MINA2 错误解决方法-- Linux下tomcat报错“java.net.SocketException: Too many open files”
部署到linux下的tomcat，今天发现包了“java.net.SocketException: Too many open files”，以前从来没有遇到过，在此记录一下：

彻底解决问题的是第三步, 所以，可以直接跳到第三步去看解决方法和步骤，当日第一、第二步是我不断探索，尝试解决问题的过程，虽然没有找到点上，但是还是有些意义的，因为linux切实有打开资源数量的限制，肯定需要修改的。

异常信息：

............
Oct 17, 2011 5:22:41 PM org.apache.tomcat.util.net.JIoEndpoint$Acceptor run
SEVERE: Socket accept failed
java.net.SocketException: Too many open files
        at java.net.PlainSocketImpl.socketAccept(Native Method)
        at java.net.AbstractPlainSocketImpl.accept(AbstractPlainSocketImpl.java:375)
        at java.net.ServerSocket.implAccept(ServerSocket.java:470)
        at java.net.ServerSocket.accept(ServerSocket.java:438)
        at org.apache.tomcat.util.net.DefaultServerSocketFactory.acceptSocket(DefaultServerSocketFactory.java:59)
        at org.apache.tomcat.util.net.JIoEndpoint$Acceptor.run(JIoEndpoint.java:210)
        at java.lang.Thread.run(Thread.java:636)
Oct 17, 2011 5:22:43 PM org.apache.tomcat.util.net.JIoEndpoint$Acceptor run
SEVERE: Socket accept failed
java.net.SocketException: Too many open files
        at java.net.PlainSocketImpl.socketAccept(Native Method)
        at java.net.AbstractPlainSocketImpl.accept(AbstractPlainSocketImpl.java:375)
        at java.net.ServerSocket.implAccept(ServerSocket.java:470)
        at java.net.ServerSocket.accept(ServerSocket.java:438)
        at org.apache.tomcat.util.net.DefaultServerSocketFactory.acceptSocket(DefaultServerSocketFactory.java:59)
        at org.apache.tomcat.util.net.JIoEndpoint$Acceptor.run(JIoEndpoint.java:210)
        at java.lang.Thread.run(Thread.java:636)
Oct 17, 2011 5:22:44 PM org.apache.tomcat.util.net.JIoEndpoint$Acceptor run
SEVERE: Socket accept failed
java.net.SocketException: Too many open files
        at java.net.PlainSocketImpl.socketAccept(Native Method)
        at java.net.AbstractPlainSocketImpl.accept(AbstractPlainSocketImpl.java:375)
        at java.net.ServerSocket.implAccept(ServerSocket.java:470)
        at java.net.ServerSocket.accept(ServerSocket.java:438)
        at org.apache.tomcat.util.net.DefaultServerSocketFactory.acceptSocket(DefaultServerSocketFactory.java:59)
        at org.apache.tomcat.util.net.JIoEndpoint$Acceptor.run(JIoEndpoint.java:210)
        at java.lang.Thread.run(Thread.java:636)
............

原因：
   linux下有有文件限制，结果文件数操作最大限制，导致程序异常：问题是程序中有个静态方法打开文件时忘记关闭。两种解决方法，一是设置linux的最大文件打开数量（无法根本解决问题），二是解决程序中的bugs，即消除有问题的代码。

第一次解决
解决：
方法一、增大系统打开文件的数量（无法根本解决问题）、
   1、默认linux同时最大打开文件数量为1024个，用命令查看如下：ulimit -a:查看系统上受限资源的设置（open files (-n) 1024）：

[root@**** bin]# ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 16384
max locked memory       (kbytes, -l) 32
max memory size         (kbytes, -m) unlimited
open files                      (-n) 1024
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 10240
cpu time               (seconds, -t) unlimited
max user processes              (-u) 16384
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited
[root@**** bin]#

2、可以修改同时打开文件的最大数基本可以解决：ulimit -n 4096

[root@**** bin]# ulimit -n 4096
[root@**** bin]# ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 16384
max locked memory       (kbytes, -l) 32
max memory size         (kbytes