上一篇文章介绍了 spring-boot整合mybatis+druid连接池实现多数据源，在这个例子中我们为每个DataSource都初始化一个与之对应的SessionFactory，从而实现连接化多个数据源。再仔细体会一下，会发现这种方式有一点静态的味道。
在实际需求中，我们经常会遇到mysql的读写分离、冷热分离等需求，这种情况虽然也可以看成多数据源的一种情况，用上面的方式去处理，但是有没有更好的解决方法呢？
答案是：有。我们可以设计一种数据源动态切换的架构，整个系统中就初始化一个SessionFactory，设计一个DynamicDataSource类，把所有数据源放进去，然后根据不同需求动态的切换数据源，实现mysql的读写分离、冷热分离。。。
基于这种方式，不仅可是实现真正意义上的多数据源的切换（第二种实现多数据源的思路），还可以实现在程序的运行过程中，实现动态添加一个或多个新的数据源。这里重点关注的是配置文件之间的关系，对象模型如下：
首先分析一下AbstractRoutingDataSource抽象类的源码：
public abstract class AbstractRoutingDataSource extends AbstractDataSource implements InitializingBean {
private Map<Object, Object> targetDataSources;
private Object defaultTargetDataSource;
private boolean lenientFallback = true;
private DataSourceLookup dataSourceLookup = new JndiDataSourceLookup();
private Map<Object, DataSource> resolvedDataSources;
private DataSource resolvedDefaultDataSource;
public AbstractRoutingDataSource() {
}
public void setTargetDataSources(Map<Object, Object> targetDataSources) {
this.targetDataSources = targetDataSources;
}
public void setDefaultTargetDataSource(Object defaultTargetDataSource) {
this.defaultTargetDataSource = defaultTargetDataSource;
}
public void setLenientFallback(boolean lenientFallback) {
this.lenientFallback = lenientFallback;
}
public void setDataSourceLookup(DataSourceLookup dataSourceLookup) {
this.dataSourceLookup = (DataSourceLookup)(dataSourceLookup != null ? dataSourceLookup : new JndiDataSourceLookup());
}
public void afterPropertiesSet() {
if (this.targetDataSources == null) {
throw new IllegalArgumentException("Property 'targetDataSources' is required");
} else {
this.resolvedDataSources = new HashMap(this.targetDataSources.size());
Iterator var1 = this.targetDataSources.entrySet().iterator();
while(var1.hasNext()) {
Entry<Object, Object> entry = (Entry)var1.next();
Object lookupKey = this.resolveSpecifiedLookupKey(entry.getKey());
DataSource dataSource = this.resolveSpecifiedDataSource(entry.getValue());
this.resolvedDataSources.put(lookupKey, dataSource);
}
if (this.defaultTargetDataSource != null) {
this.resolvedDefaultDataSource = this.resolveSpecifiedDataSource(this.defaultTargetDataSource);
}
}
}
protected Object resolveSpecifiedLookupKey(Object lookupKey) {
return lookupKey;
}
protected DataSource resolveSpecifiedDataSource(Object dataSource) throws IllegalArgumentException {
if (dataSource instanceof DataSource) {
return (DataSource)dataSource;
} else if (dataSource instanceof String) {
return this.dataSourceLookup.getDataSource((String)dataSource);
} else {
throw new IllegalArgumentException("Illegal data source value - only [javax.sql.DataSource] and String supported: " + dataSource);
}
}
public Connection getConnection() throws SQLException {
return this.determineTargetDataSource().getConnection();
}
public Connection getConnection(String username, String password) throws SQLException {
return this.determineTargetDataSource().getConnection(username, password);
}
public <T> T unwrap(Class<T> iface) throws SQLException {
return iface.isInstance(this) ? this : this.determineTargetDataSource().unwrap(iface);
}
public boolean isWrapperFor(Class<?> iface) throws SQLException {
return iface.isInstance(this) || this.determineTargetDataSource().isWrapperFor(iface);
}
protected DataSource determineTargetDataSource() {
