有的时候我们的代码同时会用到多个数据库，因此需要在请求mysql前，切换数据源
通过aop+注解的方式能轻松实现多数据源
这里介绍使用spring+aspectj自动代理+注解的方式实现mybatis多数据源的切换

知识点

• 数据源路由器AbstractRoutingDataSource，继承该类的数据源，每次请求时都会通过determineCurrentLookupKey方法决定使用的数据源
• @annotation切入点表达式

多数据源

首先我们需要创建多个链接池（数据源）

/** DynamicDataSourceProperties.java **/
//配置类

package com.sinbxeunha.josechan.dynamicDataSource.config;

import org.springframework.boot.autoconfigure.jdbc.DataSourceProperties;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Component;

/**
 * 数据源配置，这里继承了springboot的单数据源配置类，并且为配置分配了key
 */
@Component
@Primary
@ConfigurationProperties("datasource.dynamic.properties")
public class DynamicDataSourceProperties extends DataSourceProperties {

    private String key;

    public String getKey() {
        return key;
    }

    public void setKey(String key) {
        this.key = key;
    }
}

/** DynamicDataSourceRegisterProperties.java **/
package com.sinbxeunha.josechan.dynamicDataSource.config;

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

import java.util.List;

/**
 * 动态多数据源配置文件
 */
@Component
@ConfigurationProperties("datasource.dynamic.register")
public class DynamicDataSourceRegisterProperties {

    public String defaultKey;

    public List<DynamicDataSourceProperties> properties;

    public List<DynamicDataSourceProperties> getProperties() {
        return properties;
    }

    public void setProperties(List<DynamicDataSourceProperties> properties) {
        this.properties = properties;
    }

    public String getDefaultKey() {
        return defaultKey;
    }

    public void setDefaultKey(String defaultKey) {
        this.defaultKey = defaultKey;
    }
}

# application.properties
# 多数据源配置
# 第一个数据源
datasource.dynamic.register.properties[0].key=xss
datasource.dynamic.register.properties[0].url=jdbc:mysql://127.0.0.1:3306/xss
datasource.dynamic.register.properties[0].username=root
datasource.dynamic.register.properties[0].password=**********
datasource.dynamic.register.properties[0].driver-class-name=com.mysql.cj.jdbc.Driver
# 第二个数据源
datasource.dynamic.register.properties[1].key=forecast
datasource.dynamic.register.properties[1].url=jdbc:mysql://127.0.0.1:3306/forecast
datasource.dynamic.register.properties[1].username=root
datasource.dynamic.register.properties[1].password=**********
datasource.dynamic.register.properties[1].driver-class-name=com.mysql.cj.jdbc.Driver

/** DynamicDataSourceContextHolder.java **/
package com.sinbxeunha.josechan.dynamicDataSource.config;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.ArrayList;
import java.util.List;

/**
 * 用来存储数据源的key
 */
public class DynamicDataSourceContextHolder {

    private static final Logger logger = LoggerFactory.getLogger(DynamicDataSourceContextHolder.class);

    /**
     * 存储已经注册的数据源的key，所有配置的数据源
     */
    public static List<String> dataSourceIds = new ArrayList<>();

    /**
     * 线程级别的私有变量，当前线程的数据源key
     */
    private static final ThreadLocal<String> HOLDER = new ThreadLocal<>();

    public static String getDataSourceRouterKey () {
        return HOLDER.get();
    }

    public static void setDataSourceRouterKey (String dataSourceRouterKey) {
        logger.info("切换至{}数据源", dataSourceRouterKey);
        HOLDER.set(dataSourceRouterKey);
    }

    /**
     * 设置数据源之前一定要先移除
     */
    public static void removeDataSourceRouterKey () {
        HOLDER.remove();
    }

    /**
     * 判断指定DataSrouce当前是否存在
     *
     * @param dataSourceId 数据源ID
     * @return 是否存在Datasource
     */
    public static boolean containsDataSource(String dataSourceId){
        return dataSourceIds.contains(dataSourceId);
    }
}

