mybatis-plus多數據源解析

文章已收錄到我的Github精選，歡迎Star：https://github.com/yehongzhi/learningSummary

寫在前面

上一篇文章大致介紹了dynamic-datasource的功能，用起來的確很方便，只需要一個@DS注解，加上一些簡單的配置即可完成多數據源的切換。究竟是怎么做到的呢，底層是怎么實現(xiàn)呢？帶著這個疑問，一起研究了一下源碼。

由于框架本身功能點比較多，有很多小功能比如支持spel、正則表達式匹配，動態(tài)增刪數據源這種功能的源碼就不去細講了。我們只關心核心的功能，就是多數據源的切換。

源碼解析

首先我們都記得，一開始需要引入spring-boot-starter：

<dependency>
????<groupId>com.baomidougroupId>
????<artifactId>dynamic-datasource-spring-boot-starterartifactId>
????<version>3.3.0version>
dependency>

一般starter自動配置，都是從 META-INF/spring.factories文件中指定自動配置類：

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.baomidou.dynamic.datasource.spring.boot.autoconfigure.DynamicDataSourceAutoConfiguration

接著打開這個類：

/**
?*?動態(tài)數據源核心自動配置類
?*
?*?@author?TaoYu?Kanyuxia
?*?@see?DynamicDataSourceProvider
?*?@see?DynamicDataSourceStrategy
?*?@see?DynamicRoutingDataSource
?*?@since?1.0.0
?*/
@Slf4j
@Configuration
@AllArgsConstructor
//以spring.datasource.dynamic為前綴讀取配置
@EnableConfigurationProperties(DynamicDataSourceProperties.class)
//在SpringBoot注入DataSourceAutoConfiguration的bean自動配置之前，先加載注入當前這個類的bean到容器中
@AutoConfigureBefore(DataSourceAutoConfiguration.class)
//引入了Druid的autoConfig和各種數據源連接池的Creator
@Import(value?=?{DruidDynamicDataSourceConfiguration.class,?DynamicDataSourceCreatorAutoConfiguration.class})
//條件加載，當前綴是"spring.datasource.dynamic"配置的時候啟用這個autoConfig
@ConditionalOnProperty(prefix?=?DynamicDataSourceProperties.PREFIX,?name?=?"enabled",?havingValue?=?"true",?matchIfMissing?=?true)
public?class?DynamicDataSourceAutoConfiguration?{
?
????private?final?DynamicDataSourceProperties?properties;

????//讀取多數據源配置，注入到spring容器中
????@Bean
????@ConditionalOnMissingBean
????public?DynamicDataSourceProvider?dynamicDataSourceProvider()?{
????????Map?datasourceMap?=?properties.getDatasource();
????????return?new?YmlDynamicDataSourceProvider(datasourceMap);
????}

????//注冊自己的動態(tài)多數據源DataSource
????@Bean
????@ConditionalOnMissingBean
????public?DataSource?dataSource(DynamicDataSourceProvider?dynamicDataSourceProvider)?{
????????DynamicRoutingDataSource?dataSource?=?new?DynamicRoutingDataSource();
????????dataSource.setPrimary(properties.getPrimary());
????????dataSource.setStrict(properties.getStrict());
????????dataSource.setStrategy(properties.getStrategy());
????????dataSource.setProvider(dynamicDataSourceProvider);
????????dataSource.setP6spy(properties.getP6spy());
????????dataSource.setSeata(properties.getSeata());
????????return?dataSource;
????}

????//AOP切面，對DS注解過的方法進行增強，達到切換數據源的目的
????@Role(value?=?BeanDefinition.ROLE_INFRASTRUCTURE)
????@Bean
????@ConditionalOnMissingBean
????public?DynamicDataSourceAnnotationAdvisor?dynamicDatasourceAnnotationAdvisor(DsProcessor?dsProcessor)?{
????????DynamicDataSourceAnnotationInterceptor?interceptor?=?new?DynamicDataSourceAnnotationInterceptor(properties.isAllowedPublicOnly(),?dsProcessor);
????????DynamicDataSourceAnnotationAdvisor?advisor?=?new?DynamicDataSourceAnnotationAdvisor(interceptor);
????????advisor.setOrder(properties.getOrder());
????????return?advisor;
????}

