org.kitesdk.data.spi

Class Marker

java.lang.Object

org.kitesdk.data.spi.Marker

Direct Known Subclasses:

StorageKey

public abstract class Marker
extends Object

A Marker is a bookmark in the partition space, which is the space of each possible partition in a PartitionStrategy. A Marker holds un-ordered values that can be used to create keys by a PartitionStrategy. It can hold either source values, like a timestamp, or concrete values, like a year. A Marker can be used as a generic placeholder or bookmark for an entity (an object in a Dataset. For example, when fetching a record from HBase, you can use a Marker to hold the information that PartitionStrategy uses to build a concrete key and fetch the entity. A Marker can also be used as a partial key, where some of the values needed to create a complete key are missing. In this case, a Marker contains a subset of the partition space: all Marker the keys that share the values that are set in the Marker. The Marker.Builder class is the easiest way to make a Marker. Any Marker created by the Marker.Builder is Immutable and will not change. The Builder can copy values from other Marker objects and provides a fluent interface to easily create new instances:

 // a partial Marker for all events with the same hash code and approx time
 Marker partial = new Marker.Builder()
    .add("shard", id.hashCode())
    .add("timestamp", System.getTimeMillis())
    .build();

 // a Marker that represents a particular object
 Marker concrete = new Marker.Builder(partial).add("id", id).build();

 // a partial Marker for approx time, for all shards
 new Marker.Builder("timestamp", System.getTimeMillis()).build();
 

Since:

0.9.0

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Marker.Builder A fluent builder for creating Marker instances.

Constructor Summary

Constructors

Constructor and Description
Marker()

Method Summary

Methods

Modifier and Type	Method and Description
abstract Object	get(String name) Returns the value for name.
<T> T	getAs(String name, Class<T> returnType) Returns the value for name coerced to the given type, T.
abstract boolean	has(String name) Returns whether name is stored in this Marker.
<S,T> T	valueFor(FieldPartitioner<S,T> fp) Return the value of a FieldPartitioner field for this Marker.

Methods inherited from class java.lang.Object

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

Constructor Detail

Marker

public Marker()

Method Detail

has

public abstract boolean has(String name)

Returns whether name is stored in this Marker.

Parameters:

name - a String name

Returns:

true if there is a value for name

get

public abstract Object get(String name)

Returns the value for name.

Parameters:

name - the String name of the value to return

Returns:

the Object stored for name

getAs

public <T> T getAs(String name,
          Class<T> returnType)

Returns the value for name coerced to the given type, T.

Type Parameters:

T - the return type

Parameters:

name - the String name of the value to return

returnType - The return type, which must be assignable from Long, Integer, String, or Object

Returns:

the Object stored for name coerced to a T

Throws:

ClassCastException - if the return type is unknown

valueFor

@Nullable
public <S,T> T valueFor(FieldPartitioner<S,T> fp)

Return the value of a FieldPartitioner field for this Marker. If the Marker has a value for the field's name, that value is returned using getAs(java.lang.String, java.lang.Class). If the Marker only has a value for the the source field name, then that value is retrieved using getAs(java.lang.String, java.lang.Class) and the field's transformation is applied to it as the source value.

Parameters:

fp - a FieldPartitioner

Returns:

the value of the field for this marker, or null

Since:

0.9.0