Using Multiple DataSources with Spring Boot and RoutingDataSource

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1- The objective of this post

Sometimes you need to create a Web application connecting to multiple databases. And you can do it easily in Spring Boot.
Spring provides you with class AbstractRoutingDataSource, you can write an extended class from the class. Routing Datasource contains a Map of real Datasources.
Note: Routing Datasource is also a Datasource but it is a special one.
And DataSource Interceptor will determine what DataSource is used for each request from the user respectively.
In the post, I simulate a Website with 2 datasources. Each datasource is connected to a different database. A database stores information for Publisher system and the other stores information for Advertiser system.
In some situations, you also can build a multi-language news website, you can create more Databases, each database stores content of the posts in a specific language.
In another case, if your application needs a lot of DataSources, and each function (each page) can work with multiple DataSources at the same time, you can refer to the following instructions:

2- Preparing the Database

I will create 2 databases, one is for PUBLISHER system and the other is for  ADVERTISER system. Both may not be the same type. You can use Oracle, MySQL or SQL Server,...

Database1:

PUBLISHER database system has a table of  Publishers.
Database1 - (MySQL, SQL Server, PostGres)
-- ===========================================
-- DATABASE FOR PUBLISHER SYSTEM
-- ===========================================
create table PUBLISHERS
(
  ID Bigint,
  NAME VARCHAR(255),
  Primary key (ID)
);

insert into publishers (ID, NAME)
values (1, 'publisher 1');

insert into publishers (ID, NAME)
values (2, 'publisher 2');
Database1 - (ORACLE)
-- ===========================================
-- DATABASE FOR PUBLISHER SYSTEM
-- ===========================================
create table PUBLISHERS
(
  ID NUMBER(19),
  NAME VARCHAR(255),
  Primary key (ID)
);

insert into publishers (ID, NAME)
values (1, 'publisher 1');

insert into publishers (ID, NAME)
values (2, 'publisher 2');

Commit;

Database 2:

ADVERTISER database system has a table of Advertisers.
Database2 (MySQL, SQL Server, PostGres)
-- ===========================================
-- DATABASE FOR ADVERTISER SYSTEM
-- ===========================================
create table ADVERTISERS
(
  ID Bigint,
  NAME VARCHAR(255),
  Primary key (ID)
);

insert into advertisers (ID, NAME)
values (1, 'Advertiser 1');

insert into advertisers (ID, NAME)
values (2, 'Advertiser 2');
Database2 - (ORACLE)
-- ===========================================
-- DATABASE FOR ADVERTISER SYSTEM
-- ===========================================
create table ADVERTISERS
(
  ID NUMBER(19),
  NAME VARCHAR(255),
  Primary key (ID)
);

insert into advertisers (ID, NAME)
values (1, 'Advertiser 1');

insert into advertisers (ID, NAME)
values (2, 'Advertiser 2');

Commit;

3- Create Spring Boot Project

pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
    http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.o7planning</groupId>
    <artifactId>SpringBootRoutingDS</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>SpringBootRoutingDS</name>
    <description>Spring Boot + Multi DataSource + Routing DataSource</description>
 
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.0.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        
        <!-- For Thymeleaf VIEW. Remove it if using Jsp VIEW -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <scope>runtime</scope>
        </dependency>
        
                
        <!-- SQL Server - Mssql-Jdbc driver -->
        <dependency>
            <groupId>com.microsoft.sqlserver</groupId>
            <artifactId>mssql-jdbc</artifactId>
            <scope>runtime</scope>
        </dependency>
        
        <!-- SQL Server - JTDS driver -->
        <dependency>
            <groupId>net.sourceforge.jtds</groupId>
            <artifactId>jtds</artifactId>
            <scope>runtime</scope>
        </dependency>
        
        <dependency>
            <groupId>com.oracle</groupId>
            <artifactId>ojdbc6</artifactId>
            <version>11.2.0.3</version>
        </dependency>
        
        
        <!-- For JSP VIEW (Need REMOVE spring-boot-starter-thymeleaf) -->
        <dependency>
            <groupId>org.apache.tomcat.embed</groupId>
            <artifactId>tomcat-embed-jasper</artifactId>
        </dependency>
        
        <!-- For JSP VIEW (Need REMOVE spring-boot-starter-thymeleaf) -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
        </dependency>
        
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        
    </dependencies>

