手撸dynamic源码详细讲解
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本文源码解析基于3.3.1版本。只截了重点代码，如果需要看完整代码，可以去github拉取。
1 自动配置的实现
一般情况下，一个starter的最好入手点就是自动配置类，在 META-INF/spring.factories文件中指定自动配置类入口
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.baomidou.dynamic.datasource.spring.boot.autoconfigure.DynamicDataSourceAutoConfiguration
在spring.factories配置文件中，可以看到这个项目的自动配置类，从核心配置类入手，可以说DynamicDataSourceAutoConfiguration这个是整个程序的main方法，spring启动时会去执行 下面简单的给出DynamicDataSourceAutoConfiguration这个类的核心部分：
/**
* 动态数据源核心自动配置类
*/
@Slf4j
@Configuration
@AllArgsConstructor
// 读取以spring.datasource.dynamic为前缀的配置
@EnableConfigurationProperties(DynamicDataSourceProperties.class)
// 需要在spring boot的DataSource bean自动配置之前注入我们的DataSource bean
@AutoConfigureBefore(DataSourceAutoConfiguration.class)
// 引入了Druid的autoConfig和各种数据源连接池的Creator
@Import(value = {DruidDynamicDataSourceConfiguration.class, DynamicDataSourceCreatorAutoConfiguration.class})
// 当含有spring.datasource.dynamic配置的时候，启用这个autoConfig
@ConditionalOnProperty(prefix = DynamicDataSourceProperties.PREFIX, name = "enabled", havingValue = "true", matchIfMissing = true)
public class DynamicDataSourceAutoConfiguration {
private final DynamicDataSourceProperties properties;
/**
* 多数据源加载接口，默认从yml中读取多数据源配置
* @return DynamicDataSourceProvider
*/
@Bean
@ConditionalOnMissingBean
public DynamicDataSourceProvider dynamicDataSourceProvider() {
Map<String, DataSourceProperty> datasourceMap = properties.getDatasource();
return new YmlDynamicDataSourceProvider(datasourceMap);
}
/**
* 注册自己的动态多数据源DataSource
* @param dynamicDataSourceProvider 各种数据源连接池创建者
* @return 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，对DS注解过的方法进行增强，达到切换数据源的目的。
* @param dsProcessor 动态参数解析数据源。如果数据源名称以#开头，就会进入这个解析器链。
* @return advisor
*/
@Role(value = BeanDefinition.ROLE_INFRASTRUCTURE)
@Bean
@ConditionalOnMissingBean
public DynamicDataSourceAnnotationAdvisor dynamicDatasourceAnnotationAdvisor(DsProcessor dsProcessor) {
// aop方法拦截器在方法调用前后做操作，设置动态参数解析器
DynamicDataSourceAnnotationInterceptor interceptor = new DynamicDataSourceAnnotationInterceptor(properties.isAllowedPublicOnly(), dsProcessor);
// 使用AbstractPointcutAdvisor将pointcut和advice连接构成切面
DynamicDataSourceAnnotationAdvisor advisor = new DynamicDataSourceAnnotationAdvisor(interceptor);
advisor.setOrder(properties.getOrder());
return advisor;
}
/**
* seata分布式事务支持
*
*/
@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());
}
/**
* 动态参数解析器链
* @return DsProcessor
*/
@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;
}
}
这里自动配置的几个Bean都是非常重要的 先看下自动配置类上面的注解，比较重要的有如下的：
// 读取以spring.datasource.dynamic为前缀的配置
@EnableConfigurationProperties(DynamicDataSourceProperties.class)
@EnableConfigurationProperties这个注解：使使 @ConfigurationProperties 注解的类生效，主要是用来把properties或者yml配置文件转化为bean来使用，这个在实际使用中非常实用
2 配置文件注入
