fix(server): clean up the code (#2456)

- replace `size() == 0` with `isEmpty()`
- remove unnecessary unboxing
- remove unnecessary boxing
- replace for loop with enhanced for loop
- replace lambda with method reference

hugegraph-server/hugegraph-api/src/main/java/org/apache/hugegraph/api/filter/LoadDetectFilter.java

@@ -95,7 +95,7 @@ public void filter(ContainerRequestContext context) {
 
     public static boolean isWhiteAPI(ContainerRequestContext context) {
         List<PathSegment> segments = context.getUriInfo().getPathSegments();
-        E.checkArgument(segments.size() > 0, "Invalid request uri '%s'",
+        E.checkArgument(!segments.isEmpty(), "Invalid request uri '%s'",
                         context.getUriInfo().getPath());
         String rootPath = segments.get(0).getPath();
         return WHITE_API_LIST.contains(rootPath);

hugegraph-server/hugegraph-api/src/main/java/org/apache/hugegraph/server/RestServer.java

@@ -97,7 +97,7 @@ private HttpServer configHttpServer(URI uri, ResourceConfig rc) {
         }
 
         Collection<NetworkListener> listeners = server.getListeners();
-        E.checkState(listeners.size() > 0,
+        E.checkState(!listeners.isEmpty(),
                      "Http Server should have some listeners, but now is none");
         NetworkListener listener = listeners.iterator().next();
 

hugegraph-server/hugegraph-cassandra/src/main/java/org/apache/hugegraph/backend/store/cassandra/CassandraStore.java

@@ -538,7 +538,7 @@ private static Map<String, Object> parseReplica(HugeConfig conf) {
 
     private static int convertFactor(String factor) {
         try {
-            return Integer.valueOf(factor);
+            return Integer.parseInt(factor);
         } catch (NumberFormatException e) {
             throw new BackendException(
                     "Expect int factor value for SimpleStrategy, " +

hugegraph-server/hugegraph-cassandra/src/main/java/org/apache/hugegraph/backend/store/cassandra/CassandraTables.java

@@ -447,7 +447,7 @@ public void delete(CassandraSessionPool.Session session,
 
             // Let super class do delete if not deleting edge by label
             List<Object> idParts = this.idColumnValue(entry.id());
-            if (idParts.size() > 1 || entry.columns().size() > 0) {
+            if (idParts.size() > 1 || !entry.columns().isEmpty()) {
                 super.delete(session, entry);
                 return;
             }

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/auth/StandardAuthManager.java

@@ -180,7 +180,7 @@ public HugeUser findUser(String name) {
         }
 
         List<HugeUser> users = this.users.query(P.NAME, name, 2L);
-        if (users.size() > 0) {
+        if (!users.isEmpty()) {
             assert users.size() == 1;
             user = users.get(0);
             this.usersCache.update(username, user);

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/backend/cache/CachedGraphTransaction.java

@@ -350,7 +350,7 @@ protected Iterator<HugeEdge> queryEdgesFromBackend(Query query) {
             edges.add(rs.next());
         }
 
-        if (edges.size() == 0) {
+        if (edges.isEmpty()) {
             this.edgesCache.update(cacheKey, Collections.emptyList());
         } else if (edges.size() <= MAX_CACHE_EDGES_PER_QUERY) {
             this.edgesCache.update(cacheKey, edges);

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/backend/id/Id.java

@@ -67,7 +67,7 @@ public char prefix() {
         }
 
         public static IdType valueOfPrefix(String id) {
-            E.checkArgument(id != null && id.length() > 0,
+            E.checkArgument(id != null && !id.isEmpty(),
                             "Invalid id '%s'", id);
             switch (id.charAt(0)) {
                 case 'L':

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/backend/query/Condition.java

@@ -52,9 +52,7 @@ public enum ConditionType {
 
     public enum RelationType implements BiPredicate<Object, Object> {
 
-        EQ("==", (v1, v2) -> {
-            return equals(v1, v2);
-        }),
+        EQ("==", RelationType::equals),
 
         GT(">", (v1, v2) -> {
             return compare(v1, v2) > 0;

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/backend/query/ConditionQuery.java

@@ -241,12 +241,12 @@ public <T> T condition(Object key) {
         if (valuesEQ.isEmpty() && valuesIN.isEmpty()) {
             return null;
         }
-        if (valuesEQ.size() == 1 && valuesIN.size() == 0) {
+        if (valuesEQ.size() == 1 && valuesIN.isEmpty()) {
             @SuppressWarnings("unchecked")
             T value = (T) valuesEQ.get(0);
             return value;
         }
-        if (valuesEQ.size() == 0 && valuesIN.size() == 1) {
+        if (valuesEQ.isEmpty() && valuesIN.size() == 1) {
             @SuppressWarnings("unchecked")
             T value = (T) valuesIN.get(0);
             return value;
@@ -273,7 +273,7 @@ public <T> T condition(Object key) {
             }
         }
 
