开发某个项目过程中，就需求，搭建了一套测试环境。很快完成！
后来代码中加入了许多新功能，会涉及到反复重启，然后就发现了启动特别慢。这给原本功能就不多的应用增添了许多的负担。
我决定改变这一切！找到启动缓慢的根源，加快启动速度！
思路展开:
1. 启动慢，先看日志，有没有什么异常？
2. 看下是不是gc 有问题，是否占用很长时间？
3. 日志卡住，是否是存在网络请求不通情况？
4. 抓包查看卡住的时候，应用都做什么？
5. 把线程堆栈打印出来，线程都在做什么？把内存dump 出来瞅瞅吧？
6. 实在不行，本地debug不行，换一台测试机试试？
7. 实在不行，远程debug吧？
8. 定位到点后，再来思考解决好的解决方案？
9. 除了解决这个问题，我们还能思考点什么？
让我按思路一个个来看解决过程！
1. 启动慢，先看日志，有没有什么异常？
这个基本上很快就有答案了，看日志，等待期间没有问题！
但是，我们往往会停留在这个阶段较长一段时间，因为我们总想通过其他方式，打印点什么出来！
所以，我们可以会改日志级别，try... catch... 等等一顿操作，然后，才说算了吧，我们想想别的招！我个人还是觉得这种思路是ok的！
2. 看下是不是gc 有问题，是否占用很长时间？
这里可能就会涉及，之前并没有打印gc日志，然后还得回去在启动参数里加上gc输出！姿势如下:
-Xloggc:/opt/logs/a_gc.log -XX:+PrintGCDetails -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/opt/logs/ -XX:+UseG1GC -XX:MaxGCPauseMillis=100 -XX:+ParallelRefProcEnabled -XX:ErrorFile=/run/dump/hs_err_pid%p.lo3g -XX:HeapDumpPath=/run/dump
打开后，你看到的gc 日志可能是这样的。 你想从里面发现点什么，好像频繁没有 FullGC 之类的操作，然后又悻悻而归！
10.224: [GC concurrent-root-region-scan-start]
10.249: [GC concurrent-root-region-scan-end, 0.0252691 secs]
10.249: [GC concurrent-mark-start]
10.250: [GC concurrent-mark-end, 0.0005479 secs]
10.250: [GC remark 10.251: [Finalize Marking, 0.0001862 secs] 10.251: [GC ref-proc, 0.0026452 secs] 10.253: [Unloading, 0.0125200 secs], 0.0156381 secs]
[Times: user=0.06 sys=0.00, real=0.02 secs]
10.266: [GC cleanup 33M->33M(1024M), 0.0012152 secs]
[Times: user=0.00 sys=0.00, real=0.00 secs]
13.768: [GC pause (G1 Evacuation Pause) (young), 0.0411037 secs]
[Parallel Time: 34.5 ms, GC Workers: 4]
[GC Worker Start (ms): Min: 13768.7, Avg: 13769.8, Max: 13773.1, Diff: 4.4]
[Ext Root Scanning (ms): Min: 0.0, Avg: 1.8, Max: 4.1, Diff: 4.1, Sum: 7.3]
[Update RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
[Processed Buffers: Min: 0, Avg: 0.0, Max: 0, Diff: 0, Sum: 0]
[Scan RS (ms): Min: 0.0, Avg: 0.1, Max: 0.2, Diff: 0.2, Sum: 0.5]
[Code Root Scanning (ms): Min: 0.0, Avg: 3.1, Max: 8.8, Diff: 8.8, Sum: 12.5]
[Object Copy (ms): Min: 21.1, Avg: 28.0, Max: 30.5, Diff: 9.4, Sum: 111.9]
[Termination (ms): Min: 0.0, Avg: 0.1, Max: 0.1, Diff: 0.1, Sum: 0.2]
[Termination Attempts: Min: 1, Avg: 12.2, Max: 22, Diff: 21, Sum: 49]
[GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
[GC Worker Total (ms): Min: 29.9, Avg: 33.2, Max: 34.3, Diff: 4.4, Sum: 132.6]
[GC Worker End (ms): Min: 13803.0, Avg: 13803.0, Max: 13803.0, Diff: 0.0]
[Code Root Fixup: 0.4 ms]
[Code Root Purge: 0.0 ms]
[Clear CT: 0.2 ms]
[Other: 5.9 ms]
[Choose CSet: 0.0 ms]
[Ref Proc: 4.6 ms]
[Ref Enq: 0.1 ms]
[Redirty Cards: 0.1 ms]
[Humongous Register: 0.1 ms]
[Humongous Reclaim: 0.0 ms]
[Free CSet: 0.9 ms]
[Eden: 544.0M(544.0M)->0.0B(573.0M) Survivors: 31.0M->41.0M Heap: 575.0M(1024.0M)->41.0M(1024.0M)]
[Times: user=0.13 sys=0.02, real=0.04 secs]
17.178: [GC pause (G1 Evacuation Pause) (young), 0.0648366 secs]
[Parallel Time: 59.7 ms, GC Workers: 4]
[GC Worker Start (ms): Min: 17177.7, Avg: 17181.1, Max: 17184.4, Diff: 6.6]
[Ext Root Scanning (ms): Min: 0.0, Avg: 3.9, Max: 12.7, Diff: 12.7, Sum: 15.6]
[Update RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
[Processed Buffers: Min: 0, Avg: 0.0, Max: 0, Diff: 0, Sum: 0]
[Scan RS (ms): Min: 0.0, Avg: 0.1, Max: 0.3, Diff: 0.2, Sum: 0.6]
[Code Root Scanning (ms): Min: 0.0, Avg: 6.5, Max: 19.4, Diff: 19.4, Sum: 26.0]
[Object Copy (ms): Min: 34.9, Avg: 45.5, Max: 51.2, Diff: 16.3, Sum: 182.1]
[Termination (ms): Min: 0.0, Avg: 0.1, Max: 0.1, Diff: 0.1, Sum: 0.3]
[Termination Attempts: Min: 1, Avg: 16.5, Max: 24, Diff: 23, Sum: 66]
[GC Worker Other (ms): Min: 0.0, Avg: 0.1, Max: 0.1, Diff: 0.1, Sum: 0.2]
[GC Worker Total (ms): Min: 52.9, Avg: 56.2, Max: 59.5, Diff: 6.6, Sum: 224.8]
