org.apache.beam.sdk.io

Class AvroIO

java.lang.Object

org.apache.beam.sdk.io.AvroIO

public class AvroIO
extends java.lang.Object

PTransforms for reading and writing Avro files.

Reading Avro files

To read a PCollection from one or more Avro files with the same schema known at pipeline construction time, use read(java.lang.Class<T>), using AvroIO.Read.from(org.apache.beam.sdk.options.ValueProvider<java.lang.String>) to specify the filename or filepattern to read from. If the filepatterns to be read are themselves in a PCollection, apply readAll(java.lang.Class<T>). If the schema is unknown at pipeline construction time, use parseGenericRecords(org.apache.beam.sdk.transforms.SerializableFunction<org.apache.avro.generic.GenericRecord, T>) or parseAllGenericRecords(org.apache.beam.sdk.transforms.SerializableFunction<org.apache.avro.generic.GenericRecord, T>).

Many configuration options below apply to several or all of these transforms.

See FileSystems for information on supported file systems and filepatterns.

Filepattern expansion and watching

By default, read(java.lang.Class<T>) prohibits filepatterns that match no files, and readAll(java.lang.Class<T>) allows them in case the filepattern contains a glob wildcard character. Use AvroIO.Read.withEmptyMatchTreatment(org.apache.beam.sdk.io.fs.EmptyMatchTreatment) to configure this behavior.

By default, the filepatterns are expanded only once. AvroIO.Read.watchForNewFiles(org.joda.time.Duration, org.apache.beam.sdk.transforms.Watch.Growth.TerminationCondition<java.lang.String, ?>) allows streaming of new files matching the filepattern(s).

Reading records of a known schema

To read specific records, such as Avro-generated classes, use read(Class). To read GenericRecords, use readGenericRecords(Schema) which takes a Schema object, or readGenericRecords(String) which takes an Avro schema in a JSON-encoded string form. An exception will be thrown if a record doesn't match the specified schema. Likewise, to read a PCollection of filepatterns, apply readAllGenericRecords(org.apache.avro.Schema).

For example:

 Pipeline p = ...;

 // Read Avro-generated classes from files on GCS
 PCollection<AvroAutoGenClass> records =
     p.apply(AvroIO.read(AvroAutoGenClass.class).from("gs://my_bucket/path/to/records-*.avro"));

 // Read GenericRecord's of the given schema from files on GCS
 Schema schema = new Schema.Parser().parse(new File("schema.avsc"));
 PCollection<GenericRecord> records =
     p.apply(AvroIO.readGenericRecords(schema)
                .from("gs://my_bucket/path/to/records-*.avro"));
 

Reading records of an unknown schema

To read records from files whose schema is unknown at pipeline construction time or differs between files, use parseGenericRecords(org.apache.beam.sdk.transforms.SerializableFunction<org.apache.avro.generic.GenericRecord, T>) - in this case, you will need to specify a parsing function for converting each GenericRecord into a value of your custom type. Likewise, to read a PCollection of filepatterns with unknown schema, use parseAllGenericRecords(org.apache.beam.sdk.transforms.SerializableFunction<org.apache.avro.generic.GenericRecord, T>).

For example:

 Pipeline p = ...;

 PCollection<Foo> records =
     p.apply(AvroIO.parseGenericRecords(new SerializableFunction<GenericRecord, Foo>() {
       public Foo apply(GenericRecord record) {
         // If needed, access the schema of the record using record.getSchema()
         return ...;
       }
     }));
 

Reading from a PCollection of filepatterns

 Pipeline p = ...;

 PCollection<String> filepatterns = p.apply(...);
 PCollection<AvroAutoGenClass> records =
     filepatterns.apply(AvroIO.read(AvroAutoGenClass.class));
 PCollection<GenericRecord> genericRecords =
     filepatterns.apply(AvroIO.readGenericRecords(schema));
 PCollection<Foo> records =
     filepatterns.apply(AvroIO.parseAllGenericRecords(new SerializableFunction...);
 

Streaming new files matching a filepattern

 Pipeline p = ...;

 PCollection<AvroAutoGenClass> lines = p.apply(AvroIO
     .read(AvroAutoGenClass.class)
     .from("gs://my_bucket/path/to/records-*.avro")
     .watchForNewFiles(
       // Check for new files every minute
       Duration.standardMinutes(1),
       // Stop watching the filepattern if no new files appear within an hour
       afterTimeSinceNewOutput(Duration.standardHours(1))));
 

Reading a very large number of files

If it is known that the filepattern will match a very large number of files (e.g. tens of thousands or more), use AvroIO.Read.withHintMatchesManyFiles() for better performance and scalability. Note that it may decrease performance if the filepattern matches only a small number of files.

