private InputStream getPluginInputStream(String classPath) throws IllegalArgumentException {
        if (isDebug) {
            logger.debug("Get input stream className:{}", classPath);

        }
        try {
            return pluginJarReader.getInputStream(classPath);
        } catch (Exception ex) {
            if (isDebug) {
                logger.debug("Failed to read plugin jar: {}", pluginConfig.getPluginJarURLExternalForm(), ex);
            }
        }

        // not found.
        return null;
    }
@author Woonduk Kang(emeroad)
@author jaehong.kim
agent-module/profiler/src/main/java/com/navercorp/pinpoint/profiler/instrument/classloading/PlainClassLoaderHandler.java