[GC Worker End (ms): Min: 17237.3, Avg: 17237.3, Max: 17237.3, Diff: 0.0]
[Code Root Fixup: 0.5 ms]
20.648: [GC pause (G1 Evacuation Pause) (young), 0.0653569 secs]
[Parallel Time: 55.9 ms, GC Workers: 4]
[GC Worker Start (ms): Min: 20648.5, Avg: 20650.4, Max: 20652.3, Diff: 3.7]
[Ext Root Scanning (ms): Min: 0.1, Avg: 2.9, Max: 9.4, Diff: 9.4, Sum: 11.7]
[Update RS (ms): Min: 0.0, Avg: 0.2, Max: 0.5, Diff: 0.5, Sum: 0.7]
[Processed Buffers: Min: 0, Avg: 2.5, Max: 7, Diff: 7, Sum: 10]
[Scan RS (ms): Min: 0.0, Avg: 0.3, Max: 0.6, Diff: 0.6, Sum: 1.3]
[Code Root Scanning (ms): Min: 0.0, Avg: 3.2, Max: 10.8, Diff: 10.8, Sum: 12.9]
[Object Copy (ms): Min: 39.4, Avg: 46.4, Max: 52.1, Diff: 12.8, Sum: 185.5]
[Termination (ms): Min: 0.0, Avg: 0.9, Max: 1.5, Diff: 1.5, Sum: 3.7]
[Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 4]
[GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
[GC Worker Total (ms): Min: 52.1, Avg: 54.0, Max: 55.8, Diff: 3.7, Sum: 215.8]
[GC Worker End (ms): Min: 20704.4, Avg: 20704.4, Max: 20704.4, Diff: 0.0]
[Code Root Fixup: 0.2 ms]
[Code Root Purge: 0.0 ms]
[Clear CT: 0.1 ms]
[Other: 9.2 ms]
[Choose CSet: 0.0 ms]
[Ref Proc: 8.5 ms]
[Ref Enq: 0.0 ms]
[Redirty Cards: 0.2 ms]
[Humongous Register: 0.1 ms]
[Humongous Reclaim: 0.0 ms]
[Free CSet: 0.2 ms]
[Eden: 38.0M(8192.0K)->0.0B(610.0M) Survivors: 43.0M->4096.0K Heap: 83.3M(1024.0M)->54.4M(1024.0M)]
[Times: user=0.24 sys=0.02, real=0.06 secs]
2826.037: [GC pause (Metadata GC Threshold) (young) (initial-mark), 0.0101504 secs]
[Parallel Time: 7.1 ms, GC Workers: 4]
[GC Worker Start (ms): Min: 2826037.4, Avg: 2826037.5, Max: 2826037.5, Diff: 0.1]
[Ext Root Scanning (ms): Min: 1.7, Avg: 2.0, Max: 2.2, Diff: 0.5, Sum: 7.8]
[Update RS (ms): Min: 0.9, Avg: 1.0, Max: 1.0, Diff: 0.1, Sum: 3.8]
[Processed Buffers: Min: 7, Avg: 14.2, Max: 25, Diff: 18, Sum: 57]
[Scan RS (ms): Min: 0.3, Avg: 0.7, Max: 0.9, Diff: 0.6, Sum: 2.8]
[Code Root Scanning (ms): Min: 0.2, Avg: 0.4, Max: 0.8, Diff: 0.6, Sum: 1.5]
[Object Copy (ms): Min: 2.7, Avg: 2.9, Max: 3.2, Diff: 0.5, Sum: 11.7]
[Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
[Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 4]
[GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
[GC Worker Total (ms): Min: 6.9, Avg: 7.0, Max: 7.0, Diff: 0.1, Sum: 27.8]
[GC Worker End (ms): Min: 2826044.4, Avg: 2826044.4, Max: 2826044.4, Diff: 0.0]
[Code Root Fixup: 0.0 ms]
[Code Root Purge: 0.0 ms]
[Clear CT: 0.1 ms]
[Other: 2.9 ms]
[Choose CSet: 0.0 ms]
[Ref Proc: 1.6 ms]
[Ref Enq: 0.1 ms]
[Redirty Cards: 0.0 ms]
[Humongous Register: 0.0 ms]
[Humongous Reclaim: 0.0 ms]
[Free CSet: 0.5 ms]
[Eden: 354.0M(438.0M)->0.0B(603.0M) Survivors: 4096.0K->11.0M Heap: 408.3M(1024.0M)->61.4M(1024.0M)]
[Times: user=0.03 sys=0.00, real=0.01 secs]
2826.047: [GC concurrent-root-region-scan-start]
2826.054: [GC concurrent-root-region-scan-end, 0.0066742 secs]
2826.054: [GC concurrent-mark-start]
2826.116: [GC concurrent-mark-end, 0.0616457 secs]
2826.116: [GC remark 2826.116: [Finalize Marking, 0.0002202 secs] 2826.116: [GC ref-proc, 0.0031923 secs] 2826.120: [Unloading, 0.0131458 secs], 0.0169584 secs]
[Times: user=0.05 sys=0.00, real=0.01 secs]
2826.134: [GC cleanup 62M->62M(1024M), 0.0010641 secs]
[Times: user=0.00 sys=0.00, real=0.00 secs]
不管怎么样，你知道内存不是问题了。不过一般地，在启动时就存在内存问题的应用可能确实不多！
3. 日志卡住，是否是存在网络请求不通情况？
一般来说，我们的应用，每做一些关键操作时，都会有相应的日志输出。所以，当你日志卡住的时候，应该就是哪里出现了问题了！
而在排除了中间出现full gc 卡顿的问题后，我们可以认为可能是网络出现问题了。
查询网络问题必备的工具: tcpdump, lsof ...
用法也很简单，我们可以在完全没有任何信息的前提下，进行网络抓包，从而给排查问题一点提示:
tcpdump -iany -XX # 这样就可以看到应用的网络io情况了, 如果量太大可以先把 -XX 选项去除，只看来往情况:
大概结果如下:
16:54:25.770463 IP 10.5.3.215.63773 > zt-d-xx.ssh: Flags [.], ack 125340, win 552, length 0
