saturn java 热加载（一）

背景：

每次启用都要重启executor，在此之前还要确保该executor下没有任务在执行，很麻烦

 

方案：

将不常更换的公共包放在executor classpath下，仍然由saturn加载

将常变动的包放在executor类加载器可见范围外，使其不能加载

 

public class ProxyJdsJavaJob extends AbstractSaturnJavaJob {

    private static final Logger LOGGER = LoggerFactory.getLogger(ProxyJdsJavaJob.class);

    @Override
    public SaturnJobReturn handleJavaJob(final String jobName, final Integer shardItem, final String shardParam, final SaturnJobExecutionContext context) {

        LOGGER.info("saturn 传入 java job 文件路径及参数：{}", shardParam);
        AbstractJdsJavaJob abstractJdsJavaJob = null;
        try {
            String [] temp = shardParam.split(";");
            String dir = "file:"+temp[0];
            LOGGER.info("saturn 传入 java job 文件路径：{}", temp[0]);
            URL url = new URL(dir);
            URL[] urls2 = {url};

            MyUrlClassLoader myUrlClassLoader = new MyUrlClassLoader(urls2);
            LOGGER.info("saturn 传入 java job 类名：{}", temp[1]);
         //   Class CA = myUrlClassLoader.loadClass(temp[1]);
            Class CA = myUrlClassLoader.findClass(temp[1]);
            abstractJdsJavaJob = (AbstractJdsJavaJob)CA.newInstance();
            abstractJdsJavaJob.runJdsJob(jobName, shardItem, shardParam);
            LOGGER.info("success:{},{},{}", jobName, shardItem, shardParam);
            return new SaturnJobReturn(Common.createJobResString("", jobName, shardItem, shardParam, true));

        } catch (Exception e) {
            LOGGER.info("error:{},{},{}", jobName, shardItem, shardParam);
            LOGGER.error(ExceptionUtils.getStackTrace(e));
            new SendMailThread(new Date(), e, jobName, shardItem, shardParam).execute();
            throw new JdsFastJobException(e);
        } catch (Throwable throwable) {
            LOGGER.error(throwable.getMessage(), throwable);
            throw new JdsFastJobException("类加载器失败");
        } finally {
            if(abstractJdsJavaJob != null)
                abstractJdsJavaJob.release();
        }
    }


}

 

public class MyUrlClassLoader extends URLClassLoader {

    private static final Logger LOGGER = LoggerFactory.getLogger(MyUrlClassLoader.class);

    public MyUrlClassLoader(URL[] urls) {

        super(urls, Thread.currentThread().getContextClassLoader());
        // 父加载器不一定是系统类加载器，可能是saturn自定义加载器
        ClassLoader parent = Thread.currentThread().getContextClassLoader();
        LOGGER.info("parent class loader {}", parent);
    }

    @Override
    protected Class<?> findClass(final String name) throws ClassNotFoundException {
        return super.findClass(name);
    }
}

 

1. 如果待热加载jar包（后称为A）在executor类加载器可见范围内，必须使用findclass避开缓存

如果在可见范围外，loadclass与findclass都可以，但请注意：

findclass（A），A中引用B，那么jvm使用loadclass加载B，这就意味着，如果B在父加载器缓存中，则不会热加载

所以如果B也要热加载，则1）将B也放到主程序类加载可见范围外，2）在A中使用findclass避开主类加载器缓存，当然同时也打破双亲委派

 

2. 这里有个坑，executor的类加载器并不是AppClassLoader，日志显示

(MyUrlClassLoader.java:21) -> parent class loader com.vip.saturn.job.executor.JobClassLoader@5fd764ee

所以，自定义类加载器必须指定parent class loader为saturn的类加载器，而不是使用默认null作为参数，这将导致AppClassLoader作为父加载器，否则

