Add Builder in FieldDataStats and refactor usage

Signed-off-by: Jean Kim <bgshhd95@gmail.com>

Author: pado0

server/src/main/java/org/opensearch/index/fielddata/FieldDataStats.java

@@ -67,12 +67,28 @@ public FieldDataStats() {
 
     }
 
+    /**
+     * Private constructor that takes a builder.
+     * This is the sole entry point for creating a new FieldDataStats object.
+     * @param builder The builder instance containing all the values.
+     */
+    private FieldDataStats(Builder builder) {
+        this.memorySize = builder.memorySize;
+        this.evictions = builder.evictions;
+        this.fields = builder.fields;
+    }
+
     public FieldDataStats(StreamInput in) throws IOException {
         memorySize = in.readVLong();
         evictions = in.readVLong();
         fields = in.readOptionalWriteable(FieldMemoryStats::new);
     }
 
+    /**
+     * This constructor will be deprecated starting in version 3.4.0.
+     * Use {@link FieldDataStats.Builder} instead.
+     */
+    @Deprecated
     public FieldDataStats(long memorySize, long evictions, @Nullable FieldMemoryStats fields) {
         this.memorySize = memorySize;
         this.evictions = evictions;
@@ -111,6 +127,41 @@ public FieldMemoryStats getFields() {
         return fields;
     }
 
+    /**
+     * Builder for the {@link FieldDataStats} class.
+     * Provides a fluent API for constructing a FieldDataStats object.
+     */
+    public static class Builder {
+        private long memorySize = 0;
+        private long evictions = 0;
+        private FieldMemoryStats fields = null;
+
+        public Builder() {}
+
+        public Builder memorySize(long memorySize) {
+            this.memorySize = memorySize;
+            return this;
+        }
+
+        public Builder evictions(long evictions) {
+            this.evictions = evictions;
+            return this;
+        }
+
+        public Builder fields(@Nullable FieldMemoryStats fields) {
+            this.fields = fields;
+            return this;
+        }
+
+        /**
+         * Creates a {@link FieldDataStats} object from the builder's current state.
+         * @return A new FieldDataStats instance.
+         */
+        public FieldDataStats build() {
+            return new FieldDataStats(this);
+        }
+    }
+
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         out.writeVLong(memorySize);

server/src/main/java/org/opensearch/index/fielddata/ShardFieldData.java

@@ -67,11 +67,10 @@ public FieldDataStats stats(String... fields) {
                 }
             }
         }
-        return new FieldDataStats(
-            totalMetric.count(),
-            evictionsMetric.count(),
-            fieldTotals == null ? null : new FieldMemoryStats(fieldTotals)
-        );
+        return new FieldDataStats.Builder().memorySize(totalMetric.count())
+            .evictions(evictionsMetric.count())
+            .fields(fieldTotals == null ? null : new FieldMemoryStats(fieldTotals))
+            .build();
     }
 
     @Override

server/src/test/java/org/opensearch/action/admin/cluster/node/stats/NodeStatsTests.java

@@ -1373,7 +1373,10 @@ private CommonStats createRandomCommonStats() {
         commonStats.indexing = new IndexingStats();
         commonStats.completion = new CompletionStats();
         commonStats.flush = new FlushStats(randomLongBetween(0, 100), randomLongBetween(0, 100), randomLongBetween(0, 100));
-        commonStats.fieldData = new FieldDataStats(randomLongBetween(0, 100), randomLongBetween(0, 100), null);
+        commonStats.fieldData = new FieldDataStats.Builder().memorySize(randomLongBetween(0, 100))
+            .evictions(randomLongBetween(0, 100))
+            .fields(null)
+            .build();
         commonStats.queryCache = new QueryCacheStats(
             randomLongBetween(0, 100),
             randomLongBetween(0, 100),

server/src/test/java/org/opensearch/action/admin/cluster/stats/ClusterStatsNodesTests.java

@@ -372,7 +372,10 @@ private CommonStats createRandomCommonStats() {
         commonStats.indexing = new IndexingStats();
         commonStats.completion = new CompletionStats();
         commonStats.flush = new FlushStats(randomLongBetween(0, 100), randomLongBetween(0, 100), randomLongBetween(0, 100));
-        commonStats.fieldData = new FieldDataStats(randomLongBetween(0, 100), randomLongBetween(0, 100), null);
+        commonStats.fieldData = new FieldDataStats.Builder().memorySize(randomLongBetween(0, 100))
+            .evictions(randomLongBetween(0, 100))
+            .fields(null)
+            .build();
         commonStats.queryCache = new QueryCacheStats(
             randomLongBetween(0, 100),
             randomLongBetween(0, 100),

server/src/test/java/org/opensearch/action/admin/cluster/stats/ClusterStatsResponseTests.java

@@ -240,7 +240,10 @@ private CommonStats createRandomCommonStats() {
         commonStats.indexing = new IndexingStats();
         commonStats.completion = new CompletionStats();
         commonStats.flush = new FlushStats(randomLongBetween(0, 100), randomLongBetween(0, 100), randomLongBetween(0, 100));
-        commonStats.fieldData = new FieldDataStats(randomLongBetween(0, 100), randomLongBetween(0, 100), null);
+        commonStats.fieldData = new FieldDataStats.Builder().memorySize(randomLongBetween(0, 100))
+            .evictions(randomLongBetween(0, 100))
+            .fields(null)
+            .build();
         commonStats.queryCache = new QueryCacheStats(
             randomLongBetween(0, 100),
             randomLongBetween(0, 100),

server/src/test/java/org/opensearch/index/fielddata/FieldDataStatsTests.java

@@ -43,7 +43,10 @@ public class FieldDataStatsTests extends OpenSearchTestCase {
 
     public void testSerialize() throws IOException {
         FieldMemoryStats map = randomBoolean() ? null : FieldMemoryStatsTests.randomFieldMemoryStats();
-        FieldDataStats stats = new FieldDataStats(randomNonNegativeLong(), randomNonNegativeLong(), map);
+        FieldDataStats stats = new FieldDataStats.Builder().memorySize(randomNonNegativeLong())
+            .evictions(randomNonNegativeLong())
+            .fields(map)
+            .build();
         BytesStreamOutput out = new BytesStreamOutput();
         stats.writeTo(out);
         StreamInput input = out.bytes().streamInput();