[HADOOP-1230] Replace parameters with context objects in Mapper, Reducer, Partitioner, InputFormat, and OutputFormat classes

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.20.0
• Hadoop Flags: Reviewed
• Release Note: Replaced parameters with context obejcts in Mapper, Reducer, Partitioner, InputFormat, and OutputFormat classes.
• Assignee: Owen O'Malley
• Reporter: Owen O'Malley
• Created: 09/Apr/07 18:30
• Updated: 02/May/13 02:29
• Resolved: 15/Dec/08 22:22

Description

This is a big change, but it will future-proof our API's. To maintain backwards compatibility, I'd suggest that we move over to a new package name (org.apache.hadoop.mapreduce) and deprecate the old interfaces and package. Basically, it will replace:

package org.apache.hadoop.mapred;
public interface Mapper extends JobConfigurable, Closeable {
void map(WritableComparable key, Writable value, OutputCollector output, Reporter reporter) throws IOException;
}

with:

package org.apache.hadoop.mapreduce;
public interface Mapper extends Closable {
void map(MapContext context) throws IOException;
}

where MapContext has the methods like getKey(), getValue(), collect(Key, Value), progress(), etc.

Issue Links

• blocks: MAPREDUCE-252 Create an InputFormat for reading lines of text as Java Strings
• is depended upon by: HADOOP-10860 Add serialization for Protocol Buffers
• is related to: MAPREDUCE-342 Create a public scheduler API
• is related to: MAPREDUCE-245 Job and JobControl classes should return interfaces rather than implementations
• relates to: MAPREDUCE-334 Change mapred.lib code to use new api