Ubuntu 运行tomcat报错：java.net.SocketException: Permission denied
在Ubuntu系统中，使用非root用户开启tomcat时报错：
java.net.SocketException: Permission denied
at sun.nio.ch.Net.bind0(Native Method)
at sun.nio.ch.Net.bind(Net.java:433)
at sun.nio.ch.Net.bind(Net.java:425)
at sun.nio.ch.ServerSocketChannelImpl.bind(ServerSocketChannelImpl.java:223)
at sun.nio.ch.ServerSocketAdaptor.bind(ServerSocketAdaptor.java:74)
at org.apache.tomcat.util.net.NioEndpoint.bind(NioEndpoint.java:210)
at org.apache.tomcat.util.net.AbstractEndpoint.init(AbstractEndpoint.java:982)
at org.apache.tomcat.util.net.AbstractJsseEndpoint.init(AbstractJsseEndpoint.java:245)
at org.apache.coyote.AbstractProtocol.init(AbstractProtocol.java:620)
at org.apache.coyote.http11.AbstractHttp11Protocol.init(AbstractHttp11Protocol.java:66)
at org.apache.catalina.connector.Connector.initInternal(Connector.java:997)
at org.apache.catalina.util.LifecycleBase.init(LifecycleBase.java:107)
at org.apache.catalina.core.StandardService.initInternal(StandardService.java:549)
at org.apache.catalina.util.LifecycleBase.init(LifecycleBase.java:107)
at org.apache.catalina.core.StandardServer.initInternal(StandardServer.java:875)
at org.apache.catalina.util.LifecycleBase.init(LifecycleBase.java:107)
at org.apache.catalina.startup.Catalina.load(Catalina.java:621)
at org.apache.catalina.startup.Catalina.load(Catalina.java:644)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
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.apache.catalina.startup.Bootstrap.load(Bootstrap.java:311)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:494)
14-Jan-2018 22:30:57.969 SEVERE [main] org.apache.catalina.core.StandardService.initInternal Failed to initialize connector [Connector[HTTP/1.1-443]]
org.apache.catalina.LifecycleException: Failed to initialize component [Connector[HTTP/1.1-443]]
at org.apache.catalina.util.LifecycleBase.init(LifecycleBase.java:113)
at org.apache.catalina.core.StandardService.initInternal(StandardService.java:549)
at org.apache.catalina.util.LifecycleBase.init(LifecycleBase.java:107)
at org.apache.catalina.core.StandardServer.initInternal(StandardServer.java:875)
at org.apache.catalina.util.LifecycleBase.init(LifecycleBase.java:107)
at org.apache.catalina.startup.Catalina.load(Catalina.java:621)
at org.apache.catalina.startup.Catalina.load(Catalina.java:644)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
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.apache.catalina.startup.Bootstrap.load(Bootstrap.java:311)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:494)
Caused by: org.apache.catalina.LifecycleException: Protocol handler initialization failed
at org.apache.catalina.connector.Connector.initInternal(Connector.java:1000)
at org.apache.catalina.util.LifecycleBase.init(LifecycleBase.java:107)
... 12 more
Caused by: java.net.SocketException: Permission denied
at sun.nio.ch.Net.bind0(Native Method)
at sun.nio.ch.Net.bind(Net.java:433)
at sun.nio.ch.Net.bind(Net.java:425)
at sun.nio.ch.ServerSocketChannelImpl.bind(ServerSocketChannelImpl.java:223)
at sun.nio.ch.ServerSocketAdaptor.bind(ServerSocketAdaptor.java:74)
at org.apache.tomcat.util.net.NioEndpoint.bind(NioEndpoint.java:210)
at org.apache.tomcat.util.net.AbstractEndpoint.init(AbstractEndpoint.java:982)
at org.apache.tomcat.util.net.AbstractJsseEndpoint.init(AbstractJsseEndpoint.java:245)
at org.apache.coyote.AbstractProtocol.init(AbstractProtocol.java:620)
at org.apache.coyote.http11.AbstractHttp11Protocol.init(AbstractHttp11Protocol.java:66)
at org.apache.catalina.connector.Connector.initInternal(Connector.java:997)
... 13 more
原因：Ubuntu系统中，非root用户只能使用1024以上的端口。
两个解决办法：
- 使用root用户开启tomcat
- 将端口设置为1024以上的端口：
<Connector port="8443" protocol="HTTP/1.1" SSLEnabled="true" URIEncoding="UTF-8" maxThreads="150" scheme="https" secure="true" keystoreFile="" keystorePass="" clientAuth="false" sslProtocol="TLS" />将端口由443修改为8443，tomcat即可正常运行。但是这会存在一个问题，https的默认端口是443，http的默认端口是80。也就是说端口设置为443和80时，直接访问域名即可进入主页，例：http://域名/ ，https://域名/。但是设置为8443后需要在域名后加端口号才可以访问应用主页，例：https://域名:8443/，http://域名:8080/ 。很不舒服，针对这个问题可以使用端口映射的方式解决，使用root用户执行以下命令：
#443端口映射到8443 iptables -t nat -A PREROUTING -p tcp --dport 443 -j REDIRECT --to-port 8443
现在·https://域名/ ·即可直接使用8443端口了。或者可以使用Nginx等做反向代理也可以解决这个问题。