聊聊dubbo的ClassLoaderFilter

序

本文主要研究一下 dubbo 的 ClassLoaderFilter

ClassLoaderFilter

dubbo-2.7.2/dubbo-rpc/dubbo-rpc-api/src/main/java/org/apache/dubbo/rpc/filter/ClassLoaderFilter.java

@Activate(group = CommonConstants.PROVIDER, order = -30000)
public class ClassLoaderFilter implements Filter {

    @Override
    public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException {ClassLoader ocl = Thread.currentThread().getContextClassLoader();
        Thread.currentThread().setContextClassLoader(invoker.getInterface().getClassLoader());
        try {return invoker.invoke(invocation);
        } finally {Thread.currentThread().setContextClassLoader(ocl);
        }
    }

}

• ClassLoaderFilter 实现了 Filter 接口，其 invoke 方法首先获取当前线程的 contextClassLoader，然后将其 ContextClassLoader 设置为 invoker.getInterface().getClassLoader()，之后执行 invoker.invoke 方法，最后将当前线程的 classLoader 重置为原来的 contextClassLoader

实例

dubbo-2.7.2/dubbo-rpc/dubbo-rpc-api/src/test/java/org/apache/dubbo/rpc/filter/ClassLoaderFilterTest.java

public class ClassLoaderFilterTest {private ClassLoaderFilter classLoaderFilter = new ClassLoaderFilter();

    @Test
    public void testInvoke() throws Exception {URL url = URL.valueOf("test://test:11/test?accesslog=true&group=dubbo&version=1.1");

        String path = DemoService.class.getResource("/").getPath();
        final URLClassLoader cl = new URLClassLoader(new java.net.URL[]{new java.net.URL("file:" + path)}) {
            @Override
            public Class<?> loadClass(String name) throws ClassNotFoundException {
                try {return findClass(name);
                } catch (ClassNotFoundException e) {return super.loadClass(name);
                }
            }
        };
        final Class<?> clazz = cl.loadClass(DemoService.class.getCanonicalName());
        Invoker invoker = new MyInvoker(url) {
            @Override
            public Class getInterface() {return clazz;}

            @Override
            public Result invoke(Invocation invocation) throws RpcException {Assertions.assertEquals(cl, Thread.currentThread().getContextClassLoader());
                return null;
            }
        };
        Invocation invocation = Mockito.mock(Invocation.class);

        classLoaderFilter.invoke(invoker, invocation);
    }
}

• 这里 invoker 的 interface 设置为 DemoService.class，然后验证 invoke 方法里头的 Thread.currentThread().getContextClassLoader() 为加载 DemoService.class 的 URLClassLoader

小结

ClassLoaderFilter 实现了 Filter 接口，其 invoke 方法首先获取当前线程的 contextClassLoader，然后将其 ContextClassLoader 设置为 invoker.getInterface().getClassLoader()，之后执行 invoker.invoke 方法，最后将当前线程的 classLoader 重置为原来的 contextClassLoader

doc

• ClassLoaderFilter