Documentation
Unexpected exception when using Java DateTimeFormatter
Unexpected exception when using Java DateTimeFormatter
Preface
The following announcement was made at
JJUG CCC 2017 Spring
the other day.
</ iframe> <div style =" margin-bottom: 5px "> < strong> <a href="//www.slideshare.net/JSUXDesign/javajavasdk10" title="The Road to Java Chot Dekill ~ 10 Codes You Want to Copy in the Java Core SDK ~" target = "_ blank"> Java Chot Dekill Road to ~ 10 Codes to Imitate in Java Core SDK ~ </a> </ strong> from <strong> <a target="_blank" href="https://www.slideshare.net/JSUXDesign"> JustSystems Corporation </a> </ strong> </ div> <p>In the question in this session, I was asked "How did you find these 10?" I knew it from the beginning, and I reviewed it when I did this session, but after all it is sober to read the source of Java core API or try something. I thought.</p> <h1>Today's topic</h1> <p>By the way, recently I suddenly became interested in the following, so I tried it.</p> <h1>Write a lot of H</h1> <p><img src="https://qiita-image-store.s3.amazonaws.com/0/101293/a78a738f-f1f7-aac4-4302-9c4ba6bdd385.png" alt="Q1.PNG" /></p> <p>We received responses from three people. Opinions were divided. I thought it was second. But the reality was different.</p> <p><img src="https://qiita-image-store.s3.amazonaws.com/0/101293/80d7f0c6-004d-d4fd-f14e-7ef66590e5a6.png" alt="A1.PNG" /></p> <p>Looking at the implementation of the core API, it looks like this. (Excerpt from 8u131 source)</p> <h4><strong><code>java:DateTimeFormatterBuilder.java(LL.1793-1807)</code></strong></h4> <pre><code> case 'd': case 'h': case 'H': case 'k': case 'K': case 'm': case 's': if (count == 1) { appendValue(field); } else if (count == 2) { appendValue(field, count); } else { throw new IllegalArgumentException("Too many pattern letters: " + cur); } break; </code></pre> <p>Only 2 characters are accepted, so 3 or more characters are out.</p> <h1>So is it okay if there are two Hs? → In some cases, exceptions occur</h1> <p>So the next problem is this.</p> <p><img src="https://qiita-image-store.s3.amazonaws.com/0/101293/da6759cc-2063-c6d6-3df0-ba1a07491e3b.png" alt="Q2.PNG" /></p> <p>I thought this was also the second one. But the reality was different. <img src="https://qiita-image-store.s3.amazonaws.com/0/101293/3f4e3dee-384e-bb20-d363-f8c02764f338.png" alt="A2.PNG" /></p> <p>I also saw the implementation.</p> <h4><strong><code>java:Instant.java(LL.594-606)</code></strong></h4> <pre><code> @Override public long getLong(TemporalField field) { if (field instanceof ChronoField) { switch ((ChronoField) field) { case NANO_OF_SECOND: return nanos; case MICRO_OF_SECOND: return nanos / 1000; case MILLI_OF_SECOND: return nanos / 1000_000; case INSTANT_SECONDS: return seconds; } throw new UnsupportedTemporalTypeException("Unsupported field: " + field); } return field.getFrom(this); } </code></pre> <p>The <code>HOUR_OF_DAY</code> you are trying to get this time is<code> ChronoField</code>, so the above</p> <pre><code class="language-java"> if (field instanceof ChronoField) { </code></pre> <p>It is included in this ʻif<code>statement to satisfy this condition. And since there is no corresponding field in</code>switch`, it means that it is out.</p> <p>In other words, if you want to take some time, you have to have an instance of a class that supports <code>HOUR_OF_DAY</code> such as<code> LocalDateTime</code>. This was a learning experience.</p> <h1>appendix</h1> <p>Here is the code used for the test. Since I wrote it for personal use, there is no comment, and it is embarrassing to do it in a less beautiful way, such as switching between the two tests without commenting.</p> <h4><strong><code>FormatterTest.java</code></strong></h4> <pre><code class="language-java"> import java.time.Instant; import java.time.LocalDateTime; import java.time.format.DateTimeFormatter; /** * */ public class FormatterTest { /** * * @param arguments */ public static void main(String[] arguments) { //System.out.println(DateTimeFormatter.ofPattern("HH").format(Instant.now())); System.out.println(DateTimeFormatter.ofPattern("HHHH").format(LocalDateTime.now())); } } </code></pre> <!-- ENDDDDDDDDDDDDDDDDDDDDDDDDDDDDD --> <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <!-- ng_ads_new_ui --> <ins class="adsbygoogle" style="display:block" data-ad-client="ca-pub-6575041992772322" data-ad-slot="8191531813" data-ad-format="auto" data-full-width-responsive="true"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script> <div style="margin-top: 30px;"> <div class="link-top" style="margin-top: 1px;"></div> <p> <font size="4">Recommended Posts</font> <!-- BEGIN LINK ************************* --> <div style="margin-top: 10px;"> <a href="/en/9f1487340bf0bd473ff6">Unexpected exception when using Java DateTimeFormatter</a> </div> <div style="margin-top: 10px;"> <a href="/en/bb4e704a91b260558438">Java Exception StackTrace is determined when new</a> </div> <div style="margin-top: 10px;"> <a href="/en/0072b712c10c322283e2">Java exception handling?