server.port 为 0 时无法获取随机端口答案

【问题标题】：Unable to fetch random port when server.port is 0server.port 为 0 时无法获取随机端口
【发布时间】：2019-04-14 18:30:48
【问题描述】：

我需要获取 Sprint 启动应用程序启动 undertow 的端口号。我在 application.properties 中定义了 server.port=0。我不能使用像 8080 这样的固定端口号。

package com.aggregate.application;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Properties;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.context.event.ApplicationReadyEvent;
import org.springframework.boot.web.servlet.support.SpringBootServletInitializer;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationListener;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.env.Environment;


@Configuration
@ComponentScan(basePackages = {"com.aggregate"})
@EnableAutoConfiguration
public class GServiceApplication extends SpringBootServletInitializer 
    implements ApplicationListener<ApplicationReadyEvent> {

        @Autowired
        private ApplicationContext applicationContext;


        @Override
        public void onApplicationEvent(ApplicationReadyEvent event) {
            try {
                String ip = InetAddress.getLocalHost().getHostAddress();
                String port = applicationContext.getBean(Environment.class).getProperty("server.port");
               System.out.printf("ip:port=" +ip+ ":"+port);
            } catch (UnknownHostException e) {
                e.printStackTrace();
            }
        }
     public static void main(String[] args) throws UnknownHostException 
     {

            SpringApplication application = new SpringApplication(GServiceApplication.class);
            Properties properties = new Properties();
            properties.put("server.port", 0);
            properties.put("server.address", InetAddress.getLocalHost().getHostAddress());
            application.setDefaultProperties(properties);
            application.run(args);

     }

}

Undertow 已启动：- o.s.b.w.e.u.UndertowServletWebServer ：Undertow 在端口 55646 (http) 上启动，上下文路径为 ''，如控制台中打印的那样

预期结果：- ip:port=xx.xx.x.1x1:55646 实际结果：- ip:port=xx.xx.x.1x1:0

【问题讨论】：

标签： spring-boot undertow

【解决方案1】：

传递端口号 0 是 Java 核心 ServerSocket 类可以做的一个技巧。 Undertow 没有意识到这一点。它只是假设端口始终是固定的。所以没有官方API可以读取实际使用的端口号；但如果你找到Undertow 对象，你可以这样做：

// assuming you only have one:
ListenerInfo listenerInfo = undertow.getListenerInfo().iterator().next();
InetSocketAddress socketAddress = (InetSocketAddress) listenerInfo.getAddress();
URI uri = URI.create(listenerInfo.getProtcol() + "://" + socketAddress.getHostString() + ":" + socketAddress.getPort());

HTH

【讨论】：