Writing Avro files

To write a PCollection to one or more Avro files, use AvroIO.Write, using AvroIO.write().to(String) to specify the output filename prefix. The default DefaultFilenamePolicy will use this prefix, in conjunction with a ShardNameTemplate (set via AvroIO.Write.withShardNameTemplate(String)) and optional filename suffix (set via AvroIO.Write.withSuffix(String), to generate output filenames in a sharded way. You can override this default write filename policy using AvroIO.Write.to(FileBasedSink.FilenamePolicy) to specify a custom file naming policy.

By default, AvroIO.Write produces output files that are compressed using the CodecFactory.deflateCodec(6). This default can be changed or overridden using AvroIO.Write.withCodec(org.apache.avro.file.CodecFactory).

Writing specific or generic records

To write specific records, such as Avro-generated classes, use write(Class). To write GenericRecords, use either writeGenericRecords(Schema) which takes a Schema object, or writeGenericRecords(String) which takes a schema in a JSON-encoded string form. An exception will be thrown if a record doesn't match the specified schema.

For example:

 // A simple Write to a local file (only runs locally):
 PCollection<AvroAutoGenClass> records = ...;
 records.apply(AvroIO.write(AvroAutoGenClass.class).to("/path/to/file.avro"));

 // A Write to a sharded GCS file (runs locally and using remote execution):
 Schema schema = new Schema.Parser().parse(new File("schema.avsc"));
 PCollection<GenericRecord> records = ...;
 records.apply("WriteToAvro", AvroIO.writeGenericRecords(schema)
     .to("gs://my_bucket/path/to/numbers")
     .withSuffix(".avro"));
 

Writing windowed or unbounded data

By default, all input is put into the global window before writing. If per-window writes are desired - for example, when using a streaming runner - AvroIO.Write.withWindowedWrites() will cause windowing and triggering to be preserved. When producing windowed writes with a streaming runner that supports triggers, the number of output shards must be set explicitly using AvroIO.Write.withNumShards(int); some runners may set this for you to a runner-chosen value, so you may need not set it yourself. A FileBasedSink.FilenamePolicy must be set, and unique windows and triggers must produce unique filenames.

Writing data to multiple destinations

The following shows a more-complex example of AvroIO.Write usage, generating dynamic file destinations as well as a dynamic Avro schema per file. In this example, a PCollection of user events (e.g. actions on a website) is written out to Avro files. Each event contains the user id as an integer field. We want events for each user to go into a specific directory for that user, and each user's data should be written with a specific schema for that user; a side input is used, so the schema can be calculated in a different stage.

 // This is the user class that controls dynamic destinations for this avro write. The input to
 // AvroIO.Write will be UserEvent, and we will be writing GenericRecords to the file (in order
 // to have dynamic schemas). Everything is per userid, so we define a dynamic destination type
 // of Integer.
 class UserDynamicAvroDestinations
     extends DynamicAvroDestinations<UserEvent, Integer, GenericRecord> {
   private final PCollectionView<Map<Integer, String>> userToSchemaMap;
   public UserDynamicAvroDestinations( PCollectionView<Map<Integer, String>> userToSchemaMap) {
     this.userToSchemaMap = userToSchemaMap;
   }
   public GenericRecord formatRecord(UserEvent record) {
     return formatUserRecord(record, getSchema(record.getUserId()));
   }
   public Schema getSchema(Integer userId) {
     return new Schema.Parser().parse(sideInput(userToSchemaMap).get(userId));
   }
   public Integer getDestination(UserEvent record) {
     return record.getUserId();
   }
   public Integer getDefaultDestination() {
     return 0;
   }
   public FilenamePolicy getFilenamePolicy(Integer userId) {
     return DefaultFilenamePolicy.fromParams(new Params().withBaseFilename(baseDir + "/user-"
     + userId + "/events"));
   }
   public List<PCollectionView<?>> getSideInputs() {
     return ImmutableList.<PCollectionView<?>>of(userToSchemaMap);
   }
 }
 PCollection<UserEvents> events = ...;
 PCollectionView<Map<Integer, String>> userToSchemaMap = events.apply(
     "ComputePerUserSchemas", new ComputePerUserSchemas());
 events.apply("WriteAvros", AvroIO.<Integer>writeCustomTypeToGenericRecords()
     .to(new UserDynamicAvroDestinations(userToSchemaMap)));
 

