记录一次InetAddress.getLocalHost导致的项目启动过慢分析过程

1. 背景

接手一个新项目，本地启动的过程中发现启动很慢，启动一次大概20几分钟，很疑惑，下面开始排查过程

2. 分析

jps 找到当前的java进程

jstack -l pid 查看对应进程状态

每次项目启动都会在这个地方锁住

在堆栈中发现有一段AsyncExportAutoConfiguration.setApplicationContext,基本可以断定是Springboot的一个自动配置类，并且继承了ApplicationContextAware,用于加载某些配置。于是进入源码查看，终于发现问题。

该项目使用了elastic-job,启动时都需要对声明的任务进行注册（有兴趣可以了解下该框架，这里不做拓展）

1. JobScheduler的构造器中需要创建JobInstance实例

2. JobInstance的默认构造器中需要获取一些系统信息

3. 问题就出在InetAddress.getAddressesFromNameService时会有一段时间的阻塞

3. 解决

修改hosts文件,路径/etc/hosts,配置localhost->hostname，::1->hostname的映射,保存及时生效。hostname可以在命令行使用hostname直接获取

除自己配置/etc/hosts外，这里提供一个host文件检查器，启动前检查是否包含所需映射,仅供参考

@Slf4j
@Component
@Profile("local")
public class HostMappingChecker implements ApplicationContextAware {
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        log.info("Host Mapping Checker Start...");
        String fileName = null;
        // 判断系统
        String osName = System.getProperty("os.name");
        if ("linux".equalsIgnoreCase(osName) || "Mac OS X".equalsIgnoreCase(osName)) {
            fileName = "/etc/hosts";
        } else {
            fileName = System.getenv("windir") + "\\system32\\drivers\\etc\\hosts";
        }

        try {
            // 输入流
            StringBuilder sourceFileStr = new StringBuilder();
            try (BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(new FileInputStream(fileName), StandardCharsets.UTF_8))) {
                int readChar;
                while ((readChar = bufferedReader.read()) != -1) {
                    sourceFileStr.append((char) readChar);
                }
            }
            // 输出流
            try (BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(fileName), StandardCharsets.UTF_8));) {
                // 写入信息
                String hostName = InetAddress.getLocalHost().getHostName();
                String ipv4Address = InetAddress.getLocalHost().getHostAddress();
                String ipv6Address = "::1";
                String localAddress = "127.0.0.1";
                if (!containHostMapping(sourceFileStr.toString(), localAddress, hostName)) {
                    sourceFileStr.append("\n").append(localAddress).append(" ").append(hostName);
                }
                if (!containHostMapping(sourceFileStr.toString(), ipv4Address, hostName)) {
                    sourceFileStr.append("\n").append(ipv4Address).append(" ").append(hostName);
                }
                if (!containHostMapping(sourceFileStr.toString(), ipv6Address, hostName)) {
                    sourceFileStr.append("\n").append(ipv6Address).append(" ").append(hostName);
                }
                bufferedWriter.write(sourceFileStr.toString());
                bufferedWriter.flush();// 清空缓冲区
            }
        } catch (Exception ex) {
            log.error("Check Local Host Mapping Failed, ex: {}", Throwables.getStackTraceAsString(ex));
        }
        log.info("Host Mapping Checker End...");
    }

    /**
     * 判断是否存在该映射
     *
     * @param source
     * @param appendKey
     * @param appendValue
     * @return
     */
    private static boolean containHostMapping(String source, String appendKey, String appendValue) {
        // 最多允许10个空格
        for (int i = 0; i < 10; i++) {
            StringBuilder blank = new StringBuilder();
            for (int j = 0; j <= i; j++) {
                blank.append(" ");
            }
            if (source.contains(appendKey + blank + appendValue)) {
                return true;
            }

            StringBuilder tab = new StringBuilder();
            for (int j = 0; j <= i; j++) {
                tab.append("\t");
            }
            if (source.contains(appendKey + tab + appendValue)) {
                return true;
            }
        }

        return false;
    }
}