docs(java): fill Java API reference gaps (#3615)

## Summary This updates the Java API reference to close the documentation gaps that can be fixed from the current Java source and generated namespace API. The patch adds an empty table example, shows how to wrap returned Arrow IPC query bytes in a reusable `ArrowFileReader` helper, and documents the Java index operations that are currently exposed by the namespace client: vector indexes, scalar indexes, full text search indexes, and listing indexes. ## Issue Links Fixes https://github.com/lancedb/docs/issues/157 Fixes https://github.com/lancedb/docs/issues/160 Partially addresses https://github.com/lancedb/docs/issues/159 by documenting the index parameters currently exposed by Java. The requested `num_partitions` example is still blocked because `CreateTableIndexRequest` does not expose IVF training parameters yet. Not included: https://github.com/lancedb/docs/issues/158. The current Java docs and source remain remote namespace oriented, so local DB connection documentation should wait until the Java local DB API is available and can be verified. ## Validation - Built the Java core module with OpenJDK 17: `./mvnw -pl lancedb-core -am -DskipTests compile` - Checked the Markdown diff: `git diff --check -- docs/src/java/java.md` The Java build succeeds. It still reports pre-existing checkstyle warnings in the namespace client builder, but the Maven build is green.
2026-08-18 03:58:26 +00:00 · 2026-07-22 17:05:58 -04:00
parent 0bd0944062
commit d6f9f8560e
1 changed files with 164 additions and 29 deletions
@@ -249,6 +249,57 @@ try (BufferAllocator allocator = new RootAllocator();
 }
 ```

+### Creating an Empty Table
+
+To create an empty table, send an Arrow IPC stream that contains the table schema and no record batches.
+The schema in the IPC stream becomes the table schema, and rows can be inserted later.
+
+```java
+import org.lance.namespace.model.CreateTableRequest;
+import org.lance.namespace.model.CreateTableResponse;
+import org.apache.arrow.memory.BufferAllocator;
+import org.apache.arrow.memory.RootAllocator;
+import org.apache.arrow.vector.VectorSchemaRoot;
+import org.apache.arrow.vector.ipc.ArrowStreamWriter;
+import org.apache.arrow.vector.types.FloatingPointPrecision;
+import org.apache.arrow.vector.types.pojo.ArrowType;
+import org.apache.arrow.vector.types.pojo.Field;
+import org.apache.arrow.vector.types.pojo.FieldType;
+import org.apache.arrow.vector.types.pojo.Schema;
+
+import java.io.ByteArrayOutputStream;
+import java.nio.channels.Channels;
+import java.util.Arrays;
+
+Schema schema = new Schema(Arrays.asList(
+    new Field("id", FieldType.nullable(new ArrowType.Int(32, true)), null),
+    new Field("name", FieldType.nullable(new ArrowType.Utf8()), null),
+    new Field("embedding",
+        FieldType.nullable(new ArrowType.FixedSizeList(128)),
+        Arrays.asList(new Field("item",
+            FieldType.nullable(new ArrowType.FloatingPoint(FloatingPointPrecision.SINGLE)),
+            null)))
+));
+
+byte[] emptyTableData;
+try (BufferAllocator allocator = new RootAllocator();
+     VectorSchemaRoot root = VectorSchemaRoot.create(schema, allocator)) {
+    root.setRowCount(0);
+
+    ByteArrayOutputStream out = new ByteArrayOutputStream();
+    try (ArrowStreamWriter writer = new ArrowStreamWriter(root, null, Channels.newChannel(out))) {
+        writer.start();
+        writer.end();
+    }
+    emptyTableData = out.toByteArray();
+}
+
+CreateTableRequest request = new CreateTableRequest();
+request.setId(Arrays.asList("my_namespace", "empty_table"));
+
+CreateTableResponse response = namespaceClient.createTable(request, emptyTableData);
+```
+
 ### Insert

