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本文主要研究一下PowerJob的OhMyClassLoader

OhMyClassLoader

tech/powerjob/worker/container/OhMyClassLoader.java

@Slf4j
public class OhMyClassLoader extends URLClassLoader {

    public OhMyClassLoader(URL[] urls, ClassLoader parent) {
        super(urls, parent);
    }

    /**
     * 主动加载类，否则类加载器内空空如也，Spring IOC容器初始化不到任何东西
     * @param packageName 包路径，主动加载用户写的类
     * @throws Exception 加载异常
     */
    public void load(String packageName) throws Exception {
        URL[] urLs = getURLs();
        for (URL jarURL : urLs) {
            JarFile jarFile = new JarFile(new File(jarURL.toURI()));
            Enumeration<JarEntry> entries = jarFile.entries();
            while (entries.hasMoreElements()) {
                JarEntry jarEntry = entries.nextElement();
                if (jarEntry.isDirectory()) {
                    continue;
                }
                String name = jarEntry.getName();
                if (!name.endsWith(".class")) {
                    continue;
                }

                // 转换 org/spring/AAA.class -> org.spring.AAA
                String tmp = name.substring(0, name.length() - 6);
                String res = StringUtils.replace(tmp, "/", ".");

                if (res.startsWith(packageName)) {
                    loadClass(res);
                    log.info("[OhMyClassLoader] load class({}) successfully.", res);
                }
            }
        }
    }
}

OhMyClassLoader继承了URLClassLoader，它定义了load方法，遍历urls，挨个根据url创建JarFile，然后遍历jarFile.entries()，找到.class结尾的entry，判断是否是packageName开头的，是则执行父类的loadClass方法

OmsJarContainer

tech/powerjob/worker/container/OmsJarContainer.java

@Slf4j
public class OmsJarContainer implements OmsContainer {

    private final Long containerId;
    private final String name;
    private final String version;
    private final File localJarFile;
    private final Long deployedTime;

    // 引用计数器
    private final AtomicInteger referenceCount = new AtomicInteger(0);

    private OhMyClassLoader containerClassLoader;
    private ClassPathXmlApplicationContext container;

    private final Map<String, BasicProcessor> processorCache = Maps.newConcurrentMap();

    public OmsJarContainer(Long containerId, String name, String version, File localJarFile) {
        this.containerId = containerId;
        this.name = name;
        this.version = version;
        this.localJarFile = localJarFile;
        this.deployedTime = System.currentTimeMillis();
    }

    @Override
    public void init() throws Exception {

        log.info("[OmsJarContainer-{}] start to init container(name={},jarPath={})", containerId, name, localJarFile.getPath());

        URL jarURL = localJarFile.toURI().toURL();

        // 创建类加载器（父类加载为 Worker 的类加载）
        this.containerClassLoader = new OhMyClassLoader(new URL[]{jarURL}, this.getClass().getClassLoader());

        // 解析 Properties
        Properties properties = new Properties();
        try (InputStream propertiesURLStream = containerClassLoader.getResourceAsStream(ContainerConstant.CONTAINER_PROPERTIES_FILE_NAME)) {

            if (propertiesURLStream == null) {
                log.error("[OmsJarContainer-{}] can't find {} in jar {}.", containerId, ContainerConstant.CONTAINER_PROPERTIES_FILE_NAME, localJarFile.getPath());
                throw new PowerJobException("invalid jar file because of no " + ContainerConstant.CONTAINER_PROPERTIES_FILE_NAME);
            }

            properties.load(propertiesURLStream);
            log.info("[OmsJarContainer-{}] load container properties successfully: {}", containerId, properties);
        }
        String packageName = properties.getProperty(ContainerConstant.CONTAINER_PACKAGE_NAME_KEY);
        if (StringUtils.isEmpty(packageName)) {
            log.error("[OmsJarContainer-{}] get package name failed, developer should't modify the properties file!", containerId);
            throw new PowerJobException("invalid jar file");
        }

        // 加载用户类
        containerClassLoader.load(packageName);

        // 创建 Spring IOC 容器（Spring配置文件需要填相对路径）
        // 需要切换线程上下文类加载器以加载 JDBC 类驱动（SPI）
        ClassLoader oldCL = Thread.currentThread().getContextClassLoader();
        Thread.currentThread().setContextClassLoader(containerClassLoader);
        try {
            this.container = new ClassPathXmlApplicationContext(new String[]{ContainerConstant.SPRING_CONTEXT_FILE_NAME}, false);
            this.container.setClassLoader(containerClassLoader);
            this.container.refresh();
        }finally {
            Thread.currentThread().setContextClassLoader(oldCL);
        }

        log.info("[OmsJarContainer-{}] init container(name={},jarPath={}) successfully", containerId, name, localJarFile.getPath());
    }

    //......
}      

OmsJarContainer的init方法会使用构造器传入的localJarFile作为url创建OhMyClassLoader，然后读取oms-worker-container.properties，以其中的PACKAGE_NAME属性作为packageName，然后使用containerClassLoader.load进行加载

deployContainer

tech/powerjob/worker/container/OmsContainerFactory.java

    public static synchronized void deployContainer(ServerDeployContainerRequest request) {

        Long containerId = request.getContainerId();
        String containerName = request.getContainerName();
        String version = request.getVersion();

        log.info("[OmsContainer-{}] start to deploy container(name={},version={},downloadUrl={})", containerId, containerName, version, request.getDownloadURL());

        OmsContainer oldContainer = CARGO.get(containerId);
        if (oldContainer != null && version.equals(oldContainer.getVersion())) {
            log.info("[OmsContainer-{}] version={} already deployed, so skip this deploy task.", containerId, version);
            return;
        }

        String filePath = CONTAINER_DIR + containerId + "/" + version + ".jar";
        // 下载Container到本地
        File jarFile = new File(filePath);

        try {
            if (!jarFile.exists()) {
                FileUtils.forceMkdirParent(jarFile);
                FileUtils.copyURLToFile(new URL(request.getDownloadURL()), jarFile, 5000, 300000);
                log.info("[OmsContainer-{}] download jar successfully, path={}", containerId, jarFile.getPath());
            }

            // 创建新容器
            OmsContainer newContainer = new OmsJarContainer(containerId, containerName, version, jarFile);
            newContainer.init();

            // 替换容器
            CARGO.put(containerId, newContainer);
            log.info("[OmsContainer-{}] deployed new version:{} successfully!", containerId, version);

            if (oldContainer != null) {
                // 销毁旧容器
                oldContainer.destroy();
            }

        } catch (Exception e) {
            log.error("[OmsContainer-{}] deployContainer(name={},version={}) failed.", containerId, containerName, version, e);
            // 如果部署失败，则删除该 jar（本次失败可能是下载jar出错导致，不删除会导致这个版本永久无法重新部署）
            CommonUtils.executeIgnoreException(() -> FileUtils.forceDelete(jarFile));
        }
    }

OmsContainerFactory提供了deployContainer方法，它会根据containerId以及version去下载指定的jar包，然后创建OmsJarContainer，执行init方法

小结

OhMyClassLoader继承了URLClassLoader，它定义了load方法，遍历urls，挨个根据url创建JarFile，然后遍历jarFile.entries()，找到.class结尾的entry，判断是否是packageName开头的，是则执行父类的loadClass方法。不过这里貌似没有对JarFile进行关闭，可能会导致资源泄露。