16:54:25.770478 IP zt-d-xx.ssh > 10.5.3.215.63773: Flags [P.], seq 127152:127332, ack 1, win 561, length 180
16:54:25.770482 IP 10.1.2.215.63773 > zt-d-xx.ssh: Flags [.], ack 125340, win 552, options [nop,nop,sack 1 {125504:125684}], length 0
16:54:25.770487 IP 10.1.2.215.63773 > zt-d-xx.ssh: Flags [.], ack 125684, win 556, length 0
16:54:25.770554 IP zt-d-xx.ssh > 10.1.2.215.63773: Flags [P.], seq 127332:127864, ack 1, win 561, length 532
16:54:25.770579 IP zt-d-xx.ssh > 10.1.2.215.63773: Flags [P.], seq 127864:127916, ack 1, win 561, length 52
16:54:25.770612 IP zt-d-xx.ssh > 10.1.2.215.63773: Flags [P.], seq 127916:128208, ack 1, win 561, length 292
16:54:25.771813 IP 10.1.2.215.63773 > zt-d-xx.ssh: Flags [.], ack 125684, win 556, options [nop,nop,sack 1 {125864:126044}], length 0
16:54:25.771822 IP zt-d-xx.ssh > 10.1.2.215.63773: Flags [P.], seq 128208:128388, ack 1, win 561, length 180
16:54:25.771837 IP 10.1.2.215.63773 > zt-d-xx.ssh: Flags [.], ack 126044, win 555, length 0
16:54:25.771840 IP 10.1.2.215.63773 > zt-d-xx.ssh: Flags [.], ack 126792, win 552, length 0
16:54:25.771868 IP zt-d-xx.ssh > 10.1.2.215.63773: Flags [P.], seq 128388:128808, ack 1, win 561, length 420
16:54:25.771884 IP zt-d-xx.ssh > 10.1.2.215.63773: Flags [P.], seq 128808:128972, ack 1, win 561, length 164
16:54:25.771891 IP 10.1.2.215.63773 > zt-d-xx.ssh: Flags [.], ack 127152, win 556, length 0
16:54:25.771934 IP zt-d-xx.ssh > 10.1.2.215.63773: Flags [P.], seq 128972:129376, ack 1, win 561, length 404
16:54:25.771959 IP zt-d-xx.ssh > 10.5.2.215.63773: Flags [P.], seq 129376:129556, ack 1, win 561, length 180
16:54:25.771982 IP zt-d-xx.ssh > 10.5.2.215.63773: Flags [P.], seq 129556:129736, ack 1, win 561, length 180
16:54:25.779454 IP 10.5.2.215.63773 > zt-d-xx.ssh: Flags [.], ack 127864, win 553, length 0
16:54:25.779469 IP zt-d-xx.ssh > 10.5.2.215.63773: Flags [P.], seq 129736:129916, ack 1, win 561, length 180
16:54:25.779474 IP 10.5.2.215.63773 > zt-d-xx.ssh: Flags [.], ack 128208, win 552, length 0
16:54:25.779476 IP 10.5.2.215.63773 > zt-d-xx.ssh: Flags [.], ack 128808, win 556, length 0
16:54:25.779478 IP 10.5.2.215.63773 > zt-d-xx.ssh: Flags [.], ack 129376, win 554, length 0
16:54:25.779480 IP 10.5.2.215.63773 > zt-d-xx.ssh: Flags [.], ack 129736, win 553, length 0
16:54:25.779529 IP zt-d-xx.ssh > 10.5.3.215.63773: Flags [P.], seq 129916:130496, ack 1, win 561, length 580
16:54:25.779567 IP zt-d-xx.ssh > 10.5.3.215.63773: Flags [P.], seq 130496:130660, ack 1, win 561, length 164
其中，我们主要关注 Flags 参数. man tcpdump 后可以看到解释:
Tcpflags are some combination of S (SYN), F (FIN), P (PUSH), R (RST), U (URG), W (ECN CWR), E (ECN-Echo) or '.' (ACK)
详细说明就是:
# SYN 表示建立连接;
# FIN 表示关闭连接;
# ACK 表示响应;
# PSH 表示有 DATA数据传输;
# RST 表示连接重置;
# URG 表示紧急停止位;
所以，我们在这里需要关注这么多吗？ 其实不需要的，我觉得咱们可以先看下是否有 RST 连接重置的情况，如果存在，则说明这个网络是不通的，基本定位网络问题！~ 如下抓包:
17:30:41.635937 IP zt-d-xx.43062 > 172.1.0.17.http: Flags [S], seq 3503889751, win 29200, options [mss 1460,sackOK,TS val 1904549734 ecr 0,nop,wscale 7], length 0
17:30:41.636084 IP 172.1.0.17.http > zt-d-xx.43062: Flags [R.], seq 0, ack 3503889752, win 0, length 0
另外，要查看下是不是某个网络请求 只有 [S] 信号，没有 [P] 的信号, 则说明只有一端在建立连接，另一边则无响应，网络问题定位！如下请求一个不存在的地址:
17:13:57.744349 IP zt-d-xx.37604 > 172-1-1-2.lightspeed.hstntx.sbcglobal.net.http: Flags [S], seq 3312915935, win 29200, options [mss 1460,sackOK,TS val 1903545842 ecr 0,nop,wscale 7], length 0
17:13:58.745584 IP zt-d-xx.37604 > 172-1-1-2.lightspeed.hstntx.sbcglobal.net.http: Flags [S], seq 3312915935, win 29200, options [mss 1460,sackOK,TS val 1903546844 ecr 0,nop,wscale 7], length 0
