How to Debug Java Stream Operations Easily in IntelliJ IDEA

Stream API is a major feature of Java 8, but many developers avoid it because debugging is hard; the operations execute in a single line, making it difficult to pinpoint which step fails.

Plugin: Java Stream Debugger

If you use a recent version of IntelliJ IDEA, the plugin is built‑in; otherwise install it manually.

Debugging Stream Operations

Consider the following example:

public class StreamTest {
    @Test
    void test() {
        List<String> list = List.of("blog.didispace.com", "spring4all.com", "openwrite.cn", "www.didispace.com");
        List<String> result = list.stream()
                .filter(e -> e.contains("didispace.com"))
                .filter(e -> e.length() > 17)
                .toList();
        System.out.println(result);
    }
}

This code filters a list with two filter operations, so when an error occurs it is unclear which filter is responsible.

In IDEA, click the Stream Debugger button (shown below):

The Stream Tracking window appears, displaying a tab for each step of the pipeline. Clicking a tab shows the input and output of that step, allowing you to verify whether each filter behaved as expected.

Using this visual debugger makes stream troubleshooting much simpler.