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marccarre/AsynchronousExceptionsHandlingWithHandle.java

Created May 8, 2016 17:59
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  1. marccarre created this gist May 8, 2016.
    52 changes: 52 additions & 0 deletions AsynchronousExceptionsHandlingWithHandle.java
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,52 @@
    import java.util.concurrent.CompletableFuture;
    import java.util.concurrent.ExecutionException;
    import static java.lang.String.format;

    public class AsynchronousExceptionsHandlingWithHandle {
    public static void main(final String[] args) throws InterruptedException, ExecutionException {
    for (final boolean failure : new boolean[]{false, true}) {

    CompletableFuture<Integer> x = CompletableFuture.supplyAsync(() -> {
    if (failure) {
    throw new RuntimeException("Oops, something went wrong");
    }
    return 42;
    });

    /**
    * Returns a new CompletableFuture that, when this CompletableFuture completes either normally or exceptionally,
    * is executed with this stage's result and exception as arguments to the supplied function.
    */
    CompletableFuture<HttpResponse> tryX = x.handle((value, ex) -> { // Note that tryX and x are of different type.
    if (value != null) {
    // We get a chance to transform the result...
    return new HttpResponse(200, format("{\"value\": %s}", value));
    } else {
    // ... or return details on the error using the ExecutionException's message:
    return new HttpResponse(500, format("{\"error\": \"%s\"}", ex.getMessage()));
    }
    });

    // Blocks (avoid this in production code!), and either returns the promise's value:
    System.out.println(tryX.get());
    System.out.println("isCompletedExceptionally = " + tryX.isCompletedExceptionally());

    // Output[failure=false]: 200 - {"value": 42}
    // Output[failure=false]: isCompletedExceptionally = false

    // Output[failure=true]: 500 - {"error": "java.lang.RuntimeException: Oops, something went wrong"}
    // Output[failure=true]: isCompletedExceptionally = false
    }
    }

    private static class HttpResponse {
    private final int status;
    private final String body;

    public HttpResponse(final int status, final String body) {
    this.status = status;
    this.body = body;
    }
    public String toString() { return status + " - " + body; }
    }
    }