CUE files into individial MP3 files you need a specialized tool. Lately I used Medieval CUE Splitter to achieve this. It is a small freeware application which splits the MP3 and even fill the ID3-Tags from the information in the CUE files.

On way to provide the “continue later” functionality is to use a tool that saves your web browser’s form state. Lazarus: Form Recovery is one of those tools for Firefox that constantly saves the state of your web forms and allows you to load previous content when you return to a website. This works very well with Google Docs Forms. You can interrupt filling out the form at any time, return later and restore the information you previously entered with a few clicks.

To summarize my requirements:

• A List (ArrayList) which can be modified as usual
• A way to find objects (contains and get) in constant time by a custom attribute (like a HashMap)
• No reliance on equals() and hashcode() because they cover more attributes (an can not be changed)

The LinkedHashMap seems to almost fit the bill but it is not a true List and therefore not a great drop in replacement.

What I’m using right now is a wrapper around a List which maintains an additional HashMap to find objects by the index criterium. The index is automatically updated whenever the list is modified. This is an example on how I use it:

// function to index Persons by their social security number
Function<Person, String> getSsnrForPerson =
  new Function<Person, String>() {
    String apply(Person person) {
      return person.getSocialSecurityNumber();
    }
  }

To create an indexed list for an empty ArrayList<Person> with an index on a person’s social security number you can then easily use the Class UniqueIndexedList:

UnqiueIndexedList<Person, String> myList =
  UnqiueIndexedList.create(getSsnrForPerson);

Of course all the usual methods of the List<Person> interface can be used as usual:

myList.add(somePerson);
myList.add(anotherPerson);
myList.get(i);
myList.iterator();

Additionaly there are  methods to access objects by index:

boolean personIsInList = myList.containsByIndex("34897634853");

Person p = myList.getByIndex("34897634853");

The code for the list implementation currently resides here:

• IndexedList.java
• UniqueIndexedList.java

It is basically a hybrid of a List and a special index-Map and works well so far. I am sure that finding objects in list for a given attribute is a very common usecase. Why hasn’t anyone solved this yet? Are there (better) alternatives that I’ve missed?

Wordpress is updated, a new fresh theme is installed, now I’m going to update some about data and clean up the sidebar. Expect upcoming posts about Java, Alfresco, GWT and some general development topics that cross my mind.

The main reason I’m writing this post though is, that I’d like to share how I integrated freemind mindmaps into Alfresco. The freemind mindmaps are .mm-files which can already be stored in alfresco but are "unknown binary" files. What we have to do is tell alfresco what .mm-files are by defining them as mime-types. The Alfresco wiki describes how to add a mime-type so I did this accordingly:

The result of including the preceding xml files as tomcat\shared\classes\alfresco\mimetype\mimetype-custom-extensions.xml is that the new content type Freemind appears in the Add Content Dialog.

The next step would be adding the icons for the freemind documents. To achieve this you simply have to copy a file named mm.gif into the alfresco/images/filetypes (16×16 pixels) and alfresco/images/filetypes32 (32×32 pixels) folder in the web application. The new file is automatically recognized after a restart of the web-app and the new icon is available.

Then I thought it would be nifty to have a preview of the mindmap right in the web interface. Fortunately freemind provides a java applet and a flash viewer. I decided to use the flash viewer and found the alfresco templates as a extremely easily way to integrate custom display logic. For my viewer I would only have to include the html code to open the flash object in a freemaker template. Alfresco provides a template directory within the data dictionary (a space in the repository) where I included the following code in the file freemind.fts:

This is basically the code that freemind generates when exporting to flash. More information on templates can also be found in the alfresco wiki in the Template Guide. The template can be easily edited right from the web interface:

This templates refers to a javascript and the flash viewer which I stored in the web application under alfresco/custom/freemind. The fixed height of 500px, which I included, is not the best to solution but is needed to prevent the window from collapsing to a very small area.

Using this template as a custom view in the details page of the mindmap file, which we added earlier, produces this interactive preview of the mindmap:

Using "Preview in Template" the viewer can also be used without the menu on the right:

This little customization has took me not much longer than writing this post which is pretty amazing. Most if the impressiveness of the result is due to the ready-to-use functionality of the freemind flash viewer though

Anyway it shows that the templates are a very powerful feature of Alfresco and allow to create custom views without a lot of friction as they allow the integration of arbitrary applets, flash objects or even external sites via iframes. For now I’m pretty happy with alfresco and look into deploying it more solidly on my home-server and look into backup options.

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