: null 解决
文章目录
- : null 解决
- 解决方法
- 问题原因
今天工作中，遇到一个问题，日志
: null 相当懵逼，没有详细堆栈信息。
解决方法
在java启动命令中添加-XX:-OmitStackTraceInFastThrow即可输出详细堆栈信息。
问题原因
JVM（HotSpot JVM）进行了优化。当第一次发生异常（通常为NullPointerException）时，将打印完整的堆栈跟踪，并且JVM会记住堆栈跟踪（或者可能只是代码的位置）。 当该异常经常发生时，将不再打印堆栈跟踪，这既可以实现更好的性能，又不会使相同的堆栈跟踪充满日志。
参看JVM源码（参见下），可见这个优化同时试用于以下异常：
- NullPointerException
- ArrayIndexOutOfBoundsException
- ClassCastException
- ArrayIndexOutOfBoundsException
- ArrayStoreException
- ArithmeticExceptio
相关核心代码片段：
// If this throw happens frequently, an uncommon trap might cause // a performance pothole. If there is a local exception handler, // and if this particular bytecode appears to be deoptimizing often, // let us handle the throw inline, with a preconstructed instance. // Note: If the deopt count has blown up, the uncommon trap // runtime is going to flush this nmethod, not matter what.
if (treat_throw_as_hot && (!StackTraceInThrowable || OmitStackTraceInFastThrow)) {// If the throw is local, we use a pre-existing instance and// punt on the backtrace. This would lead to a missing backtrace// (a repeat of 4292742) if the backtrace object is ever asked// for its backtrace.// Fixing this remaining case of 4292742 requires some flavor of// escape analysis. Leave that for the * ex_obj = NULL;switch (reason) {case Deoptimization::Reason_null_check:
ex_obj = env()->NullPointerException_instance(); break;case Deoptimization::Reason_div0_check:
ex_obj = env()->ArithmeticException_instance(); break;case Deoptimization::Reason_range_check:
ex_obj = env()->ArrayIndexOutOfBoundsException_instance(); break;case Deoptimization::Reason_class_check: if (java_bc() == Bytecodes::_aastore) {
ex_obj = env()->ArrayStoreException_instance();
} else {
ex_obj = env()->ClassCastException_instance();
} break;default: break;
}
参考
: null”原因解决
NullPointerException in Java with no StackTrace