Spring boot 多数据源 - HelloWorld开发者社区

网上多是基于XML文件，本文使用基于配置类的方式使用动态数据源。

多数据源原理

Spring作为项目的应用容器，也对多数据源提供了很好的支持，当我们的持久化框架需要数据库连接时，我们需要做到动态的切换数据源，这些Spring的AbstractRoutingDataSource都给我们留了拓展的空间，可以先来看看抽象类AbstractRoutingDataSource在获取数据库连接时做了什么。

//从配置文件读取到的DataSources的Map
private Map<Object, DataSource> resolvedDataSources; 

//默认数据源
private DataSource resolvedDefaultDataSource;
  
public Connection getConnection() throws SQLException {
   return determineTargetDataSource().getConnection();
}
 
public Connection getConnection(String username, String password) throws SQLException {
   return determineTargetDataSource().getConnection(username, password);
}
  
protected DataSource determineTargetDataSource() {
   Assert.notNull(this.resolvedDataSources, "DataSource router not initialized");
   Object lookupKey = determineCurrentLookupKey();
   DataSource dataSource = this.resolvedDataSources.get(lookupKey);
   if (dataSource == null && (this.lenientFallback || lookupKey == null)) {
      dataSource = this.resolvedDefaultDataSource;
   }
   if (dataSource == null) {
      throw new IllegalStateException("Cannot determine target DataSource for lookup key [" + lookupKey + "]");
   }
   return dataSource;
}
  
protected abstract Object determineCurrentLookupKey();

可以看到AbstractRoutingDataSource在决定目标数据源的时候，会先调用determineCurrentLookupKey()方法得到一个key，我们通过这个key从配置好的resolvedDataSources(Map结构)拿到这次调用对应的数据源，而determineCurrentLookupKey()开放出来让我们实现。

简单实现AbstractRoutingDataSource

基于上述分析，继承抽象类AbstractRoutingDataSource，并实现determineCurrentLookupKey()方法。

public class MyDataSource extends AbstractRoutingDataSource {
 
    private static final ThreadLocal<String> dataSourceKey = new ThreadLocal<String>();
 
    public static void setDataSourceKey(String dataSource) {
        dataSourceKey.set(dataSource);
    }
 
    protected Object determineCurrentLookupKey() {
        String dsName = dataSourceKey.get();
        //这里需要注意的时，每次我们返回当前数据源的值得时候都需要移除ThreadLocal的值，
        //这是为了避免同一线程上一次方法调用对之后调用的影响
        dataSourceKey.remove(); 
        return dsName;
    }
 
}

实际项目中与mybatis的结合

配置AbstractRoutingDataSource
使用AbstractRoutingDataSource作为SqlSessionFactory的数据源
在使用具体的dao层的相关方法前，设置指定的datasource，动态切换数据源
执行dao方法的时候就会使用该数据源执行。 ### 配置datasource 说明：默认使用druid连接池。

在application.yml中配置Spring数据库连接相关属性。

Springboot 默认会自动加载classpath下的application.yml和application.properties文件。
问题：当两个文件同时使用，会同时加载吗？出现冲突会优先选择哪个文件的？
两种文件同时使用时都会加载，如果两文件出现相同的属性名，则application.properties中的会为最终值（测试过。）。

多数据源配置：

datasource:
  type: com.alibaba.druid.pool.DruidDataSource.class
  write:
    name: pushopt
    url: jdbc:mysql://127.0.0.1:3306/pushopt
    username: root
    password: hgfgood
    driver-class-name: com.mysql.jdbc.Driver
    max-active: 20
    initial-size: 1
    max-wait: 6000
    pool-prepared-statements: true
    max-open-prepared-statements: 20
  read1:
    name: test
    url: jdbc:mysql://127.0.0.1:3306/test
    username: root
    password: hgfgood
    driver-class-name: com.mysql.jdbc.Driver
    max-active: 20
    initial-size: 1
    max-wait: 6000
    pool-prepared-statements: true
    max-open-prepared-statements: 20

