Using IntelliJ IDEA Stream Trace to Debug Java Streams

Java's Stream API can be difficult to debug, but IntelliJ IDEA provides a Stream Trace feature that visualizes each operation's relationship and result, making debugging much easier.

First Encounter with Stream Trace

The author demonstrates converting a string to its length and setting a breakpoint to start debugging, showing screenshots of the trace view where element counts, results, and object contents are clearly displayed.

Using Stream Trace

Stream Trace works only in debug mode; after placing a breakpoint on Stream code and launching the debugger, clicking the stream button opens the trace view, which defaults to Split mode. Users can switch to Flat mode via the button at the lower left.

Practical Demonstration

A sample Stream pipeline that converts city names to their lengths and filters out values less than 5 is shown, with the full Java test method provided below.

@Test
public void TestTrace() {
    Stream.of("beijing","tianjin","shanghai","wuhan")
        .map(String::length)
        .filter(e -> e > 5)
        .collect(Collectors.toList());
}

Final Note

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