????//關于分布式事務加強
????@Role(value?=?BeanDefinition.ROLE_INFRASTRUCTURE)
????@ConditionalOnProperty(prefix?=?DynamicDataSourceProperties.PREFIX,?name?=?"seata",?havingValue?=?"false",?matchIfMissing?=?true)
????@Bean
????public?Advisor?dynamicTransactionAdvisor()?{
????????AspectJExpressionPointcut?pointcut?=?new?AspectJExpressionPointcut();
????????pointcut.setExpression("@annotation(com.baomidou.dynamic.datasource.annotation.DSTransactional)");
????????return?new?DefaultPointcutAdvisor(pointcut,?new?DynamicTransactionAdvisor());
????}

????//動態(tài)參數解析器鏈
????@Bean
????@ConditionalOnMissingBean
????public?DsProcessor?dsProcessor()?{
????????DsHeaderProcessor?headerProcessor?=?new?DsHeaderProcessor();
????????DsSessionProcessor?sessionProcessor?=?new?DsSessionProcessor();
????????DsSpelExpressionProcessor?spelExpressionProcessor?=?new?DsSpelExpressionProcessor();
????????headerProcessor.setNextProcessor(sessionProcessor);
????????sessionProcessor.setNextProcessor(spelExpressionProcessor);
????????return?headerProcessor;
????}

}

我們可以發(fā)現(xiàn)，在使用的時候配置的前綴為spring.datasource.dynamic的配置都會被讀取到DynamicDataSourceProperties類，作為一個Bean注入到Spring容器。其實這種讀取配置文件信息的方式在日常開發(fā)中也是很常見的。

@Slf4j
@Getter
@Setter
@ConfigurationProperties(prefix?=?DynamicDataSourceProperties.PREFIX)
public?class?DynamicDataSourceProperties?{

????public?static?final?String?PREFIX?=?"spring.datasource.dynamic";
????public?static?final?String?HEALTH?=?PREFIX?+?".health";

????/**
?????*?必須設置默認的庫,默認master
?????*/
????private?String?primary?=?"master";
????/**
?????*?是否啟用嚴格模式,默認不啟動.?嚴格模式下未匹配到數據源直接報錯,?非嚴格模式下則使用默認數據源primary所設置的數據源
?????*/
????private?Boolean?strict?=?false;
????/**
?????*?是否使用p6spy輸出，默認不輸出
?????*/
????private?Boolean?p6spy?=?false;
????/**
?????*?是否使用開啟seata，默認不開啟
?????*/
????private?Boolean?seata?=?false;
????/**
?????*?seata使用模式，默認AT
?????*/
????private?SeataMode?seataMode?=?SeataMode.AT;
????/**
?????*?是否使用?spring?actuator?監(jiān)控檢查，默認不檢查
?????*/
????private?boolean?health?=?false;
????/**
?????*?每一個數據源
?????*/
????private?Map?datasource?=?new?LinkedHashMap<>();
????/**
?????*?多數據源選擇算法clazz，默認負載均衡算法
?????*/
????private?Class?strategy?=?LoadBalanceDynamicDataSourceStrategy.class;
????/**
?????*?aop切面順序，默認優(yōu)先級最高
?????*/
????private?Integer?order?=?Ordered.HIGHEST_PRECEDENCE;
????/**
?????*?Druid全局參數配置
?????*/
????@NestedConfigurationProperty
????private?DruidConfig?druid?=?new?DruidConfig();
????/**
?????*?HikariCp全局參數配置
?????*/
????@NestedConfigurationProperty
????private?HikariCpConfig?hikari?=?new?HikariCpConfig();

????/**
?????*?全局默認publicKey
?????*/
????private?String?publicKey?=?CryptoUtils.DEFAULT_PUBLIC_KEY_STRING;
????/**
?????*?aop?切面是否只允許切?public?方法
?????*/
????private?boolean?allowedPublicOnly?=?true;
}

