java lost exception stack traces

tomcat运行时报错，但查看日志时，只能看到一句NPE，却没有相关的异常栈信息。

java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException

示例代码

public class NullPointerExceptionMissingStack {

    public static void main(String[] args) {
        int i = 0;
        int j = 0;
        String x = null;
        while (i++ < 1_000_000) {
            try {
                throwNPE(x);
            } catch (Exception e) {
                int length = e.getStackTrace().length;
                e.printStackTrace();
                if (length == 0) {
                    j++;
                    if (j > 100) {
                        System.out.println(i);
                        System.out.println(j);
                        return;
                    }
                }
            }
        }

    }

    private static void throwNPE(String x) {
        x.toString();
    }

}

异常抛出次数到达一定程度时，这里jvm会进行优化，只保留了固定的错误，却不再保留异常堆栈，打印内容部分如下：

java.lang.NullPointerException
    at com.example.test.lang.NullPointerExceptionMissingStack.throwNPE(NullPointerExceptionMissingStack.java:63)
    at com.example.test.lang.NullPointerExceptionMissingStack.main(NullPointerExceptionMissingStack.java:45)
java.lang.NullPointerException
    at com.example.test.lang.NullPointerExceptionMissingStack.throwNPE(NullPointerExceptionMissingStack.java:63)
    at com.example.test.lang.NullPointerExceptionMissingStack.main(NullPointerExceptionMissingStack.java:45)
java.lang.NullPointerException
    at com.example.test.lang.NullPointerExceptionMissingStack.throwNPE(NullPointerExceptionMissingStack.java:63)
    at com.example.test.lang.NullPointerExceptionMissingStack.main(NullPointerExceptionMissingStack.java:45)
java.lang.NullPointerException
    at com.example.test.lang.NullPointerExceptionMissingStack.throwNPE(NullPointerExceptionMissingStack.java:63)
    at com.example.test.lang.NullPointerExceptionMissingStack.main(NullPointerExceptionMissingStack.java:45)
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException

oracle的官方说明

The compiler in the server VM now provides correct stack backtraces for all "cold" built-in exceptions.
For performance purposes, when such an exception is thrown a few times, the method may be recompiled.
After recompilation, the compiler may choose a faster tactic using preallocated exceptions that do not provide a stack trace.
To disable completely the use of preallocated exceptions, use this new flag: -XX:-OmitStackTraceInFastThrow.

再将之前tomcat的日志往前查找，的确有完整的异常栈信息。

References

1. Hotspot caused exceptions to lose their stack traces in production – and the fix
2. NullPointerException in Java with no StackTrace
3. NullPointerException丢失异常堆栈信息