生成DataSource Bean：

package com.meituan.service.web.opt.config;

import com.meituan.service.web.opt.enums.DataSourceType;
import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.spring.SqlSessionFactoryBean;
import org.springframework.boot.autoconfigure.jdbc.DataSourceBuilder;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.DependsOn;
import org.springframework.context.annotation.Primary;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.jdbc.datasource.DataSourceTransactionManager;

import javax.sql.DataSource;
import java.util.HashMap;
import java.util.Map;

/**
 * Created by hgf on 16/7/29.
 */
@Configuration
public class DataSourceConfiguration {

    private Class<? extends DataSource> datasourceType = com.alibaba.druid.pool.DruidDataSource.class;

    @Bean(name = "writeDataSource")
    @ConfigurationProperties(prefix = "datasource.write")
    public DataSource writeDataSource() {
        return DataSourceBuilder.create().type(datasourceType).build();
    }

    @Bean(name = "readDataSource1")
    @ConfigurationProperties(prefix = "datasource.read1")
    public DataSource readDataSource1() {
        return DataSourceBuilder.create().type(datasourceType).build();
    }

    /**
     * 有多少个数据源就要配置多少个bean
     *
     * @return
     */
    @Bean
    @Primary
    @DependsOn({"writeDataSource", "readDataSource1"})
    public DynamicDataSource dynamicDataSource() {
        DynamicDataSource proxy = new DynamicDataSource();

        //表示可用的数据源,包括写和读数据源
        Map<Object, Object> targetDataSources = new HashMap<Object, Object>();
        // 写
        targetDataSources.put(DataSourceType.WRITE.getType(), writeDataSource());

        //如果有多个DataSource,需要设置多个
        targetDataSources.put(DataSourceType.READ.getType(), readDataSource1());

        //设置默认的数据源为写数据源
        proxy.setDefaultTargetDataSource(writeDataSource());
        proxy.setTargetDataSources(targetDataSources);

        return proxy;
    }

    @Bean
    public SqlSessionFactory sqlSessionFactorys() throws Exception {
        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
        sqlSessionFactoryBean.setConfigLocation(new ClassPathResource("mybatis-config.xml"));
        sqlSessionFactoryBean.setDataSource(dynamicDataSource());
        sqlSessionFactoryBean.setTypeAliasesPackage("com.meituan.service.web.opt.model");

        PathMatchingResourcePatternResolver pathMatchingResourcePatternResolver = new PathMatchingResourcePatternResolver();
        sqlSessionFactoryBean.setMapperLocations(pathMatchingResourcePatternResolver.getResources("classpath:/mapper/*.xml"));

        SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBean.getObject();
        return sqlSessionFactory;
    }

    @Bean
    DataSourceTransactionManager dataSourceTransactionManager() {
        DataSourceTransactionManager dataSourceTransactionManager = new DataSourceTransactionManager(dynamicDataSource());
        return dataSourceTransactionManager;
    }