17:14:00.749570 IP zt-d-xx.37604 > 172-1-1-2.lightspeed.hstntx.sbcglobal.net.http: Flags [S], seq 3312915935, win 29200, options [mss 1460,sackOK,TS val 1903548848 ecr 0,nop,wscale 7], length 0
17:14:04.757571 IP zt-d-xx.37604 > 172-1-1-2.lightspeed.hstntx.sbcglobal.net.http: Flags [S], seq 3312915935, win 29200, options [mss 1460,sackOK,TS val 1903552856 ecr 0,nop,wscale 7], length 0
17:14:12.765568 IP zt-d-xx.37604 > 172-1-1-2.lightspeed.hstntx.sbcglobal.net.http: Flags [S], seq 3312915935, win 29200, options [mss 1460,sackOK,TS val 1903560864 ecr 0,nop,wscale 7], length 0
17:14:28.797584 IP zt-d-xx.37604 > 172-1-1-2.lightspeed.hstntx.sbcglobal.net.http: Flags [S], seq 3312915935, win 29200, options [mss 1460,sackOK,TS val 1903576896 ecr 0,nop,wscale 7], length 0
17:15:00.861591 IP zt-d-xx.37604 > 172-1-1-2.lightspeed.hstntx.sbcglobal.net.http: Flags [S], seq 3312915935, win 29200, options [mss 1460,sackOK,TS val 1903608960 ecr 0,nop,wscale 7], length 0
发了n个 [S] 包，都没有响应; 说明整个网络都是不通的;
通过这个排查，我们一般可以排除网络问题！
4. 抓包查看卡住的时候，应用都做什么？
这个点其实可以早点做，使用 top 查看内存，cpu 占用情况！
使用 vmstat 查看系统虚拟内存状态，也可以报告关于进程、内存、I/O等系统整体运行状态！
使用 lsof -p <pid> 查看打开的文件情况！应该可以看到一些不一样的东西，比如你会看到一些你不知道被打开的文件，你会看到一些你不知道的连接请求！
lsof -i # 列出所有的网络连接
lsof -p <pid> # 列出进程对应的文件信息
lsof -i4:8080 # 列表8080 端口对应的 ipv4 的连接
5. 把线程堆栈打印出来，线程都在做什么？把内存dump 出来瞅瞅吧？
如果还是没有发现什么，那我们还得回来。看看线程卡在了哪里！
使用 jstack 把线程堆栈打印出来，使用 jmap 把内存dump 出来，分析！
jstack <pid> | less # 查看线程信息，是否存在死锁
jmap -dump:format=b,file=/tmp/dumpid.dump <pid> # 查看堆信息，是否需要特别的对象
6. 实在不行，本地debug不行，换一台测试机试试？
对于本地debug, 我只能说，一般环境都不通的，而且本地一般也很复现场景！
换台机器测试的目的，其实是想确认问题是否在所有机器上复现，因为如果是和机器本身相关的问题，往往是很难排查的。（我说的没有相关经验的同学）
所以，找一台另外机器，代码跑起来，如果其他地方正常，则该问题是机器相关的。
那么机器相关的bug又该怎么办呢？其实，还得具体问题，具体分析！
不过幸好，我们还有 remote debug 功能，直接连接上去就可以调试了。问题自然也就清晰起来！
7. 实在不行，远程debug吧？
remote debug 请查看上一篇文章: 排障利器之远程调试与监控 --jmx & remote debug
连接上之后，先大概猜测可能会出问题的地方，进行断点。判断依据，应该是之前的排查结果，线程情况等等！
进行大概估计后，在可能的地方进行单步，卡住的地方，其中必然出现了问题。只需再进入内部重复刚才的做法即可！
优点是这样调试下来，必定能找到问题出现的地方。缺点是：可能需要反复重现问题（可能就是反复重启）。但是这样显得没有技术含量，还有就是在问题难以复现的场景，很难抓住机会解决问题。
所以，经验真的很重要！
卡住时的堆栈如下:
"main@1" prio=5 tid=0x1 nid=NA runnable
java.lang.Thread.State: RUNNABLE
at java.io.FileInputStream.readBytes(FileInputStream.java:-1)
at java.io.FileInputStream.read(FileInputStream.java:255)
at sun.security.provider.SeedGenerator$URLSeedGenerator.getSeedBytes(SeedGenerator.java:539)
at sun.security.provider.SeedGenerator.generateSeed(SeedGenerator.java:144)
at sun.security.provider.SecureRandom$SeederHolder.<clinit>(SecureRandom.java:203)
at sun.security.provider.SecureRandom.engineNextBytes(SecureRandom.java:221)
- locked <0x1af3> (a sun.security.provider.SecureRandom)
at java.security.SecureRandom.nextBytes(SecureRandom.java:468)
at java.security.SecureRandom.next(SecureRandom.java:491)
at java.util.Random.nextLong(Random.java:424)
at com.taobao.notify.utils.StrongRandom.<init>(StrongRandom.java:45)
at com.taobao.notify.utils.UniqId.<init>(UniqId.java:38)
at com.taobao.notify.utils.UniqId.<clinit>(UniqId.java:36)
at com.taobao.notify.client.impl.DefaultNotifyClient.<init>(DefaultNotifyClient.java:91)
at com.taobao.notify.client.impl.DefaultNotifyClient.<init>(DefaultNotifyClient.java:97)
at com.taobao.notify.client.NotifyClientFactory.<clinit>(NotifyClientFactory.java:13)
at com.taobao.notify.remotingclient.DefaultNotifyManager.<init>(DefaultNotifyManager.java:38)
at com.taobao.notify.remotingclient.NotifyManagerBean.init(NotifyManagerBean.java:90)
- locked <0x1a78> (a com.alipay.common.event.tbnotify.adapter.UniformEventPublisherAdapter)
at com.alipay.common.event.tbnotify.client.NotifyManagerBeanEx.init(NotifyManagerBeanEx.java:64)
