Spring boot 多数据源

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。

1//从配置文件读取到的DataSources的Map
2private Map<Object, DataSource> resolvedDataSources; 
3
4//默认数据源
5private DataSource resolvedDefaultDataSource;
6  
7public Connection getConnection() throws SQLException {
8   return determineTargetDataSource().getConnection();
9}
10 
11public Connection getConnection(String username, String password) throws SQLException {
12   return determineTargetDataSource().getConnection(username, password);
13}
14  
15protected DataSource determineTargetDataSource() {
16   Assert.notNull(this.resolvedDataSources, "DataSource router not initialized");
17   Object lookupKey = determineCurrentLookupKey();
18   DataSource dataSource = this.resolvedDataSources.get(lookupKey);
19   if (dataSource == null && (this.lenientFallback || lookupKey == null)) {
20      dataSource = this.resolvedDefaultDataSource;
21   }
22   if (dataSource == null) {
23      throw new IllegalStateException("Cannot determine target DataSource for lookup key [" + lookupKey + "]");
24   }
25   return dataSource;
26}
27  
28protected 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。

1public class MyDataSource extends AbstractRoutingDataSource {
2 
3    private static final ThreadLocal<String> dataSourceKey = new ThreadLocal<String>();
4 
5    public static void setDataSourceKey(String dataSource) {
6        dataSourceKey.set(dataSource);
7    }
8 
9    protected Object determineCurrentLookupKey() {
10        String dsName = dataSourceKey.get();
11        //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，
12        //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
13        dataSourceKey.remove(); 
14        return dsName;
15    }
16 
17}
18

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：

1datasource:
2  type: com.alibaba.druid.pool.DruidDataSource.class
3  write:
4    name: pushopt
5    url: jdbc:mysql://127.0.0.1:3306/pushopt
6    username: root
7    password: hgfgood
8    driver-class-name: com.mysql.jdbc.Driver
9    max-active: 20
10    initial-size: 1
11    max-wait: 6000
12    pool-prepared-statements: true
13    max-open-prepared-statements: 20
14  read1:
15    name: test
16    url: jdbc:mysql://127.0.0.1:3306/test
17    username: root
18    password: hgfgood
19    driver-class-name: com.mysql.jdbc.Driver
20    max-active: 20
21    initial-size: 1
22    max-wait: 6000
23    pool-prepared-statements: true
24    max-open-prepared-statements: 20

生成DataSource Bean：

1package com.meituan.service.web.opt.config;
2
3import com.meituan.service.web.opt.enums.DataSourceType;
4import org.apache.ibatis.session.SqlSessionFactory;
5import org.mybatis.spring.SqlSessionFactoryBean;
6import org.springframework.boot.autoconfigure.jdbc.DataSourceBuilder;
7import org.springframework.boot.context.properties.ConfigurationProperties;
8import org.springframework.context.annotation.Bean;
9import org.springframework.context.annotation.Configuration;
10import org.springframework.context.annotation.DependsOn;
11import org.springframework.context.annotation.Primary;
12import org.springframework.core.io.ClassPathResource;
13import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
14import org.springframework.jdbc.datasource.DataSourceTransactionManager;
15
16import javax.sql.DataSource;
17import java.util.HashMap;
18import java.util.Map;
19
20/**
21 * Created by hgf on 16/7/29.
22 */
23@Configuration
24public class DataSourceConfiguration {
25
26    private Class<? extends DataSource> datasourceType = com.alibaba.druid.pool.DruidDataSource.class;
27
28    @Bean(name = "writeDataSource")
29    @ConfigurationProperties(prefix = "datasource.write")
30    public DataSource writeDataSource() {
31        return DataSourceBuilder.create().type(datasourceType).build();
32    }
33
34    @Bean(name = "readDataSource1")
35    @ConfigurationProperties(prefix = "datasource.read1")
36    public DataSource readDataSource1() {
37        return DataSourceBuilder.create().type(datasourceType).build();
38    }
39
40    /**
41     * 有多少个数据源就要配置多少个bean
42     *
43     * @return
44     */
45    @Bean
46    @Primary
47    @DependsOn({"writeDataSource", "readDataSource1"})
48    public DynamicDataSource dynamicDataSource() {
49        DynamicDataSource proxy = new DynamicDataSource();
50
51        //表示可用的数据源,包括写和读数据源
52        Map<Object, Object> targetDataSources = new HashMap<Object, Object>();
53        // 写
54        targetDataSources.put(DataSourceType.WRITE.getType(), writeDataSource());
55
56        //如果有多个DataSource,需要设置多个
57        targetDataSources.put(DataSourceType.READ.getType(), readDataSource1());
58
59        //设置默认的数据源为写数据源
60        proxy.setDefaultTargetDataSource(writeDataSource());
61        proxy.setTargetDataSources(targetDataSources);
62
63        return proxy;
64    }
65
66    @Bean
67    public SqlSessionFactory sqlSessionFactorys() throws Exception {
68        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
69        sqlSessionFactoryBean.setConfigLocation(new ClassPathResource("mybatis-config.xml"));
70        sqlSessionFactoryBean.setDataSource(dynamicDataSource());
71        sqlSessionFactoryBean.setTypeAliasesPackage("com.meituan.service.web.opt.model");
72
73        PathMatchingResourcePatternResolver pathMatchingResourcePatternResolver = new PathMatchingResourcePatternResolver();
74        sqlSessionFactoryBean.setMapperLocations(pathMatchingResourcePatternResolver.getResources("classpath:/mapper/*.xml"));
75
76        SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBean.getObject();
77        return sqlSessionFactory;
78    }
79
80    @Bean
81    DataSourceTransactionManager dataSourceTransactionManager() {
82        DataSourceTransactionManager dataSourceTransactionManager = new DataSourceTransactionManager(dynamicDataSource());
83        return dataSourceTransactionManager;
84    }
85
86}
87

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：
1  @Bean(name = "dynamicDataSource")
2  public AbstractRoutingDataSource dynamicDataSource(@Qualifier("writeDataSource") DataSource writeDataSource, @Qualifier("readDataSource1") DataSource readDataSource1) {
3      //self defined AbstractRoutingDataSource
4      DynamicDataSource proxy = new DynamicDataSource();
5      ...
6      return proxy;
7  }
错误方法：
1  @Autowired
2  @Qualifier("writeDataSource")
3  DataSource writeDataSource;
4  @Autowired
5  @Qualifier("readDataSource1")
6  DataSource readDataSource1;
7  @Bean(name = "dynamicDataSource")
8  public AbstractRoutingDataSource dynamicDataSource() {
9      DynamicDataSource proxy = new DynamicDataSource();
10      ...
11      return proxy;
12  }
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：

1    @Bean
2    public SqlSessionFactory sqlSessionFactorys(AbstractRoutingDataSource dynamicDataSource) throws Exception {
3        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
4        //设置mybatis的配置文件路径
5        sqlSessionFactoryBean.setConfigLocation(new ClassPathResource("mybatis-config.xml"));
6        //设置数据源为动态数据源
7        sqlSessionFactoryBean.setDataSource(dynamicDataSource);
8        //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。
9        sqlSessionFactoryBean.setTypeAliasesPackage("com.meituan.service.web.opt.model");
10
11        //配置路径匹配器，获取匹配的文件
12        PathMatchingResourcePatternResolver pathMatchingResourcePatternResolver = new PathMatchingResourcePatternResolver();
13        sqlSessionFactoryBean.setMapperLocations(pathMatchingResourcePatternResolver.getResources("classpath:/mapper/*.xml"));
14
15        SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBean.getObject();
16        return sqlSessionFactory;
17    }