Assert.notNull(this.resolvedDataSources, "DataSource router not initialized");
Object lookupKey = this.determineCurrentLookupKey();
DataSource 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 + "]");
} else {
return dataSource;
}
}
protected abstract Object determineCurrentLookupKey();
}
对于该抽象类，关注两组变量：
Map<Object, Object> targetDataSources和Object defaultTargetDataSource、Map<Object, DataSource> resolvedDataSources和DataSource resolvedDefaultDataSource；这两组变量是相互对应的；在熟悉多实例数据源切换代码的不难发现，当有多个数据源的时候，一定要指定一个作为默认的数据源，在这里也同理，当同时初始化多个数据源的时候，需要显示的调用setDefaultTargetDataSource方法指定一个作为默认数据源； Map<Object, Object> targetDataSources和Map<Object, DataSource> resolvedDataSources，targetDataSources是暴露给外部程序用来赋值的，而resolvedDataSources是程序内部执行时的依据，因此会有一个赋值的操作，如下图所示：
根据这段源码可以看出，每次执行时，都会遍历targetDataSources内的所有元素并赋值给resolvedDataSources；这样如果我们在外部程序新增一个新的数据源，都会添加到内部使用，从而实现数据源的动态加载。
protected abstract Object determineCurrentLookupKey()，该方法用于指定到底需要使用哪一个数据源。
到此基本上清楚了该抽象类的使用方法，接下来贴下具体的实现代码。
1、pom.xml
同上一篇文章中的pom；
2、application.properties和数据源配置：
1）application.properties
#---------------------使用durid连接池
ds1.w.datasource.url=jdbc:mysql://jy.ttengine.w.abc.db:1883/ttengine?useUnicode=true&characterEncoding=utf8
ds1.w.datasource.username=ttengine
ds1.w.datasource.password=TTengine123
ds1.w.datasource.driverClassName=com.mysql.jdbc.Driver
ds1.r.datasource.url=jdbc:mysql://jy.ttengine.r.abc.db:1883/ttengine?useUnicode=true&characterEncoding=utf8
ds1.r.datasource.username=ttengine
ds1.r.datasource.password=TTengine123
ds1.r.datasource.driverClassName=com.mysql.jdbc.Driver
ds1.datasource.initialSize=20
ds1.datasource.minIdle=20
ds1.datasource.maxActive=200
ds1.datasource.maxWait=60000
ds1.datasource.timeBetweenEvictinotallow=60000
ds1.datasource.minEvictableIdleTimeMillis=300000
ds1.datasource.testWhileIdle=true
ds1.datasource.testOnBorrow=false
ds1.datasource.testOnReturn=false
ds1.datasource.poolPreparedStatements=true
ds1.datasource.maxPoolPreparedStatementPerCnotallow=20
# 页面默认前缀目录
spring.mvc.view.prefix=/WEB-INF/page/
spring.mvc.view.suffix=.jsp
2）自定义数据源切换类：
package cn.edu.nuc.Test1.dao.mysql.config;
public class DatabaseContextHolder {
private static final ThreadLocal<String> contextHolder = new ThreadLocal<String>();
public static void setDBKey(String dataSourceKey) {
contextHolder.set(dataSourceKey);
}
public static String getDBKey() {
return contextHolder.get();
}
public static void clearDBKey() {
contextHolder.remove();
}
}
通过ThreadLocal维护一个全局唯一的map来实现数据源的动态切换。
3）自定义DynamicDataSource：
package cn.edu.nuc.Test1.dao.mysql.config;
import java.util.HashMap;
import java.util.Map;
import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;
/**
* 动态数据源
* @author kevinliu
*
*/
public class DynamicDataSource extends AbstractRoutingDataSource {
private static DynamicDataSource instance;
private static byte[] lock=new byte[0];
private static Map<Object,Object> dataSourceMap=new HashMap<Object, Object>();
@Override
public void setTargetDataSources(Map<Object, Object> targetDataSources) {
super.setTargetDataSources(targetDataSources);
dataSourceMap.putAll(targetDataSources);
super.afterPropertiesSet();// 必须添加该句，否则新添加数据源无法识别到
}
public Map<Object, Object> getDataSourceMap() {
return dataSourceMap;
}
@Override
protected Object determineCurrentLookupKey() {
String dbKey = DatabaseContextHolder.getDBKey();
