How to use caldav4j as a library in my own Android project?

[Jens Rabe]

I want to write a small Android app which uses calendar information from a CalDav server and discovered caldav4j. I am using the latest Android studio and set up an empty app as a starting point. When I run the generated ApplicationTest against an emulator, it runs fine.

I now added the following lines to my build.gradle:

repositories {

    mavenCentral()

    maven { url "https://caldav4j.googlecode.com/svn/maven" }

    maven { url "http://builds.osafoundation.org/maven2" }

    maven { url "http://m2.modularity.net.au/releases" }

}

dependencies {

    compile fileTree(dir: 'libs', include: ['*.jar'])

    compile 'com.android.support:appcompat-v7:21.0.3'

    compile 'com.android.support:support-v4:21.0.3'

    compile 'org.osaf:caldav4j:0.7'

}

When I sync the project, it resolves all the dependencies and builds fine, but when running the ApplicationTest again, compiling fails with:

:app:preDexDebug

trouble processing "javax/xml/parsers/DocumentBuilder.class":

Ill-advised or mistaken usage of a core class (java.* or javax.*)

when not building a core library.

This is often due to inadvertently including a core library file

in your application's project, when using an IDE (such as

Eclipse). If you are sure you're not intentionally defining a

core class, then this is the most likely explanation of what's

going on.

However, you might actually be trying to define a class in a core

namespace, the source of which you may have taken, for example,

from a non-Android virtual machine project. This will most

assuredly not work. At a minimum, it jeopardizes the

compatibility of your app with future versions of the platform.

It is also often of questionable legality.

If you really intend to build a core library -- which is only

appropriate as part of creating a full virtual machine

distribution, as opposed to compiling an application -- then use

the "--core-library" option to suppress this error message.

If you go ahead and use "--core-library" but are in fact

building an application, then be forewarned that your application

will still fail to build or run, at some point. Please be

prepared for angry customers who find, for example, that your

application ceases to function once they upgrade their operating

system. You will be to blame for this problem.

If you are legitimately using some code that happens to be in a

core package, then the easiest safe alternative you have is to

repackage that code. That is, move the classes in question into

your own package namespace. This means that they will never be in

conflict with core system classes. JarJar is a tool that may help

you in this endeavor. If you find that you cannot do this, then

that is an indication that the path you are on will ultimately

lead to pain, suffering, grief, and lamentation.

1 error; aborting

 FAILED

FAILURE: Build failed with an exception.

* What went wrong:

Execution failed for task ':app:preDexDebug'.

> com.android.ide.common.internal.LoggedErrorException: Failed to run command:

  /Users/jens/Library/Android/sdk/build-tools/21.1.2/dx --dex --output /Users/jens/AndroidStudioProjects/Things4Today/app/build/intermediates/pre-dexed/debug/xml-apis-2.0.2-58ffbbfd7d4382e988f8a0d689d06ff148a020ef.jar /Users/jens/.gradle/caches/modules-2/files-2.1/xml-apis/xml-apis/2.0.2/3136ca936f64c9d68529f048c2618bd356bf85c9/xml-apis-2.0.2.jar

  Error Code:

  1

  Output:

 

  trouble processing "javax/xml/parsers/DocumentBuilder.class":

 

  Ill-advised or mistaken usage of a core class (java.* or javax.*)

  when not building a core library.

 

  This is often due to inadvertently including a core library file

  in your application's project, when using an IDE (such as

  Eclipse). If you are sure you're not intentionally defining a

  core class, then this is the most likely explanation of what's

  going on.

 

  However, you might actually be trying to define a class in a core

  namespace, the source of which you may have taken, for example,

  from a non-Android virtual machine project. This will most

  assuredly not work. At a minimum, it jeopardizes the

  compatibility of your app with future versions of the platform.

  It is also often of questionable legality.

 

  If you really intend to build a core library -- which is only

  appropriate as part of creating a full virtual machine

  distribution, as opposed to compiling an application -- then use

  the "--core-library" option to suppress this error message.

 

  If you go ahead and use "--core-library" but are in fact

  building an application, then be forewarned that your application

  will still fail to build or run, at some point. Please be

  prepared for angry customers who find, for example, that your

  application ceases to function once they upgrade their operating

  system. You will be to blame for this problem.

 

  If you are legitimately using some code that happens to be in a

  core package, then the easiest safe alternative you have is to

  repackage that code. That is, move the classes in question into

  your own package namespace. This means that they will never be in

  conflict with core system classes. JarJar is a tool that may help

  you in this endeavor. If you find that you cannot do this, then

  that is an indication that the path you are on will ultimately

  lead to pain, suffering, grief, and lamentation.

 

  1 error; aborting

* Try:

Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.

BUILD FAILED

Total time: 1.838 secs

I do know there is a BuildAndroid wiki page, but that is for creating a whole Calendar app. I just want to use the library in my own project. Do I have to create a library with the relevant source code for myself, or can I somehow use the Maven dependency?

[Roberto Polli]

Hi Jens,

2015-01-03 23:19 GMT+01:00 Jens Rabe <schaumwa...@googlemail.com>:
> I do know there is a BuildAndroid wiki page, but that is for creating a
> whole Calendar app.

Maybe Sudheer - which wrote the calendar app - can give you some hint.
I actually work only on the standard jar part :(

Let me know anyway + Peace,
R.