看到一個帖子，爲何Exception對象創建緩慢
http://www.blogjava.net/stone2083/archive/2010/07/09/325649.html
貌似問題集中在Throwable的fillInStackTrace方法，用hprof測試一下：
java -agentlib:hprof=cpu=samples NewExceptionTester
o: 10369
e: 372768
exte: 24102
Dumping CPU usage by sampling running threads ... done.
查看dump文件，果然.....
CPU SAMPLES BEGIN (total = 16147) Thu Oct 10 21:29:45 2013
rank self accum count trace method
1 90.64% 90.64% 14636 300051 java.lang.Throwable.fillInStackTrace
2 4.61% 95.25% 744 300067 TestExceptionTime$NewException.call
3 2.22% 97.47% 358 300058 TestExceptionTime$NewExtException.call
4 0.63% 98.10% 102 300066 TestExceptionTime$NewObject.call
5 0.53% 98.63% 86 300064 java.util.HashMap.<init>
6 0.32% 98.95% 52 300069 TestExceptionTime$ExtCustomException.<init>
7 0.22% 99.17% 35 300052 TestExceptionTime$NewObject.call
8 0.18% 99.35% 29 300078 TestExceptionTime$CustomException.<init>
調用14636次？！ 那將創建普通的Exception對象註銷掉，比較一下重寫fillInStackTrace方法的Exception對象的創建速度：
o: 2152
exte: 6290
看下dump文件：
CPU SAMPLES BEGIN (total = 168) Thu Oct 10 21:45:51 2013
rank self accum count trace method
1 45.83% 45.83% 77 300053 TestExceptionTime$ExtCustomException.<init>
2 36.31% 82.14% 61 300051 TestExceptionTime$NewExtException.call
3 7.14% 89.29% 12 300048 TestExceptionTime$NewObject.call
4 5.95% 95.24% 10 300055 java.lang.Long.valueOf
5 1.79% 97.02% 3 300050 TestExceptionTime$NewObject.call
果然不見了