This is a small collection of examples of collecting streams of custom types or built-in types into a custom object type for Java streams (Java 8 and above).

This was prompted by the fact that there were no examples to be found in the official docs on how to collect a stream into a custom object type. My project, Functional Nim required precisely such functionality, and I determined to create some custom collectors and demos of collecting into arbitrary types so that it might be useful for others.

Please check the com.z0ltan.custom.collectors.collectors package for custom implementations of the Collector interface which is required in order to be able to collect intermediate results into a final result. For more details on exactly how the custom collectors work, please consult my blog: Talking with a Lisp.

Perusing the tests in the src/test/java folder is also recommended to get a better feel of how to implement and use your own custom collector(s).

Usage

To run the sample tests:

	$ mvn clean && mvn compiler
	$ mvn test

To compile and run the sample examples:

	$ mvn clean && mvn compile
	$ mvn exec:java -Dexec.mainClass=com.z0ltan.custom.collectors.Main

Alternatively,

	$ mvn clean && mvn package
	$ java -jar java -jar target/custom-collectors-1.0-SNAPSHOT.jar

Build

	$ mvn clean && mvn compiler

or

	$ mvn clean && mvn package 

Demo

Sample run:

Macushla:custom-collectors z0ltan$ java -jar target/custom-collectors-1.0-SNAPSHOT.jar
[wrapperDemo] original wrapper = Wrapper { values = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] }

[wrapperDemo] modified wrapper = Wrapper { values = [2, 2, 6, 4, 10, 6, 14, 8, 18, 10] }



[splitterDemo] original wrappers = [Wrapper { values = [1, 2, 3, 4, 5] } , Wrapper { values = [6, 7, 8, 9, 10] } , Wrapper { values = [11, 12, 13, 14, 15] } ]

[splitterDemo] splitValue = Splitter { firstHalf = [1, 2, 3, 4, 5, 6, 7], secondHalf = [8, 9, 10, 11, 12, 13, 14, 15]}



[fooToBarDemo] original foos = [Foo { id = 1, name = Hello}, Foo { id = 6, name = Again}, Foo { id = 2, name = World}, Foo { id = 3, name = We}, Foo { id = 4, name = We}, Foo { id = 5, name = Meet}]

[fooToBarDemo] bar = Bar { ids = [1, 2, 3, 4, 5, 6], names = [Meet, Hello, Again, World, We]}



[fooFilterBarDemo] foos = [Foo { id = 1, name = Hello}, Foo { id = 5, name = Again}, Foo { id = 2, name = World}, Foo { id = 3, name = We}, Foo { id = 4, name = Meet}]

[fooFilterBarDemo] bar = Bar { ids = [1, 3, 5], names = [Hello, Again, We]}



[fooFilterMapBarDemo] foos = [Foo { id = 1, name = Hello}, Foo { id = 5, name = Again}, Foo { id = 2, name = World}, Foo { id = 3, name = We}, Foo { id = 4, name = Meet}]

[fooFilterMapBarDemo] bar = Bar { ids = [2, 4], names = [MEET, WORLD]}