3种方式实现多数据源控制/切换、实现读写分离；演示借助AbstractRoutingDataSource实现多数据源的动态切换代码【享学Spring】（上）

## 主库master配置
datasource.drivername=com.mysql.jdbc.Driver
datasource.username=root
datasource.password=root
datasource.url=jdbc:mysql://localhost:3306/jedi
## 从库slave配置
datasource.slave.drivername=com.mysql.jdbc.Driver
datasource.slave.username=root
datasource.slave.password=root
datasource.slave.url=jdbc:mysql://localhost:3306/jedi_slave

@EnableTransactionManagement
@Configuration
@PropertySource(value = "classpath:jdbc.properties", ignoreResourceNotFound = false, encoding = "UTF-8")
public class JdbcConfig implements TransactionManagementConfigurer {
    @Value("${datasource.username}")
    private String userName;
    @Value("${datasource.password}")
    private String password;
    @Value("${datasource.url}")
    private String url;
    // 从库配置
    @Value("${datasource.slave.username}")
    private String slaveUserName;
    @Value("${datasource.slave.password}")
    private String slavePassword;
    @Value("${datasource.slave.url}")
    private String slaveUrl;
    =====配置好两个数据源：
    @Primary
    @Bean
    public DataSource masterDataSource() {
        MysqlDataSource dataSource = new MysqlDataSource();
        dataSource.setUser(userName);
        dataSource.setPassword(password);
        dataSource.setURL(url);
        return dataSource;
    }
    @Bean
    public DataSource slaveDataSource() {
        MysqlDataSource dataSource = new MysqlDataSource();
        dataSource.setUser(slaveUserName);
        dataSource.setPassword(slavePassword);
        dataSource.setURL(slaveUrl);
        return dataSource;
    }
    // 手动配置好两个JdbcTemplate  分别用于操作
    @Primary
    @Bean
    public JdbcTemplate masterJdbcTemplate() {
        return new JdbcTemplate(masterDataSource());
    }
    @Bean
    public JdbcTemplate slaveJdbcTemplate() {
        return new JdbcTemplate(slaveDataSource());
    }
    // 事务管理器自己具体配置（如果是真的主从模式，从库可以不用事务管理器  只需要配置主库的即可）
    @Primary
    @Bean
    public PlatformTransactionManager transactionManager() {
        DataSourceTransactionManager dataSourceTransactionManager = new DataSourceTransactionManager(masterDataSource());
        dataSourceTransactionManager.setEnforceReadOnly(true); // 让事务管理器进行只读事务层面上的优化  建议开启
        return dataSourceTransactionManager;
    }
    // 指定注解使用的事务管理器
    @Override
    public PlatformTransactionManager annotationDrivenTransactionManager() {
        return transactionManager();
    }
}

// @since 07.05.2003   它是个抽象类：实现了DataSource一些无关紧要的方法… 
public abstract class AbstractDataSource implements DataSource {
  ... // 实现接口javax.sql.DataSource一些无关紧要的方法
}

// @since 2.5.5   此抽象类出现得较晚  但是木有关系
public abstract class AbstractDriverBasedDataSource extends AbstractDataSource {
  // 需要准备url、username、password等参数  属于更偏底层的处理方式~~~
  @Nullable
  private String url;
  @Nullable
  private String username;
  @Nullable
  private String password;
  @Nullable
  private String catalog;
  @Nullable
  private String schema;
  @Nullable
  private Properties connectionProperties;
  ... // 省略所有的get/set方法
  // 此处getConnectionFromDriver方法是它的特色~~~
  @Override
  public Connection getConnection() throws SQLException {
    return getConnectionFromDriver(getUsername(), getPassword());
  }
  @Override
  public Connection getConnection(String username, String password) throws SQLException {
    return getConnectionFromDriver(username, password);
  }
  // 从Driver里获取到链接~~~~
  protected Connection getConnectionFromDriver(@Nullable String username, @Nullable String password) throws SQLException {
    Properties mergedProps = new Properties();
    Properties connProps = getConnectionProperties();
    // 可以看到  就连username  password其实都是可以放在Properties属性文件里的
    if (connProps != null) {
      mergedProps.putAll(connProps);
    }
    if (username != null) {
      mergedProps.setProperty("user", username);
    }
    if (password != null) {
      mergedProps.setProperty("password", password);
    }
    // 根据Properties属性文件 从Driver里获取链接   抽象方法，由子类去实现
    Connection con = getConnectionFromDriver(mergedProps);
    if (this.catalog != null) {
      con.setCatalog(this.catalog);
    }
    if (this.schema != null) {
      con.setSchema(this.schema);
    }
    return con;
  }
  // 待子类实现
  protected abstract Connection getConnectionFromDriver(Properties props) throws SQLException;
}

public class DriverManagerDataSource extends AbstractDriverBasedDataSource {
  ...
  // 指定驱动
  // 参考：java.sql.DriverManager#registerDriver(java.sql.Driver)
  public void setDriverClassName(String driverClassName) {
    ...
    Class.forName(driverClassNameToUse, true, ClassUtils.getDefaultClassLoader());
  }
  // 复写父类方法：从Driver里拿到链接
  // 本类使用的是从事务管理器里获取链接：DriverManager.getConnection(url, props);
  @Override
  protected Connection getConnectionFromDriver(Properties props) throws SQLException {
    String url = getUrl();
    return getConnectionFromDriverManager(url, props);
  }
  protected Connection getConnectionFromDriverManager(String url, Properties props) throws SQLException {
    return DriverManager.getConnection(url, props);
  }
}

    public static void main(String[] args) throws Exception {
        Class.forName("com.mysql.jdbc.Driver");
        String username = "root";
        String password = "root";
        Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/jedi", username, password);
        System.out.println(connection);
    }