greenrobot-common

General purpose utilities and hash functions for Android and Java (aka java-common)

Code Quality Rank: L4

Programming language: Java

License: Apache License 2.0

Tags: Utility    

Latest version: v2.0.0

README

Essentials

Essentials are a collection of general-purpose classes we found useful in many occasions.

• Beats standard Java API performance, e.g. LongHashMap can be twice as fast as HashMap<Long, Object>.
• Adds missing pieces without pulling in heavy-weights like Guava
  
• Improved convenience: do more with less code
• Super lightweight: < 100k in size
• Compatible with Android and Java

This project is bare bones compared to a rich menu offered by Guava or Apache Commons. Essentials is not a framework, it's rather a small set of utilities to make Java standard approaches more convenient or more efficient.

Website | JavaDoc | Changelog

Features

• [Hash set][6] and [map][7] for primitive long keys outperform the generic versions of the Java Collection APIs
• [Multimaps][9] provide a map of lists or sets to simplify storing multiple values for a single key
• [Object cache][10] with powerful configuration options: soft/weak/strong references, maximum size, and time-based expiration
• [IO utilities][2] help with streams (byte and character based)
• [File utilities][3] simplify reading and writing strings/bytes/objects from or to files. Also includes getting hashes from files and copying files.
• [String utilities][4] allow efficient splitting and joining of strings, fast hex creation, and other useful string helpers.
• [Date utilities][5]
• Better hash functions: our Murmur3 implementation provides superior hash quality and outperforms standard [Java hash functions](web-resources/hash-functions-benchmark.pdf)
• Specialized Streams: for example an optimized [PipedOutputStream replacement][8] (based on a circular byte buffer)

Read more on our website.

Performance

Some classes where motivated by less than optimal performance offered by standard Java.

For long keys (also works for int), Essentials provides a specialized implementation, that can be twice as fast.

Here are some (completely non-scientific) benchmarking results running on Ubuntu 20.04 LTS using OpenJDK 11.0.9:

Essentials Class	Java (seconds)	Essentials (seconds)	Speed up
LongHashSet (Dynamic)	19.756	13.079	+ 51%
LongHashSet (Prealloc)	16.480	8.171	+ 102%
LongHashMap (Dynamic)	20.311	14.659	+ 39%
LongHashMap (Prealloc)	17.496	8.677	+ 102%
PipelineStream (1024KB)	8.036	1.424	+ 564%
StringHex (vs. Guava)	6.849	3.732	+ 84%

The benchmarking sources are available in the java-essentials-performance directory.

Add the dependency to your project

For Gradle, you add this dependency (from repository mavenCentral()):

implementaion 'org.greenrobot:essentials:3.1.0'

And for Maven:

<dependency>
    <groupId>org.greenrobot</groupId>
    <artifactId>essentials</artifactId>
    <version>3.1.0</version>
</dependency>

Code samples

Example code for some of the utility classes:

// Get all bytes from stream and close the stream safely
byte[] bytes = IoUtils.readAllBytesAndClose(inputStream);

// Read the contents of an file as a string (use readBytes to get byte[])
String contents = FileUtils.readUtf8(file);

// How many days until new year's eve?
long time2 = DateUtils.getTimeForDay(2015, 12, 31);
int daysToNewYear = DateUtils.getDayDifference(time, time2);

Multimaps:

ListMap<String,String> multimap = new ListMap<>();
multimap.putElement("a", "1");
multimap.putElement("a", "2");
multimap.putElement("a", "3");
List<String> strings = multimap.get("a"); // Contains "1", "2", and "3"

Our hash functions implement java.util.zip.Checksum, so this code might look familiar to you:

Murmur3A murmur = new Murmur3A();
murmur.update(bytes);
long hash = murmur.getValue();

All hashes can be calculated progressively by calling update(...) multiple times. Our Murmur3A implementation goes a step further by offering updates with primitive data in a very efficient way:

// reuse the previous instance and start over to calculate a new hash
murmur.reset();

murmur.updateLong(42L);

// Varargs and arrays are supported natively, too  
murmur.updateInt(2014, 2015, 2016);

// Hash for the previous update calls. No conversion to byte[] necessary.
hash = murmur.getValue();

The utility classes are straight forward and don't have dependencies, so you should be fine to grasp them by having a look at their source code. Most of the method names should be self-explaining, and often you'll find JavaDocs where needed.

Build setup

We use Gradle as a primary build system. Previously, Maven is used to build greenrobot-common. Inside of [build-common](build-common), there are two parent POMs defined that might be useful: parent-pom and parent-pom-with-checks. The latter integrates FindBugs and Checkstyle in your build. Use it like this:

<parent>
    <groupId>de.greenrobot</groupId>
    <artifactId>parent-pom-with-checks</artifactId>
    <version>2.0.0</version>
    <relativePath></relativePath>
</parent>

License

Copyright (C) 2012-2020 Markus Junginger, greenrobot (https://greenrobot.org)

EventBus binaries and source code can be used according to the [Apache License, Version 2.0](LICENSE).

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