Flink中的DataSet任務用於實現data sets的轉換，data set通常是固定的資料來源，比如可讀檔案，或者本地集合等。

Ref

https://ci.apache.org/projects/flink/flink-docs-release-1.12/zh/dev/batch/

使用DataSet API需要使用 批處理 env

ExecutionEnvironment env = ExecutionEnvironment.getExecutionEnvironment();

DataSet支援的Data Source有：File-based，Collection-based，Generic

1.File-based

readTextFile(path) / TextInputFormat - Reads files line wise and returns them as Strings.

readTextFileWithValue(path) / TextValueInputFormat - Reads files line wise and returns them as StringValues. StringValues are mutable strings.

readCsvFile(path) / CsvInputFormat - Parses files of comma (or another char) delimited fields. Returns a DataSet of tuples or POJOs. Supports the basic java types and their Value counterparts as field types.

readFileOfPrimitives(path, Class) / PrimitiveInputFormat - Parses files of new-line (or another char sequence) delimited primitive data types such as String or Integer.

readFileOfPrimitives(path, delimiter, Class) / PrimitiveInputFormat - Parses files of new-line (or another char sequence) delimited primitive data types such as String or Integer using the given delimiter.

2.Collection-based

fromCollection(Collection) - Creates a data set from a Java.util.Collection. All elements in the collection must be of the same type.

fromCollection(Iterator, Class) - Creates a data set from an iterator. The class specifies the data type of the elements returned by the iterator.

fromElements(T ...) - Creates a data set from the given sequence of objects. All objects must be of the same type.

fromParallelCollection(SplittableIterator, Class) - Creates a data set 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.

3.Generic

readFile(inputFormat, path) / FileInputFormat - Accepts a file input format.

createInput(inputFormat) / InputFormat - Accepts a generic input format.

Data Set支援的transformations運算元

https://ci.apache.org/projects/flink/flink-docs-release-1.12/zh/dev/batch/dataset_transformations.html

DataSet支援的Data Sink有：

writeAsText() / TextOutputFormat - Writes elements line-wise as Strings. The Strings are obtained by calling the toString() method of each element.
writeAsFormattedText() / TextOutputFormat - Write elements line-wise as Strings. The Strings are obtained by calling a user-defined format() method for 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() / print(String msg) / printToErr(String msg) - 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.
write() / FileOutputFormat - Method and base class for custom file outputs. Supports custom object-to-bytes conversion.
output()/ OutputFormat - Most generic output method, for data sinks that are not file based (such as storing the result in a database).