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;
+    }
+}