com.android.build.api.transform

Class Transform

java.lang.Object

com.android.build.api.transform.Transform

@Beta
public abstract class Transform
extends Object

A Transform that processes intermediary build artifacts.

For each added transform, a new task is created. The action of adding a transform takes care of handling dependencies between the tasks. This is done based on what the transform processes. The output of the transform becomes consumable by other transforms and these tasks get automatically linked together.

The Transform indicates what it applies to (content, scope) and what it generates (content).

A transform receives input as a collection TransformInput, which is composed of JarInputs and DirectoryInputs. Both provide information about the QualifiedContent.Scopes and QualifiedContent.ContentTypes associated with their particular content.

The output is handled by TransformOutputProvider which allows creating new self-contained content, each associated with their own Scopes and Content Types. The content handled by TransformInput/Output is managed by the transform system, and their location is not configurable.

It is best practice to write into as many outputs as Jar/Folder Inputs have been received by the transform. Combining all the inputs into a single output prevents downstream transform from processing limited scopes.

While it's possible to differentiate different Content Types by file extension, it's not possible to do so for Scopes. Therefore if a transform request a Scope but the only available Output contains more than the requested Scope, the build will fail.
If a transform request a single content type but the only available content includes more than the requested type, the input file/folder will contain all the files of all the types, but the transform should only read, process and output the type(s) it requested.

Additionally, a transform can indicate secondary inputs/outputs. These are not handled by upstream or downstream transforms, and are not restricted by type handled by transform. They can be anything. It's up to each transform to manage where these files are, and to make sure that these files are generated before the transform is called. This is done through additional parameters when register the transform.

These secondary inputs/outputs allow a transform to read but not process any content. This can be achieved by having getScopes() return an empty list and use getReferencedScopes() to indicate what to read instead.

This API is non final and is subject to change. We are looking for feedback, and will attempt to stabilize it in the 1.6 time frame.

Constructor Summary

Constructors

Constructor and Description
Transform()

Method Summary

Modifier and Type	Method and Description
abstract Set<QualifiedContent.ContentType>	getInputTypes() Returns the type(s) of data that is consumed by the Transform.
abstract String	getName() Returns the unique name of the transform.
Set<QualifiedContent.ContentType>	getOutputTypes() Returns the type(s) of data that is generated by the Transform.
Map<String,Object>	getParameterInputs() Returns a map of non-file input parameters using a unique identifier as the map key.
Set<QualifiedContent.Scope>	getReferencedScopes() Returns the referenced scope(s) for the Transform.
abstract Set<QualifiedContent.Scope>	getScopes() Returns the scope(s) of the Transform.
Collection<File>	getSecondaryDirectoryOutputs() Returns a list of additional (out of streams) directory(ies) that this Transform creates.
Collection<File>	getSecondaryFileInputs() Returns a list of additional file(s) that this Transform needs to run.
Collection<File>	getSecondaryFileOutputs() Returns a list of additional (out of streams) file(s) that this Transform creates.
abstract boolean	isIncremental() Returns whether the Transform can perform incremental work.
abstract void	transform(Context context, Collection<TransformInput> inputs, Collection<TransformInput> referencedInputs, TransformOutputProvider outputProvider, boolean isIncremental) Executes the Transform.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Transform

public Transform()

Method Detail

getName

@NonNull
public abstract String getName()

Returns the unique name of the transform.

This is associated with the type of work that the transform does. It does not have to be unique per variant.

getInputTypes

@NonNull
public abstract Set<QualifiedContent.ContentType> getInputTypes()

Returns the type(s) of data that is consumed by the Transform. This may be more than one type. This must be of type QualifiedContent.DefaultContentType

getOutputTypes

@NonNull
public Set<QualifiedContent.ContentType> getOutputTypes()

Returns the type(s) of data that is generated by the Transform. This may be more than one type.

The default implementation returns getInputTypes().