at com.alipay.common.event.tbnotify.adapter.EventSendFacadeTBNotifyImpl.init(EventSendFacadeTBNotifyImpl.java:99)
at com.alipay.common.event.tbnotify.client.NotifyManagerBeanEx.init(NotifyManagerBeanEx.java:84)
at com.alipay.common.event.tbnotify.adapter.UniformEventPublisherAdapter.init(UniformEventPublisherAdapter.java:80)
at com.alipay.boot.dms.client.util.InitializeUtil.initializePublisher(InitializeUtil.java:14)
at com.alipay.boot.dms.spring.factory.DmsPublisherFactoryBean.afterPropertiesSet(DmsPublisherFactoryBean.java:59)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1642)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1579)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:553)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
- locked <0x1af4> (a java.util.concurrent.ConcurrentHashMap)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:351)
at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:108)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1486)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1231)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:551)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.autowireResource(CommonAnnotationBeanPostProcessor.java:522)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.getResource(CommonAnnotationBeanPostProcessor.java:496)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor$ResourceElement.getResourceToInject(CommonAnnotationBeanPostProcessor.java:627)
at org.springframework.beans.factory.annotation.InjectionMetadata$InjectedElement.inject(InjectionMetadata.java:169)
at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessPropertyValues(CommonAnnotationBeanPostProcessor.java:318)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1219)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:551)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202)
at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:207)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1131)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1059)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.autowireResource(CommonAnnotationBeanPostProcessor.java:518)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.getResource(CommonAnnotationBeanPostProcessor.java:496)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor$ResourceElement.getResourceToInject(CommonAnnotationBeanPostProcessor.java:627)
at org.springframework.beans.factory.annotation.InjectionMetadata$InjectedElement.inject(InjectionMetadata.java:169)
at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessPropertyValues(CommonAnnotationBeanPostProcessor.java:318)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1219)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:551)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:754)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:866)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:542)
- locked <0x1af5> (a java.lang.Object)
at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:761)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:371)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:315)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1186)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1175)
at com.xx.SOFABootSpringApplication.main(SOFABootSpringApplication.java:15)
at sun.reflect.NativeMethodAccessorImpl.invoke0(NativeMethodAccessorImpl.java:-1)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.boot.loader.MainMethodRunner.run(MainMethodRunner.java:48)
at org.springframework.boot.loader.Launcher.launch(Launcher.java:87)
at org.springframework.boot.loader.Launcher.launch(Launcher.java:50)
