BAEL-1314 Guide to AbstractRoutingDatasource (#2989)

* BAEL-1314 initial import.  Guide to AbstractRoutingDatasource.

* BAEL-1314 Guide to Spring AbstractRoutingDatasource

* update test name and rename test classes

* move dsrouting example to spring-boot project.  rename db create script.

spring-boot/src/main/java/org/baeldung/dsrouting/ClientDao.java

@@ -0,0 +1,29 @@
+package org.baeldung.dsrouting;
+
+import javax.sql.DataSource;
+
+import org.springframework.jdbc.core.JdbcTemplate;
+import org.springframework.jdbc.core.RowMapper;
+
+/**
+ * Database access code for datasource routing example.
+ */
+public class ClientDao {
+
+    private static final String SQL_GET_CLIENT_NAME = "select name from client";
+
+    private final JdbcTemplate jdbcTemplate;
+
+    public ClientDao(DataSource datasource) {
+        this.jdbcTemplate = new JdbcTemplate(datasource);
+    }
+
+    public String getClientName() {
+        return this.jdbcTemplate.query(SQL_GET_CLIENT_NAME, rowMapper)
+            .get(0);
+    }
+
+    private static RowMapper<String> rowMapper = (rs, rowNum) -> {
+        return rs.getString("name");
+    };
+}

spring-boot/src/main/java/org/baeldung/dsrouting/ClientDataSourceRouter.java

@@ -0,0 +1,14 @@
+package org.baeldung.dsrouting;
+
+import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;
+
+/**
+ * Returns thread bound client lookup key for current context.
+ */
+public class ClientDataSourceRouter extends AbstractRoutingDataSource {
+
+    @Override
+    protected Object determineCurrentLookupKey() {
+        return ClientDatabaseContextHolder.getClientDatabase();
+    }
+}

spring-boot/src/main/java/org/baeldung/dsrouting/ClientDatabase.java

@@ -0,0 +1,7 @@
+package org.baeldung.dsrouting;
+
+public enum ClientDatabase {
+
+    ACME_WIDGETS, WIDGETS_ARE_US, WIDGET_DEPOT
+
+}

spring-boot/src/main/java/org/baeldung/dsrouting/ClientDatabaseContextHolder.java

@@ -0,0 +1,26 @@
+package org.baeldung.dsrouting;
+
+import org.springframework.util.Assert;
+
+/**
+ * Thread shared context to point to the datasource which should be used. This
+ * enables context switches between different clients.
+ */
+public class ClientDatabaseContextHolder {
+
+    private static final ThreadLocal<ClientDatabase> CONTEXT = new ThreadLocal<>();
+
+    public static void set(ClientDatabase clientDatabase) {
+        Assert.notNull(clientDatabase, "clientDatabase cannot be null");
+        CONTEXT.set(clientDatabase);
+    }
+
+    public static ClientDatabase getClientDatabase() {
+        return CONTEXT.get();
+    }
+
+    public static void clear() {
+        CONTEXT.remove();
+    }
+
+}

spring-boot/src/main/java/org/baeldung/dsrouting/ClientService.java

@@ -0,0 +1,21 @@
+package org.baeldung.dsrouting;
+
+/**
+ * Service layer code for datasource routing example.  Here, the service methods are responsible
+ * for setting and clearing the context.
+ */
+public class ClientService {
+
+    private final ClientDao clientDao;
+
+    public ClientService(ClientDao clientDao) {
+        this.clientDao = clientDao;
+    }
+
+    public String getClientName(ClientDatabase clientDb) {
+        ClientDatabaseContextHolder.set(clientDb);
+        String clientName = this.clientDao.getClientName();
+        ClientDatabaseContextHolder.clear();
+        return clientName;
+    }
+}

spring-boot/src/test/java/org/baeldung/dsrouting/DataSourceRoutingTestConfiguration.java