/*if (StringUtils.isBlank(dbKey)) {
dbKey = "read";
}*/
return dbKey;
}
private DynamicDataSource() {}
public static synchronized DynamicDataSource getInstance(){
if(instance==null){
synchronized (lock){
if(instance==null){
instance=new DynamicDataSource();
}
}
}
return instance;
}
}
该类有以下几个方法：
- 私有构造方法和获取单例的方法；
- 实现了抽象类的determineCurrentLookupKey方法，从上面的map中获取数据源，然后动态切换；
- 覆盖了抽象类的setTargetDataSources方法，主要用来动态创建数据源，然后动态切换；
4）定制DataSourceConfig：
package cn.edu.nuc.Test1.dao.mysql.config;
import java.sql.SQLException;
import java.util.HashMap;
import java.util.Map;
import javax.sql.DataSource;
import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.spring.SqlSessionFactoryBean;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.jdbc.datasource.DataSourceTransactionManager;
import com.alibaba.druid.pool.DruidDataSource;
import com.alibaba.druid.support.http.StatViewServlet;
import com.alibaba.druid.support.http.WebStatFilter;
@Configuration
//扫描 Mapper 接口并容器管理
@MapperScan(basePackages = DatasourceConfig.PACKAGE, sqlSessionFactoryRef = "sqlSessionFactory")
public class DatasourceConfig {
// 精确到 master 目录，以便跟其他数据源隔离
static final String PACKAGE = "cn.edu.nuc.Test1.dao.mysql";
static final String MAPPER_LOCATION = "classpath:mapper/*.xml";
@Value("${ds1.w.datasource.url}")
private String wurl;
@Value("${ds1.w.datasource.username}")
private String wuser;
@Value("${ds1.w.datasource.password}")
private String wpassword;
@Value("${ds1.w.datasource.driverClassName}")
private String wdriverClass;
@Value("${ds1.r.datasource.url}")
private String rurl;
@Value("${ds1.r.datasource.username}")
private String ruser;
@Value("${ds1.r.datasource.password}")
private String rpassword;
@Value("${ds1.r.datasource.driverClassName}")
private String rdriverClass;
@Value("${ds1.datasource.maxActive}")
private Integer maxActive;
@Value("${ds1.datasource.minIdle}")
private Integer minIdle;
@Value("${ds1.datasource.initialSize}")
private Integer initialSize;
@Value("${ds1.datasource.maxWait}")
private Long maxWait;
@Value("${ds1.datasource.timeBetweenEvictionRunsMillis}")
private Long timeBetweenEvictionRunsMillis;
@Value("${ds1.datasource.minEvictableIdleTimeMillis}")
private Long minEvictableIdleTimeMillis;
@Value("${ds1.datasource.testWhileIdle}")
private Boolean testWhileIdle;
@Value("${ds1.datasource.testWhileIdle}")
private Boolean testOnBorrow;
@Value("${ds1.datasource.testOnBorrow}")
private Boolean testOnReturn;
@Bean(name = "dynamicDataSource")
public DynamicDataSource dynamicDataSource() {
DynamicDataSource dynamicDataSource = DynamicDataSource.getInstance();
//jdbc配置
DruidDataSource wdataSource = new DruidDataSource();
wdataSource.setDriverClassName(wdriverClass);
wdataSource.setUrl(wurl);
wdataSource.setUsername(wuser);
wdataSource.setPassword(wpassword);
//连接池配置
wdataSource.setMaxActive(maxActive);
wdataSource.setMinIdle(minIdle);
wdataSource.setInitialSize(initialSize);
wdataSource.setMaxWait(maxWait);
wdataSource.setTimeBetweenEvictionRunsMillis(timeBetweenEvictionRunsMillis);
wdataSource.setMinEvictableIdleTimeMillis(minEvictableIdleTimeMillis);
wdataSource.setTestWhileIdle(testWhileIdle);
wdataSource.setTestOnBorrow(testOnBorrow);
wdataSource.setTestOnReturn(testOnReturn);
wdataSource.setValidationQuery("SELECT 'x'");
wdataSource.setPoolPreparedStatements(true);
