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| − | ==Introduction==
| + | This tutorial has been deprecated in favor of the RSA for [http://ipopo.readthedocs.io iPOPO] implementation. For a tutorial, [https://wiki.eclipse.org/OSGi_R7_Remote_Services_between_Python_and_Java see this wiki page]. |
| − | | + | |
| − | OSGi Services are an excellent way to implement small, dynamic, component-based systems. With features like service versioning, dynamics, service injection and instance dependency-handling, and a clear separation between contract and implementation make it a valuable technology for the Internet of Things.
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| − | | + | |
| − | Since OSGi is a Java-based framework, services have traditionally been both declared and implemented in Java. With the OSGi Remote Services specification, and ECF's implementation of both the Remote Services and Remote Service Admin specifications -[https://www.osgi.org/developer/specifications/ specification], it's now possible to implement and use OSGi services implemented in Python or Java.
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| − | | + | |
| − | This tutorial shows a simple example of implementing an OSGi service implemented in Python, that uses [https://developers.google.com/protocol-buffers/ Google Protocol Buffers] for high-performance cross-language serialization. These services automatically inherit all of the aspects of a Java-only OSGi service (dynamics, service injection, versioning support, etc.). | + | |
| − | | + | |
| − | ==Declaring a Service==
| + | |
| − | | + | |
| − | Here is a simple example Java interface declaring a single 'sayHello' method:
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| − | | + | |
| − | <pre>
| + | |
| − | public interface IHello {
| + | |
| − | | + | |
| − | HelloMsgContent sayHello(HelloMsgContent message) throws Exception;
| + | |
| − | }
| + | |
| − | </pre>
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| − | This interface is declared [https://github.com/ECF/Py4j-RemoteServicesProvider/blob/master/examples/org.eclipse.ecf.examples.protobuf.hello/src/org/eclipse/ecf/examples/protobuf/hello/IHello.java here] in [https://github.com/ECF/Py4j-RemoteServicesProvider/tree/master/examples/org.eclipse.ecf.examples.protobuf.hello this project].
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| − | The HelloMsgContent class was generated by the Protocol Buffers protoc compiler based upon the following message declaration
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| − | | + | |
| − | <pre>
| + | |
| − | syntax = "proto3";
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| − | | + | |
| − | package org.eclipse.ecf.examples.protobuf.hello;
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| − | message HelloMsgContent {
| + | |
| − | string h = 1;
| + | |
| − | string f = 2;
| + | |
| − | string to = 3;
| + | |
| − | string hellomsg = 4;
| + | |
| − | repeated double x = 5;
| + | |
| − | }
| + | |
| − | </pre>
| + | |
| − | | + | |
| − | This message declaration, when run through the protoc compiler, generates the Java HelloMsgContent source code, and also generates a Python version of the same class. The hellomsg.proto file is [https://github.com/ECF/Py4j-RemoteServicesProvider/blob/master/examples/org.eclipse.ecf.examples.protobuf.hello/hellomsg.proto here].
| + | |
| − | | + | |
| − | With the IHello interface and the HelloMsgContent class, the IHello service declaration is complete.