This must be of type QualifiedContent.DefaultContentType

getScopes

@NonNull
public abstract Set<QualifiedContent.Scope> getScopes()

Returns the scope(s) of the Transform. This indicates which scopes the transform consumes.

getReferencedScopes

@NonNull
public Set<QualifiedContent.Scope> getReferencedScopes()

Returns the referenced scope(s) for the Transform. These scopes are not consumed by the Transform. They are provided as inputs, but are still available as inputs for other Transforms to consume.

The default implementation returns an empty Set.

getSecondaryFileInputs

@NonNull
public Collection<File> getSecondaryFileInputs()

Returns a list of additional file(s) that this Transform needs to run.

Changes to files returned in this list will trigger a new execution of the Transform even if the qualified-content inputs haven't been touched.

Any changes to these files will trigger a non incremental execution.

The default implementation returns an empty collection.

getSecondaryFileOutputs

@NonNull
public Collection<File> getSecondaryFileOutputs()

Returns a list of additional (out of streams) file(s) that this Transform creates.

These File instances can only represent files, not directories. For directories, use getSecondaryDirectoryOutputs()

Changes to files returned in this list will trigger a new execution of the Transform even if the qualified-content inputs haven't been touched.

Changes to these output files force a non incremental execution.

The default implementation returns an empty collection.

getSecondaryDirectoryOutputs

@NonNull
public Collection<File> getSecondaryDirectoryOutputs()

Returns a list of additional (out of streams) directory(ies) that this Transform creates.

These File instances can only represent directories. For files, use getSecondaryFileOutputs()

Changes to directories returned in this list will trigger a new execution of the Transform even if the qualified-content inputs haven't been touched.

Changes to these output directories force a non incremental execution.

The default implementation returns an empty collection.

getParameterInputs

@NonNull
public Map<String,Object> getParameterInputs()

Returns a map of non-file input parameters using a unique identifier as the map key.

Changes to values returned in this map will trigger a new execution of the Transform even if the content inputs haven't been touched.

Changes to these values force a non incremental execution.

The default implementation returns an empty Map.

isIncremental

public abstract boolean isIncremental()

Returns whether the Transform can perform incremental work.

If it does, then the TransformInput may contain a list of changed/removed/added files, unless something else triggers a non incremental run.

transform

public abstract void transform(@NonNull
                               Context context,
                               @NonNull
                               Collection<TransformInput> inputs,
                               @NonNull
                               Collection<TransformInput> referencedInputs,
                               @Nullable
                               TransformOutputProvider outputProvider,
                               boolean isIncremental)
                        throws IOException,
                               TransformException,
                               InterruptedException

Executes the Transform.

The inputs are

• The inputs collection of TransformInput. These are the inputs that are consumed by this Transform. A transformed version of these inputs must be written into the output. What is received is controlled through getInputTypes(), and getScopes().
• The referencedInputs collection of TransformInput. This is for reference only and should be not be transformed. What is received is controlled through getReferencedScopes().

A transform that does not want to consume anything but instead just wants to see the content of some inputs should return an empty set in getScopes(), and what it wants to see in getReferencedScopes().

Even though a transform's isIncremental() returns true, this method may be receive false in isIncremental. This can be due to

• a change in secondary files (getSecondaryFileInputs(), getSecondaryFileOutputs(), getSecondaryDirectoryOutputs())
• a change to a non file input (getParameterInputs())
• an unexpected change to the output files/directories. This should not happen unless tasks are improperly configured and clobber each other's output.
• a file deletion that the transform mechanism could not match to a previous input. This should not happen in most case, except in some cases where dependencies have changed.

In such an event, when isIncremental is false, the inputs will not have any incremental change information:

• JarInput.getStatus() will return Status.NOTCHANGED even though the file may be added/changed.
• DirectoryInput.getChangedFiles() will return an empty map even though some files may be added/changed.

Parameters:

context - the context in which the transform is run.

inputs - the inputs/outputs of the transform.

referencedInputs - the referenced-only inputs.

outputProvider - the output provider allowing to create content.

isIncremental - whether the transform execution is incremental.

Throws:

IOException - if an IO error occurs.

InterruptedException

TransformException - Generic exception encapsulating the cause.