常規(guī)方法1： gcore或jmap －F 強(qiáng)行dump舔株；
?常規(guī)方法2：jinfo／jcmd 增加?HeapDumpBeforeFullGC／HeapDumpAfterFullGC flag
常規(guī)方法3：重啟 設(shè)置 JVM 參數(shù) -XX:+UseHeapDumpBeforeFullGC
常規(guī)方法4：jmx删铃，mxbean直接動(dòng)態(tài)修改，比如去Jconsole里setVmOption稿存，直接將HeapDumpBeforeFullGC和HeapDumpAfterFullGC設(shè)置成true；
非常規(guī)方法：無限FGC時(shí)用
先用ps -ef|grep java 到j(luò)vm進(jìn)程，gdb attach上去， 例如gdb -p 34567
通過p命令顯示HeapDumpBeforeFullGC變量的地址（默認(rèn)是false）
(gdb) p &HeapDumpBeforeFullGC
$1 = ( *) 0x10f35754f
runtime設(shè)置這個(gè)變量為true（1）
(gdb) set *0x10f35754f=1
(gdb) p HeapDumpBeforeFullGC
$2 = 1
下次FullGC觸發(fā)前瞭空，就會(huì)自動(dòng)HeapDump了到默認(rèn)的 java_pidxxx.hprof了。
有了dump文件后要恢復(fù)flag回去
(gdb) p HeapDumpBeforeFullGC
$1 = 1
(gdb) p &HeapDumpBeforeFullGC
$2 = ( *) 0x10f35754f
(gdb) set *0x10f35754f=0
(gdb) p HeapDumpBeforeFullGC
$3 = 0