但是讀取到配置文件怎么讓這些配置文件信息跟spring的DataSource結合起來呢？我們利用反向思維，從結果往回推，要整合一個數據源到spring，是需要實現(xiàn)DataSource接口，那么Mybatis-Plus的動態(tài)數據源也是有實現(xiàn)的，就是這個：

/**
?*?抽象動態(tài)獲取數據源
?*
?*?@author?TaoYu
?*?@since?2.2.0
?*/
public?abstract?class?AbstractRoutingDataSource?extends?AbstractDataSource?{

????//抽象方法，由子類實現(xiàn)，讓子類決定最終使用的數據源
????protected?abstract?DataSource?determineDataSource();

????//重寫getConnection()方法，實現(xiàn)切換數據源的功能
????@Override
????public?Connection?getConnection()?throws?SQLException?{
????????//這里xid涉及分布式事務的處理
????????String?xid?=?TransactionContext.getXID();
????????if?(StringUtils.isEmpty(xid))?{
????????????//不使用分布式事務，就是直接返回一個數據連接
????????????return?determineDataSource().getConnection();
????????}?else?{
????????????String?ds?=?DynamicDataSourceContextHolder.peek();
????????????ConnectionProxy?connection?=?ConnectionFactory.getConnection(ds);
????????????return?connection?==?null???getConnectionProxy(ds,?determineDataSource().getConnection())?:?connection;
????????}
????}
}

上面的源碼如果學過模板模式肯定都熟悉，他把獲取DataSource的行為延伸到子類去實現(xiàn)了，所以關鍵在于看子類的實現(xiàn)：

@Slf4j
public?class?DynamicRoutingDataSource?extends?AbstractRoutingDataSource?implements?InitializingBean,?DisposableBean?{

????private?static?final?String?UNDERLINE?=?"_";
????/**
?????*?所有數據庫
?????*/
????private?final?Map?dataSourceMap?=?new?ConcurrentHashMap<>();
????/**
?????*?分組數據庫
?????*/
????private?final?Map?groupDataSources?=?new?ConcurrentHashMap<>();
????@Setter
????private?DynamicDataSourceProvider?provider;
????@Setter
????private?Class?strategy?=?LoadBalanceDynamicDataSourceStrategy.class;
????@Setter
????private?String?primary?=?"master";
????@Setter
????private?Boolean?strict?=?false;
????@Setter
????private?Boolean?p6spy?=?false;
????@Setter
????private?Boolean?seata?=?false;

????@Override
????public?DataSource?determineDataSource()?{
????????return?getDataSource(DynamicDataSourceContextHolder.peek());
????}
????
????private?DataSource?determinePrimaryDataSource()?{
????????log.debug("dynamic-datasource?switch?to?the?primary?datasource");
????????return?groupDataSources.containsKey(primary)???groupDataSources.get(primary).determineDataSource()?:?dataSourceMap.get(primary);
????}
????
????@Override
????public?void?afterPropertiesSet()?throws?Exception?{
????????//?檢查開啟了配置但沒有相關依賴
????????checkEnv();
????????//?添加并分組數據源
????????Map?dataSources?=?provider.loadDataSources();
????????for?(Map.Entry?dsItem?:?dataSources.entrySet())?{
????????????addDataSource(dsItem.getKey(),?dsItem.getValue());
????????}
????????//?檢測默認數據源是否設置
????????if?(groupDataSources.containsKey(primary))?{
????????????log.info("dynamic-datasource?initial?loaded?[{}]?datasource,primary?group?datasource?named?[{}]",?dataSources.size(),?primary);
????????}?else?if?(dataSourceMap.containsKey(primary))?{
????????????log.info("dynamic-datasource?initial?loaded?[{}]?datasource,primary?datasource?named?[{}]",?dataSources.size(),?primary);
????????}?else?{
????????????throw?new?RuntimeException("dynamic-datasource?Please?check?the?setting?of?primary");
????????}
????}
}

他實現(xiàn)了InitializingBean接口，這個接口需要實現(xiàn)afterPropertiesSet()方法，這是一個Bean的生命周期函數，在Bean初始化的時候做一些操作。

