server.xml文件中的Tomcat连接器定义

Question

I would like to understand Tomcat's connectors definitions in server.xml file. What is the difference between the following configurations:

    <Connector port="8080"
               protocol="HTTP/1.1"
               socket.directBuffer="true"
               redirectPort="8083"
               keyAlias="tomcat"
               enableLookups="true"
               connectionTimeout="60000"
               URIEncoding="UTF-8"
               server="NA"
               minSpareThreads="2"
               maxThreads="10"
               acceptCount="10"/>

    <Connector address="127.0.0.1"
               port="8080"
               protocol="HTTP/1.1"
               socket.directBuffer="true"
               redirectPort="8083"
               keyAlias="tomcat"
               enableLookups="false"
               connectionTimeout="60000"
               URIEncoding="UTF-8"
               server="NA"
               minSpareThreads="2"
               maxThreads="10"
               acceptCount="10"/>

    <Connector address="::1"
               port="8080"
               protocol="HTTP/1.1"
               redirectPort="8083"
               enableLookups="false"
               connectionTimeout="60000"
               URIEncoding="UTF-8"
               server="NA"
               minSpareThreads="2"
               maxThreads="5"
               acceptCount="10"/>

According to Tomcat 8 connectors documentation the address property should be used only when the server has more than one IP address. Usually this configuration leads to the next 2 exception during Tomcat startup (since all 3 connectors tries to listen on the same IP and port):

26/10/2015 10:07:56 SEVERE org.apache.coyote.AbstractProtocol init Failed to initialize end point associated with ProtocolHandler ["http-nio-127.0.0.1-8080"]
java.net.BindException: Address already in use
    at sun.nio.ch.Net.bind0(Native Method)
    at sun.nio.ch.Net.bind(Net.java:437)
    at sun.nio.ch.Net.bind(Net.java:429)
    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:340)
    at org.apache.tomcat.util.net.AbstractEndpoint.init(AbstractEndpoint.java:743)
    at org.apache.coyote.AbstractProtocol.init(AbstractProtocol.java:457)
    at org.apache.coyote.http11.AbstractHttp11JsseProtocol.init(AbstractHttp11JsseProtocol.java:120)
    at org.apache.catalina.connector.Connector.initInternal(Connector.java:960)
    at org.apache.catalina.util.LifecycleBase.init(LifecycleBase.java:102)
    at org.apache.catalina.core.StandardService.initInternal(StandardService.java:567)
    at org.apache.catalina.util.LifecycleBase.init(LifecycleBase.java:102)
    at org.apache.catalina.core.StandardServer.initInternal(StandardServer.java:851)
    at org.apache.catalina.util.LifecycleBase.init(LifecycleBase.java:102)
    at org.apache.catalina.startup.Catalina.load(Catalina.java:576)
    at org.apache.catalina.startup.Catalina.load(Catalina.java:599)
    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:497)
    at org.apache.catalina.startup.Bootstrap.load(Bootstrap.java:310)
    at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:484)

26/10/2015 10:07:56 SEVERE org.apache.coyote.AbstractProtocol init Failed to initialize end point associated with ProtocolHandler ["http-nio-0:0:0:0:0:0:0:1-8080"]
java.net.BindException: Address already in use
    at sun.nio.ch.Net.bind0(Native Method)
    at sun.nio.ch.Net.bind(Net.java:437)
    at sun.nio.ch.Net.bind(Net.java:429)
    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:340)
    at org.apache.tomcat.util.net.AbstractEndpoint.init(AbstractEndpoint.java:743)
    at org.apache.coyote.AbstractProtocol.init(AbstractProtocol.java:457)
    at org.apache.coyote.http11.AbstractHttp11JsseProtocol.init(AbstractHttp11JsseProtocol.java:120)
    at org.apache.catalina.connector.Connector.initInternal(Connector.java:960)
    at org.apache.catalina.util.LifecycleBase.init(LifecycleBase.java:102)
    at org.apache.catalina.core.StandardService.initInternal(StandardService.java:567)
    at org.apache.catalina.util.LifecycleBase.init(LifecycleBase.java:102)
    at org.apache.catalina.core.StandardServer.initInternal(StandardServer.java:851)
    at org.apache.catalina.util.LifecycleBase.init(LifecycleBase.java:102)
    at org.apache.catalina.startup.Catalina.load(Catalina.java:576)
    at org.apache.catalina.startup.Catalina.load(Catalina.java:599)
    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:497)
    at org.apache.catalina.startup.Bootstrap.load(Bootstrap.java:310)
    at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:484)

There is any reason to define 3 connectors like above?

Answer 1

You can't bind to the same TCP port multiple times unless every bind is also to a specific IP address. Your first Connector fails this test. The other two specify address= , which makes them valid.

According to Tomcat 8 connectors documentation the address property should be used only when the server has more than one IP address

It doesn't actually say that, but it isn't relevant, as every host has at least two addresses: 127.0.0.1 and its real IP address. In your case 3, as you also have ::1 , the IPv6 loopback address.