Example usage for java.util.concurrent CompletableFuture exceptionally

Introduction

In this page you can find the example usage for java.util.concurrent CompletableFuture exceptionally.

Prototype

public CompletableFuture<T> exceptionally(Function<Throwable, ? extends T> fn) 

Source Link

Usage

From source file:org.apache.tinkerpop.gremlin.server.handler.HttpGremlinEndpointHandler.java

@Override
public void channelRead(final ChannelHandlerContext ctx, final Object msg) {
    if (msg instanceof FullHttpRequest) {
        final FullHttpRequest req = (FullHttpRequest) msg;

        if ("/favicon.ico".equals(req.getUri())) {
            sendError(ctx, NOT_FOUND, "Gremlin Server doesn't have a favicon.ico");
            ReferenceCountUtil.release(msg);
            return;
        }//from   w  ww  .  jav  a2s.  c o m

        if (is100ContinueExpected(req)) {
            ctx.write(new DefaultFullHttpResponse(HTTP_1_1, CONTINUE));
        }

        if (req.getMethod() != GET && req.getMethod() != POST) {
            sendError(ctx, METHOD_NOT_ALLOWED, METHOD_NOT_ALLOWED.toString());
            ReferenceCountUtil.release(msg);
            return;
        }

        final Quartet<String, Map<String, Object>, String, Map<String, String>> requestArguments;
        try {
            requestArguments = getRequestArguments(req);
        } catch (IllegalArgumentException iae) {
            sendError(ctx, BAD_REQUEST, iae.getMessage());
            ReferenceCountUtil.release(msg);
            return;
        }

        final String acceptString = Optional.ofNullable(req.headers().get("Accept")).orElse("application/json");
        final Pair<String, MessageTextSerializer> serializer = chooseSerializer(acceptString);
        if (null == serializer) {
            sendError(ctx, BAD_REQUEST,
                    String.format("no serializer for requested Accept header: %s", acceptString));
            ReferenceCountUtil.release(msg);
            return;
        }

        final String origin = req.headers().get(ORIGIN);
        final boolean keepAlive = isKeepAlive(req);

        // not using the req any where below here - assume it is safe to release at this point.
        ReferenceCountUtil.release(msg);

        try {
            logger.debug("Processing request containing script [{}] and bindings of [{}] on {}",
                    requestArguments.getValue0(), requestArguments.getValue1(),
                    Thread.currentThread().getName());
            final ChannelPromise promise = ctx.channel().newPromise();
            final AtomicReference<Object> resultHolder = new AtomicReference<>();
            promise.addListener(future -> {
                // if failed then the error was already written back to the client as part of the eval future
                // processing of the exception
                if (future.isSuccess()) {
                    logger.debug(
                            "Preparing HTTP response for request with script [{}] and bindings of [{}] with result of [{}] on [{}]",
                            requestArguments.getValue0(), requestArguments.getValue1(), resultHolder.get(),
                            Thread.currentThread().getName());
                    final FullHttpResponse response = new DefaultFullHttpResponse(HTTP_1_1, OK,
                            (ByteBuf) resultHolder.get());
                    response.headers().set(CONTENT_TYPE, serializer.getValue0());
                    response.headers().set(CONTENT_LENGTH, response.content().readableBytes());

                    // handle cors business
                    if (origin != null)
                        response.headers().set(ACCESS_CONTROL_ALLOW_ORIGIN, origin);

                    if (!keepAlive) {
                        ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
                    } else {
                        response.headers().set(CONNECTION, HttpHeaders.Values.KEEP_ALIVE);
                        ctx.writeAndFlush(response);
                    }
                }
            });

            final Timer.Context timerContext = evalOpTimer.time();

            final Bindings bindings;
            try {
                bindings = createBindings(requestArguments.getValue1(), requestArguments.getValue3());
            } catch (IllegalStateException iae) {
                sendError(ctx, BAD_REQUEST, iae.getMessage());
                ReferenceCountUtil.release(msg);
                return;
            }

            // provide a transform function to serialize to message - this will force serialization to occur
            // in the same thread as the eval. after the CompletableFuture is returned from the eval the result
            // is ready to be written as a ByteBuf directly to the response.  nothing should be blocking here.
            final CompletableFuture<Object> evalFuture = gremlinExecutor.eval(requestArguments.getValue0(),
                    requestArguments.getValue2(), bindings, FunctionUtils.wrapFunction(o -> {
                        // stopping the timer here is roughly equivalent to where the timer would have been stopped for
                        // this metric in other contexts.  we just want to measure eval time not serialization time.
                        timerContext.stop();

                        logger.debug(
                                "Transforming result of request with script [{}] and bindings of [{}] with result of [{}] on [{}]",
                                requestArguments.getValue0(), requestArguments.getValue1(), o,
                                Thread.currentThread().getName());
                        final ResponseMessage responseMessage = ResponseMessage.build(UUID.randomUUID())
                                .code(ResponseStatusCode.SUCCESS).result(IteratorUtils.asList(o)).create();

                        // http server is sessionless and must handle commit on transactions. the commit occurs
                        // before serialization to be consistent with how things work for websocket based
                        // communication.  this means that failed serialization does not mean that you won't get
                        // a commit to the database
                        attemptCommit(requestArguments.getValue3(), graphManager,
                                settings.strictTransactionManagement);

                        try {
                            return Unpooled.wrappedBuffer(serializer.getValue1()
                                    .serializeResponseAsString(responseMessage).getBytes(UTF8));
                        } catch (Exception ex) {
                            logger.warn(String.format("Error during serialization for %s", responseMessage),
                                    ex);
                            throw ex;
                        }
                    }));

            evalFuture.exceptionally(t -> {
                sendError(ctx, INTERNAL_SERVER_ERROR,
                        String.format("Error encountered evaluating script: %s", requestArguments.getValue0()),
                        Optional.of(t));
                promise.setFailure(t);
                return null;
            });

            evalFuture.thenAcceptAsync(r -> {
                // now that the eval/serialization is done in the same thread - complete the promise so we can
                // write back the HTTP response on the same thread as the original request
                resultHolder.set(r);
                promise.setSuccess();
            }, gremlinExecutor.getExecutorService());
        } catch (Exception ex) {
            // tossed to exceptionCaught which delegates to sendError method
            final Throwable t = ExceptionUtils.getRootCause(ex);
            throw new RuntimeException(null == t ? ex : t);
        }
    }
}

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