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	AvroIO.Parse<T> Implementation of parseGenericRecords(org.apache.beam.sdk.transforms.SerializableFunction<org.apache.avro.generic.GenericRecord, T>).
static class	AvroIO.ParseAll<T> Implementation of parseAllGenericRecords(org.apache.beam.sdk.transforms.SerializableFunction<org.apache.avro.generic.GenericRecord, T>).
static class	AvroIO.Read<T> Implementation of read(java.lang.Class<T>) and readGenericRecords(org.apache.avro.Schema).
static class	AvroIO.ReadAll<T> Implementation of readAll(java.lang.Class<T>).
static class	AvroIO.TypedWrite<UserT,DestinationT,OutputT> Implementation of write(java.lang.Class<T>).
static class	AvroIO.Write<T> This class is used as the default return value of write(java.lang.Class<T>)

Method Summary

Modifier and Type	Method and Description
static <UserT,OutputT> DynamicAvroDestinations<UserT,java.lang.Void,OutputT>	constantDestinations(FileBasedSink.FilenamePolicy filenamePolicy, Schema schema, java.util.Map<java.lang.String,java.lang.Object> metadata, CodecFactory codec, SerializableFunction<UserT,OutputT> formatFunction) Returns a DynamicAvroDestinations that always returns the same FileBasedSink.FilenamePolicy, schema, metadata, and codec.
static <T> AvroIO.ParseAll<T>	parseAllGenericRecords(SerializableFunction<GenericRecord,T> parseFn) Like parseGenericRecords(SerializableFunction), but reads each filepattern in the input PCollection.
static <T> AvroIO.Parse<T>	parseGenericRecords(SerializableFunction<GenericRecord,T> parseFn) Reads Avro file(s) containing records of an unspecified schema and converting each record to a custom type.
static <T> AvroIO.Read<T>	read(java.lang.Class<T> recordClass) Reads records of the given type from an Avro file (or multiple Avro files matching a pattern).
static <T> AvroIO.ReadAll<T>	readAll(java.lang.Class<T> recordClass) Like read(java.lang.Class<T>), but reads each filepattern in the input PCollection.
static AvroIO.ReadAll<GenericRecord>	readAllGenericRecords(Schema schema) Like readGenericRecords(Schema), but reads each filepattern in the input PCollection.
static AvroIO.ReadAll<GenericRecord>	readAllGenericRecords(java.lang.String schema) Like readGenericRecords(String), but reads each filepattern in the input PCollection.
static AvroIO.Read<GenericRecord>	readGenericRecords(Schema schema) Reads Avro file(s) containing records of the specified schema.
static AvroIO.Read<GenericRecord>	readGenericRecords(java.lang.String schema) Reads Avro file(s) containing records of the specified schema.
static <T> AvroIO.Write<T>	write(java.lang.Class<T> recordClass) Writes a PCollection to an Avro file (or multiple Avro files matching a sharding pattern).
static <UserT,OutputT> AvroIO.TypedWrite<UserT,java.lang.Void,OutputT>	writeCustomType() A PTransform that writes a PCollection to an avro file (or multiple avro files matching a sharding pattern), with each element of the input collection encoded into its own record of type OutputT.
static <UserT> AvroIO.TypedWrite<UserT,java.lang.Void,GenericRecord>	writeCustomTypeToGenericRecords() Similar to writeCustomType(), but specialized for the case where the output type is GenericRecord.
static AvroIO.Write<GenericRecord>	writeGenericRecords(Schema schema) Writes Avro records of the specified schema.
static AvroIO.Write<GenericRecord>	writeGenericRecords(java.lang.String schema) Writes Avro records of the specified schema.