這里做的操作就是檢查配置，然后通過調用provider.loadDataSources()方法獲取到關于DataSource的Map集合，Key是數據源的名稱，Value則是DataSource。

@Slf4j
@AllArgsConstructor
public?class?YmlDynamicDataSourceProvider?extends?AbstractDataSourceProvider?{
????/**
?????*?所有數據源
?????*/
????private?final?Map?dataSourcePropertiesMap;

????@Override
????public?Map?loadDataSources()?{
????????//調AbstractDataSourceProvider的createDataSourceMap()方法
????????return?createDataSourceMap(dataSourcePropertiesMap);
????}
}

@Slf4j
public?abstract?class?AbstractDataSourceProvider?implements?DynamicDataSourceProvider?{

????@Autowired
????private?DefaultDataSourceCreator?defaultDataSourceCreator;

????protected?Map?createDataSourceMap(
????????????Map?dataSourcePropertiesMap)?{
????????Map?dataSourceMap?=?new?HashMap<>(dataSourcePropertiesMap.size()?*?2);
????????for?(Map.Entry?item?:?dataSourcePropertiesMap.entrySet())?{
????????????DataSourceProperty?dataSourceProperty?=?item.getValue();
????????????String?poolName?=?dataSourceProperty.getPoolName();
????????????if?(poolName?==?null?||?"".equals(poolName))?{
????????????????poolName?=?item.getKey();
????????????}
????????????dataSourceProperty.setPoolName(poolName);
????????????dataSourceMap.put(poolName,?defaultDataSourceCreator.createDataSource(dataSourceProperty));
????????}
????????return?dataSourceMap;
????}
}

這里的defaultDataSourceCreator.createDataSource()方法使用到適配器模式。

因為每種配置數據源創(chuàng)建的DataSource實現(xiàn)類都不一定相同的，所以需要根據配置的數據源類型進行具體的DataSource創(chuàng)建。

@Override
public?DataSource?createDataSource(DataSourceProperty?dataSourceProperty,?String?publicKey)?{
????DataSourceCreator?dataSourceCreator?=?null;
????//this.creators是所有適配的DataSourceCreator實現(xiàn)類
????for?(DataSourceCreator?creator?:?this.creators)?{
????????//根據配置匹配對應的dataSourceCreator
????????if?(creator.support(dataSourceProperty))?{
????????????//如果匹配，則使用對應的dataSourceCreator
????????????dataSourceCreator?=?creator;
????????????break;
????????}
????}
????if?(dataSourceCreator?==?null)?{
????????throw?new?IllegalStateException("creator?must?not?be?null,please?check?the?DataSourceCreator");
????}
????//然后再調用createDataSource方法進行創(chuàng)建對應DataSource
????DataSource?dataSource?=?dataSourceCreator.createDataSource(dataSourceProperty,?publicKey);
????this.runScrip(dataSource,?dataSourceProperty);
????return?wrapDataSource(dataSource,?dataSourceProperty);
}

對應的全部實現(xiàn)類是放在creator包下：

我們看其中一個實現(xiàn)類就：

@Data
@AllArgsConstructor
public?class?HikariDataSourceCreator?extends?AbstractDataSourceCreator?implements?DataSourceCreator?{

????private?static?Boolean?hikariExists?=?false;

????static?{
????????try?{
????????????Class.forName(HIKARI_DATASOURCE);
????????????hikariExists?=?true;
????????}?catch?(ClassNotFoundException?ignored)?{
????????}
????}

????private?HikariCpConfig?hikariCpConfig;

