Flink中的DataStream任务用于实现data streams的转换，data stream可以来自不同的数据源，比如消息队列，socket，文件等。
Ref
https://ci.apache.org/projects/flink/flink-docs-stable/zh/dev/datastream_api.html
使用DataStream API需要使用stream env
StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
DataStream支持的Data Source有：File-based，Socket-based，Collection-based，Custom
1.File-based
readTextFile(path) - Reads text files, i.e. files that respect the TextInputFormat specification, line-by-line and returns them as Strings. readFile(fileInputFormat, path) - Reads (once) files as dictated by the specified file input format. readFile(fileInputFormat, path, watchType, interval, pathFilter, typeInfo) - This is the method called internally by the two previous ones. It reads files in the path based on the given fileInputFormat. Depending on the provided watchType, this source may periodically monitor (every interval ms) the path for new data (FileProcessingMode.PROCESS_CONTINUOUSLY), or process once the data currently in the path and exit (FileProcessingMode.PROCESS_ONCE). Using the pathFilter, the user can further exclude files from being processed.
2.Socket-based
socketTextStream - Reads from a socket. Elements can be separated by a delimiter
3.Collection-based
fromCollection(Collection) - Creates a data stream from the Java Java.util.Collection. All elements in the collection must be of the same type. fromCollection(Iterator, Class) - Creates a data stream from an iterator. The class specifies the data type of the elements returned by the iterator. fromElements(T ...) - Creates a data stream from the given sequence of objects. All objects must be of the same type. fromParallelCollection(SplittableIterator, Class) - Creates a data stream from an iterator, in parallel. The class specifies the data type of the elements returned by the iterator. generateSequence(from, to) - Generates the sequence of numbers in the given interval, in parallel.
4.Custom
addSource - Attach a new source function. For example, to read from Apache Kafka you can use addSource(new FlinkKafkaConsumer<>(...)). See connectors for more details
Data Stream支持的transformations算子
https://ci.apache.org/projects/flink/flink-docs-release-1.12/zh/dev/stream/operators/
DataStream支持的Data Sink有：
writeAsText() / TextOutputFormat - Writes elements line-wise as Strings. The Strings are obtained by calling the toString() method of each element. writeAsCsv(...) / CsvOutputFormat - Writes tuples as comma-separated value files. Row and field delimiters are configurable. The value for each field comes from the toString() method of the objects. print() / printToErr() - Prints the toString() value of each element on the standard out / standard error stream. Optionally, a prefix (msg) can be provided which is prepended to the output. This can help to distinguish between different calls to print. If the parallelism is greater than 1, the output will also be prepended with the identifier of the task which produced the output. writeUsingOutputFormat() / FileOutputFormat - Method and base class for custom file outputs. Supports custom object-to-bytes conversion. writeToSocket - Writes elements to a socket according to a SerializationSchema addSink - Invokes a custom sink function. Flink comes bundled with connectors to other systems (such as Apache Kafka) that are implemented as sink functions.