wdataSource.setMaxPoolPreparedStatementPerConnectionSize(20);
try {
wdataSource.setFilters("stat");
} catch (SQLException e) {
e.printStackTrace();
}
//jdbc配置
DruidDataSource rdataSource = new DruidDataSource();
rdataSource.setDriverClassName(rdriverClass);
rdataSource.setUrl(rurl);
rdataSource.setUsername(ruser);
rdataSource.setPassword(rpassword);
//连接池配置
rdataSource.setMaxActive(maxActive);
rdataSource.setMinIdle(minIdle);
rdataSource.setInitialSize(initialSize);
rdataSource.setMaxWait(maxWait);
rdataSource.setTimeBetweenEvictionRunsMillis(timeBetweenEvictionRunsMillis);
rdataSource.setMinEvictableIdleTimeMillis(minEvictableIdleTimeMillis);
rdataSource.setTestWhileIdle(testWhileIdle);
rdataSource.setTestOnBorrow(testOnBorrow);
rdataSource.setTestOnReturn(testOnReturn);
rdataSource.setValidationQuery("SELECT 'x'");
rdataSource.setPoolPreparedStatements(true);
rdataSource.setMaxPoolPreparedStatementPerConnectionSize(20);
try {
rdataSource.setFilters("stat");
} catch (SQLException e) {
e.printStackTrace();
}
Map<Object,Object> map = new HashMap<>();
map.put("ds1_w", wdataSource);
map.put("ds1_r", rdataSource);
dynamicDataSource.setTargetDataSources(map);
dynamicDataSource.setDefaultTargetDataSource(rdataSource);
return dynamicDataSource;
}
@Bean(name = "transactionManager")
public DataSourceTransactionManager transactionManager() {
return new DataSourceTransactionManager(dynamicDataSource());
}
@Bean(name = "sqlSessionFactory")
public SqlSessionFactory sqlSessionFactory(@Qualifier("dynamicDataSource") DataSource dynamicDataSource)
throws Exception {
final SqlSessionFactoryBean sessionFactory = new SqlSessionFactoryBean();
sessionFactory.setDataSource(dynamicDataSource);
sessionFactory.setTypeAliasesPackage("cn.edu.nuc.Test1.entity");
sessionFactory.setMapperLocations(new PathMatchingResourcePatternResolver()
.getResources(DatasourceConfig.MAPPER_LOCATION));
return sessionFactory.getObject();
}
@Bean
public ServletRegistrationBean druidServlet() {
ServletRegistrationBean servletRegistrationBean = new ServletRegistrationBean();
servletRegistrationBean.setServlet(new StatViewServlet());
servletRegistrationBean.addUrlMappings("/druid/*");
Map<String, String> initParameters = new HashMap<String, String>();
initParameters.put("loginUsername", "admin");// 用户名
initParameters.put("loginPassword", "admin");// 密码
initParameters.put("resetEnable", "false");// 禁用HTML页面上的“Reset All”功能
initParameters.put("allow", ""); // IP白名单 (没有配置或者为空，则允许所有访问)
//initParameters.put("deny", "192.168.20.38");// IP黑名单 (存在共同时，deny优先于allow)
servletRegistrationBean.setInitParameters(initParameters);
return servletRegistrationBean;
}
@Bean
public FilterRegistrationBean filterRegistrationBean() {
FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
filterRegistrationBean.setFilter(new WebStatFilter());
filterRegistrationBean.addUrlPatterns("/*");
filterRegistrationBean.addInitParameter("exclusions", "*.js,*.gif,*.jpg,*.png,*.css,*.ico,/druid/*");
return filterRegistrationBean;
}
}
该类和上一篇文章中的略有不同：
- 获取数据源时返回的是自定义DynamicDataSource（继承了AbstractRoutingDataSource抽象类），在其方法上，创建读和写两个DruidDataSource对象，然后放到了DynamicDataSource中；此外，下面只创建了一个sessionFactory对象；
- 在创建好DruidSource后，调用下面两个方法初始化数据源：dynamicDataSource.setTargetDataSources(map);dynamicDataSource.setDefaultTargetDataSource(rdataSource);