}

注：此处有两个坑，其一是配置DataSource的时候有坑，在实例化AbstractRoutingDataSource的时候不要在属性上设置@Autowired注入，直接使用属性注入或者调用Bean的配置函数否则会产生循环依赖。
正确使用方法：
  @Bean(name = "dynamicDataSource")
  public AbstractRoutingDataSource dynamicDataSource(@Qualifier("writeDataSource") DataSource writeDataSource, @Qualifier("readDataSource1") DataSource readDataSource1) {
      //self defined AbstractRoutingDataSource
      DynamicDataSource proxy = new DynamicDataSource();
      ...
      return proxy;
  }
错误方法：
  @Autowired
  @Qualifier("writeDataSource")
  DataSource writeDataSource;
  @Autowired
  @Qualifier("readDataSource1")
  DataSource readDataSource1;
  @Bean(name = "dynamicDataSource")
  public AbstractRoutingDataSource dynamicDataSource() {
      DynamicDataSource proxy = new DynamicDataSource();
      ...
      return proxy;
  }
错误异常：
Caused by: org.springframework.beans.factory.UnsatisfiedDependencyException:
Error creating bean with name 'mybatisConfiguration': Unsatisfied dependency expressed through field 'writeDataSource':
Error creating bean with name 'writeDataSource' defined in class path resource [com/meituan/service/web/opt/config/DataSourceConfiguration.class]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'dataSourceInitializer': Invocation of init method failed; nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'dynamicDataSource' defined in class path resource [com/meituan/service/web/opt/config/MybatisConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource]: Circular reference involving containing bean 'mybatisConfiguration' - consider declaring the factory method as static for independence from its containing instance. Factory method 'dynamicDataSource' threw exception; nested exception is java.lang.IllegalArgumentException: [Assertion failed] - this argument is required; it must not be null; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'writeDataSource' defined in class path resource [com/meituan/service/web/opt/config/DataSourceConfiguration.class]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'dataSourceInitializer': Invocation of init method failed; nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'dynamicDataSource' defined in class path resource [com/meituan/service/web/opt/config/MybatisConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource]: Circular reference involving containing bean 'mybatisConfiguration' - consider declaring the factory method as static for independence from its containing instance. Factory method 'dynamicDataSource' threw exception; nested exception is java.lang.IllegalArgumentException: [Assertion failed] - this argument is required; it must not be null

主要意思就是：mybatisConfigurationbean需要先注入writeDataSourceBean，该Bean依赖dataSourceInitializer，而dataSourceInitializer依赖dynamicDataSource，此时dynamicDataSource由于依赖writeDataSource而没有初始化，所以依赖注入writeDataSource此时没有正确的生成bean，而是null。所以造成初始化Bean失败。

其二就是需要自定义Bean加载顺序。由于DataSource使用DataSourceBuilder创建，该类依赖datasource实例，所以容易产生循环依赖，特别是在先加载DynamicDataSource，的同时加载writeDataSource时。解决方法：使用Spring提供的@DependsOn注解，注解DynamicDataSource。当加载DynamicDataSource，会等待加载writeDataSource，等writeDataSource加载完成后，再加载DynamicDataSource。就不会出现DynamicDataSource->DatasourceInitlizer->writeDataSource->DataSourceInitlizer循环依赖了。

注：当spring容器中有多个datasource时，使用[@Primary](https://my.oschina.net/primary)决定当有同类别的beans时，如何选择注入那个类。

多数据源集成mybatis

生成AbstractRoutingDataSource的Bean后，使用该Bean配置SqlSessionFactory，就能使动态数据源生效。

注：如果手动配置SqlSessionFactoryBean，那么Spring boot默认会从Ioc容器中选择一个（一般是最先生成的Datasource Bean）DataSource注入到默认的自动加载的SqlSessionFactory中，此时动态数据源不能生效。

自定义SqlSessionFactory，使用SqlSessionFactoryBean来生成SqlSessionFactory：

    @Bean
    public SqlSessionFactory sqlSessionFactorys(AbstractRoutingDataSource dynamicDataSource) throws Exception {
        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
        //设置mybatis的配置文件路径
        sqlSessionFactoryBean.setConfigLocation(new ClassPathResource("mybatis-config.xml"));
        //设置数据源为动态数据源
        sqlSessionFactoryBean.setDataSource(dynamicDataSource);
        //设置类型前缀包名，在mapper文件中就不用使用详细的包名了，直接使用类名。
        sqlSessionFactoryBean.setTypeAliasesPackage("com.meituan.service.web.opt.model");

        //配置路径匹配器，获取匹配的文件
        PathMatchingResourcePatternResolver pathMatchingResourcePatternResolver = new PathMatchingResourcePatternResolver();
        sqlSessionFactoryBean.setMapperLocations(pathMatchingResourcePatternResolver.getResources("classpath:/mapper/*.xml"));

        SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBean.getObject();
        return sqlSessionFactory;
    }