 ```java
@@ -431,9 +482,88 @@ query.setVector(vector);
 byte[] result = namespaceClient.queryTable(query);
 ```

-### Reading Query Results
+## Indexing

-Query results are returned in Apache Arrow IPC file format. Here's how to read them:
+The Java SDK exposes the REST namespace index operations through the same `LanceNamespace` client.
+Index creation runs asynchronously, so use `listTableIndices` or `describeTableIndexStats` to check progress.
+
+### Creating a Vector Index
+
+```java
+import org.lance.namespace.model.CreateTableIndexRequest;
+import org.lance.namespace.model.CreateTableIndexResponse;
+
+CreateTableIndexRequest request = new CreateTableIndexRequest();
+request.setId(Arrays.asList("my_namespace", "my_table"));
+request.setColumn("embedding");
+request.setIndexType("IVF_PQ");
+request.setDistanceType("cosine");
+request.setName("embedding_idx");
+
+CreateTableIndexResponse response = namespaceClient.createTableIndex(request);
+System.out.println("Index transaction: " + response.getTransactionId());
+```
+
+### Creating a Scalar Index
+
+```java
+import org.lance.namespace.model.CreateTableIndexRequest;
+import org.lance.namespace.model.CreateTableScalarIndexResponse;
+
+CreateTableIndexRequest request = new CreateTableIndexRequest();
+request.setId(Arrays.asList("my_namespace", "my_table"));
+request.setColumn("category");
+request.setIndexType("BTREE");
+request.setName("category_idx");
+
+CreateTableScalarIndexResponse response = namespaceClient.createTableScalarIndex(request);
+System.out.println("Index transaction: " + response.getTransactionId());
+```
+
+### Creating a Full Text Search Index
+
+```java
+import org.lance.namespace.model.CreateTableIndexRequest;
+import org.lance.namespace.model.CreateTableScalarIndexResponse;
+
+CreateTableIndexRequest request = new CreateTableIndexRequest();
+request.setId(Arrays.asList("my_namespace", "my_table"));
+request.setColumn("text_column");
+request.setIndexType("FTS");
+request.setName("text_idx");
+request.setBaseTokenizer("simple");
+request.setLowerCase(true);
+request.setWithPosition(true);
+
+CreateTableScalarIndexResponse response = namespaceClient.createTableScalarIndex(request);
+System.out.println("Index transaction: " + response.getTransactionId());
+```
+
+### Listing Indexes
+
+```java
+import org.lance.namespace.model.IndexContent;
+import org.lance.namespace.model.ListTableIndicesRequest;
+import org.lance.namespace.model.ListTableIndicesResponse;
+
+ListTableIndicesRequest request = new ListTableIndicesRequest();
+request.setId(Arrays.asList("my_namespace", "my_table"));
+
+ListTableIndicesResponse response = namespaceClient.listTableIndices(request);
+for (IndexContent index : response.getIndexes()) {
+    System.out.println(index.getIndexName() + ": " + index.getStatus());
+}
+```
+
+!!! note
+    The current Java namespace API exposes index type, index name, distance type, and full text search tokenizer options.
+    IVF training parameters such as `num_partitions` are not exposed by `CreateTableIndexRequest` yet.
+    To make those configurable from Java, the namespace API must add those fields first.
+
+## Reading Query Results
+
+Query results are returned as bytes in Apache Arrow IPC file format. Put the byte-channel
+adapter behind a small helper so query code can work with `ArrowFileReader` directly:

 ```java
 import org.apache.arrow.vector.ipc.ArrowFileReader;
@@ -441,45 +571,50 @@ import org.apache.arrow.vector.VectorSchemaRoot;
 import org.apache.arrow.memory.BufferAllocator;
 import org.apache.arrow.memory.RootAllocator;

+import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.nio.channels.SeekableByteChannel;

-// Helper class to read Arrow data from byte array
-class ByteArraySeekableByteChannel implements SeekableByteChannel {
-    private final byte[] data;
-    private long position = 0;
-    private boolean isOpen = true;
-
-    public ByteArraySeekableByteChannel(byte[] data) {
-        this.data = data;
+final class ArrowIpc {
+    static ArrowFileReader openFileReader(byte[] data, BufferAllocator allocator) throws IOException {
+        return new ArrowFileReader(new ByteArraySeekableByteChannel(data), allocator);
    }

-    @Override
-    public int read(ByteBuffer dst) {
-        int remaining = dst.remaining();
-        int available = (int) (data.length - position);
-        if (available <= 0) return -1;
-        int toRead = Math.min(remaining, available);
-        dst.put(data, (int) position, toRead);
-        position += toRead;
-        return toRead;
-    }
+    private static final class ByteArraySeekableByteChannel implements SeekableByteChannel {
+        private final byte[] data;
+        private long position = 0;
+        private boolean isOpen = true;

-    @Override public long position() { return position; }
-    @Override public SeekableByteChannel position(long newPosition) { position = newPosition; return this; }
-    @Override public long size() { return data.length; }
-    @Override public boolean isOpen() { return isOpen; }
-    @Override public void close() { isOpen = false; }
-    @Override public int write(ByteBuffer src) { throw new UnsupportedOperationException(); }
-    @Override public SeekableByteChannel truncate(long size) { throw new UnsupportedOperationException(); }
+        private ByteArraySeekableByteChannel(byte[] data) {
+            this.data = data;
+        }
+
+        @Override
+        public int read(ByteBuffer dst) {
+            int remaining = dst.remaining();
+            int available = (int) (data.length - position);
+            if (available <= 0) return -1;
+            int toRead = Math.min(remaining, available);
+            dst.put(data, (int) position, toRead);
+            position += toRead;
+            return toRead;
+        }
+
+        @Override public long position() { return position; }
+        @Override public SeekableByteChannel position(long newPosition) { position = newPosition; return this; }
+        @Override public long size() { return data.length; }
+        @Override public boolean isOpen() { return isOpen; }
+        @Override public void close() { isOpen = false; }
+        @Override public int write(ByteBuffer src) { throw new UnsupportedOperationException(); }
+        @Override public SeekableByteChannel truncate(long size) { throw new UnsupportedOperationException(); }
+    }
 }

 // Read query results
 byte[] queryResult = namespaceClient.queryTable(query);

 try (BufferAllocator allocator = new RootAllocator();
-     ArrowFileReader reader = new ArrowFileReader(
-         new ByteArraySeekableByteChannel(queryResult), allocator)) {
+     ArrowFileReader reader = ArrowIpc.openFileReader(queryResult, allocator)) {

    for (int i = 0; i < reader.getRecordBlocks().size(); i++) {
        reader.loadRecordBatch(reader.getRecordBlocks().get(i));