????//創(chuàng)建HikariCp數據源
????@Override
????public?DataSource?createDataSource(DataSourceProperty?dataSourceProperty,?String?publicKey)?{
????????if?(StringUtils.isEmpty(dataSourceProperty.getPublicKey()))?{
????????????dataSourceProperty.setPublicKey(publicKey);
????????}
????????HikariConfig?config?=?dataSourceProperty.getHikari().toHikariConfig(hikariCpConfig);
????????config.setUsername(dataSourceProperty.getUsername());
????????config.setPassword(dataSourceProperty.getPassword());
????????config.setJdbcUrl(dataSourceProperty.getUrl());
????????config.setPoolName(dataSourceProperty.getPoolName());
????????String?driverClassName?=?dataSourceProperty.getDriverClassName();
????????if?(!StringUtils.isEmpty(driverClassName))?{
????????????config.setDriverClassName(driverClassName);
????????}
????????return?new?HikariDataSource(config);
????}

?//判斷是否是HikariCp數據源
????@Override
????public?boolean?support(DataSourceProperty?dataSourceProperty)?{
????????Class?type?=?dataSourceProperty.getType();
????????return?(type?==?null?&&?hikariExists)?||?(type?!=?null?&&?HIKARI_DATASOURCE.equals(type.getName()));
????}
}

再回到之前的，當拿到DataSource的Map集合之后，再做什么呢？

接著調addDataSource()方法，這個方法是根據下劃線"_"對數據源進行分組，最后放到groupDataSources成員變量里面。

/**
?????*?新數據源添加到分組
?????*
?????*?@param?ds?????????新數據源的名字
?????*?@param?dataSource?新數據源
?????*/
private?void?addGroupDataSource(String?ds,?DataSource?dataSource)?{
????if?(ds.contains(UNDERLINE))?{
????????String?group?=?ds.split(UNDERLINE)[0];
????????GroupDataSource?groupDataSource?=?groupDataSources.get(group);
????????if?(groupDataSource?==?null)?{
????????????try?{
????????????????//順便設置負載均衡策略，strategy默認是LoadBalanceDynamicDataSourceStrategy
????????????????groupDataSource?=?new?GroupDataSource(group,?strategy.getDeclaredConstructor().newInstance());
????????????????groupDataSources.put(group,?groupDataSource);
????????????}?catch?(Exception?e)?{
????????????????throw?new?RuntimeException("dynamic-datasource?-?add?the?datasource?named?"?+?ds?+?"?error",?e);
????????????}
????????}
????????groupDataSource.addDatasource(ds,?dataSource);
????}
}

分組的時候，會順便把負載均衡策略也一起設置進去。這個負載均衡是做什么呢？

比如一個組master里有三個數據源（A、B、C），需要合理地分配使用的頻率，不可能全都使用某一個，那么這就需要負載均衡策略，默認是輪詢，對應的類是：

public?class?LoadBalanceDynamicDataSourceStrategy?implements?DynamicDataSourceStrategy?{

????/**
?????*?負載均衡計數器
?????*/
????private?final?AtomicInteger?index?=?new?AtomicInteger(0);

????@Override
????public?DataSource?determineDataSource(List?dataSources)?{
????????return?dataSources.get(Math.abs(index.getAndAdd(1)?%?dataSources.size()));
????}
}

獲取數據源的時候就通過：

@Override
public?DataSource?determineDataSource()?{
????return?getDataSource(DynamicDataSourceContextHolder.peek());
}

/**
?????*?獲取數據源
?????*
?????*?@param?ds?數據源名稱
?????*?@return?數據源
?????*/
public?DataSource?getDataSource(String?ds)?{
????//沒有傳數據源名稱，默認使用主數據源
????if?(StringUtils.isEmpty(ds))?{
????????return?determinePrimaryDataSource();
????//判斷分組數據源是否包含，如果包含則從分組數據源獲取返回
????}?else?if?(!groupDataSources.isEmpty()?&&?groupDataSources.containsKey(ds))?{
????????log.debug("dynamic-datasource?switch?to?the?datasource?named?[{}]",?ds);
????????return?groupDataSources.get(ds).determineDataSource();
????//如果普通數據源包含，則從普通數據源返回
????}?else?if?(dataSourceMap.containsKey(ds))?{
????????log.debug("dynamic-datasource?switch?to?the?datasource?named?[{}]",?ds);
????????return?dataSourceMap.get(ds);
????}
????if?(strict)?{
????????throw?new?RuntimeException("dynamic-datasource?could?not?find?a?datasource?named"?+?ds);
????}
????return?determinePrimaryDataSource();
}

