Akka stream IOResult:如何检查错误？

import akka.Done;
import akka.actor.ActorSystem;
import akka.stream.ActorMaterializer;
import akka.stream.IOResult;
import akka.stream.javadsl.FileIO;
import akka.stream.javadsl.Sink;
import akka.stream.javadsl.Source;

import java.nio.file.Paths;
import java.util.concurrent.CompletionStage;

public class AkkaStreamExample {
    public static void main(String[] args) {
        // 创建Actor系统和材料化器
        ActorSystem system = ActorSystem.create("AkkaStreamExample");
        ActorMaterializer materializer = ActorMaterializer.create(system);

        // 创建一个文件源和一个文件汇
        Source<String, CompletionStage<IOResult>> source = Source.single("Hello, Akka Stream!");
        Sink<String, CompletionStage<IOResult>> sink = FileIO.toPath(Paths.get("output.txt"));

        // 运行流处理
        CompletionStage<IOResult> result = source.runWith(sink, materializer);

        // 处理结果
        result.thenAccept(ioResult -> {
            if (ioResult.isSuccess()) {
                System.out.println("操作成功");
            } else {
                System.out.println("操作失败，错误信息：" + ioResult.getError());
            }
            system.terminate();
        });
    }
}