</a> </div> <div style="margin-top: 10px;"> <a href="/en/63f769fc583870b9d574">[Java] Exception instance</a> </div> <div style="margin-top: 10px;"> <a href="/en/b32023a797e8fc819e5b">[Java] Exception handling</a> </div> <div style="margin-top: 10px;"> <a href="/en/c26d23cfb36012d149b0">☾ Java / Exception handling</a> </div> <div style="margin-top: 10px;"> <a href="/en/c9910edddc007126df41">Java exception handling</a> </div> <div style="margin-top: 10px;"> <a href="/en/d12fab75034a2e63a593">Java exception handling</a> </div> <div style="margin-top: 10px;"> <a href="/en/46b232bb8fe56c0bac7d">Verification of performance impact when using Java volatile</a> </div> <div style="margin-top: 10px;"> <a href="/en/6f1675166223960a1e85">Specify ClassPath when using jupyter + Java with WSL</a> </div> <div style="margin-top: 10px;"> <a href="/en/07a35f132f756097e55b">Sorting using java comparator</a> </div> <div style="margin-top: 10px;"> <a href="/en/10cab26ff2161a2ca2f5">Don't forget setCalendar or setTimeZone when using Java DateFormat</a> </div> <div style="margin-top: 10px;"> <a href="/en/45330e015d373390f6ca">[java] throw an exception</a> </div> <div style="margin-top: 10px;"> <a href="/en/5541b42c311d47d0486e">Exception when closing try-with-resources</a> </div> <div style="margin-top: 10px;"> <a href="/en/56f7837f73a506bfc41d">Error when using SnapKit</a> </div> <div style="margin-top: 10px;"> <a href="/en/71b9fd25668004e403a1">Scraping practice using Java ②</a> </div> <div style="margin-top: 10px;"> <a href="/en/a856c06accdab922153c">Scraping practice using Java ①</a> </div> <div style="margin-top: 10px;"> <a href="/en/dd0e2f51859ccfda54ff">Differences in code when using the length system in Java</a> </div> <div style="margin-top: 10px;"> <a href="/en/86c9e9efb5358601b25b">[Unresolved] An exception occurs when an SSH connection is executed using JSch from a Java 6 application.</a> </div> <div style="margin-top: 10px;"> <a href="/en/edb9d684b36fec08df98">Common misconceptions about Java application resource limitations when using Kubernetes</a> </div> <div style="margin-top: 10px;"> <a href="/en/0260194ecb92b5519cf1">Java Object Serialization why & when</a> </div> <div style="margin-top: 10px;"> <a href="/en/0a7abb5ce68b047c0510">Java basic learning content 7 (exception)</a> </div> <div style="margin-top: 10px;"> <a href="/en/0fb2ecdb281587a34a44">Try using RocksDB in Java</a> </div> <div style="margin-top: 10px;"> <a href="/en/3165db3b0df3b4d39baa">[Java] Practice of exception handling [Exception]</a> </div> <div style="margin-top: 10px;"> <a href="/en/3bc5142a28ee99f2550f">Try scraping using java [Notes]</a> </div> <div style="margin-top: 10px;"> <a href="/en/560facd781aab385e3c6">[Java] About try-catch exception handling</a> </div> <div style="margin-top: 10px;"> <a href="/en/765a59042d24ba3bc436">Java exception handling usage rules</a> </div> <div style="margin-top: 10px;"> <a href="/en/a187b2b5efc41393f0a2">Error when playing with java</a> </div> <div style="margin-top: 10px;"> <a href="/en/a2aea39fbfad17543a06">Using Mapper with Java (Spring)</a> </div> <div style="margin-top: 10px;"> <a href="/en/b23dfd5b069d11535cf0">I tried using Java REPL</a> </div> <div style="margin-top: 10px;"> <a href="/en/c3b6cae78e31e3614e2e">Error when using rails capybara</a> </div> <div style="margin-top: 10px;"> <a href="/en/ceafd0aea8e419bd1197">Using Docker from Java Gradle</a> </div> <div style="margin-top: 10px;"> <a href="/en/d5d13c1b6aff811501f3">Detailed tips when using Rails</a> </div> <div style="margin-top: 10px;"> <a href="/en/e8397def269a3819aea8">Exception handling techniques in Java</a> </div> <div style="margin-top: 10px;"> <a href="/en/e9c7d5137b90cdccae25">Make a rhombus using Java</a> </div> <div style="margin-top: 10px;"> <a href="/en/f9047f3826c844eeacbf">Bubble sort using ArrayList (JAVA)</a> </div> <div style="margin-top: 10px;"> <a href="/en/72e0b88fabb210f6e68f">Three JDKs to consider when using Java for free for commercial use</a> </div> <div style="margin-top: 10px;"> <a href="/en/baca14a933ddc9d3d562">When using JDBC, NLS parameters are affected by the Java locale.</a> </div> <div style="margin-top: 10px;"> <a href="/en/c07ff4767198fdddfde8">Avoid character code error in java when using VScode extension RUN-CODE</a> </div> <div style="margin-top: 10px;"> <a href="/en/c6484b60e0f1a666d0d8">How to solve the unknown error when using slf4j in Java</a> </div> <!-- END LINK ************************* --> </p> </div> </div> </div> <div class="footer text-center" style="margin-top: 40px;"> <!-- <p> Licensed under cc by-sa 3.0 with attribution required. </p> --> </div> <script src="https://cdn.jsdelivr.net/npm/jquery@3.4.1/dist/jquery.min.js"></script> <script src="https://cdn.jsdelivr.net/npm/bootstrap@4.3.1/dist/js/bootstrap.min.js"></script> <script src="https://cdn.jsdelivr.net/gh/highlightjs/cdn-release@10.1.2/build/highlight.min.js"></script> <!-- ads --> <script data-ad-client="ca-pub-6575041992772322" async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <!-- end ads --> </body> </html>