Add description to Java pipeline examples

Java/src/main/java/jdbc/ReadPartitionsJdbc.java

@@ -31,6 +31,12 @@
 import java.sql.ResultSet;
 import java.util.Objects;
 
+/**
+ * Pipeline for reading data from a JDBC source with partitioning. The pipeline reads records from a
+ * specified table using the {@code JdbcIO.readWithPartitions()} transform, which partitions the
+ * table based on the specified number of partitions, the partition column, and the lower and upper
+ * bounds for the partitioning.
+ */
 public class ReadPartitionsJdbc {
 
   private static final Logger LOG = LoggerFactory.getLogger(ReadPartitionsJdbc.class);

Java/src/main/java/jdbc/WriteJdbc.java

@@ -28,6 +28,11 @@
 import java.util.Arrays;
 import java.util.List;
 
+/**
+ * The pipeline uses the {@code JdbcIO.write()} transform to insert {@code ExampleRow} instances
+ * into a specified JDBC table using {@code PreparedStatementSetter} to map {@code ExampleRow}
+ * fields to the SQL statement parameters.
+ */
 public class WriteJdbc {
 
     /**

Java/src/main/java/mongodb/ReadMongoDB.java

@@ -28,6 +28,9 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+/**
+ * Pipeline for reading data from MongoDB using the {@code MongoDbIO.read()} transform.
+ */
 public class ReadMongoDB {
 
     private static final Logger LOG =

Java/src/main/java/mongodb/WriteMongoDB.java

@@ -28,6 +28,9 @@
 import java.util.Arrays;
 import java.util.List;
 
+/**
+ * Pipeline for writing data to MongoDB using the {@code MongoDbIO.write()} transform.
+ */
 public class WriteMongoDB {
 
     private static final String ID_COLUMN = "id";

Java/src/main/java/parquet/ReadParquet.java

@@ -32,6 +32,9 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+/**
+ * Pipeline for reading data from Parquet files using the{@code ParquetIO.read()} transform.
+ */
 public class ReadParquet {
 
     private static final Logger LOG = LoggerFactory.getLogger(ReadParquet.class);

Java/src/main/java/parquet/WriteParquet.java

@@ -34,6 +34,9 @@
 import org.apache.beam.sdk.transforms.MapElements;
 import org.apache.beam.sdk.transforms.SimpleFunction;
 
+/**
+ * Pipeline for writing data to Parquet files using the {@code ParquetIO.sink()} sink.
+ */
 public class WriteParquet {
 
     /** Represents an Example Parquet record. */

Java/src/main/java/spanner/ReadWithTransactionSpanner.java

@@ -33,6 +33,11 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+/**
+ * Pipeline for reading data from Google Cloud Spanner with transactional consistency. The pipeline
+ * retrieves records from a specified Spanner table, using a high-priority transaction bound to the
+ * strong timestamp consistency mode.
+ */
 public class ReadWithTransactionSpanner {
 
     private static final Logger LOG = LoggerFactory.getLogger(ReadWithTransactionSpanner.class);

Java/src/main/java/tfrecord/ReadTFRecord.java

@@ -28,6 +28,9 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+/**
+ * Pipeline for reading data from TFRecord files using the {@code TFRecordIO.read()} transform.
+ */
 public class ReadTFRecord {
 
     private static final Logger LOG =

Java/src/main/java/tfrecord/WriteTFRecord.java

@@ -30,6 +30,9 @@
 import java.util.Arrays;
 import java.util.List;
 
+/**
+ * Pipeline for writing data to TFRecord files using the {@code TFRecordIO.write()} transform.
+ */
 public class WriteTFRecord {
 
     /**