Prepare your local Java environment

1. Install the following on your development machine if they are not already installed:

   • Java 8 JDK (download).
   • Maven 3 (download).

2. Clone the sample app repository to your local machine:

   git clone https://github.com/googleapis/java-spanner.git
   

3. Change to the directory that contains the Spanner sample code:

   cd java-spanner/samples/snippets
   

4. Generate the sample JAR file:

   mvn clean package
   

Create an instance

When you first use Spanner, you must create an instance, which is an allocation of resources that are used by Spanner databases. When you create an instance, you choose an instance configuration, which determines where your data is stored, and also the number of nodes to use, which determines the amount of serving and storage resources in your instance.

See Create an instance to learn how to create a Spanner instance using any of the following methods. You can name your instance test-instance to use it with other topics in this document that reference an instance named test-instance.

• The Google Cloud CLI
• The Google Cloud console
• A client library (C++, C#, Go, Java, Node.js, PHP, Python, or Ruby)

Look through sample files

The samples repository contains a sample that shows how to use Spanner with Java.

Create a database

java -jar target/spanner-snippets/spanner-google-cloud-samples.jar \
createdatabase test-instance example-db

java -jar target/spanner-snippets/spanner-google-cloud-samples.jar \
createpgdatabase test-instance example-db

You should see:

Created database [example-db]

The following code creates a database and two tables in the database.

The next step is to write data to your database.

Create a database client

Before you can do reads or writes, you must create a DatabaseClient. You can think of a DatabaseClient as a database connection: all of your interactions with Spanner must go through a DatabaseClient. Typically you create a DatabaseClient when your application starts up, then you re-use that DatabaseClient to read, write, and execute transactions.

Each client uses resources in Spanner, so it is good practice to close unneeded clients by calling close().

Read more in the DatabaseClient Javadoc reference.

Write data with DML

You can insert data using Data Manipulation Language (DML) in a read-write transaction.

You use the executeUpdate() method to execute a DML statement.

Run the sample using the writeusingdml argument.

java -jar target/spanner-snippets/spanner-google-cloud-samples.jar \
    writeusingdml test-instance example-db

You should see:

4 records inserted.

Write data with mutations

You can also insert data using mutations.

You can write data using a Mutation object. A Mutation object is a container for mutation operations. A Mutation represents a sequence of inserts, updates, and deletes that Spanner applies atomically to different rows and tables in a Spanner database.

The newInsertBuilder() method in the Mutation class constructs an INSERT mutation, which inserts a new row in a table. If the row already exists, the write fails. Alternatively, you can use the newInsertOrUpdateBuilder method to construct an INSERT_OR_UPDATE mutation, which updates column values if the row already exists.

The write() method in the DatabaseClient class writes the mutations. All mutations in a single batch are applied atomically.

This code shows how to write the data using mutations:

Run the sample using the write argument.

java -jar target/spanner-snippets/spanner-google-cloud-samples.jar \
    write test-instance example-db

You should see the command run successfully.

Query data using SQL

Spanner supports a SQL interface for reading data, which you can access on the command line using the Google Cloud CLI or programmatically using the Spanner client library for Java.

On the command line

Execute the following SQL statement to read the values of all columns from the Albums table:

gcloud spanner databases execute-sql example-db --instance=test-instance \
    --sql='SELECT SingerId, AlbumId, AlbumTitle FROM Albums'

The result shows:

SingerId AlbumId AlbumTitle
1        1       Total Junk
1        2       Go, Go, Go
2        1       Green
2        2       Forever Hold Your Peace
2        3       Terrified

Use the Spanner client library for Java

In addition to executing a SQL statement on the command line, you can issue the same SQL statement programmatically using the Spanner client library for Java.

The following methods and classes are used to run the SQL query:

• The singleUse() method in the DatabaseClient class: use this to read the value of one or more columns from one or more rows in a Spanner table. singleUse() returns a ReadContext object, which is used for running a read or SQL statement.
• The executeQuery() method of the ReadContext class: use this method to execute a query against a database.
• The Statement class: use this to construct a SQL string.
• The ResultSet class: use this to access the data returned by a SQL statement or read call.

Here's how to issue the query and access the data:

Run the sample using the query argument.

java -jar target/spanner-snippets/spanner-google-cloud-samples.jar \
    query test-instance example-db

You should see the following result:

1 1 Total Junk
1 2 Go, Go, Go
2 1 Green
2 2 Forever Hold Your Peace
2 3 Terrified

Query using a SQL parameter

If your application has a frequently executed query, you can improve its performance by parameterizing it. The resulting parametric query can be cached and reused, which reduces compilation costs. For more information, see Use query parameters to speed up frequently executed queries.