Methods inherited from class java.lang.Object

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

Method Detail

read

public static <T> AvroIO.Read<T> read(java.lang.Class<T> recordClass)

Reads records of the given type from an Avro file (or multiple Avro files matching a pattern).

The schema must be specified using one of the withSchema functions.

readAll

public static <T> AvroIO.ReadAll<T> readAll(java.lang.Class<T> recordClass)

Like read(java.lang.Class<T>), but reads each filepattern in the input PCollection.

readGenericRecords

public static AvroIO.Read<GenericRecord> readGenericRecords(Schema schema)

Reads Avro file(s) containing records of the specified schema.

readAllGenericRecords

public static AvroIO.ReadAll<GenericRecord> readAllGenericRecords(Schema schema)

Like readGenericRecords(Schema), but reads each filepattern in the input PCollection.

readGenericRecords

public static AvroIO.Read<GenericRecord> readGenericRecords(java.lang.String schema)

Reads Avro file(s) containing records of the specified schema. The schema is specified as a JSON-encoded string.

readAllGenericRecords

public static AvroIO.ReadAll<GenericRecord> readAllGenericRecords(java.lang.String schema)

Like readGenericRecords(String), but reads each filepattern in the input PCollection.

parseGenericRecords

public static <T> AvroIO.Parse<T> parseGenericRecords(SerializableFunction<GenericRecord,T> parseFn)

Reads Avro file(s) containing records of an unspecified schema and converting each record to a custom type.

parseAllGenericRecords

public static <T> AvroIO.ParseAll<T> parseAllGenericRecords(SerializableFunction<GenericRecord,T> parseFn)

Like parseGenericRecords(SerializableFunction), but reads each filepattern in the input PCollection.

write

public static <T> AvroIO.Write<T> write(java.lang.Class<T> recordClass)

Writes a PCollection to an Avro file (or multiple Avro files matching a sharding pattern).

writeGenericRecords

public static AvroIO.Write<GenericRecord> writeGenericRecords(Schema schema)

Writes Avro records of the specified schema.

writeCustomType

public static <UserT,OutputT> AvroIO.TypedWrite<UserT,java.lang.Void,OutputT> writeCustomType()

A PTransform that writes a PCollection to an avro file (or multiple avro files matching a sharding pattern), with each element of the input collection encoded into its own record of type OutputT.

This version allows you to apply AvroIO writes to a PCollection of a custom type UserT. A format mechanism that converts the input type UserT to the output type that will be written to the file must be specified. If using a custom DynamicAvroDestinations object this is done using FileBasedSink.DynamicDestinations.formatRecord(UserT), otherwise the AvroIO.TypedWrite.withFormatFunction(org.apache.beam.sdk.transforms.SerializableFunction<UserT, OutputT>) can be used to specify a format function.

The advantage of using a custom type is that is it allows a user-provided DynamicAvroDestinations object, set via AvroIO.Write.to(DynamicAvroDestinations) to examine the custom type when choosing a destination.

If the output type is GenericRecord use writeCustomTypeToGenericRecords() instead.

writeCustomTypeToGenericRecords

public static <UserT> AvroIO.TypedWrite<UserT,java.lang.Void,GenericRecord> writeCustomTypeToGenericRecords()

Similar to writeCustomType(), but specialized for the case where the output type is GenericRecord. A schema must be specified either in DynamicAvroDestinations.getSchema(DestinationT) or if not using dynamic destinations, by using AvroIO.TypedWrite.withSchema(Schema).

writeGenericRecords

public static AvroIO.Write<GenericRecord> writeGenericRecords(java.lang.String schema)

Writes Avro records of the specified schema. The schema is specified as a JSON-encoded string.

constantDestinations

public static <UserT,OutputT> DynamicAvroDestinations<UserT,java.lang.Void,OutputT> constantDestinations(FileBasedSink.FilenamePolicy filenamePolicy,
                                                                                                         Schema schema,
                                                                                                         java.util.Map<java.lang.String,java.lang.Object> metadata,
                                                                                                         CodecFactory codec,
                                                                                                         SerializableFunction<UserT,OutputT> formatFunction)

Returns a DynamicAvroDestinations that always returns the same FileBasedSink.FilenamePolicy, schema, metadata, and codec.