https://mksiva.com/tags/java/ Recent content in Java on Siva Kalidasan Hugo en-us Sat, 20 Jun 2026 00:00:00 +0000 https://mksiva.com/tech/building-a-simple-cli-with-picocli/ Sat, 20 Jun 2026 00:00:00 +0000 https://mksiva.com/tech/building-a-simple-cli-with-picocli/ <p><em>Picocli is a small Java library that makes it easy to build command-line tools. You write plain Java classes, add a few annotations, and Picocli handles parsing, help text, and error messages for you.</em></p> <h2 id="why-build-a-cli-tool">Why build a CLI tool?</h2> <p>Many useful tools run in the terminal:</p> <ul> <li>Build scripts</li> <li>Data migration utilities</li> <li>Dev helpers (rename files, check configs, seed databases)</li> <li>Internal admin tools</li> </ul> <p>You <em>can</em> parse <code>args</code> manually with <code>String[] args</code>, but that gets messy quickly when you need flags, subcommands, defaults, and <code>--help</code>.</p> https://mksiva.com/tech/dealing-with-java-and-json-conversion/ Fri, 23 Sep 2016 00:00:00 +0000 https://mksiva.com/tech/dealing-with-java-and-json-conversion/ <p>When you are trying to convert any java object to json, you may run in to this problem.</p> <pre tabindex="0"><code>com.fasterxml.jackson.core.JsonGenerationException: Null key for a Map not allowed in JSON (use a converting NullKeySerializer?) </code></pre><p>This is due to null key in the map of objects (or collection of objects). JsonGenerator cannot serialize the null key into json.</p> <h2 id="ignore-null-values-in-the-map">Ignore &rsquo;null&rsquo; values in the map</h2> <p>So we can ignore &rsquo;null&rsquo; key and values from the ObjectMapper by using:</p>