Here is an example of using a parameter in the WHERE clause to query records containing a specific value for LastName.

Run the sample using the queryWithParameter argument.

java -jar target/spanner-snippets/spanner-google-cloud-samples.jar \
    querywithparameter test-instance example-db

You should see the following result:

12 Melissa Garcia

Read data using the read API

In addition to Spanner's SQL interface, Spanner also supports a read interface.

Use the read() method of the ReadContext class to read rows from the database. Use a KeySet object to define a collection of keys and key ranges to read.

Here's how to read the data:

Run the sample using the read argument.

java -jar target/spanner-snippets/spanner-google-cloud-samples.jar \
    read test-instance example-db

You should see output similar to:

1 1 Total Junk
1 2 Go, Go, Go
2 1 Green
2 2 Forever Hold Your Peace
2 3 Terrified

Update the database schema

Assume you need to add a new column called MarketingBudget to the Albums table. Adding a new column to an existing table requires an update to your database schema. Spanner supports schema updates to a database while the database continues to serve traffic. Schema updates don't require taking the database offline and they don't lock entire tables or columns; you can continue writing data to the database during the schema update. Read more about supported schema updates and schema change performance in Make schema updates.

Add a column

You can add a column on the command line using the Google Cloud CLI or programmatically using the Spanner client library for Java.

On the command line

Use the following ALTER TABLE command to add the new column to the table:

gcloud spanner databases ddl update example-db --instance=test-instance \
    --ddl='ALTER TABLE Albums ADD COLUMN MarketingBudget INT64'

gcloud spanner databases ddl update example-db --instance=test-instance \
    --ddl='ALTER TABLE Albums ADD COLUMN MarketingBudget BIGINT'

You should see:

Schema updating...done.

Use the Spanner client library for Java

Use the updateDatabaseDdl() method of the DatabaseAdminClient class to modify the schema:

Run the sample using the addmarketingbudget argument.

java -jar target/spanner-snippets/spanner-google-cloud-samples.jar \
    addmarketingbudget test-instance example-db

You should see:

Added MarketingBudget column.

Write data to the new column

The following code writes data to the new column. It sets MarketingBudget to 100000 for the row keyed by Albums(1, 1) and to 500000 for the row keyed by Albums(2, 2).

Run the sample using the update argument.

java -jar target/spanner-snippets/spanner-google-cloud-samples.jar \
    update test-instance example-db

You can also execute a SQL query or a read call to fetch the values that you just wrote.

Here's the code to execute the query:

To execute this query, run the sample using the querymarketingbudget argument.

java -jar target/spanner-snippets/spanner-google-cloud-samples.jar \
    querymarketingbudget test-instance example-db

You should see:

1 1 100000
1 2 NULL
2 1 NULL
2 2 500000
2 3 NULL

Update data

You can update data using DML in a read-write transaction.

You use the executeUpdate() method to execute a DML statement.

Run the sample using the writewithtransactionusingdml argument.

java -jar target/spanner-snippets/spanner-google-cloud-samples.jar \
    writewithtransactionusingdml test-instance example-db

Use a secondary index

Suppose you wanted to fetch all rows of Albums that have AlbumTitle values in a certain range. You could read all values from the AlbumTitle column using a SQL statement or a read call, and then discard the rows that don't meet the criteria, but doing this full table scan is expensive, especially for tables with a lot of rows. Instead you can speed up the retrieval of rows when searching by non-primary key columns by creating a secondary index on the table.

Adding a secondary index to an existing table requires a schema update. Like other schema updates, Spanner supports adding an index while the database continues to serve traffic. Spanner automatically backfills the index with your existing data. Backfills might take a few minutes to complete, but you don't need to take the database offline or avoid writing to the indexed table during this process. For more details, see Add a secondary index.

After you add a secondary index, Spanner automatically uses it for SQL queries that are likely to run faster with the index. If you use the read interface, you must specify the index that you want to use.

Add a secondary index

You can add an index on the command line using the gcloud CLI or programmatically using the Spanner client library for Java.

On the command line

Use the following CREATE INDEX command to add an index to the database:

gcloud spanner databases ddl update example-db --instance=test-instance \
    --ddl='CREATE INDEX AlbumsByAlbumTitle ON Albums(AlbumTitle)'

You should see:

Schema updating...done.

