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Ankur in Java

Java Flight Recorder and Mission Control: Profiling a Live Spring Boot App in 20 Minutes

A hands-on guide to profiling a live Spring Boot app with Java Flight Recorder: real jcmd and jfr sessions finding a CPU hot method, allocation pressure and lock contention, a custom business event, and four traps that corrupt or hide data — a threshold that silently discards 12ms waits, a shared threshold between concurrent recordings, events lost to a missing try/finally, and a dump/stop bug that doubles every event.

Ankur in Java

Immutable Collections in Java: List.of vs unmodifiableList vs copyOf

Collections.unmodifiableList, List.of and List.copyOf all refuse direct mutation, but only two of them reject null elements and only one of them is a real snapshot rather than a live view over a list you still hold a mutable reference to. Covers null handling, views vs copies, real JMH construction/read overhead, a brief Guava ImmutableList comparison, and the record field that looks immutable but isn't.

Ankur in Java

Sequenced Collections in Java 21+: getFirst, getLast and reversed()

JEP 431's SequencedCollection, SequencedSet and SequencedMap give List, Deque, LinkedHashSet, LinkedHashMap and TreeMap a shared getFirst/getLast/reversed() contract. This replaces the stream.reduce((a,b)->b) and skip(size-1) tricks people use to find the last element of a Set, with real javap-verified interface output and a working demo of why reversed() is a live view, not a copy.

Ankur in Java

ArrayList vs LinkedList in 2026: JMH Benchmarks and Why LinkedList Rarely Wins

Real JMH numbers for add, get, iterate and remove on ArrayList and LinkedList, why the gap is bigger than Big-O suggests, the one case LinkedList actually wins, and why ArrayDeque is usually the right answer for stack and queue code instead of either.

Ankur in Java

HTTP/3 in the Java HTTP Client (JEP 517): Migrating from HttpClient 11

JEP 517 added HTTP/3 to java.net.http in Java 26 as an opt-in. What the opt-in looks like, how the three H3_DISCOVERY modes behave, what fallback costs in seconds, why proxies silently downgrade you, and how HTTP/1.1, HTTP/2 and HTTP/3 compare under simulated packet loss, all measured on a local server with captured transcripts.

Ankur in Java

Java NIO.2 File API: Files, Path, WatchService, and Streaming Large Files Without OOM

Stream a 5 GB file at a 64 MB heap with GC evidence, then see the failure modes: readAllLines/readString OOM, unclosed Files.lines and Files.walk leaking file handles, WatchService event folding and the 512-event overflow cliff on Linux, and memory-mapped files. All measured on JDK 25 with a runnable companion module.

Ankur in Java

How to Sort a HashMap by Value (and Key) in Java

The shortest correct way to sort a Java HashMap by value or key (stream into a LinkedHashMap), plus the traps: a TreeMap with a value comparator silently drops tied entries, top-N with a PriorityQueue measured against sort-and-limit in JMH, and JDK 21+ sequenced collections (reversed, firstEntry).

Ankur in Java

Java Strings Deep Dive: Interning, StringBuilder, Text Blocks, and the Concatenation Benchmark

What the string pool and intern() really do, what + compiles to on JDK 25 (invokedynamic, not StringBuilder), a JMH benchmark showing + is fine in one expression but quadratic in a loop, the four text-block rules, and what JEPs 430, 459 and 465 actually say about why string templates never shipped.

Ankur in Java

Java Serialization in 2026: Why It’s Dangerous and What Replaced It

Why ObjectInputStream.readObject() on untrusted bytes is dangerous, shown with harmless stand-ins: serialVersionUID drift, code that runs before your cast, and a 37-byte stream that asks for 1 GB. Then the JDK's answer (JEP 290 filters, JEP 415 filter factories), records, and a measured size and speed comparison with Jackson 3 and Protobuf, all from a runnable companion repo.