Lsp4j

[Quincey Homer]

The first thing you should do is to implement your language server.To do so just implement the interface org.eclipse.lsp4j.LanguageServer.If you are implementing a client (e.g. an editor) you would need to implement org.eclipse.lsp4j.LanguageClient instead.

With this we have a Launcher object on which we can obtain the remote proxy (of type LanguageClient in this case).Usually a language server should also implement LanguageClientAware, which defines a single method connect(LanguageClient) over which you can pass the remote proxy to the language server.

Now your language server is not only able to receive messages from the other side, but can send messages back as well.The final thing you need to to do in order to start listening on the given input stream, is calling launcher.startListening(); This will start the listening process in a new thread.

As mentioned in the beginning LSP4J is based on JSON RPC.The implementation is completely independent of the LSP, so can be used for other protocols.Also we made sure that it is easy to extend the LSP with new messages.This is important to bridge the last non-standard 20% and to prototype possible extensions for the LSP.We are for instance currently experimenting with support for semantic coloring and will submit an enhancement request once we are happy with it.Please refer to the documentation to learn more about the JSON RPC layer.

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In order to be able to define a multithread LS is necessary wrap the previous code snippet into a callable object.Each thread (that could be defined using different implementations of ExecutorService interface) will execute the callable task.

The server needs to understand who is the client that asked to communicate with it. For this reason inside the callable activity there is an async task that execute a Runnable in order to add the LanguageClient retrieved from the launcher into the server instance that will use this class to access to the methods that it needs to use to send notification messages and other things to the connected client.

The launcher object provides all the underwood configuration in order to connect the remote endpoint via input and output stream.In particular the LSP launcher need some parameters:- local service = the concrete server implementation- remote interface = the LanguageClient class- input stream- output stream

Create an instance of MessageJsonHandler (using internal method createJsonHandler()): MessageJsonHandler works as a wrapper around Gson that includes configuration necessary for the RPC communication. Using its routine getSupportedMethods() the MessageJsonHandler will be populated with the list of all RPC supported methods both for client and server.

Next is necessary define the remoteProxy object that will be used by the LS to set the LanguageClient class (that will be used to inspect methods available that the server will use to send messages to the server)

java /** * Wraps a given @link Endpoint in the given service interface. * * @return the wrapped service object */ @SuppressWarnings("unchecked") public static T toServiceObject(Endpoint endpoint, Class interface_) Class[] interfArray = new Class[]interface_, Endpoint.class; EndpointProxy invocationHandler = new EndpointProxy(endpoint, interface_); return (T) Proxy.newProxyInstance(interface_.getClassLoader(), interfArray, invocationHandler); 4. After that is necessary define the MessageConsumer that reads from an input stream and parses messages from JSON5. Finally is necessary define a new ExecutorService or use one already defined and sent to the createLauncher() method6. After all these steps, a new anonymous class for Launcher is created and are also defined methods that the new class need to override from the Launcher interface:

The startListening() method is defined by each class that implements the Launcher interface, and also anonymous classes.This method invoke the static startProcessing() method defined by the class ConcurrentMessageProcessor, defined into the package org.eclipse.lsp4j.jsonrpc.json.The class ConcurrentMessageProcessor implements the Runnable interface and its static method startProcessing return a Future that will be resolved when the started thread is terminated:

The Language Server Protocol (LSP) defines the protocol used between an editor or IDE and a language server.The language server provides language features like auto complete, go to definition, find all references etc.To learn about the language server protocol see -server-protocol and -server-protocol/specification

LSP4J (Language Server Protocol for Java) is an Eclipse project which provides Java bindings for the Language Server Protocol.The LSP is based on an extended version of JSON RPC v2.0, for which LSP4J provides a Java implementation.Therefore, we are able to use it to create a language server without having to deal with the JSON specifics of the LSP and instead create endpoints for which we are given parameters from the client and return the required actions in object form based on which message our server receives.

Use the p2 repository from to install the lsp4e package and its dependencies.Install the package org.eclipse.lsp4j and Language Server Protocol client for Eclipse IDE (Incubation) Source.This will give enough functionality to add the language server features to your plug-in.

The list of available extensions will be empty at first.To fix this uncheck the Show only extension points from the required plugins checkbox.This will give you the ability to choose from all available extension points.Filter and choose the extension org.eclipse.core.contenttype.contentTypes from the list and click Finish.

Ensure your run configuration also includes org.eclipse.ui.genericeditor.One way of ensuring this is to add it as Dependency to your com.vogella.dartlanguageserver plug-in.Alternatively, you can modify the runtime configuration.

The Eclipse project TM4E adds syntax highlighting capabilities to the Eclipse IDE.Using special "grammar" files that define the colors and words used by your language it can display code with the proper syntax highlight.