apache / flink

# Apache Flink
Apache Flink is an open source stream processing framework with powerful stream- and batch-processing capabilities.
Learn more about Flink at https://flink.apache.org/
### Features
* A streaming-first runtime that supports both batch processing and data streaming programs
* Elegant and fluent APIs in Java
* A runtime that supports very high throughput and low event latency at the same time
* Support for *event time* and *out-of-order* processing in the DataStream API, based on the *Dataflow Model*
* Flexible windowing (time, count, sessions, custom triggers) across different time semantics (event time, processing time)
* Fault-tolerance with *exactly-once* processing guarantees
* Natural back-pressure in streaming programs
* Libraries for Graph processing (batch), Machine Learning (batch), and Complex Event Processing (streaming)
* Custom memory management for efficient and robust switching between in-memory and out-of-core data processing algorithms
* Compatibility layers for Apache Hadoop MapReduce
* Integration with YARN, HDFS, HBase, and other components of the Apache Hadoop ecosystem
### Streaming Example
 [code] 
### Batch Example
 [code] 
## Building Apache Flink from Source
Prerequisites for building Flink:
* Unix-like environment (we use Linux, Mac OS X, Cygwin, WSL)
* Git
* Maven (we require version 3.9.16)
* Java (version 11, 17, or 21)
### Basic Build Instructions
First, clone the repository:
 [code] 
Then, choose one of the following commands based on your preferred Java version:
**For Java 11**
 [code] 
**For Java 17 (Default)**
 [code] 
**For Java 21**
 [code] 
The build process will take approximately 10 minutes to complete.
Flink will be installed in `build-target`.
### Notes
* Make sure your JAVA_HOME environment variable points to the correct JDK version
* The build command uses Maven wrapper (mvnw) which ensures the correct Maven version is used
* The -DskipTests flag skips running tests to speed up the build process
* Each Java version requires its corresponding profile (-Pjava -target) and JDK flag (-Djdk )
## Developing Flink
The Flink committers use IntelliJ IDEA to develop the Flink codebase.
We recommend IntelliJ IDEA for developing projects that involve Scala code.
Minimal requirements for an IDE are:
* Support for Java and Scala (also mixed projects)
* Support for Maven with Java and Scala
### IntelliJ IDEA
The IntelliJ IDE supports Maven out of the box and offers a plugin for Scala development.
* IntelliJ download: https://www.jetbrains.com/idea/
* IntelliJ Scala Plugin: https://plugins.jetbrains.com/plugin/?id=1347
Check out our DEVELOPMENT.md guide for detailed IDE setup instructions.
### Eclipse Scala IDE
**NOTE:** From our experience, this setup does not work with Flink
due to deficiencies of the old Eclipse version bundled with Scala IDE 3.0.3 or
due to version incompatibilities with the bundled Scala version in Scala IDE 4.4.1.
**We recommend to use IntelliJ instead (see above)**
## Support
Don’t