/** DynamicRoutingDataSource.java **/
package com.sinbxeunha.josechan.dynamicDataSource.register;

import com.sinbxeunha.josechan.dynamicDataSource.config.DynamicDataSourceContextHolder;
import com.sinbxeunha.josechan.dynamicDataSource.config.DynamicDataSourceProperties;
import com.sinbxeunha.josechan.dynamicDataSource.config.DynamicDataSourceRegisterProperties;
import com.zaxxer.hikari.HikariDataSource;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.boot.context.properties.bind.Bindable;
import org.springframework.boot.context.properties.bind.Binder;
import org.springframework.boot.context.properties.source.ConfigurationPropertyName;
import org.springframework.boot.context.properties.source.ConfigurationPropertyNameAliases;
import org.springframework.boot.context.properties.source.ConfigurationPropertySource;
import org.springframework.boot.context.properties.source.MapConfigurationPropertySource;
import org.springframework.boot.jdbc.DataSourceBuilder;
import org.springframework.context.EnvironmentAware;
import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
import org.springframework.core.env.Environment;
import org.springframework.core.type.AnnotationMetadata;
import org.springframework.stereotype.Component;
import org.springframework.util.StringUtils;

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

/**
 * 动态数据源注册
 * 实现 ImportBeanDefinitionRegistrar 实现数据源注册
 * 实现 EnvironmentAware 用于读取application.yml配置
 */
@Component
public class DynamicDataSourceRegister implements InitializingBean {

    /** 自动注入配置类 */
    @Autowired
    DynamicDataSourceRegisterProperties dynamicDataSourceRegisterProperties;

    private static final Logger logger = LoggerFactory.getLogger(DynamicDataSourceRegister.class);


    /**
     * 别名
     */
    private final static ConfigurationPropertyNameAliases aliases = new ConfigurationPropertyNameAliases();

    static {
        aliases.addAliases("url", "jdbc-url");
        aliases.addAliases("username", "user");
    }

    /**
     * 存储我们注册的数据源
     */
    private final Map<Object, Object> customDataSources = new HashMap<Object, Object>();

    /** 记录默认数据源 */
    private DataSource defaultDatasource = null;

    /**
     * 继承自InitializingBean，对象生成后自动执行
     * @throws Exception 异常
     */
    @Override
    public void afterPropertiesSet() throws Exception {
        List<DynamicDataSourceProperties> properties = dynamicDataSourceRegisterProperties.getProperties();
        String defaultKey = dynamicDataSourceRegisterProperties.getDefaultKey();
        for (DynamicDataSourceProperties property : properties){
            DataSourceBuilder<?> builder = property.initializeDataSourceBuilder();
            DataSource dataSource = builder.type(property.getType()).build();
            customDataSources.put(property.getKey(), dataSource);
            DynamicDataSourceContextHolder.dataSourceIds.add(property.getKey());

            if(property.getKey().equals(defaultKey)){
                defaultDatasource = dataSource;
            }
        }
    }

    public Map<Object, Object> getCustomDataSources() {
        return customDataSources;
    }

    public DataSource getDefaultDatasource() {
        return defaultDatasource;
    }
}

/** DynamicRoutingDataSource.java **/
package com.sinbxeunha.josechan.dynamicDataSource.config;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;

/**
 * 动态数据源类，继承了AbstractRoutingDataSource，实现其中的determineCurrentLookupKey
 * 该方法会在每次查询前被调用，用于获取数据源
 */
public class DynamicRoutingDataSource extends AbstractRoutingDataSource {

    private static final Logger logger = LoggerFactory.getLogger(DynamicRoutingDataSource.class);

    @Override
    protected Object determineCurrentLookupKey() {
        String dataSourceName = DynamicDataSourceContextHolder.getDataSourceRouterKey();
        logger.info("当前数据源是：{}", dataSourceName);
        return DynamicDataSourceContextHolder.getDataSourceRouterKey();
    }
}