Using the Spanner client library for Java

Use the updateDatabaseDdl() method of the DatabaseAdminClient class to add an index:

Run the sample using the addindex argument.

java -jar target/spanner-snippets/spanner-google-cloud-samples.jar \
    addindex test-instance example-db

Adding an index can take a few minutes. After the index is added, you should see:

Added the AlbumsByAlbumTitle index.

Read using the index

For SQL queries, Spanner automatically uses an appropriate index. In the read interface, you must specify the index in your request.

To use the index in the read interface, use the readUsingIndex() method of the ReadContext class.

The following code fetches all AlbumId, and AlbumTitle columns from the AlbumsByAlbumTitle index.

Run the sample using the readindex argument.

java -jar target/spanner-snippets/spanner-google-cloud-samples.jar \
    readindex test-instance example-db

You should see:

2 Forever Hold Your Peace
2 Go, Go, Go
1 Green
3 Terrified
1 Total Junk

Add an index for index-only reads

You might have noticed that the previous read example doesn't include reading the MarketingBudget column. This is because Spanner's read interface doesn't support the ability to join an index with a data table to look up values that are not stored in the index.

Create an alternate definition of AlbumsByAlbumTitle that stores a copy of MarketingBudget in the index.

On the command line

gcloud spanner databases ddl update example-db --instance=test-instance \
    --ddl='CREATE INDEX AlbumsByAlbumTitle2 ON Albums(AlbumTitle) STORING (MarketingBudget)

gcloud spanner databases ddl update example-db --instance=test-instance \
    --ddl='CREATE INDEX AlbumsByAlbumTitle2 ON Albums(AlbumTitle) INCLUDE (MarketingBudget)

Adding an index can take a few minutes. After the index is added, you should see:

Schema updating...done.

Using the Spanner client library for Java

Use the updateDatabaseDdl() method of the DatabaseAdminClient class to add an index with a STORING clause for GoogleSQL and INCLUDE clause for PostgreSQL:

Run the sample using the addstoringindex argument.

java -jar target/spanner-snippets/spanner-google-cloud-samples.jar \
    addstoringindex test-instance example-db

Adding an index can take a few minutes. After the index is added, you should see:

Added AlbumsByAlbumTitle2 index

Now you can execute a read that fetches all AlbumId, AlbumTitle, and MarketingBudget columns from the AlbumsByAlbumTitle2 index:

Run the sample using the readstoringindex argument.

java -jar target/spanner-snippets/spanner-google-cloud-samples.jar \
    readstoringindex test-instance example-db

You should see output similar to:

2 Forever Hold Your Peace 300000
2 Go, Go, Go NULL
1 Green NULL
3 Terrified NULL
1 Total Junk 300000

Retrieve data using read-only transactions

Suppose you want to execute more than one read at the same timestamp. Read-only transactions observe a consistent prefix of the transaction commit history, so your application always gets consistent data. Use a ReadOnlyTransaction object for executing read-only transactions. Use the readOnlyTransaction() method of the DatabaseClient class to get a ReadOnlyTransaction object.

The following shows how to run a query and perform a read in the same read-only transaction:

Run the sample using the readonlytransaction argument.

java -jar target/spanner-snippets/spanner-google-cloud-samples.jar \
    readonlytransaction test-instance example-db

You should see output similar to:

2 2 Forever Hold Your Peace
1 2 Go, Go, Go
2 1 Green
2 3 Terrified
1 1 Total Junk
1 1 Total Junk
1 2 Go, Go, Go
2 1 Green
2 2 Forever Hold Your Peace
2 3 Terrified

Cleanup

To avoid incurring additional charges to your Cloud Billing account for the resources used in this tutorial, drop the database and delete the instance that you created.

Delete the database

If you delete an instance, all databases within it are automatically deleted. This step shows how to delete a database without deleting an instance (you would still incur charges for the instance).

On the command line

gcloud spanner databases delete example-db --instance=test-instance

Using the Google Cloud console

1. Go to the Spanner Instances page in the Google Cloud console.

   Go to the Instances page

2. Click the instance.

3. Click the database that you want to delete.

4. In the Database details page, click Delete.

5. Confirm that you want to delete the database and click Delete.

Delete the instance

Deleting an instance automatically drops all databases created in that instance.

On the command line

gcloud spanner instances delete test-instance

Using the Google Cloud console

1. Go to the Spanner Instances page in the Google Cloud console.

   Go to the Instances page

2. Click your instance.

3. Click Delete.

4. Confirm that you want to delete the instance and click Delete.