How to Group Strings by Empty Lines Using Java Streams

How can I group lines of strings that are separated by empty lines in Java using Stream API?

List<List<String>> groupedLines = Lines.stream()
    .collect(Collectors.groupingBy(line -> line.isEmpty() ? "EMPTY" : "CONTENT"))
    .values()
    .stream()
    .map(group -> new ArrayList<>(group))
    .collect(Collectors.toList());

In Java, you can efficiently group lines of strings separated by empty lines using the Stream API. This allows you to create distinct groups for each block of content, making data processing simpler and more structured.

List<String> lines = Arrays.asList(
    "Line 1",
    "Line 2",
    "",
    "Line 3",
    "Line 4",
    "",
    "Line 5"
);

List<List<String>> groupedLines = 
    lines.stream().collect(
        Collectors.groupingBy(line -> line.isEmpty() ? "EMPTY" : "CONTENT"))
        .values().stream()
        .filter(group -> !group.isEmpty())
        .collect(Collectors.toList());

Causes

• The need to process multi-line strings where groups of lines are delimited by empty lines is common in text processing or data input scenarios.
• Java Streams provide a functional approach to handle collections, making it easier to manipulate and process data sequences.

Solutions

• Use the Java Stream API to read lines from a source, filtering and grouping them based on whether the line is empty or contains content.
• Group content into lists where each list corresponds to a block of non-empty lines.

Mistake: Not handling leading or trailing empty lines which may lead to empty groups being created.

Solution: Ensure to filter out empty groups after grouping.

Mistake: Using a mutable collection inside a stream operation which may cause concurrency issues.

Solution: Use immutable lists or proper collection types that are thread-safe for any concurrent operations.