at org.springframework.boot.loader.JarLauncher.main(JarLauncher.java:58)
而根据堆栈进行的大概猜想，开始排查，过程如下:
// 初始代码位置:
// com.taobao.notify.remotingclient.NotifyManagerBean
public synchronized void init() {
if (inited.get()) {
return;
}
if (StringUtil.isEmpty(this.name) || StringUtil.isEmpty(this.description)) {
throw new RuntimeException("The name and description property is required.");
}
if (null == notifyManager) {
AllNotifyClientProperties properties = new AllNotifyClientProperties();
properties.setCheckMessageTPConfig(checkMessageTPConfig);
properties.setMessageTPConfig(messageTPConfig);
properties.setMessageProperties(messageProperties);
properties.setAntVipConfig(antVipConfig);
// 问题出在这里，new 这个对象时，会触发很多的其他类加载，而这里面就包含了有问题的类
notifyManager = new DefaultNotifyManager(groupId, appName, name, description,
messageListener, checkMessageListener, 1, enableCrc, properties);
notifyManager.subscribeAllMessages(this.subscribeMessages, this.bindingList);
/** ������ظ���groupId������ɾ��֮ǰ��publish topic*/
//notifyManager.resetPublishTopics(publishTopics);
for (String publishTopic : publishTopics) {
notifyManager.addPublishTopic(publishTopic);
}
// ��ʼ��ʱ����servertag��url�Ķ�Ӧ�б�
notifyManager.resetServerTagUrls();
}
inited.set(true);
}
// com.taobao.notify.remotingclient.DefaultNotifyManager 这个构造方法是 ok 的
public DefaultNotifyManager(String groupId, String appName, String name, String description,
MessageListener msgListener, CheckMessageListener checkMsgListener,
int connCount, boolean enableCrc,
AllNotifyClientProperties properties) {
initNotifyClient(properties);
if (StringUtil.isBlank(groupId)) {
throw new IllegalArgumentException("GroupID cannot be blank.");
}
if (StringTools.containsWhitespace(groupId)) {
throw new IllegalArgumentException("GroupID cannot contain the blank character. ["
+ groupId + "]");
}
this.groupId = groupId.trim();
this.appName = StringUtil.trim(appName);
if (null == properties) {
properties = new AllNotifyClientProperties();
}
this.notifyclient.addGroup(this.groupId, this.appName, name, description, msgListener,
checkMsgListener, properties.getMessageProperties(), properties.getWaitForConnTime(),
enableCrc, properties.getAntVipConfig());
this.notifyclient.setConnectionCount(connCount);
}
// 但是问题在静态字段的初始化问题
// com.taobao.notify.remotingclient.DefaultNotifyManager
public class DefaultNotifyManager implements NotifyManager, DefaultNotifyManagerMBean {
//��־
private static final Logger logger = MsgBrokerClientLoggerFactory
.getLogger(DefaultNotifyManager.class);
// 这看起来像是个单例的 client
private NotifyClient notifyclient = NotifyClientFactory
.getSingletonNotifyClient();
}
// com.taobao.notify.client.NotifyClientFactory
public class NotifyClientFactory implements FactoryBean {
// 初始化类时，会先初始化一个单例
static NotifyClient notifyClient = new DefaultNotifyClient();
/**
*
* @return
*/
public static NotifyClient getSingletonNotifyClient() {
return notifyClient;
}
}
// 到此，一切看起来都很美好，让我继续往下看
// com.taobao.notify.client.impl.DefaultNotifyClient
public class DefaultNotifyClient implements NotifyClient {
private static final String LogPrefix = LoggerPrefix
.makeLogPrefix(DefaultNotifyClient.class);
static final Logger logger = MsgBrokerClientLoggerFactory
.getLogger(DefaultNotifyClient.class);
private volatile NotifyClientConfig notifyClientConfig = null;
private static final int MAX_TIMES = 3;
protected final NotifyGroupManager notifyGroupManager = new NotifyGroupManager();
private final RemotingService remotingService;
protected final ClientSubscriptionManager clientSubscriptionManager = new ClientSubscriptionManager();
protected final PublishTopicsManager publishTopicsManager = new PublishTopicsManager();