-        if (intersectValues.size() == 0) {
+        if (intersectValues.isEmpty()) {
             return null;
         }
         E.checkState(intersectValues.size() == 1,
@@ -516,7 +516,7 @@ public boolean hasNeqCondition() {
 
     public boolean matchUserpropKeys(List<Id> keys) {
         Set<Id> conditionKeys = this.userpropKeys();
-        return keys.size() > 0 && conditionKeys.containsAll(keys);
+        return !keys.isEmpty() && conditionKeys.containsAll(keys);
     }
 
     @Override
@@ -808,7 +808,7 @@ public boolean checkRangeIndex(HugeElement element, Condition cond) {
              */
             boolean hasRightValue = removeFieldValue(fieldValues,
                                                      property.value());
-            if (fieldValues.size() > 0) {
+            if (!fieldValues.isEmpty()) {
                 this.addLeftIndex(element.id(), propId, fieldValues);
             }
 

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/backend/query/QueryResults.java

@@ -59,7 +59,7 @@ private QueryResults(Iterator<R> results) {
     }
 
     public void setQuery(Query query) {
-        if (this.queries.size() > 0) {
+        if (!this.queries.isEmpty()) {
             this.queries.clear();
         }
         this.addQuery(query);

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/backend/serializer/BinarySerializer.java

@@ -527,7 +527,7 @@ public HugeEdge readEdge(HugeGraph graph, BackendEntry bytesEntry) {
     @Override
     public BackendEntry writeIndex(HugeIndex index) {
         BinaryBackendEntry entry;
-        if (index.fieldValues() == null && index.elementIds().size() == 0) {
+        if (index.fieldValues() == null && index.elementIds().isEmpty()) {
             /*
              * When field-values is null and elementIds size is 0, it is
              * meaningful for deletion of index data by index label.

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/backend/serializer/TableSerializer.java

@@ -308,7 +308,7 @@ public BackendEntry writeIndex(HugeIndex index) {
          * When field-values is null and elementIds size is 0, it is
          * meaningful for deletion of index data in secondary/range index.
          */
-        if (index.fieldValues() == null && index.elementIds().size() == 0) {
+        if (index.fieldValues() == null && index.elementIds().isEmpty()) {
             entry.column(HugeKeys.INDEX_LABEL_ID, index.indexLabel().longId());
         } else {
             entry.column(HugeKeys.FIELD_VALUES, index.fieldValues());

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/backend/serializer/TextSerializer.java

@@ -355,7 +355,7 @@ public HugeEdge readEdge(HugeGraph graph, BackendEntry backendEntry) {
     @Override
     public BackendEntry writeIndex(HugeIndex index) {
         TextBackendEntry entry = newBackendEntry(index.type(), index.id());
-        if (index.fieldValues() == null && index.elementIds().size() == 0) {
+        if (index.fieldValues() == null && index.elementIds().isEmpty()) {
             /*
              * When field-values is null and elementIds size is 0, it is
              * meaningful for deletion of index data in secondary/range index.
@@ -497,7 +497,7 @@ private Query writeQueryEdgePrefixCondition(ConditionQuery cq) {
             }
         }
 
-        if (condParts.size() > 0) {
+        if (!condParts.isEmpty()) {
             // Conditions to id
             String id = EdgeId.concat(condParts.toArray(new String[0]));
             return new IdPrefixQuery(cq, IdGenerator.of(id));

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/backend/store/memory/InMemoryDBTable.java

@@ -232,7 +232,7 @@ private Iterator<BackendEntry> queryByRange(ConditionQuery query) {
 
     protected Map<Id, BackendEntry> queryById(Collection<Id> ids,
                                               Map<Id, BackendEntry> entries) {
-        assert ids.size() > 0;
+        assert !ids.isEmpty();
         Map<Id, BackendEntry> rs = InsertionOrderUtil.newMap();
 
         for (Id id : ids) {
@@ -262,7 +262,7 @@ protected Map<Id, BackendEntry> queryByIdRange(Id start,
     protected Map<Id, BackendEntry> queryByFilter(
             Collection<Condition> conditions,
             Map<Id, BackendEntry> entries) {
-        assert conditions.size() > 0;
+        assert !conditions.isEmpty();
 
         Map<Id, BackendEntry> rs = new HashMap<>();
 

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/backend/store/memory/InMemoryDBTables.java

