背景

最近项目中为了提高数据库读写速度，想要横向扩展Oracle数据库，一个Master,多个Slave。master可以读写数据，Slave只能读数据。这就是多数据源问题了。怎么利用Spring解决这个问题呢？

测试代码

1. pom.xml

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.6.2</version>
		<relativePath />
	</parent>

	<dependencies>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-context</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-jdbc</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-test</artifactId>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>com.h2database</groupId>
			<artifactId>h2</artifactId>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-data-jpa</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>4.12</version>
		</dependency>
	</dependencies>

2. 定义两个数据源名字

public enum ClientDatabase {
    CLIENT_A, CLIENT_B
}

3、利用Threadlocal 数据源的名字绑定到当前执行的线程上

public class ClientDatabaseContextHolder {

    private static 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();
    }
}

4. 继承AbstractRoutingDataSource ，Spring会在取数据源之前调用determineCurrentLookupKey方法取数据源的名字，通过数据源的名字查找数据源。这样就可以实现动态更改数据源了。readonly事务的时候，就可以切换到读的那个数据库了。

public class ClientDataSourceRouter extends AbstractRoutingDataSource {

	private static final Logger log = LoggerFactory.getLogger(ClientDataSourceRouter.class);
	
    @Override
    protected Object determineCurrentLookupKey() {
    	ClientDatabase clientDatabase = ClientDatabaseContextHolder.getClientDatabase();
        
        if (clientDatabase != null) { //有指定切换数据源切换的时候，才给输出日志 并且也只给输出成debug级别的 否则日志太多了
            log.info("线程[{}]，此时切换到的数据源为:{}", Thread.currentThread().getId(), clientDatabase);
        }
        return clientDatabase;

    }
}

5. 定义两个数据源，不同的H2数据库。

@Configuration
public class RoutingTestConfiguration {
	@Autowired
	private ClientADetails clientADetails;
	@Autowired
	private ClientBDetails clientBDetails;

	@Bean
	public DataSource clientDatasource() {
		Map<Object, Object> targetDataSources = new HashMap<>();
		DataSource clientADatasource = clientADatasource();
		DataSource clientBDatasource = clientBDatasource();
		targetDataSources.put(ClientDatabase.CLIENT_A, clientADatasource);
		targetDataSources.put(ClientDatabase.CLIENT_B, clientBDatasource);

		ClientDataSourceRouter clientRoutingDatasource = new ClientDataSourceRouter();
		clientRoutingDatasource.setTargetDataSources(targetDataSources);
		clientRoutingDatasource.setDefaultTargetDataSource(clientADatasource);
		return clientRoutingDatasource;
	}

	private DataSource clientADatasource() {
		EmbeddedDatabaseBuilder dbBuilder = new EmbeddedDatabaseBuilder();
		return dbBuilder.setType(EmbeddedDatabaseType.H2).setName(clientADetails.getName())
				.addScript(clientADetails.getScript()).build();
	}

	private DataSource clientBDatasource() {
		EmbeddedDatabaseBuilder dbBuilder = new EmbeddedDatabaseBuilder();
		return dbBuilder.setType(EmbeddedDatabaseType.H2).setName(clientBDetails.getName())
				.addScript(clientBDetails.getScript()).build();
	}	
}

6.  创建两个类取两个数据的名字等等。

@Component
@ConfigurationProperties(prefix = "client-a.datasource")
public class ClientBDetails {

    private String name = "CLIENT_B";
    private String script = "SOME_SCRIPT.sql";
    // Getters & Setters
}

@Component
@ConfigurationProperties(prefix = "client-a.datasource")
public class ClientADetails {

    private String name = "CLIENT_A";
    private String script = "SOME_SCRIPT.sql";
    // Getters & Setters
}

7. application.properties

#database details for CLIENT_A
client-a.datasource.name=CLIENT_A
client-a.datasource.script=SOME_SCRIPT.sql

#database details for CLIENT_B
client-b.datasource.name=CLIENT_B
client-b.datasource.script=SOME_SCRIPT.sql

8.  测试类

@SpringJUnitConfig
@ContextConfiguration(classes = {RoutingTestConfiguration.class, ClientBDetails.class, ClientADetails.class})
public class TestSpringBean {

    @Autowired
    private DataSource dataSource;

    @Test
    public void test1() throws SQLException {
    	System.out.println(dataSource.getConnection());
    	ClientDatabaseContextHolder.set(ClientDatabase.CLIENT_B);
    	System.out.println(dataSource.getConnection());
    	
    }
}

执行结果

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conn2: url=jdbc:h2:mem:CLIENT_A user=SA
19:29:04.576 [main] INFO ClientDataSourceRouter - 线程[1]，此时切换到的数据源为:CLIENT_B
[jdbc:h2:mem:CLIENT_B;DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=false]
conn3: url=jdbc:h2:mem:CLIENT_B user=SA