有没有办法打开某种JVM日志记录,所以我可以看到在类加载等过程中发生了什么

Question

我正在尝试优化我的Java Web应用程序的启动时间/类加载时间,因为它在Google App Engine和启动时间非常重要.

有没有办法可以打开某种类加载调试消息,或者某种方式来查看类加载时花费的时间？我想看看是否有任何特定的库需要一段时间才能加载,然后如果它们不是必需的话就去掉它们.

Answer 1

如果要查看已加载的类以及可以使用该-verbose标志运行的顺序.

例:

java -verbose:class <MyProgram>

输出:

[Loaded java.lang.Object from shared objects file]
[Loaded java.io.Serializable from shared objects file]
[Loaded java.lang.Comparable from shared objects file]
[Loaded java.lang.CharSequence from shared objects file]
[Loaded java.lang.String from shared objects file]
[Loaded java.lang.reflect.GenericDeclaration from shared objects file]
[Loaded java.lang.reflect.Type from shared objects file]
[Loaded java.lang.reflect.AnnotatedElement from shared objects file]
[Loaded java.lang.Class from shared objects file]
[Loaded java.lang.Cloneable from shared objects file]
[Loaded java.lang.ClassLoader from shared objects file]
[Loaded java.lang.System from shared objects file]
[Loaded java.lang.Throwable from shared objects file]
[Loaded java.lang.Error from shared objects file]
..
..
..