@@ -181,7 +181,7 @@ protected Map<Id, BackendEntry> queryByIdRange(
         private Map<Id, BackendEntry> queryEdgeById(
                 Collection<Id> ids, boolean prefix,
                 Map<Id, BackendEntry> entries) {
-            assert ids.size() > 0;
+            assert !ids.isEmpty();
             Map<Id, BackendEntry> rs = InsertionOrderUtil.newMap();
 
             for (Id id : ids) {

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/backend/store/ram/RamTable.java

@@ -306,9 +306,7 @@ public Iterator<HugeEdge> query(Query query) {
             ConditionQuery cq = cqs.get(0);
             return this.query(cq);
         }
-        return new FlatMapperIterator<>(cqs.iterator(), cq -> {
-            return this.query(cq);
-        });
+        return new FlatMapperIterator<>(cqs.iterator(), this::query);
     }
 
     private Iterator<HugeEdge> query(ConditionQuery query) {
@@ -540,7 +538,7 @@ protected long load(Iterator<Vertex> vertices) {
 
         private void addVertex(Id vertex) {
             Id lastId = IdGenerator.ZERO;
-            if (this.vertices.size() > 0) {
+            if (!this.vertices.isEmpty()) {
                 lastId = this.vertices.get(this.vertices.size() - 1);
             }
             LOG.info("scan from hbase source {} lastId value: {} compare {} size {}",

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/backend/tx/GraphIndexTransaction.java

@@ -1704,7 +1704,7 @@ public String toString() {
             }
 
             private static Query parent(Collection<Query> queries) {
-                if (queries.size() > 0) {
+                if (!queries.isEmpty()) {
                     // Chose the first one as origin query (any one is OK)
                     return queries.iterator().next();
                 }

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/backend/tx/GraphTransaction.java

@@ -180,23 +180,23 @@ public boolean hasUpdate() {
     public boolean hasUpdate(HugeType type, Action action) {
         if (type.isVertex()) {
             if (action == Action.DELETE) {
-                if (this.removedVertices.size() > 0) {
+                if (!this.removedVertices.isEmpty()) {
                     return true;
                 }
             } else {
-                if (this.addedVertices.size() > 0 ||
-                    this.updatedVertices.size() > 0) {
+                if (!this.addedVertices.isEmpty() ||
+                    !this.updatedVertices.isEmpty()) {
                     return true;
                 }
             }
         } else if (type.isEdge()) {
             if (action == Action.DELETE) {
-                if (this.removedEdges.size() > 0) {
+                if (!this.removedEdges.isEmpty()) {
                     return true;
                 }
             } else {
-                if (this.addedEdges.size() > 0 ||
-                    this.updatedEdges.size() > 0) {
+                if (!this.addedEdges.isEmpty() ||
+                    !this.updatedEdges.isEmpty()) {
                     return true;
                 }
             }
@@ -300,16 +300,16 @@ protected final boolean removingEdgeOwner(HugeEdge edge) {
     @Override
     protected BackendMutation prepareCommit() {
         // Serialize and add updates into super.deletions
-        if (this.removedVertices.size() > 0 || this.removedEdges.size() > 0) {
+        if (!this.removedVertices.isEmpty() || !this.removedEdges.isEmpty()) {
             this.prepareDeletions(this.removedVertices, this.removedEdges);
         }
 
-        if (this.addedProps.size() > 0 || this.removedProps.size() > 0) {
+        if (!this.addedProps.isEmpty() || !this.removedProps.isEmpty()) {
             this.prepareUpdates(this.addedProps, this.removedProps);
         }
 
         // Serialize and add updates into super.additions
-        if (this.addedVertices.size() > 0 || this.addedEdges.size() > 0) {
+        if (!this.addedVertices.isEmpty() || !this.addedEdges.isEmpty()) {
             this.prepareAdditions(this.addedVertices, this.addedEdges);
         }
 
@@ -690,7 +690,7 @@ public void removeVertex(HugeVertex vertex) {
         // Override vertices in local `addedVertices`
         this.addedVertices.remove(vertex.id());
         // Force load vertex to ensure all properties are loaded (refer to #2181)
-        if (vertex.schemaLabel().indexLabels().size() > 0) {
+        if (!vertex.schemaLabel().indexLabels().isEmpty()) {
             vertex.forceLoad();
         }
         // Collect the removed vertex
@@ -710,7 +710,7 @@ public Iterator<Vertex> queryAdjacentVertices(Iterator<Edge> edges) {
             for (Edge edge : batchEdges) {
                 vertexIds.add(((HugeEdge) edge).otherVertex().id());
             }
-            assert vertexIds.size() > 0;
+            assert !vertexIds.isEmpty();
             return this.queryAdjacentVertices(vertexIds.toArray());
         });
     }

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/job/algorithm/comm/LouvainTraverser.java