| + | |
| − | | + | |
| − | ==Python Implementation of IHello Service==
| + | |
| − | | + | |
| − | To implement this IHello service in Python it's necessary to provide a Python implementation class. Here's an example:
| + | |
| − | | + | |
| − | <pre>
| + | |
| − | from hellomsg_pb2 import HelloMsgContent
| + | |
| − | from osgiservicebridge.protobuf import protobuf_remote_service
| + | |
| − | from osgiservicebridge.protobuf import protobuf_remote_service_method
| + | |
| − | from osgiservicebridge import ECF_SERVICE_EXPORTED_ASYNC_INTERFACES
| + | |
| − | | + | |
| − | def create_hellomsgcontent(message):
| + | |
| − | resmsg = HelloMsgContent()
| + | |
| − | resmsg.h = 'Another response from Python'
| + | |
| − | resmsg.f = 'frompython'
| + | |
| − | resmsg.to = 'tojava'
| + | |
| − | resmsg.hellomsg = message
| + | |
| − | for x in range(0,5):
| + | |
| − | resmsg.x.append(float(x))
| + | |
| − | return resmsg
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| − | | + | |
| − | @protobuf_remote_service(objectClass=['org.eclipse.ecf.examples.protobuf.hello.IHello'],export_properties = { ECF_SERVICE_EXPORTED_ASYNC_INTERFACES: 'org.eclipse.ecf.examples.protobuf.hello.IHello' })
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| − | class HelloServiceImpl:
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| − |
| + | |
| − | def __init__(self,props):
| + | |
| − | self.props = props
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| − |
| + | |
| − | @protobuf_remote_service_method(arg_type=HelloMsgContent,return_type=HelloMsgContent)
| + | |
| − | def sayHello(self,pbarg):
| + | |
| − | print("sayHello called with arg="+str(pbarg))
| + | |
| − | return create_hellomsgcontent('responding back to java hello ')
| + | |
| − | | + | |
| − | </pre>
| + | |
| − | | + | |
| − | Notes about this code:
| + | |
| − | | + | |
| − | #A HelloServiceImpl class that implements the '''sayHello''' method
| + | |
| − | #The HelloServiceImpl class has a decorator:
| + | |
| − | <pre>
| + | |
| − | @protobuf_remote_service(objectClass=['org.eclipse.ecf.examples.protobuf.hello.IHello'])
| + | |
| − | class HelloServiceImpl:
| + | |
| − | </pre>
| + | |
| − | associates the HelloServiceImpl Python class with the IHello Java service interface.
| + | |
| − | #The '''sayHello''' method also has a decorator:
| + | |
| − | <pre>
| + | |
| − | @protobuf_remote_service_method(arg_type=HelloMsgContent,return_type=HelloMsgContent)
| + | |
| − | def sayHello(self,pbarg):
| + | |
| − | </pre>
| + | |
| − | indicates the types (Python class) of the pbarg type and the '''sayHello''' return type. In this example they are both HelloMsgContent, but they may be of any type as long as it is a protocol buffers Message type.
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| − | The complete Python code is available [https://github.com/ECF/Py4j-RemoteServicesProvider/blob/master/examples/org.eclipse.ecf.examples.protobuf.hello.pythonhost/python-src/hello.py here] in the org.eclipse.ecf.examples.protobuf.hello.pythonhost [https://github.com/ECF/Py4j-RemoteServicesProvider/tree/master/examples/org.eclipse.ecf.examples.protobuf.hello.pythonhost project].
| + | |
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| − | The HelloServiceImpl class, along with the @protobuf_remote_service and @protobuf_remote_service_method decorators completes the python implementation.
| + | |
| − | | + | |
| − | ===Accessing the hello Module===
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| − | To create an instance of HelloServiceImpl at runtime, some other python code has to be able to import the hello module. Python 3 has support for creating an '''Import Hook''', that allows Java code (in this case an OSGi bundle) to resolve and import statement like this
| + | |
| − | | + | |
| − | <pre>
| + | |
| − | import hello
| + | |
| − | </pre>
| + | |
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| − | This Py4j remote services provider now allows a '''Module Resolver''' service to be registered resulting in a Python 3 Import Hook to call back the Module Resolver to provide the Python code for the hello module. In the org.eclipse.ecf.examples.protobuf.hello.pythonhost bundle, there is a Module Resolver service implementation called [https://github.com/ECF/Py4j-RemoteServicesProvider/blob/master/examples/org.eclipse.ecf.examples.protobuf.hello.pythonhost/src/org/eclipse/ecf/examples/protobuf/hello/pythonhost/PythonHostBundleModuleResolver.java PythonHostBundleModuleResolver] this implementation of the [https://github.com/ECF/Py4j-RemoteServicesProvider/blob/master/bundles/org.eclipse.ecf.provider.direct/src/org/eclipse/ecf/provider/direct/ModuleResolver.java ModuleResolver] service interface simply reads the hello module source code from /python-src directory inside the bundle when the hook is hit by the 'import hello' python statement.
