feat(core): support output filter (#303)

## Main Changes

1. computation results output supports custom write.
2. `SingleSourceShortestPathOutput` implements `org.apache.hugegraph.computer.core.output.ComputerOutput#filter`

---------

Co-authored-by: imbajin <jin@apache.org>

Author: diaohancai

computer-algorithm/src/main/java/org/apache/hugegraph/computer/algorithm/path/shortest/SingleSourceShortestPath.java

@@ -278,4 +278,8 @@ private boolean isAllTargetsReached(Vertex vertex) {
         }
         return false;
     }
+
+    public IdSet getTargetIdSet() {
+        return this.targetIdSet;
+    }
 }

computer-algorithm/src/main/java/org/apache/hugegraph/computer/algorithm/path/shortest/SingleSourceShortestPathOutput.java

@@ -20,8 +20,10 @@
 import java.util.HashMap;
 import java.util.Map;
 
+import org.apache.hugegraph.computer.core.config.Config;
 import org.apache.hugegraph.computer.core.graph.vertex.Vertex;
 import org.apache.hugegraph.computer.core.output.hg.HugeGraphOutput;
+import org.apache.hugegraph.computer.core.worker.Computation;
 import org.apache.hugegraph.util.JsonUtil;
 
 public class SingleSourceShortestPathOutput extends HugeGraphOutput<String> {
@@ -45,4 +47,10 @@ protected String value(Vertex vertex) {
         map.put("total_weight", value.totalWeight());
         return JsonUtil.toJson(map);
     }
+
+    @Override
+    public boolean filter(Config config, Computation computation, Vertex vertex) {
+        SingleSourceShortestPath sssp = (SingleSourceShortestPath) computation;
+        return sssp.getTargetIdSet() == null || sssp.getTargetIdSet().contains(vertex.id());
+    }
 }

computer-api/src/main/java/org/apache/hugegraph/computer/core/output/ComputerOutput.java

@@ -19,6 +19,7 @@
 
 import org.apache.hugegraph.computer.core.config.Config;
 import org.apache.hugegraph.computer.core.graph.vertex.Vertex;
+import org.apache.hugegraph.computer.core.worker.Computation;
 
 /**
  * Computer output is used to output computer results. There is an output object
@@ -37,6 +38,14 @@ public interface ComputerOutput {
      */
     void write(Vertex vertex);
 
+    /**
+     * Write filter.
+     * True to commit the computation result, otherwise not to commit.
+     */
+    default boolean filter(Config config, Computation computation, Vertex vertex) {
+        return true;
+    }
+
     /**
      * Merge output files of multiple partitions if applicable.
      */

computer-core/src/main/java/org/apache/hugegraph/computer/core/compute/FileGraphPartition.java

@@ -255,7 +255,9 @@ protected PartitionStat output() {
             Edges edges = this.edgesInput.edges(this.vertexInput.idPointer());
             vertex.edges(edges);
 
-            output.write(vertex);
+            if (output.filter(this.context.config(), this.computation, vertex)) {
+                output.write(vertex);
+            }
         }
 
         try {