@@ -536,7 +536,7 @@ private boolean allMembersExist(Collection<Pair<Community, Set<Id>>> comms,
         for (Pair<Community, Set<Id>> comm : comms) {
             all.removeAll(comm.getRight());
         }
-        if (all.size() > 0) {
+        if (!all.isEmpty()) {
             LOG.warn("Lost members of last pass: {}", all);
         }
         return all.isEmpty();
@@ -649,7 +649,7 @@ public Collection<Object> showCommunity(String community) {
         final String C_PASS0 = labelOfPassN(0);
         Collection<Object> comms = Collections.singletonList(community);
         boolean reachPass0 = false;
-        while (comms.size() > 0 && !reachPass0) {
+        while (!comms.isEmpty() && !reachPass0) {
             Iterator<Vertex> subComms = this.vertices(comms.iterator());
             comms = new HashSet<>();
             while (subComms.hasNext()) {
@@ -703,7 +703,7 @@ public long clearPass(int pass) {
         if (pass < 0) {
             // drop edges of all pass
             List<String> els = this.cpassEdgeLabels();
-            if (els.size() > 0) {
+            if (!els.isEmpty()) {
                 String first = els.remove(0);
                 te = te.hasLabel(first, els.toArray(new String[0]));
                 this.drop(te);
@@ -727,7 +727,7 @@ public long clearPass(int pass) {
         if (pass < 0) {
             // drop vertices of all pass
             List<String> vls = this.cpassVertexLabels();
-            if (vls.size() > 0) {
+            if (!vls.isEmpty()) {
                 String first = vls.remove(0);
                 tv = tv.hasLabel(first, vls.toArray(new String[0]));
                 this.drop(tv);

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/job/algorithm/comm/LpaAlgorithm.java

@@ -203,7 +203,7 @@ private String voteCommunityOfVertex(Vertex vertex, String edgeLabel,
             }
 
             // isolated vertex
-            if (labels.size() == 0) {
+            if (labels.isEmpty()) {
                 return this.labelOfVertex(vertex);
             }
 

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/job/algorithm/rank/PageRankAlgorithm.java

@@ -196,7 +196,7 @@ private long initRankMap() {
 
         private void contributeToAdjacentVertices(Id sourceVertexId,
                                                   List<Id> adjacentVertices) {
-            if (adjacentVertices.size() == 0) {
+            if (adjacentVertices.isEmpty()) {
                 return;
             }
             DoublePair sourcePair = this.vertexRankMap.get(sourceVertexId);

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/schema/EdgeLabel.java

@@ -105,7 +105,7 @@ public boolean checkLinkEqual(Id sourceLabel, Id targetLabel) {
     }
 
     public boolean existSortKeys() {
-        return this.sortKeys.size() > 0;
+        return !this.sortKeys.isEmpty();
     }
 
     public List<Id> sortKeys() {

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/schema/builder/VertexLabelBuilder.java

@@ -476,7 +476,7 @@ private void checkNullableKeys(Action action) {
 
     private void checkIdStrategy() {
         IdStrategy strategy = this.idStrategy;
-        boolean hasPrimaryKey = this.primaryKeys.size() > 0;
+        boolean hasPrimaryKey = !this.primaryKeys.isEmpty();
         switch (strategy) {
             case DEFAULT:
                 if (hasPrimaryKey) {

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/structure/HugeElement.java

@@ -252,7 +252,7 @@ public boolean hasProperty(Id key) {
     }
 
     public boolean hasProperties() {
-        return this.properties.size() > 0;
+        return !this.properties.isEmpty();
     }
 
     public int sizeOfProperties() {

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/structure/HugeVertex.java

@@ -224,7 +224,7 @@ protected List<Object> primaryValues() {
     }
 
     public boolean existsEdges() {
-        return this.edges.size() > 0;
+        return !this.edges.isEmpty();
     }
 
     public Collection<HugeEdge> getEdges() {

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/traversal/algorithm/NeighborRankTraverser.java

@@ -214,7 +214,7 @@ private Ranks contributeNewLayer(List<Adjacencies> adjacencies,
 
     private List<Map<Id, Double>> topRanks(List<Ranks> ranks,
                                            List<Step> steps) {
-        assert ranks.size() > 0;
+        assert !ranks.isEmpty();
         List<Map<Id, Double>> results = newList(ranks.size());
         // The first layer is root node so skip i=0
         results.add(ranks.get(0));

hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/traversal/optimize/HugeVertexStep.java

@@ -151,7 +151,7 @@ protected ConditionQuery constructEdgesQuery(
                 withEdgeCond = false;
             } else {
                 // Partial sysprop conditions are in sort-keys
-                assert query.userpropKeys().size() > 0;
+                assert !query.userpropKeys().isEmpty();
             }
         }