那么上面的DynamicDataSourceContextHolder這個類是干嘛的呢？注解@DS的值又是怎么傳進來的呢？

回到最開始的自動配置類，其中有一個是配置DynamicDataSourceAnnotationAdvisor的，還設置了一個攔截器：

@Role(value?=?BeanDefinition.ROLE_INFRASTRUCTURE)
@Bean
@ConditionalOnMissingBean
public?DynamicDataSourceAnnotationAdvisor?dynamicDatasourceAnnotationAdvisor(DsProcessor?dsProcessor)?{
????//創(chuàng)建攔截器
????DynamicDataSourceAnnotationInterceptor?interceptor?=?new?DynamicDataSourceAnnotationInterceptor(properties.isAllowedPublicOnly(),?dsProcessor);
????DynamicDataSourceAnnotationAdvisor?advisor?=?new?DynamicDataSourceAnnotationAdvisor(interceptor);
????advisor.setOrder(properties.getOrder());
????return?advisor;
}

DynamicDataSourceAnnotationAdvisor是用于AOP切面編程的，針對注解@DS的切面進行處理：

public?class?DynamicDataSourceAnnotationAdvisor?extends?AbstractPointcutAdvisor?implements?BeanFactoryAware?{

????//通知
????private?final?Advice?advice;

????//切入點
????private?final?Pointcut?pointcut;

????public?DynamicDataSourceAnnotationAdvisor(@NonNull?DynamicDataSourceAnnotationInterceptor?dynamicDataSourceAnnotationInterceptor)?{
????????this.advice?=?dynamicDataSourceAnnotationInterceptor;
????????this.pointcut?=?buildPointcut();
????}

????@Override
????public?Pointcut?getPointcut()?{
????????return?this.pointcut;
????}

????@Override
????public?Advice?getAdvice()?{
????????return?this.advice;
????}

????@Override
????public?void?setBeanFactory(BeanFactory?beanFactory)?throws?BeansException?{
????????if?(this.advice?instanceof?BeanFactoryAware)?{
????????????((BeanFactoryAware)?this.advice).setBeanFactory(beanFactory);
????????}
????}

????private?Pointcut?buildPointcut()?{
????????//類上面添加了注解
????????Pointcut?cpc?=?new?AnnotationMatchingPointcut(DS.class,?true);
????????//方法上添加了注解
????????Pointcut?mpc?=?new?AnnotationMethodPoint(DS.class);
????????//方法優(yōu)于類
????????return?new?ComposablePointcut(cpc).union(mpc);
????}
}

切入點我們都清楚了，是@DS注解。那么做了什么處理，主要看advice，也就是傳進來的那個攔截器

DynamicDataSourceAnnotationInterceptor。

public?class?DynamicDataSourceAnnotationInterceptor?implements?MethodInterceptor?{

????/**
?????*?The?identification?of?SPEL.
?????*/
????private?static?final?String?DYNAMIC_PREFIX?=?"#";

????private?final?DataSourceClassResolver?dataSourceClassResolver;
????private?final?DsProcessor?dsProcessor;

????public?DynamicDataSourceAnnotationInterceptor(Boolean?allowedPublicOnly,?DsProcessor?dsProcessor)?{
????????dataSourceClassResolver?=?new?DataSourceClassResolver(allowedPublicOnly);
????????this.dsProcessor?=?dsProcessor;
????}

????@Override
????public?Object?invoke(MethodInvocation?invocation)?throws?Throwable?{
????????//找到@DS注解的屬性值，也就是數據源名稱
????????String?dsKey?=?determineDatasourceKey(invocation);
????????//把數據源名稱push到當前線程的棧
????????DynamicDataSourceContextHolder.push(dsKey);
????????try?{
????????????//執(zhí)行當前方法
????????????return?invocation.proceed();
????????}?finally?{
????????????//從棧里釋放數據源
????????????DynamicDataSourceContextHolder.poll();
????????}
????}

