[NCL-6344] Implement Supplier interface (#603)

Implement Supplier interface for `BuildFinder` and
`DistributionAnalyzer`. This is useful when invoking both of them in a
`CompletableFuture.supplyAsync` to produce a `CompletableFuture`. The
latter can then be composed and combined with other `CompletableFuture`s.

One reason for using that composability for NCL-6344 is to implement a
cancellation feature. The flow goes from:

url -> DistributionAnalyzer -> BuildFinder

When running `DistributionAnalyzer` and `BuildFinder` as a future, it is
really impossible to stop them in case of cancellation. However, we can
cancel the rest of the flow after them.

url -> future(DistributionAnalyzer) -> check if cancelled -> future(BuildFinder)

Using a `CompletableFuture` makes this much easier.

core/src/main/java/org/jboss/pnc/build/finder/core/BuildFinder.java

@@ -38,10 +38,12 @@
 import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.Callable;
+import java.util.concurrent.CompletionException;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
+import java.util.function.Supplier;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
@@ -70,7 +72,8 @@
 import com.redhat.red.build.koji.model.xmlrpc.KojiTagInfo;
 import com.redhat.red.build.koji.model.xmlrpc.KojiTaskInfo;
 
-public class BuildFinder implements Callable<Map<BuildSystemInteger, KojiBuild>> {
+public class BuildFinder
+        implements Callable<Map<BuildSystemInteger, KojiBuild>>, Supplier<Map<BuildSystemInteger, KojiBuild>> {
     private static final Logger LOGGER = LoggerFactory.getLogger(BuildFinder.class);
 
     private static final String BUILDS_FILENAME = "builds.json";
@@ -1203,6 +1206,23 @@ public Map<BuildSystemInteger, KojiBuild> call() throws KojiClientException {
         return allBuilds;
     }
 
+    /**
+     * Provide a Supplier version of the Callable. This is useful when using the BuildFinder to obtain a
+     * CompletableFuture (via {@link java.util.concurrent.CompletableFuture#supplyAsync(Supplier)})
+     *
+     * throws CompletionException if a KojiClientException is thrown
+     *
+     * @return For each checksum type (key), the checksum values of the files
+     */
+    @Override
+    public Map<BuildSystemInteger, KojiBuild> get() {
+        try {
+            return call();
+        } catch (KojiClientException e) {
+            throw new CompletionException(e);
+        }
+    }
+
     public void setListener(BuildFinderListener listener) {
         this.listener = listener;
 

core/src/main/java/org/jboss/pnc/build/finder/core/DistributionAnalyzer.java

@@ -39,12 +39,14 @@
 import java.util.Set;
 import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.Callable;
+import java.util.concurrent.CompletionException;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Supplier;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
@@ -64,7 +66,8 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-public class DistributionAnalyzer implements Callable<Map<ChecksumType, MultiValuedMap<String, LocalFile>>> {
+public class DistributionAnalyzer implements Callable<Map<ChecksumType, MultiValuedMap<String, LocalFile>>>,
+        Supplier<Map<ChecksumType, MultiValuedMap<String, LocalFile>>> {
     private static final Logger LOGGER = LoggerFactory.getLogger(DistributionAnalyzer.class);
 
     /**
@@ -574,6 +577,23 @@ public Map<ChecksumType, MultiValuedMap<String, LocalFile>> call() throws IOExce
         return Collections.unmodifiableMap(map);
     }
 
+    /**
+     * Provide a Supplier version of the Callable. This is useful when using the DistributionAnalyzer to obtain a
+     * CompletableFuture (via {@link java.util.concurrent.CompletableFuture#supplyAsync(Supplier)})
+     *
+     * throws CompletionException if an IO exception is thrown
+     *
+     * @return For each checksum type (key), the checksum values of the files
+     */
+    @Override
+    public Map<ChecksumType, MultiValuedMap<String, LocalFile>> get() {
+        try {
+            return call();
+        } catch (IOException e) {
+            throw new CompletionException(e);
+        }
+    }
+
     public BlockingQueue<Checksum> getQueue() {
         return queue;
     }