    <repositories>
    
        <!-- Repository for ORACLE JDBC Driver -->
        <repository>
            <id>codelds</id>
            <url>https://code.lds.org/nexus/content/groups/main-repo</url>
        </repository>
 
    </repositories>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
    
</project>

4- Configure DataSource & RoutingDataSource

Information of Databases is configured in datasource-cfg.properties file.
datasource-cfg.properties (MySQL + MySQL)
# DataSource (PUBLISHER System).

spring.datasource.driver-class-name.1=com.mysql.jdbc.Driver
spring.datasource.url.1=jdbc:mysql://localhost:3306/publisher
spring.datasource.username.1=root
spring.datasource.password.1=12345



# DataSource (ADVERTISER System).

spring.datasource.driver-class-name.2=com.mysql.jdbc.Driver
spring.datasource.url.2=jdbc:mysql://localhost:3306/advertiser
spring.datasource.username.2=root
spring.datasource.password.2=12345
datasource-cfg.properties (SQL Server + SQL Server) (JTDS Driver)
# DataSource  (PUBLISHER System).

spring.datasource.driver-class-name.1=net.sourceforge.jtds.jdbc.Driver
spring.datasource.url.1=jdbc:jtds:sqlserver://localhost:1433/publisher;instance=SQLEXPRESS
spring.datasource.username.1=sa
spring.datasource.password.1=12345


# DataSource  (ADVERTISER System).

spring.datasource.driver-class-name.2=net.sourceforge.jtds.jdbc.Driver
spring.datasource.url.2=jdbc:jtds:sqlserver://localhost:1433/advertiser;instance=SQLEXPRESS
spring.datasource.username.2=sa
spring.datasource.password.2=12345
datasource-cfg.properties (SQL Server + SQL Server) (Mssql-Jdbc Driver)
# DataSource  (PUBLISHER System).

spring.datasource.driver-class-name.1=com.microsoft.sqlserver.jdbc.SQLServerDriver
spring.datasource.url.1=jdbc:sqlserver://tran-vmware-pc\\SQLEXPRESS:1433;databaseName=publisher
spring.datasource.username.1=sa
spring.datasource.password.1=12345


# DataSource  (ADVERTISER System).

spring.datasource.driver-class-name.2=com.microsoft.sqlserver.jdbc.SQLServerDriver
spring.datasource.url.2=jdbc:sqlserver://tran-vmware-pc\\SQLEXPRESS:1433;databaseName=advertiser
spring.datasource.username.2=sa
spring.datasource.password.2=12345
datasource-cfg.properties (ORACLE + ORACLE)

# DataSource (PUBLISHER System).

spring.datasource.driver-class-name.1=oracle.jdbc.driver.OracleDriver
spring.datasource.url.1=jdbc:oracle:thin:@localhost:1521:db12c
spring.datasource.username.1=publisher
spring.datasource.password.1=12345


# DataSource (ADVERTISER System).

spring.datasource.driver-class-name.2=oracle.jdbc.driver.OracleDriver
spring.datasource.url.2=jdbc:oracle:thin:@localhost:1521:db12c
spring.datasource.username.2=advertiser
spring.datasource.password.2=12345
datasource-cfg.properties (PostGres + PostGres)
# DataSource (PUBLISHER System).

spring.datasource.driver-class-name.1=org.postgresql.Driver
spring.datasource.url.1=jdbc:postgresql://tran-vmware-pc:5432/publisher
spring.datasource.username.1=postgres
spring.datasource.password.1=12345



# DataSource (ADVERTISER System).

spring.datasource.driver-class-name.2=org.postgresql.Driver
spring.datasource.url.2=jdbc:postgresql://tran-vmware-pc:5432/advertiser
spring.datasource.username.2=postgres
spring.datasource.password.2=12345
 
By default, Spring Boot will automatically configure a DataSource, therefore, you need to disable it so that you can configure your DataSource by yourself. These automatical configurations include:
  1. DataSourceAutoConfiguration
  2. DataSourceTransactionManagerAutoConfiguration
SpringBootRoutingDsApplication.java
package org.o7planning.sbroutingds;

import java.sql.SQLException;

import javax.sql.DataSource;

import org.o7planning.sbroutingds.routing.MyRoutingDataSource;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration;
import org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.PropertySource;
import org.springframework.context.annotation.PropertySources;
import org.springframework.core.env.Environment;
import org.springframework.jdbc.datasource.DataSourceTransactionManager;
import org.springframework.jdbc.datasource.DriverManagerDataSource;

