解決java網絡編程IPv6問題

 若是系統中開啓了IPV6協議（好比window7），java網絡編程常常會獲取到IPv6的地址，這明顯不是咱們想要的結果，搜索發現不少蹩腳的作法是：禁止IPv6協議。其實查看官方文檔有詳細的說明：

java.net.preferIPv4Stack (default: false)

If IPv6 is available on the operating system the underlying native socket
will be an IPv6 socket. This allows Java(tm) applications to connect too, and
accept connections from, both IPv4 and IPv6 hosts.

If an application has a preference to only use IPv4 sockets then this
property can be set to true. The implication is that the application will not be
able to communicate with IPv6 hosts.

在實際的運用中有如下幾種辦法能夠實現指定獲取IPv4的地址：

一、在java啓動命令中增長一個屬性配置:-Djava.net.preferIPv4Stack=true

java -Djava.net.preferIPv4Stack=true -cp .;classes/ michael.net.TestInetAddress
java -Djava.net.preferIPv6Addresses=true -cp .;classes/ michael.net.TestInetAddress

二、在java程序裏設置系統屬性值以下：

import java.net.InetAddress;

public class TestInetAddress {
    public static void main(String[] args) throws Exception {

        // 註釋指定系統屬性值
        // System.setProperty("java.net.preferIPv4Stack", "true");
        // System.setProperty("java.net.preferIPv6Addresses", "true");
        System.out.println("-------InetAddress.getLocalHost()");
        InetAddress addr = InetAddress.getLocalHost();
        System.out.println("HostName := " + addr.getHostName());
        System.out.println("HostAddress := " + addr.getHostAddress());

        System.out.println("-------InetAddress.getByName(\"micmiu.com\")");

        InetAddress addr2 = InetAddress.getByName("micmiu.com");

        System.out.println("HostName := " + addr2.getHostName());

        System.out.println("HostAddress := " + addr2.getHostAddress());
    }
}

java.net.preferIPv4Stack=true 運行結果以下：

——-InetAddress.getLocalHost()
HostName := Michael-PC
HostAddress := 10.7.246.163
——-InetAddress.getByName(「micmiu.com」)
HostName := micmiu.com
HostAddress := 173.254.28.17

java.net.preferIPv6Addresses=true 運行結果以下：

——-InetAddress.getLocalHost()
HostName := Michael-PC
HostAddress := fe80:0:0:0:6518:85da:8690:16eb%13
——-InetAddress.getByName(「micmiu.com」)
HostName := micmiu.com
HostAddress := 173.254.28.17

三、Tomcat Web容器

可在 catalina.bat 或者 catalina.sh 中增長以下環境變量便可：

SET CATALINA_OPTS=-Djava.net.preferIPv4Stack=true