3、其他:
动态数据源配置好后，接下来就和正常spring-boot的用法一样了。整个结构：
1）crontroller：
package cn.edu.nuc.Test1.controller;
import javax.servlet.http.HttpServletRequest;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import cn.edu.nuc.Test1.entity.Test;
import cn.edu.nuc.Test1.service.TestService;
@Controller
public class TestController {
private static final Logger logger = LoggerFactory.getLogger(TestController.class);
@Autowired
private TestService testService;
@RequestMapping("/test")
@ResponseBody
public String test(HttpServletRequest request) {
String name = request.getParameter("name");
Test test = null;
try {
test = testService.findByName(name);
} catch (Exception e) {
test = new Test();
logger.error("test error.",e);
}
logger.info("test....{}",name);
return test.toString();
}
@RequestMapping("/save")
@ResponseBody
public String saveTest(HttpServletRequest request) {
String res = "0";
String name = request.getParameter("name");
try {
testService.saveTest(name);
} catch (Exception e) {
res = "1";
logger.error("save test error.",e);
}
logger.info("save test....{}",name);
return res;
}
}
两个方法：一个读方法（连接从库），一个写方法（连接主库）
2）service：
package cn.edu.nuc.Test1.service;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import cn.edu.nuc.Test1.dao.mysql.TestDao;
import cn.edu.nuc.Test1.dao.mysql.config.DatabaseContextHolder;
import cn.edu.nuc.Test1.entity.Test;
@Service
public class TestService{
private static final Logger logger = LoggerFactory.getLogger(TestService.class);
@Autowired
private TestDao testDao;
public Test findByName(String name) throws Exception{
logger.info("findByName...");
return testDao.findByName(name);
}
public void saveTest(String name) throws Exception{
logger.info("saveTest...");
DatabaseContextHolder.setDBKey("ds1_w");
Test t = new Test();
t.setName(name);
testDao.saveTest(t);
}
}
3）entity：
package cn.edu.nuc.Test1.entity;
public class Test {
private Long id;
private String name;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Test [id=" + id + ", name=" + name + "]";
}
}
4）dao：
package cn.edu.nuc.Test1.dao.mysql;
import org.apache.ibatis.annotations.Param;
import cn.edu.nuc.Test1.entity.Test;
public interface TestDao {
Test findByName(@Param("name") String n) throws Exception;
void saveTest(Test t) throws Exception;
}
5）mapper文件：
<?xml versinotallow="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="cn.edu.nuc.Test1.dao.mysql.TestDao">
<resultMap id="BaseResultMap" type="cn.edu.nuc.Test1.entity.Test">
<result column="id" property="id" />
<result column="name" property="name" />
</resultMap>
<parameterMap id="Test" type="cn.edu.nuc.Test1.entity.Test"/>
<sql id="Base_Column_List">
id,name
</sql>
<select id="findByName" resultMap="BaseResultMap" parameterType="java.lang.String">
select
<include refid="Base_Column_List" />
from test
where name = #{name}
</select>
<!-- 插入 -->
<insert id="saveTest" parameterType="Test">
insert into test
(name)
values
(#{name})
</insert>
</mapper>
6）主类：
package cn.edu.nuc.Test1;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
/**
* Hello world!
* 可以统一用@MapperScan指定扫描的dao，也可以在每个dao上添加@Mapper
*/
@SpringBootApplication
//mapper 接口类扫描包配置
@MapperScan("cn.edu.nuc.Test1.dao.mysql")
public class App
{
public static void main( String[] args )
{
SpringApplication.run(App.class, args);
}
}
