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java-merge-sort

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Basic stand-alone disk-based N-way merge sort component for Java

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# Overview

This project implements basic disk-backed multi-way merge sort, with configurable input and output formats (i.e. not just textual sort).
It should be useful for systems that process large amounts of data, as a simple building block for sort phases.

# Documentation

Checkout [project wiki](https://github.com/cowtowncoder/java-merge-sort/wiki) for more documentation, including Javadocs.

# License

Library is licensed under [Apache License 2.0](http://www.apache.org/licenses/LICENSE-2.0.txt).

# JDK Requirement

Version 1.1.0 (released on 2022-11-19) requires Java 8.

Earlier versions (1.0.2 and before) require Java 6.

# Usage

## Programmatic access

Main class to interact with is `com.fasterxml.sort.Sorter`, which needs to be constructed with four things:

* Configuration settings (default `SortConfig` works fine)
* `DataReaderFactory` which is used for creating readers for intermediate sort files (and input, if stream passed)
* `DataWriterFactory` which is used for creating writers for intermediate sort files (and results, if stream passed)
* `Comparator` for data items

An example of how this can be done can be found from `com.fasterxml.sort.std.TextFileSorter`.
Basic implementations exist for line-based text input (in package `com.fasterxml.sort.std`), and additional implementations may be added: for example, a JSON data sorter could be implement as an extension module of `Jackson`.
Fortunately implementing your own readers and writers is trivial.

With a Sorter instance, you can call one of two main sort methods:

```java
public void sort(InputStream source, OutputStream destination)
public boolean sort(DataReader<T>  inputReader, DataWriter<T> resultWriter)
```

where former takes input as streams and uses configured reader/writer factories to construct `DataReader` for input and `DataWriter` for output; and latter just uses pre-constructed instances.

In addition to core sorting functionality, `Sorter` instance also gives access to progress information (it implements `SortingState` interface with accessor methods).

A very simple example of sorting a text file using line-by-line comparison is:

```java
TextSorter sorter = new TextFileSorter(new SortConfig().withMaxMemoryUsage(20 * 1000 * 1000));
sorter.sort(new FileInputStream("input.txt"), new FileOutputStream("output.txt"));
```

which would read text from file "input.txt", sort using about 20 megs of heap (note: estimates for memory usage are rough), use temporary files if necessary (i.e. for small files it's just in-memoryu sort, for bigger real merge sort), and write output as file "output.txt".

## Command-line utility

Project jar is packaged such that it can be used as a primitive 'sort' tool like so:

```java
java -jar java-merge-sort-1.1.0.jar [input-file]
```

where sorted output gets printed to `stdout`; and argument is optional (if missing, reads input from stdout).
(implementation note: this uses standard `TextFileSorter` mentioned above)

Format is assumed to be basic text lines, similar to unix `sort`, and sorting order basic byte sorting (which works for most common encodings).

## More documentation

Here are some external links:

* [Sorting large data sets](http://www.cowtowncoder.com/blog/archives/2011/12/entry_465.html) (includes example for sorting JSON files)

# Getting involved

To access source, just clone [project](https://github.com/cowtowncoder/java-merge-sort)

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