@SpringBootApplication

// Disable Auto Config DataSource & DataSourceTransactionManager
@EnableAutoConfiguration(exclude = { //
		DataSourceAutoConfiguration.class, //
		DataSourceTransactionManagerAutoConfiguration.class })

// Load to Environment
// (@see resources/datasource-cfg.properties).
@PropertySources({ @PropertySource("classpath:datasource-cfg.properties") })
public class SpringBootRoutingDsApplication {

	// Stores all the properties loaded by the @PropertySource
	@Autowired
	private Environment env;

	public static void main(String[] args) {
		SpringApplication.run(SpringBootRoutingDsApplication.class, args);
	}

	// Returns Routing DataSource (MyRoutingDataSource)
	@Autowired
	@Bean(name = "dataSource")
	public DataSource getDataSource(DataSource dataSource1, DataSource dataSource2) {

		System.out.println("## Create DataSource from dataSource1 & dataSource2");

		MyRoutingDataSource dataSource = new MyRoutingDataSource();

		dataSource.initDataSources(dataSource1, dataSource2);

		return dataSource;
	}

	@Bean(name = "dataSource1")
	public DataSource getDataSource1() throws SQLException {
		DriverManagerDataSource dataSource = new DriverManagerDataSource();

		// See: datasouce-cfg.properties
		dataSource.setDriverClassName(env.getProperty("spring.datasource.driver-class-name.1"));
		dataSource.setUrl(env.getProperty("spring.datasource.url.1"));
		dataSource.setUsername(env.getProperty("spring.datasource.username.1"));
		dataSource.setPassword(env.getProperty("spring.datasource.password.1"));

		System.out.println("## DataSource1: " + dataSource);
		return dataSource;
	}

	@Bean(name = "dataSource2")
	public DataSource getDataSource2() throws SQLException {
		DriverManagerDataSource dataSource = new DriverManagerDataSource();

		// See: datasouce-cfg.properties
		dataSource.setDriverClassName(env.getProperty("spring.datasource.driver-class-name.2"));
		dataSource.setUrl(env.getProperty("spring.datasource.url.2"));
		dataSource.setUsername(env.getProperty("spring.datasource.username.2"));
		dataSource.setPassword(env.getProperty("spring.datasource.password.2"));

		System.out.println("## DataSource2: " + dataSource);

		return dataSource;
	}

	@Autowired
	@Bean(name = "transactionManager")
	public DataSourceTransactionManager getTransactionManager(DataSource dataSource) {
		DataSourceTransactionManager txManager = new DataSourceTransactionManager();

		txManager.setDataSource(dataSource);

		return txManager;
	}

}
MyRoutingDataSource is a DataSource containing a Map between keys and real Datasources.
MyRoutingDataSource.java
package org.o7planning.sbroutingds.routing;

import java.util.HashMap;
import java.util.Map;

import javax.servlet.http.HttpServletRequest;
import javax.sql.DataSource;

import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;
import org.springframework.web.context.request.RequestContextHolder;
import org.springframework.web.context.request.ServletRequestAttributes;

// This is a DataSource.
public class MyRoutingDataSource extends AbstractRoutingDataSource {

   @Override
   protected Object determineCurrentLookupKey() {

      HttpServletRequest request = ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes())
            .getRequest();

      // See more: DataSourceInterceptor
      String keyDS = (String) request.getAttribute("keyDS");

      System.out.println("KeyDS=" + keyDS);

      if (keyDS == null) {
         keyDS = "PUBLISHER_DS";
      }

      return keyDS;
   }

   public void initDataSources(DataSource dataSource1, DataSource dataSource2) {
      Map<Object, Object> dsMap = new HashMap<Object, Object>();
      dsMap.put("PUBLISHER_DS", dataSource1);
      dsMap.put("ADVERTISER_DS", dataSource2);

      this.setTargetDataSources(dsMap);
   }

}

5- DataSourceInterceptor & Configuration

The DataSourceInterceptor will analyze the request's URL, and decide which Datasource will be used.
DataSourceIntercetor.java
package org.o7planning.sbroutingds.interceptor;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;

public class DataSourceIntercetor extends HandlerInterceptorAdapter {

    // Request:

    // /publisher/list
    // /advertiser/list
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {

        String contextPath = request.getServletContext().getContextPath();

        // /SomeContextPath/publisher
        String prefixPublisher = contextPath + "/publisher";
        
