Apache Ivy Resolvers and Repository


April 4, 2014 Maithilish

5.2. Apache Ivy Resolvers and Repository

Apache Ivy Repositories

Until now, we used the public repository to resolve dependencies. But you may want to set up your own repository for reasons like

  • restricted Internet access – your network may have Internet access or usage policy. This may limit or even restrict access to Internet. Setting up an enterprise repository helps to overcome this issue.
  • reliability/accuracy – modules available in public repository may have quality issues.
  • security – module available in public repository may have security issues and Information Security policy of your organisation may deny the access to these repositories.
The Default configuration of Ivy allows following types of repository.
  • Public – repositories available publicly in Internet
  • Local – private repository, access is restricted to the user
  • Shared – a common repository shared between the members of a team
Default settings of these repositories are defined by Ivy in its own ivysettings.xml which is packaged within the ivy.jar.
Apache Ivy Resolvers

One of the configurable items in the ivysettings.xml is Resolvers. Repositories are not homogeneous and they may be hosted on a web server, local file-system, VFS file-system, ssh server, etc. Layout of the repositories and naming of artifacts differs among repositories. To accommodate all these variations in location and structure of the repositories, Ivy uses a concept called Resolver to contact the repository and fetch the files. Resolver takes care of following aspects.

  • decide network or file-system protocol to access the repository.
  • locate and fetch the Ivy file which may follow different layout/naming in different repositories.
  • locate and fetch proper artifacts which may follow different layout/naming in different repositories.
Resolver defines these aspects so that Ivy can properly resolve the dependencies. <resolvers> element in ivysettings.xml defines a list of dependency resolvers <resolver>. Each <resolver> is identified by its name. Ivy ships with built-in dependency resolvers that handle most common needs. Next table lists the Built-in resolvers.

Table 5.3. Ivy Built-in Resolvers

Name Type Description
IBiblio Standard Finds artifacts on ibiblio.
FileSystem Standard This resolver finds ivy files and artifacts in your file system.
Url Standard This resolver finds ivy files and artifacts in your file system.
Chain Composite Delegates the resolve to a chain of sub resolvers.
Dual Composite Delegates the resolve of ivy file to one resolver and artifacts to another.


There are two types of resolvers
  • standard – these resolvers are used by Ivy for actual resolve task
  • composite – these resolvers delegate the work to standard resolvers
Let’s go through an ivysettings.xml with a Url resolver :
ivysettings.xml

<ivysettings>
  <resolvers>
    <url name="url-example">
      <ivy pattern="http://ivyrep.xyz.com/[module]/[revision]/ivy-[revision].xml" />
      <artifact pattern="http://ivyrep.xyz.com/[module]/[revision]/[artifact].[ext]" />
    </url>
  </resolvers>
</ivysettings>

The resolver named url-example will look for ivy.xml using <ivy> element and artifacts using <artifact>. In the both elements, location and layout of the repository are defined in pattern attribute.
Apache Ivy Resolvers Examples

Resolver is one the important concepts in Apache Ivy and understanding it thoroughly is quite essential. Examples listed below will help to reinforce the concept.

<resolvers>
      <ibiblio name="xyz" m2compatible="true" />
<resolvers>
The above snippet defines a resolver called xyz using the maven 2 public repository to find module metadata (using maven 2 poms) and artifacts.
<resolvers>
   <url name="test" m2compatible="true">
      <artifact 
         pattern= "http://repo1.maven.org/maven2/[organisation]/[module]/[revision]/
                     [artifact]-[revision].[ext]"/>
   </url>
<resolvers>
defines a resolver named test using url. This is equivalent to the in-built ibiblio resolver.
<resolvers>
   <ibiblio name="pentaho" m2compatible="true"
         root="http://repo.pentaho.org/artifactory/repo" />
<resolvers>
defines a resolver using ibiblio pointing to http://repo.pentaho.org/artifactory/repo instead of the default http://repo1.maven.org/maven2.
<resolvers>
   <filesystem name="mylocal">
      <ivy pattern= "${ivy.default.ivy.user.dir}/local/[organisation]/
                        [module]/[type]s/[artifact]-[revision]-[type]s.[ext]" />
      <artifact pattern= "${ivy.default.ivy.user.dir}/local/[organisation]/
                           [module]/[type]s/[artifact]-[revision]-[type]s.[ext]" />
   </filesystem>
</resolvers>
defines a local filesystem resolver named mylocal. Pattern uses Ivy variable ivy.default.ivy.user.dir which by default points .ivy2 directory in user home directory and ${ivy.default.ivy.user.dir}/local points to $HOME/.ivy2/local directory. Rest of the tokens in the pattern [organisation]/[module]/[type]s/[artifact]-[revision]-[type]s.[ext] defines the repository layout.
<settings defaultResolver="chain-resolver" />
<resolvers>
   <chain name="chain-resolver">
      <filesystem name="mylocal">
         <ivy pattern= "${ivy.default.ivy.user.dir}/local/[organisation]/
                           [module]/type]s/artifact]-[revision]-[type]s.[ext]" />
         <artifact pattern= "${ivy.default.ivy.user.dir}/local/[organisation]/
                                [module]/type]s/artifact]-[revision]-[type]s.[ext]" />
      </filesystem>
      <ibiblio name="ibiblio" m2compatible="true" />
   </chain>
</resolvers>
defines a Chain resolver. Chain is a composite resolver which delegates to a chain of sub resolvers. Here Ivy first tries to resolve through the local filesystem resolver and on failure, it will try maven2 public repository.
Apache Ivy Default Resolvers

In the absence of user defined resolvers, Ivy uses default resolvers which comes bundled with it.

Table 5.4. Default Resolvers

Name Type Description
local standard Filesystem resolver points to $HOME/.ivy2/local
shared standard Filesystem resolver points to $HOME/.ivy2/shared
public standard Ibiblio resolver points http://repo1.maven.org/maven2
main composite Chain and Dual resolver to shared and public
default composite Chain resolver to local and main


Hierarchical relationship of default resolvers is as follows
  • default
    • local
    • main
      • shared
      • public
Ivy by default uses resolver named default which first tries the local and on failure looks for shared and finally public. We can check this by running resolve task after deleting the $HOME/.ivy2/cache directory and disabling Internet connection of the machine.

Clearing the Cache

Once the cache directory is deleted, Ivy has to resolve and rebuild the cache by downloading the artifacts from Internet. So try this when you have less artifacts in cache.
The screen shot shows that it has tried local, shared and public in that order

Apache Ivy Repository and Ivy Resolvers

Figure 5.1. Default Resolve Order


Having gone through some of the important concepts, we are ready to build our own repositories.