Prompt:
Write a sample Java code snippet that writes data to a Google Spanner table using Apache Beam.

Response:
Your Apache Beam pipeline can write data to a Spanner table using the Apache Beam SpannerIO connector.

Here is an example of how to use the SpannerIO connector to accomplish this:

```java
 package spanner;

 import com.google.cloud.spanner.Mutation;
 import org.apache.beam.runners.dataflow.options.DataflowPipelineOptions;
 import org.apache.beam.sdk.Pipeline;
 import org.apache.beam.sdk.io.gcp.spanner.SpannerIO;
 import org.apache.beam.sdk.options.Default;
 import org.apache.beam.sdk.options.Description;
 import org.apache.beam.sdk.options.PipelineOptionsFactory;
 import org.apache.beam.sdk.transforms.Create;
 import org.apache.beam.sdk.transforms.DoFn;
 import org.apache.beam.sdk.transforms.ParDo;
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

 import java.util.Arrays;
 import java.util.List;

 // Pipeline to write data to a Spanner table.
 public class WriteSpannerTable {

     private static final Logger LOG = LoggerFactory.getLogger(WriteSpannerTable.class);

    // Pipeline options for writing to Spanner tables.
     public interface WriteSpannerTableOptions extends DataflowPipelineOptions {
         @Description("Spanner Instance ID")
         @Default.String("spanner-instance")
         String getInstanceId();

         void setInstanceId(String value);

         @Description("Spanner Database Name")
         @Default.String("spanner-db")
         String getDatabaseName();

         void setDatabaseName(String value);

         @Description("Spanner Table Name")
         @Default.String("spanner-table")
         String getTableName();

         void setTableName(String value);

         @Nullable
         @Description("Spanner Project ID")
         String getSpannerProjectId();

         void setSpannerProjectId(String value);
     }

     public static void main(String[] args) {
        // Parse the pipeline options from the command line.
        WriteSpannerTableOptions options = PipelineOptionsFactory.fromArgs(args).withValidation().as(WriteSpannerTableOptions.class);

        // Create the pipeline.
         Pipeline p = Pipeline.create(options);

        // Sample data to write to the Spanner table.
         final List<String> elements = Arrays.asList(
                 "1, January, $1000",
                 "2, February, $2000",
                 "3, March , $3000",
                 "4, April, $4000",
         );

         String table = options.getTableName();

        // Get the project ID from the pipeline options or the default project.
         String project = (options.getSpannerProjectId() == null) ? options.getProject() : options.getSpannerProjectId();

         p
                // Create a PCollection of strings from the sample data.
                 .apply(Create.of(elements))
                 // Convert the strings to Spanner mutations.
                 .apply("To Spanner Mutation", ParDo.of(new DoFn<String, Mutation>() {
                             @ProcessElement
                             public void processElement(ProcessContext c) {
                                 String[] records = c.element().split(", ");
                                 Long recordId = Long.parseLong(records[0]);
                                // Create a Spanner mutation for each record.
                                 Mutation mutation = Mutation.newInsertOrUpdateBuilder(table)
                                         .set("id").to(recordId)
                                         .set("month").to(records[1])
                                         .set("amount").to(records[2])
                                         .build();

                                 c.output(mutation);
                             }
                         })
                 )
                 // Write the mutations to the Spanner table.
                 .apply(SpannerIO.write()
                         .withInstanceId(options.getInstanceId())
                         .withDatabaseId(options.getDatabaseName())
                         .withProjectId(project)
                 );
        // Execute the pipeline.
         p.run();
     }
 }
```

This code snippet utilizes the pipeline options pattern to parse command-line arguments.