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| − | | + | |
| − | ==Example Hello Consumer==
| + | |
| − | | + | |
| − | The example service consumer is available in [https://github.com/ECF/Py4j-RemoteServicesProvider/tree/master/examples/org.eclipse.ecf.examples.protobuf.hello.consumer this project]. This consumer uses has the IHello service instance dynamically injected by Declarative Services and then it uses the service via this code (in activate method):
| + | |
| − | | + | |
| − | <pre>
| + | |
| − | HelloMsgContent.Builder b1 = HelloMsgContent.newBuilder();
| + | |
| − | b1.addX(1.1);
| + | |
| − | b1.addX(1.2);
| + | |
| − | b1.setF("fromjava");
| + | |
| − | b1.setTo("topython");
| + | |
| − | b1.setHellomsg("Hello message from java!");
| + | |
| − | b1.setH("An additional message from java");
| + | |
| − | HelloMsgContent request = b1.build();
| + | |
| − | HelloMsgContent result = this.helloService.sayHello(request);
| + | |
| − | System.out.println("Received result="+result);
| + | |
| − | | + | |
| − | </pre>
| + | |
| − | The second to last line makes the call from Java to Python via the '''IHello''' service proxy.
| + | |
| − | | + | |
| − | ==The Java Gateway==
| + | |
| − | | + | |
| − | The only other piece required is a bundle to start the Java-side gateway, so that when the Python code is run it can connect to the Java gateway. The Java Gateway is created and configured via [https://github.com/ECF/Py4j-RemoteServicesProvider/blob/master/examples/org.eclipse.ecf.examples.protobuf.hello.provider/src/org/eclipse/ecf/examples/protobuf/hello/provider/ExampleProtobufPy4jProvider.java this component] in [https://github.com/ECF/Py4j-RemoteServicesProvider/tree/master/examples/org.eclipse.ecf.examples.protobuf.hello.provider this project].
| + | |
| − | | + | |
| − | ==Running the Hello Example==
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| − | First, start the Java side (with the org.eclipse.ecf.examples.protobuf.hello bundle, org.eclipse.ecf.examples.protobuf.hello.consumer, and org.eclipse.ecf.examples.protobuf.hello.provider bundles). If run within Eclipse you may use the protobufhello.javaconsumer.launch config (note that the target platform must be set first to this target: releng/org.eclipse.ecf.provider.py4j.releng.target/ecf-oxygen.target).
| + | |
| − | | + | |
| − | Then the run.py should be started from Python. Prior to starting the following Python libraries must be installed: '''protobuf version 3.2.0''', '''py4j version 0.10.6''', and the '''osgiservicebridge''' package located in [https://github.com/ECF/Py4j-RemoteServicesProvider/tree/master/python/osgiservicebridge this project].
| + | |
| − | | + | |
| − | Once the '''run.py''' is started and the Py4jServiceBridge is connected to the JavaGateway, the IHello proxy will be created, injected into the [https://github.com/ECF/Py4j-RemoteServicesProvider/blob/master/examples/org.eclipse.ecf.examples.protobuf.hello.consumer/src/org/eclipse/ecf/examples/protobuf/hello/consumer/HelloConsumer.java HelloConsumer class], and then the '''sayHello''' call will be made to Python->HelloServiceImpl->sayHello.
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| − | | + | |
| − | This IHello service is just an example. Any other service could be similarly declared, implemented in Python, and injected and consumed in Java.
| + | |
| − | | + | |
| − | ==Background and Related Articles==
| + | |
| − | | + | |
| − | [[Tutorial:_Creating_Custom_Distribution_Providers]]
| + | |
| − | | + | |
| − | [[Getting Started with ECF's OSGi Remote Services Implementation]]
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| − | | + | |
| − | [[OSGi Remote Services and ECF]]
| + | |
| − | | + | |
| − | [[Asynchronous Proxies for Remote Services]]
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| − | | + | |
| − | [[File-based Discovery | Static File-based Discovery of Remote Service Endpoints]]
| + | |
| − | | + | |
| − | [[EIG:Download|Download ECF Remote Services/RSA Implementation]]
| + | |
| − | | + | |
| − | [[EIG:Add to Target Platform|How to Add Remote Services/RSA to Your Target Platform]]
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