skywalking 比较有意思的地方

获取agent jar包路径的方法：

findPath();

private static File findPath() throws AgentPackageNotFoundException {
    String classResourcePath = AgentPackagePath.class.getName().replaceAll("\\.", "/") + ".class";// .../.../.../.../.../AgentPackagePath.class

    URL resource = ClassLoader.getSystemClassLoader().getResource(classResourcePath);
  	// jar:file:/.../.../.../.../.../...jar!/.../.../.../.../.../AgentPackagePath.class
    if (resource != null) {
        String urlString = resource.toString();
        int insidePathIndex = urlString.indexOf('!');
        boolean isInJar = insidePathIndex > -1;
        if (isInJar) {
            urlString = urlString.substring(urlString.indexOf("file:"), insidePathIndex);
          	// urlString = file:/.../.../.../cat-agent.jar
            File agentJarFile = null;
            try {
                agentJarFile = new File(new URL(urlString).toURI());
            } catch (MalformedURLException e) {
	        ...
            }
            if (agentJarFile.exists()) {
                return agentJarFile.getParentFile();
            }
        } else {
	     ...
        }
    }
   ...
}

加载plugin:

public List<AbstractClassEnhancePluginDefine> loadPlugins() throws AgentPackageNotFoundException {
    AgentClassLoader.initDefaultLoader();

    PluginResourcesResolver resolver = new PluginResourcesResolver();
    List<URL> resources = resolver.getResources();
    ...
    ...
    for (URL pluginUrl : resources) {
        try {
            PluginCfg.INSTANCE.load(pluginUrl.openStream());
        } catch (Throwable t) {
            ...
        }
    }

    List<PluginDefine> pluginClassList = PluginCfg.INSTANCE.getPluginClassList();

    List<AbstractClassEnhancePluginDefine> plugins = new ArrayList<AbstractClassEnhancePluginDefine>();
    for (PluginDefine pluginDefine : pluginClassList) {
        try {
            ...
            AbstractClassEnhancePluginDefine plugin =
                (AbstractClassEnhancePluginDefine)Class.forName(pluginDefine.getDefineClass(),
                    true,
                    AgentClassLoader.getDefault())
                    .newInstance();
            plugins.add(plugin);
        } catch (Throwable t) {
            ...
        }
    }

    plugins.addAll(DynamicPluginLoader.INSTANCE.load(AgentClassLoader.getDefault()));

    return plugins;

}

public List<URL> getResources() {
    ......
    ......
    try {
        urls = AgentClassLoader.getDefault().getResources("skywalking-plugin.def");

        while (urls.hasMoreElements()) {
            URL pluginUrl = urls.nextElement();
          	// pluginUrl = jar:file:/../.../activemq-5.x-plugin...jar!/cat-plugin.def
	    ...
  	    ...
            ...
        }

       ...
    } catch (IOException e) {
       ...
    }
    return null;
}

// PluginCfg.INSTANCE.load
void load(InputStream input) throws IOException {
    try {
        BufferedReader reader = new BufferedReader(new InputStreamReader(input));
        String pluginDefine = null;
        while ((pluginDefine = reader.readLine()) != null) {
            try {
                if (pluginDefine == null || pluginDefine.trim().length() == 0 || pluginDefine.startsWith("#")) {
                    continue;
                }
                PluginDefine plugin = PluginDefine.build(pluginDefine);
                pluginClassList.add(plugin);
            } catch (IllegalPluginDefineException e) {
                logger.error(e, "Failed to format plugin({}) define.", pluginDefine);
            }
        }
    } finally {
        input.close();
    }
}