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This article mainly introduces the relevant knowledge of Bug analysis in Java, the content is detailed and easy to understand, the operation is simple and fast, and it has a certain reference value. I believe you will gain something after reading this Java Bug analysis article. Let's take a look at it.

Background

During the 15 years of continuous integration in CITIC Bank, because the project was based on the Java configuration development platform purchased by three parties, the platform realized incremental and hot deployment based on Ant plug-ins.

During continuous integration deployment, several of these projects often find that the new version of the code does not take effect (decompilation of class) after the successful deployment of the Linux platform (Windows does not appear, Linux is also an occasional phenomenon).

At first I tracked and debugged the Ant plug-in-based code on the local windows, but never reproduced it (in the end, the test found that Windows did not have this Bug).

Later, through the analysis of the code logic, there is a section of logic that determines whether to overwrite the deployment by the last modification time of the file (File.lastModified ()). Finally, through a single test, it is found that it is due to the difference in precision obtained by Java's File.lastModified () method in Windows and Linux/Unix platforms, the accuracy of Windows is millisecond, while Linux/Unix can only reach seconds (JDK Bug:JDK-8177809).

So it also explains why it is an occasional phenomenon. If the file modification time is judged to be exactly across seconds, the deployment will be successful, otherwise it will fail.

Bug reproduction

Test code: FileTest.java

Import java.io.File;import java.io.IOException;import java.nio.file.Files;import java.text.SimpleDateFormat;public class FileTest {private static final long LM = 1599276952718L; public static void main (String [] args) throws IOException {/ / java version number System.out.println ("Java Version:" + System.getProperty ("java.version")); File f = new File ("test.txt"); f.createNewFile () / / set the last modification time f.setLastModified (LM); / / get the modification time. There is bug System.out.printf ("Test f.lastModified [% s]:% b\ n", f.lastModified (), f.lastModified () = = LM). / / formatted output, correct absence of bug System.out.printf ("Test f.lastModified DateFormat [% s]\ n", new SimpleDateFormat ("yyyy-MM-dd HH:mm:ss.sss") .format (f.lastModified () / / Files.getLastModifiedTime () gets the modification time, and there is also bug System.out.printf ("Test Files.getLastModifiedTime [% s]:% b\ n", Files.getLastModifiedTime (f.toPath ()) .toMillis (), (Files.getLastModifiedTime (f.toPath ()) .toMillis () = = LM) / / formatted output, correct no bug System.out.printf ("Test Files.getLastModifiedTime DateFormat [% s]\ n", new SimpleDateFormat ("yyyy-MM-dd HH:mm:ss.sss") .format (f.lastModified ()); f.delete ();}}

Compile and execute under the command line:

# compile and execute $javac FileTest.java & & java FileTestWindows execution result

This Bug does not exist on the Windows platform.

# compile and execute $javac FileTest.java & & java FileTestJava Version:1.8.0_202Test f.lastModified [1599276952718]: trueTest f.lastModified DateFormat [2020-09-05 11Test Files.getLastModifiedTime] Test Files.getLastModifiedTime [1599276952718]: trueTest Files.getLastModifiedTime DateFormat [1599276952718] Mac execution result

The latest version of JDK 8 has not yet fixed this issue.

# compile and execute $javac FileTest.java & & java FileTestJava Version:1.8.0_261Test f.lastModified [1599276952000]: falseTest f.lastModified DateFormat [2020-09-05 11falseTest Files.getLastModifiedTime DateFormat 11falseTest f.lastModified DateFormat [1599276952000] Test Files.getLastModifiedTime [1599276952000]: falseTest Files.getLastModifiedTime DateFormat [1599276952000] Linux execution result # compile execution $javac FileTest.java & & java FileTestJava Version:1.8.0_171Test f.lastModified [1599276952000]: falseTest f.lastModified DateFormat -09-05 11 Java 35 Bug 52.052] Test Files.getLastModifiedTime [1599276952000]: falseTest Files.getLastModifiedTime DateFormat [1599276952000]: 52.052] this is the end of the article on "Bug Analysis in Java". Thank you for reading! I believe you all have a certain understanding of "Bug Analysis in Java". If you want to learn more, you are welcome to follow the industry information channel.

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