AbstractJdsJavaJob是由saturn类加载器加载

而具体的被热加载的类继承AbstractJdsJavaJob，由自定义类加载器加载，缺省情况下，其parent为系统类加载器，导致自定义加载器和saturn类加载器变为平行关系，saturn加载的类，对我们要热加载的类不可见，从而抛出error

 

3. 永远要确保finally中的语句是安全的，因为如果它抛异常，将覆盖catch中所有代码

详细见：https://www.cnblogs.com/silyvin/p/9993458.html

 

4. 由第2点抛出的异常，catch Exception是catch不到的，详细见：https://www.cnblogs.com/silyvin/p/10274898.html

故使用了catch Throwable，成功抓取

 

 

[INFO] 2019-01-15 17:26:43 985 [jds.fast.job.ProxyJdsJavaJob] [Saturn-test_ProxyJdsJavaJob-24-thread-1] (ProxyJdsJavaJob.java:30) -> saturn 传入 java job 类名：saturn.DemoJob
[ERROR] 2019-01-15 17:26:43 987 [jds.fast.job.ProxyJdsJavaJob] [Saturn-test_ProxyJdsJavaJob-24-thread-1] (ProxyJdsJavaJob.java:45) -> jds/fast/job/AbstractJdsJavaJob
java.lang.NoClassDefFoundError: jds/fast/job/AbstractJdsJavaJob
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:468)
        at java.net.URLClassLoader.access$100(URLClassLoader.java:74)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:369)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:363)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:362)
        at jds.fast.job.MyUrlClassLoader.findClass(MyUrlClassLoader.java:17)
        at jds.fast.job.ProxyJdsJavaJob.handleJavaJob(ProxyJdsJavaJob.java:32)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at com.vip.saturn.job.java.SaturnJavaJob$1.internalCall(SaturnJavaJob.java:218)
        at com.vip.saturn.job.basic.AbstractSaturnJob$JobBusinessClassMethodCaller.call(AbstractSaturnJob.java:205)
        at com.vip.saturn.job.java.SaturnJavaJob.handleJavaJob(SaturnJavaJob.java:214)
        at com.vip.saturn.job.java.SaturnJavaJob.doExecution(SaturnJavaJob.java:204)
        at com.vip.saturn.job.basic.JavaShardingItemCallable.call(JavaShardingItemCallable.java:158)
        at com.vip.saturn.job.basic.ShardingItemFutureTask.call(ShardingItemFutureTask.java:88)
        at com.vip.saturn.job.basic.ShardingItemFutureTask.call(ShardingItemFutureTask.java:17)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.ClassNotFoundException: jds.fast.job.AbstractJdsJavaJob
        at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
        at jds.fast.job.MyUrlClassLoader.findClass(MyUrlClassLoader.java:17)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
        ... 26 common frames omitted

 

 

5 7.13补充：

public class MyUrlClassLoader extends URLClassLoader {

    private static final Logger LOGGER = LoggerFactory.getLogger(MyUrlClassLoader.class);

    public MyUrlClassLoader(URL[] urls) {

        super(urls, Thread.currentThread().getContextClassLoader());
        // 父加载器不一定是系统类加载器，可能是saturn自定义加载器
        ClassLoader parent = Thread.currentThread().getContextClassLoader();
        LOGGER.info("parent class loader {}", parent);
        ClassLoader grandParent = parent.getParent();
        LOGGER.info("grand class loader {}", grandParent);
    }

    @Override
    protected Class<?> findClass(final String name) throws ClassNotFoundException {
        return super.findClass(name);
    }

    @Override
    protected void finalize() throws Throwable {
        LOGGER.info("回收MyUrlClassLoader");
        super.finalize();
    }
}

 

grandParent 居然是null，这也导致了与以premain方式注入监控的jmx_exporter所在的系统类加载器相互不可见：https://www.cnblogs.com/silyvin/articles/10600530.html

 

2019.12.26

这篇文章能干啥

1）任务隔离

2）热加载

3）加解密

4）任务状态统一记录