@@ -0,0 +1,64 @@
+package org.baeldung.dsrouting;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import javax.sql.DataSource;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.jdbc.datasource.embedded.EmbeddedDatabase;
+import org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseBuilder;
+import org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseType;
+
+@Configuration
+public class DataSourceRoutingTestConfiguration {
+
+    @Bean
+    public ClientService clientService() {
+        return new ClientService(new ClientDao(clientDatasource()));
+    }
+
+    @Bean
+    public DataSource clientDatasource() {
+        Map<Object, Object> targetDataSources = new HashMap<>();
+        DataSource acmeWidgetsDatasource = acmeWidgetsDatasource();
+        DataSource widgetsAreUsDatasource = widgetsAreUsDatasource();
+        DataSource widgetsDepotDatasource = widgetsDepotDatasource();
+        targetDataSources.put(ClientDatabase.ACME_WIDGETS, acmeWidgetsDatasource);
+        targetDataSources.put(ClientDatabase.WIDGETS_ARE_US, widgetsAreUsDatasource);
+        targetDataSources.put(ClientDatabase.WIDGET_DEPOT, widgetsDepotDatasource);
+
+        ClientDataSourceRouter clientRoutingDatasource = new ClientDataSourceRouter();
+        clientRoutingDatasource.setTargetDataSources(targetDataSources);
+        clientRoutingDatasource.setDefaultTargetDataSource(acmeWidgetsDatasource);
+        return clientRoutingDatasource;
+    }
+
+    private DataSource acmeWidgetsDatasource() {
+        EmbeddedDatabaseBuilder dbBuilder = new EmbeddedDatabaseBuilder();
+        EmbeddedDatabase embeddedDb = dbBuilder.setType(EmbeddedDatabaseType.H2)
+            .setName("ACMEWIDGETS")
+            .addScript("classpath:dsrouting-db.sql")
+            .build();
+        return embeddedDb;
+    }
+
+    private DataSource widgetsAreUsDatasource() {
+        EmbeddedDatabaseBuilder dbBuilder = new EmbeddedDatabaseBuilder();
+        EmbeddedDatabase embeddedDb = dbBuilder.setType(EmbeddedDatabaseType.H2)
+            .setName("WIDGETSAREUS")
+            .addScript("classpath:dsrouting-db.sql")
+            .build();
+        return embeddedDb;
+    }
+
+    private DataSource widgetsDepotDatasource() {
+        EmbeddedDatabaseBuilder dbBuilder = new EmbeddedDatabaseBuilder();
+        EmbeddedDatabase embeddedDb = dbBuilder.setType(EmbeddedDatabaseType.H2)
+            .setName("WIDGETDEPOT")
+            .addScript("classpath:dsrouting-db.sql")
+            .build();
+        return embeddedDb;
+    }
+}

spring-boot/src/test/java/org/baeldung/dsrouting/DataSourceRoutingTests.java

@@ -0,0 +1,62 @@
+package org.baeldung.dsrouting;
+
+import static org.junit.Assert.assertEquals;
+
+import javax.sql.DataSource;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.jdbc.core.JdbcTemplate;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringRunner;
+
+@RunWith(SpringRunner.class)
+@ContextConfiguration(classes = DataSourceRoutingTestConfiguration.class)
+public class DataSourceRoutingTests {
+
+    @Autowired
+    DataSource routingDatasource;
+
+    @Autowired
+    ClientService clientService;
+
+    @Before
+    public void setup() {
+        final String SQL_ACME_WIDGETS = "insert into client (id, name) values (1, 'ACME WIDGETS')";
+        final String SQL_WIDGETS_ARE_US = "insert into client (id, name) values (2, 'WIDGETS ARE US')";
+        final String SQL_WIDGET_DEPOT = "insert into client (id, name) values (3, 'WIDGET DEPOT')";
+
+        JdbcTemplate jdbcTemplate = new JdbcTemplate();
+        jdbcTemplate.setDataSource(routingDatasource);
+
+        ClientDatabaseContextHolder.set(ClientDatabase.ACME_WIDGETS);
+        jdbcTemplate.execute(SQL_ACME_WIDGETS);
+        ClientDatabaseContextHolder.clear();
+
+        ClientDatabaseContextHolder.set(ClientDatabase.WIDGETS_ARE_US);
+        jdbcTemplate.execute(SQL_WIDGETS_ARE_US);
+        ClientDatabaseContextHolder.clear();
+
+        ClientDatabaseContextHolder.set(ClientDatabase.WIDGET_DEPOT);
+        jdbcTemplate.execute(SQL_WIDGET_DEPOT);
+        ClientDatabaseContextHolder.clear();
+    }
+
+    @Test
+    public void givenClientDbs_whenContextsSwitch_thenRouteToCorrectDatabase() throws Exception {
+
+        // test ACME WIDGETS
+        String clientName = clientService.getClientName(ClientDatabase.ACME_WIDGETS);
+        assertEquals(clientName, "ACME WIDGETS");
+
+        // test WIDGETS_ARE_US
+        clientName = clientService.getClientName(ClientDatabase.WIDGETS_ARE_US);
+        assertEquals(clientName, "WIDGETS ARE US");
+
+        // test WIDGET_DEPOT
+        clientName = clientService.getClientName(ClientDatabase.WIDGET_DEPOT);
+        assertEquals(clientName, "WIDGET DEPOT");
+    }
+}

spring-boot/src/test/resources/dsrouting-db.sql

@@ -0,0 +1,5 @@
+create table client (
+  id numeric,
+  name  varchar(50),
+  constraint pk_client primary key (id)
+);