Netty源码心的

1：

三种类加载器和不同的获取方式以及作用介绍

获取当前classLoader   获取不同的类加载器，作用不同

集合遍历的方法两种

 // Collect all properties.
        Properties props = new Properties();
        try {
            Enumeration<URL> resources = classLoader.getResources("META-INF/io.netty.versions.properties");
            while (resources.hasMoreElements()) {
                URL url = resources.nextElement();
                InputStream in = url.openStream();
                try {
                    props.load(in);
                } finally {
                    try {
                        in.close();
                    } catch (Exception ignore) {
                        // Ignore.
                    }
                }
            }
        } catch (Exception ignore) {
            // Not critical. Just ignore.
        }

学会用其他的集合，不同的场景

   	1:    Map<String, Version> versions = new TreeMap<String, Version>();
        for (String artifactId: artifactIds) {
            versions.put(
                    artifactId,
                    new Version(
                            artifactId,
                            props.getProperty(artifactId + PROP_VERSION),
                            parseIso8601(props.getProperty(artifactId + PROP_BUILD_DATE)),
                            parseIso8601(props.getProperty(artifactId + PROP_COMMIT_DATE)),
                            props.getProperty(artifactId + PROP_SHORT_COMMIT_HASH),
                            props.getProperty(artifactId + PROP_LONG_COMMIT_HASH),
                            props.getProperty(artifactId + PROP_REPO_STATUS)));
        }
                // Collect all artifactIds.
  2:       Set<String> artifactIds = new HashSet<String>();
        for (Object o: props.keySet()) {
            String k = (String) o;

            int dotIndex = k.indexOf('.');
            if (dotIndex <= 0) {
                continue;
            }

            String artifactId = k.substring(0, dotIndex);

            // Skip the entries without required information.
            if (!props.containsKey(artifactId + PROP_VERSION) ||
                !props.containsKey(artifactId + PROP_BUILD_DATE) ||
                !props.containsKey(artifactId + PROP_COMMIT_DATE) ||
                !props.containsKey(artifactId + PROP_SHORT_COMMIT_HASH) ||
                !props.containsKey(artifactId + PROP_LONG_COMMIT_HASH) ||
                !props.containsKey(artifactId + PROP_REPO_STATUS)) {
                continue;
            }

            artifactIds.add(artifactId);
        }

断言的使用：

[断言的使用](https://blog.csdn.net/hezhimin1124/article/details/106397348)