????//這個是使用責任鏈模式進行一些處理，可以先不管他
????private?String?determineDatasourceKey(MethodInvocation?invocation)?{
????????String?key?=?dataSourceClassResolver.findDSKey(invocation.getMethod(),?invocation.getThis());
????????return?(!key.isEmpty()?&&?key.startsWith(DYNAMIC_PREFIX))???dsProcessor.determineDatasource(invocation,?key)?:?key;
????}
}

這里也有一個DynamicDataSourceContextHolder，這樣就跟前面獲取數據連接關聯(lián)起來了，最后我們看一下這個類的源碼：

/**
?*?核心基于ThreadLocal的切換數據源工具類
?*
?*?@author?TaoYu?Kanyuxia
?*?@since?1.0.0
?*/
public?final?class?DynamicDataSourceContextHolder?{

????/**
?????*?為什么要用鏈表存儲(準確的是棧)
?????*?

?????*?為了支持嵌套切換，如ABC三個service都是不同的數據源
?????*?其中A的某個業(yè)務要調B的方法，B的方法需要調用C的方法。一級一級調用切換，形成了鏈。
?????*?傳統(tǒng)的只設置當前線程的方式不能滿足此業(yè)務需求，必須使用棧，后進先出。
?????*?

?????*/
????private?static?final?ThreadLocal>?LOOKUP_KEY_HOLDER?=?new?NamedThreadLocal>("dynamic-datasource")?{
????????@Override
????????protected?Deque?initialValue()?{
????????????return?new?ArrayDeque<>();
????????}
????};

????private?DynamicDataSourceContextHolder()?{
????}

????/**
?????*?獲得當前線程數據源
?????*
?????*?@return?數據源名稱
?????*/
????public?static?String?peek()?{
????????return?LOOKUP_KEY_HOLDER.get().peek();
????}

????/**
?????*?設置當前線程數據源
?????*?

?????*?如非必要不要手動調用，調用后確保最終清除
?????*?

?????*
?????*?@param?ds?數據源名稱
?????*/
????public?static?void?push(String?ds)?{
????????LOOKUP_KEY_HOLDER.get().push(StringUtils.isEmpty(ds)???""?:?ds);
????}

????/**
?????*?清空當前線程數據源
?????*?

?????*?如果當前線程是連續(xù)切換數據源?只會移除掉當前線程的數據源名稱
?????*?

?????*/
????public?static?void?poll()?{
????????Deque?deque?=?LOOKUP_KEY_HOLDER.get();
????????deque.poll();
????????if?(deque.isEmpty())?{
????????????LOOKUP_KEY_HOLDER.remove();
????????}
????}

????/**
?????*?強制清空本地線程
?????*?

?????*?防止內存泄漏，如手動調用了push可調用此方法確保清除
?????*?

?????*/
????public?static?void?clear()?{
????????LOOKUP_KEY_HOLDER.remove();
????}
}

這里為什么使用棧，主要是會存在嵌套切換數據源的情況，也就是最里面那層數據源應該先釋放，最外面那層的數據源應該最后釋放，所以需要用棧的數據結構。

整體流程

可能大家還是有點暈，畢竟有點繞，很正常。那么想研究透徹一點，我建議大家自己打開IDEA，參考我寫的去研究一下。這里我畫個整體的流程圖，能有個大概的思路：

總結

源碼解析能提高讀代碼的能力，讀代碼的能力我覺得是很重要的，因為當我們加入一個新公司的時候，對項目不熟悉，那么就需要從文檔，代碼上面去了解項目。讀懂代碼才能去修改、擴展。

這篇文章介紹的這個框架的源碼解析只是涉及核心代碼，所以不是很難，有興趣的同學可以自己多看幾遍。多數據源的應用在日常項目中也是很常見的場景。

非常感謝你的閱讀，希望這篇文章能給到你幫助和啟發(fā)。

覺得有用就點個贊吧，你的點贊是我創(chuàng)作的最大動力~

我是一個努力讓大家記住的程序員。我們下期再見！！！

能力有限，如果有什么錯誤或者不當之處，請大家批評指正，一起學習交流！