https://mariano-gonzalez.com/tags/introspection/ Recent content in Introspection on Mariano Gonzalez Hugo en-us <p>Copyright © 2026 Mariano Gonzalez</p><p xmlns:dct='http://purl.org/dc/terms/' xmlns:cc='http://creativecommons.org/ns#' class='license-text'><a rel='cc:attributionURL' property='dct:title' href='https://github.com/eschizoid/eschizoid.github.io/tree/main/content'>Content</a> licensed under <a rel='license' href='https://creativecommons.org/licenses/by/4.0'>CC BY 4.0</a></p> Thu, 09 Jul 2026 00:00:00 +0000 https://mariano-gonzalez.com/posts/post-8/ Thu, 09 Jul 2026 00:00:00 +0000 https://mariano-gonzalez.com/posts/post-8/ <p><p class="md__image"> <img src="logo.png" alt="telescope" /> </p></p> <blockquote> <p><em>Telescope, part 3 of 3: <a href="https://mariano-gonzalez.com/posts/post-6/">how it got built</a> · <a href="https://mariano-gonzalez.com/posts/post-7/">why your mappings should not be strings</a> · <strong>asking your mapper what it did</strong></em></p> </blockquote> <h2 id="the-setup">The setup</h2> <p>A field arrives <code>null</code> in production. The mapper between your entity and your DTO is the suspect, and now you get to answer a simple question: what did it actually map?</p> <p>If the mapper is <a href="https://mapstruct.org/">MapStruct</a>, the answer lives in one place: the generated <code>*MapperImpl.java</code> under <code>build/generated</code>. You open it, you read the assignments, you diff what you read against what you meant. If the question is about a specific request — which values went in, which came out — generated source cannot answer it at all; you add a breakpoint or a log line, redeploy, and wait for the bug to happen again.</p>