private final ThreadPoolExecutor asynSendMessageWorkTP;
private final LoggingService loggingService = LoggingService
.getInstance();
private final ReliableAsynSendManager reliableAsynSendManager;
private final MessageProperties reliableMessageProperties = new MessageProperties();
// 问题在于 UniqId 的生成
private final UniqId uniqIdInstance = UniqId.getInstance();
/**
*
*/
public DefaultNotifyClient() {
this(new NotifyClientConfig());
}
/**
* @param notifyClientConfig
*/
public DefaultNotifyClient(final NotifyClientConfig notifyClientConfig) {
if (null == this.notifyClientConfig) {
this.notifyClientConfig = notifyClientConfig;
}
if (notifyClientConfig.isDebug()) {
this.remotingService = new IntegratedMockRemotingService(
this.clientSubscriptionManager, notifyClientConfig.getDebugRemoteSubscribers(),
this.notifyGroupManager, notifyClientConfig.getDebugLocalPort());
logger.warn(LogPrefix + "Note that, this is a MsgbrokerClient in the DEBUG mode.");
logger.warn(LogPrefix + "In the DEBUG mode, local port ["
+ notifyClientConfig.getDebugLocalPort() + "]");
logger.warn(LogPrefix + "In the DEBUG mode, connections ["
+ notifyClientConfig.getDebugRemoteSubscribers() + "]");
} else {
this.remotingService = new DefaultRemotingService(
this.notifyClientConfig.getRemotingType(), this.notifyGroupManager,
notifyClientConfig);
}
// ��ֹѹ��
this.reliableMessageProperties.setCompressSize(Integer.MAX_VALUE);
this.reliableMessageProperties.setMaxStringMessageSize(Integer.MAX_VALUE);
this.asynSendMessageWorkTP = new ManagedThreadPoolExecutor(notifyClientConfig
.getAsynSendMessageTPConfig().getCorePoolSize(), notifyClientConfig
.getAsynSendMessageTPConfig().getMaxPoolSize(), notifyClientConfig
.getAsynSendMessageTPConfig().getKeepAliveTime(), notifyClientConfig
.getAsynSendMessageTPConfig().getMaxQueueSize(), "asynSendMsgTP-" + this.hashCode(),
new ThreadPoolExecutor.AbortPolicy());
this.reliableAsynSendManager = new ReliableAsynSendManager(this, notifyGroupManager,
notifyClientConfig);
if (notifyClientConfig.isPreInitializeReliableAsynSendManager()) {
this.reliableAsynSendManager.init();
}
// DefaultNotifyClientʵ�������ж������Ҫ���䲻ͬ��ID
try {
ThreadPoolConfig messageTPConfig = notifyClientConfig.getMessageTPConfig();
Lookout.registry().info(
Lookout.registry().createId("msgbroker.client.group.infos")
.withTag("hashcode", String.valueOf(this.hashCode()))
.withTag("corePoolSize", String.valueOf(messageTPConfig.getCorePoolSize()))
.withTag("maxPoolSize", String.valueOf(messageTPConfig.getMaxPoolSize()))
.withTag("queueSize", String.valueOf(messageTPConfig.getMaxQueueSize()))
.withTag("channelSize", String.valueOf(messageTPConfig.getChannelSize())),
new Info<Set<String>>() {
public Set<String> value() {
return notifyGroupManager.getGroupIds();
}
});
} catch (Exception e) {
logger.warn("register msgbroker.client.group.infos failed, " + e.getMessage());
}
}
}
// UniqId 生成如下
// com.taobao.notify.utils.UniqId
public class UniqId {
private static final Logger log = MsgBrokerClientLoggerFactory.getLogger(UniqId.class);
private static final String LogPrefix = LoggerPrefix.makeLogPrefix(UniqId.class);
private static char[] digits = { '0', '1', '2', '3', '4', '5', '6', '7',
'8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };
private static Map<Character, Integer> rDigits = new HashMap<Character, Integer>(16);
static {
for (int i = 0; i < digits.length; ++i) {
rDigits.put(digits[i], i);
}
}
private static UniqId me = new UniqId();
private String hostAddr;
// 实际问题在于这里了， StrongRandom 的问题
private Random random = new StrongRandom();
private MessageDigest mHasher;
private UniqTimer timer = new UniqTimer();