        // /SomeContextPath/advertiser
        String prefixAdvertiser = contextPath + "/advertiser";

        // /SomeContextPath/publisher/dashboard
        // /SomeContextPath/advertiser/dashboard
        
        String uri = request.getRequestURI();
        System.out.println("URI:"+ uri);
        
        if(uri.startsWith(prefixPublisher)) {
            request.setAttribute("keyDS", "PUBLISHER_DS");
        }
        
        else if(uri.startsWith(prefixAdvertiser)) {
            request.setAttribute("keyDS", "ADVERTISER_DS");
        }

        return true;
    }

}
In WebMvcConfig you need to register DataSourceInterceptor.
WebMvcConfig.java
package org.o7planning.sbroutingds.config;

import org.o7planning.sbroutingds.interceptor.DataSourceIntercetor;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class WebMvcConfig implements WebMvcConfigurer {

    @Override
    public void addInterceptors(InterceptorRegistry registry) {

        registry.addInterceptor(new DataSourceIntercetor())//
                .addPathPatterns("/publisher/*", "/advertiser/*");
    }

}

6- DAO, Controller

DataDAO is an utility class to query data from the database.
DataDAO.java
package org.o7planning.sbroutingds.dao;

import java.util.List;

import javax.sql.DataSource;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.support.JdbcDaoSupport;
import org.springframework.stereotype.Repository;
import org.springframework.transaction.annotation.Transactional;

@Repository
@Transactional
public class DataDAO extends JdbcDaoSupport {

    @Autowired
    public DataDAO(DataSource dataSource) {
        this.setDataSource(dataSource);
    }

    public List<String> queryPublishers() {
        String sql = "Select name from Publishers";

        List<String> list = this.getJdbcTemplate().queryForList(sql, String.class);
        return list;
    }

    public List<String> queryAdvertisers() {
        String sql = "Select name from Advertisers";

        List<String> list = this.getJdbcTemplate().queryForList(sql, String.class);
        return list;
    }
    
}
MainController.java
package org.o7planning.sbroutingds.controller;

import java.sql.SQLException;
import java.util.List;

import org.o7planning.sbroutingds.dao.DataDAO;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@Controller
public class MainController {

    @Autowired
    private DataDAO dataDAO;
    
    
    @RequestMapping(value = { "/" }, method = RequestMethod.GET)
    public String home(Model model) throws SQLException {
 
        return "home";
    }

    @RequestMapping(value = { "/advertiser/list" }, method = RequestMethod.GET)
    public String advertiser(Model model) throws SQLException {

        List<String> list = dataDAO.queryAdvertisers();
        model.addAttribute("advertisers", list);

        return "advertiser";
    }

    @RequestMapping(value = { "/publisher/list" }, method = RequestMethod.GET)
    public String publisher(Model model) throws SQLException {

        List<String> list = dataDAO.queryPublishers();
        model.addAttribute("publishers", list);

        return "publisher";
    }

}

7- Thymeleaf Template

home.html
<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
   <head>
      <meta charset="UTF-8"/>
      <title>Home</title>
   </head>
   <body>
   
      <h2>Multi DataSource with RoutingDataSource</h2>
      
      <h3>/publisher/* ==> Using Publisher-DB</h3>
      <ul>
         <li><a th:href="@{/publisher/list}">Show Publisher List</a></li>
      </ul>
      
      <h3>/advertiser/* ==> Using Advertiser-DB</h3>
      <ul>
         <li> <a th:href="@{/advertiser/list}">Show Advertiser Lists</a>   </li>
      </ul>
      
   </body>
   
</html>
publisher.html
<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
   <head>
      <meta charset="UTF-8"/>
      <title>Publisher System</title>
   </head>
  
   <body>
      <a th:href="@{/}">Home</a>
      
      <h2>Using Publisher-DB</h2>
      
      <ul>
         <li th:each="publisher : ${publishers}" th:utext="${publisher}"></li>
      </ul>
   </body>
  
</html>
advertiser.html
<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
   <head>
      <meta charset="UTF-8"/>
      <title>Advertiser System</title>
   </head>
   <body>
      <a th:href="@{/}">Home</a>
      
      <h2>Using Advertiser-DB</h2>
      
      <ul>
         <li th:each="advertiser : ${advertisers}" th:utext="${advertiser}"></li>
      </ul>
      
   </body>
   
</html>

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