org.apache.beam.sdk.io

Class FileSystem<ResourceIdT extends ResourceId>

java.lang.Object

org.apache.beam.sdk.io.FileSystem<ResourceIdT>

@Experimental(value=FILESYSTEM)
public abstract class FileSystem<ResourceIdT extends ResourceId>
extends java.lang.Object

File system interface in Beam.

It defines APIs for writing file systems agnostic code.

All methods are protected, and they are for file system providers to implement. Clients should use FileSystems utility.

Constructor Summary

Constructors

Constructor and Description
FileSystem()

Method Summary

Modifier and Type	Method and Description
protected abstract void	copy(java.util.List<ResourceIdT> srcResourceIds, java.util.List<ResourceIdT> destResourceIds) Copies a List of file-like resources from one location to another.
protected abstract java.nio.channels.WritableByteChannel	create(ResourceIdT resourceId, CreateOptions createOptions) Returns a write channel for the given ResourceIdT.
protected abstract void	delete(java.util.Collection<ResourceIdT> resourceIds) Deletes a collection of resources.
protected abstract java.lang.String	getScheme() Get the URI scheme which defines the namespace of the FileSystem.
protected abstract java.util.List<MatchResult>	match(java.util.List<java.lang.String> specs) This is the entry point to convert user-provided specs to ResourceIds.
protected abstract ResourceIdT	matchNewResource(java.lang.String singleResourceSpec, boolean isDirectory) Returns a new ResourceId for this filesystem that represents the named resource.
protected abstract java.nio.channels.ReadableByteChannel	open(ResourceIdT resourceId) Returns a read channel for the given ResourceIdT.
protected abstract void	rename(java.util.List<ResourceIdT> srcResourceIds, java.util.List<ResourceIdT> destResourceIds) Renames a List of file-like resources from one location to another.

Methods inherited from class java.lang.Object

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

Constructor Detail

FileSystem

public FileSystem()

Method Detail

match

protected abstract java.util.List<MatchResult> match(java.util.List<java.lang.String> specs)
                                              throws java.io.IOException

This is the entry point to convert user-provided specs to ResourceIds. Callers should use match(java.util.List<java.lang.String>) to resolve users specs ambiguities before calling other methods.

Implementation should handle the following ambiguities of a user-provided spec:

1. spec could be a glob or a uri. match(java.util.List<java.lang.String>) should be able to tell and choose efficient implementations.
2. The user-provided spec might refer to files or directories. It is common that users that wish to indicate a directory will omit the trailing /, such as in a spec of "/tmp/dir". The FileSystem should be able to recognize a directory with the trailing / omitted, but should always return a correct ResourceIdT (e.g., "/tmp/dir/" inside the returned MatchResult.

All FileSystem implementations should support glob in the final hierarchical path component of ResourceIdT. This allows SDK libraries to construct file system agnostic spec. FileSystems can support additional patterns for user-provided specs.

Returns:

List<MatchResult> in the same order of the input specs.

Throws:

java.lang.IllegalArgumentException - if specs are invalid.

java.io.IOException - if all specs failed to match due to issues like: network connection, authorization. Exception for individual spec need to be deferred until callers retrieve metadata with MatchResult.metadata().

create

protected abstract java.nio.channels.WritableByteChannel create(ResourceIdT resourceId,
                                                                CreateOptions createOptions)
                                                         throws java.io.IOException

Returns a write channel for the given ResourceIdT.

The resource is not expanded; it is used verbatim.

Parameters:

resourceId - the reference of the file-like resource to create

createOptions - the configuration of the create operation

Throws:

java.io.IOException

open

protected abstract java.nio.channels.ReadableByteChannel open(ResourceIdT resourceId)
                                                       throws java.io.IOException

Returns a read channel for the given ResourceIdT.

The resource is not expanded; it is used verbatim.

If seeking is supported, then this returns a SeekableByteChannel.

Parameters:

resourceId - the reference of the file-like resource to open

Throws:

java.io.IOException

copy

protected abstract void copy(java.util.List<ResourceIdT> srcResourceIds,
                             java.util.List<ResourceIdT> destResourceIds)
                      throws java.io.IOException

Copies a List of file-like resources from one location to another.

The number of source resources must equal the number of destination resources. Destination resources will be created recursively.

Parameters:

srcResourceIds - the references of the source resources

destResourceIds - the references of the destination resources

Throws:

java.io.FileNotFoundException - if the source resources are missing. When copy throws, each resource might or might not be copied. In such scenarios, callers can use match() to determine the state of the resources.

java.io.IOException

rename

protected abstract void rename(java.util.List<ResourceIdT> srcResourceIds,
                               java.util.List<ResourceIdT> destResourceIds)
                        throws java.io.IOException

Renames a List of file-like resources from one location to another.

The number of source resources must equal the number of destination resources. Destination resources will be created recursively.

Parameters:

srcResourceIds - the references of the source resources

destResourceIds - the references of the destination resources

Throws:

java.io.FileNotFoundException - if the source resources are missing. When rename throws, the state of the resources is unknown but safe: for every (source, destination) pair of resources, the following are possible: a) source exists, b) destination exists, c) source and destination both exist. Thus no data is lost, however, duplicated resource are possible. In such scenarios, callers can use match() to determine the state of the resource.

java.io.IOException

delete

protected abstract void delete(java.util.Collection<ResourceIdT> resourceIds)
                        throws java.io.IOException

Deletes a collection of resources.

It is allowed but not recommended to delete directories recursively. Callers depends on FileSystems and uses DeleteOptions.

Parameters:

resourceIds - the references of the resources to delete.

Throws:

java.io.FileNotFoundException - if resources are missing. When delete throws, each resource might or might not be deleted. In such scenarios, callers can use match() to determine the state of the resources.

java.io.IOException

matchNewResource

protected abstract ResourceIdT matchNewResource(java.lang.String singleResourceSpec,
                                                boolean isDirectory)

Returns a new ResourceId for this filesystem that represents the named resource. The user supplies both the resource spec and whether it is a directory.

The supplied singleResourceSpec is expected to be in a proper format, including any necessary escaping, for this FileSystem.

This function may throw an IllegalArgumentException if given an invalid argument, such as when the specified singleResourceSpec is not a valid resource name.

getScheme

protected abstract java.lang.String getScheme()

Get the URI scheme which defines the namespace of the FileSystem.

See Also:

RFC 2396