Java verbose class loading

Question

I am trying to list the order in which the Java class loader is loading my classes. if I use -verbose parameter it will list every single interface/class it loads, including tons of interfaces such as Serializable, exceptions etc. Is there a way to tweak this output so it only shows which classes are loaded in the class my main method is defined?

score 80 · Accepted Answer · edited May 23 '17 at 10:31

80

I guess your best bet is to do the following:

Output some fixed text once your main method starts and right before it ends.
Pipe the verbose output into a file
Use things like less or grep to find the classes loaded between the two tags from the main method.

There's a similar question and some answers here: Is there a way to get which classes a ClassLoader has loaded?

Did you try -verbose:class?

edited May 23 '17 at 10:31

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answered Apr 19 '12 at 14:33

nwinkler

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In case anyone is wondering where this is documented: https://docs.oracle.com/en/java/javase/11/tools/java.html – Renato Jul 01 '21 at 13:30

Nicholas Sushkin · Answer 2 · 2017-03-24T23:48:00.467

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Here's a sed expression that will parse the output of java -verbose:class to produce pairs of loaded class name and its jar file. You can further pipe through a sort to get unique jar files. For example,

java -verbose:class -version 2>/dev/null |
  sed -ne 's/\[Loaded \(.\+\) from \(.\+\)\]/\2/p' | 
  sort -u

outputs

/usr/local/jdk1.7.0_67/jre/lib/rt.jar

edited Mar 24 '17 at 23:48

answered Mar 24 '17 at 22:57

Nicholas Sushkin

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score 2 · Answer 3 · answered May 16 '23 at 07:53

For Java 9+ you can do it with -Xlog:class+init. E.g. this command prints the order of class loading when you start JVM:

java -Xlog:class+init -version

The command prints something like

[0.018s][info][class,init] 0 Initializing 'java/lang/Object'(no method) (0x0000000800000e60)
[0.018s][info][class,init] 1 Initializing 'java/lang/CharSequence'(no method) (0x0000000800009210)
[0.018s][info][class,init] 2 Initializing 'java/lang/String' (0x00000008000089b8)
[0.018s][info][class,init] 3 Initializing 'java/util/Comparator'(no method) (0x00000008000eb588)
[0.018s][info][class,init] 4 Initializing 'java/lang/String$CaseInsensitiveComparator'(no method) (0x000000080010dff8)
[0.018s][info][class,init] 5 Initializing 'java/lang/System' (0x0000000800002b68)
[0.019s][info][class,init] 6 Initializing 'java/lang/reflect/AnnotatedElement'(no method) (0x0000000800013cd0)
[0.019s][info][class,init] 7 Initializing 'java/lang/reflect/Type'(no method) (0x0000000800015210)
[0.019s][info][class,init] 8 Initializing 'java/lang/Class' (0x00000008000139e0)

Java verbose class loading

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