private ReentrantLock opLock = new ReentrantLock();
private UniqId() {
try {
InetAddress addr = InetAddress.getLocalHost();
hostAddr = addr.getHostAddress();
} catch (IOException e) {
log.error(LogPrefix + "Get HostAddr Error", e);
hostAddr = String.valueOf(System.currentTimeMillis());
}
if (Util.isBlank(hostAddr) || "127.0.0.1".equals(hostAddr)) {
hostAddr = String.valueOf(System.currentTimeMillis());
}
if (log.isDebugEnabled()) {
log.debug(LogPrefix + "hostAddr is:" + hostAddr);
}
try {
mHasher = MessageDigest.getInstance("MD5");
} catch (NoSuchAlgorithmException nex) {
mHasher = null;
log.error(LogPrefix + "new MD5 Hasher error", nex);
}
}
/**
* ��ȡUniqIDʵ��
*
* @return UniqId
*/
public static UniqId getInstance() {
return me;
}
}
// StrongRandom 生成缓慢
// com.taobao.notify.utils.StrongRandom
public StrongRandom() {
try {
// This operation may block on some systems with low entropy. See
// this page
// for workaround suggestions:
// http://docs.codehaus.org.display.JETTY.Connectors+slow+to+startup
random = SecureRandom.getInstance(SESSION_ID_RANDOM_ALGORITHM);
} catch (NoSuchAlgorithmException e) {
try {
random = SecureRandom.getInstance(SESSION_ID_RANDOM_ALGORITHM_ALT);
weakRandom = false;
} catch (NoSuchAlgorithmException e_alt) {
random = new Random();
weakRandom = true;
}
}
// 就是这里缓慢了，卡住大约一分钟，且无法调试
random.setSeed(random.nextLong() ^ System.currentTimeMillis() ^ hashCode()
^ Runtime.getRuntime().freeMemory());
}
最后，定位到是 随机数生成有问题了！
8. 定位到点后，再来思考解决好的解决方案？
如上，我们知道了是因为 SecureRandom 生成随机数时出现了问题！
那么，如何解决？我能想到的，就是网上搜索答案了。因为这时候已经没有什么可以参考的了。
搜索内容就是， SecureRandom 生成随机缓慢解决方案？ 然后就有答案了！
当然，你可以咨询遇到过这些问题的前辈们，那样更快速！
原因如下：
java生成随机码时，会使用两个文件：
1. /dev/random ， 随机性高，和真实的物理环境有关，阻塞模式。（本文出现的启动缓慢问题，就出在这个上面）
2. /dev/urandom ，伪随机模式，非阻塞，随机性不如 random。
所以，既然是生成random模式有问题，那么想办法换掉这个模式就ok了。
jdk中，提供相应的替换方法，我们先看 $JAVA_HOME/jre/lib/security/java.security 这个里面有个随机数的配置，其说明如下：
#
# Sun Provider SecureRandom seed source.
#
# Select the primary source of seed data for the "SHA1PRNG" and
# "NativePRNG" SecureRandom implementations in the "Sun" provider.
# (Other SecureRandom implementations might also use this property.)
#
# On Unix-like systems (for example, Solaris/Linux/MacOS), the
# "NativePRNG" and "SHA1PRNG" implementations obtains seed data from
# special device files such as file:/dev/random.
#
# On Windows systems, specifying the URLs "file:/dev/random" or
# "file:/dev/urandom" will enable the native Microsoft CryptoAPI seeding
# mechanism for SHA1PRNG.
#
# By default, an attempt is made to use the entropy gathering device
# specified by the "securerandom.source" Security property. If an
# exception occurs while accessing the specified URL:
#
# SHA1PRNG:
# the traditional system/thread activity algorithm will be used.
#
# NativePRNG:
# a default value of /dev/random will be used. If neither
# are available, the implementation will be disabled.
# "file" is the only currently supported protocol type.
#
# The entropy gathering device can also be specified with the System
# property "java.security.egd". For example:
#
# % java -Djava.security.egd=file:/dev/random MainClass
#
# Specifying this System property will override the
# "securerandom.source" Security property.
#
# In addition, if "file:/dev/random" or "file:/dev/urandom" is
# specified, the "NativePRNG" implementation will be more preferred than
# SHA1PRNG in the Sun provider.
#
securerandom.source=file:/dev/random
即 可以直接改这个文件，也可以通过命令行加参数修改，且命令行优先级更高，所以我们使用命令行修改即可：
-Djava.security.egd=file:/dev/./urandom # 在项目中添加java_opts，里面添加启动参数 urandom
如此，再次验证后，启动正常了。问题done。
9. 除了解决这个问题，我们还能思考点什么？
老话：说了不一定有机会，但不说一定没机会。
本文章为转载内容，我们尊重原作者对文章享有的著作权。如有内容错误或侵权问题，欢迎原作者联系我们进行内容更正或删除文章。