在跟进DynamicDataSourceProperties中：
@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";
/**
* 必须设置默认的库,默认master
*/
private String primary = "master";
/**
* 是否启用严格模式,默认不启动. 严格模式下未匹配到数据源直接报错, 非严格模式下则使用默认数据源primary所设置的数据源
*/
private Boolean strict = false;
/**
* 是否使用p6spy输出，默认不输出
*/
private Boolean p6spy = false;
/**
* 是否使用开启seata，默认不开启
*/
private Boolean seata = false;
/**
* seata使用模式，默认AT
*/
private SeataMode seataMode = SeataMode.AT;
/**
* 是否使用 spring actuator 监控检查，默认不检查
*/
private boolean health = false;
/**
* 每一个数据源
*/
private Map<String, DataSourceProperty> datasource = new LinkedHashMap<>();
/**
* 多数据源选择算法clazz，默认负载均衡算法
*/
private Class<? extends DynamicDataSourceStrategy> strategy = LoadBalanceDynamicDataSourceStrategy.class;
/**
* aop切面顺序，默认优先级最高
*/
private Integer order = Ordered.HIGHEST_PRECEDENCE;
/**
* Druid全局参数配置
*/
@NestedConfigurationProperty
private DruidConfig druid = new DruidConfig();
/**
* HikariCp全局参数配置
*/
@NestedConfigurationProperty
private HikariCpConfig hikari = new HikariCpConfig();
/**
* 全局默认publicKey
*/
private String publicKey = CryptoUtils.DEFAULT_PUBLIC_KEY_STRING;
/**
* aop 切面是否只允许切 public 方法
*/
private boolean allowedPublicOnly = true;
}
可以发现，就是将spring.datasource.dynamic开头的配置文件注入并创建properties对象，需要注意的是，使用了@NestedConfigurationProperty嵌套了其他的配置类。如果不清楚嵌套的其他配置类是什么，看下DynamicDataSourceProperties这个类中的嵌套properties类。比如DruidConfig，代码较长就不全部粘贴进来了，有兴趣跟进看下。重点是它下面有个toProperties方法，为了实现yml配置中每个dataSource下面的durid可以独立配置(若不独立配置，则使用全局配置)，根据全局配置(druid数据池)和独立配置(每个数据源下单独的druid数据源配置)结合转换为Properties，然后在DruidDataSourceCreator类(下面回讲，作用是创建不同的数据源)中根据这个配置创建druid连接池
3 如何集成多种数据池并创建
集成连接池配置项是通过DynamicDataSourceProperties配置类实现的，其中除了上面提到的druid嵌套配置，还有hikari等，但是如何通过这些配置项生成真正的数据源连接池？让我们来看creator包下的类
见名知意，能看出这些就是根据DynamicDataSourceProperties中的配置，生成对应连接池，这里具体实现暂且不看，先看下不同数据源的数据池对象是怎么保存并在使用时获取的 还是最开始的自动配置类中的方法：
@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;
}
这里创建了个DynamicRoutingDataSource，该类实现了InitializingBean接口，在bean初始化时做一些操作。
@Slf4j
public class DynamicRoutingDataSource extends AbstractRoutingDataSource implements InitializingBean, DisposableBean {
private static final String UNDERLINE = "_";
/**
* 所有数据库
*/
private final Map<String, DataSource> dataSourceMap = new ConcurrentHashMap<>();
/**
* 分组数据库
*/
private final Map<String, GroupDataSource> groupDataSources = new ConcurrentHashMap<>();
@Setter
private DynamicDataSourceProvider provider;
@Setter
private Class<? extends DynamicDataSourceStrategy> 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);
}
/**
* 获取当前所有的数据源
*
* @return 当前所有数据源
*/
public Map<String, DataSource> getCurrentDataSources() {
return dataSourceMap;
}
/**
* 获取的当前所有的分组数据源
*
* @return 当前所有的分组数据源
*/
public Map<String, GroupDataSource> getCurrentGroupDataSources() {
return groupDataSources;
}
/**
* 获取数据源
*
* @param ds 数据源名称
* @return 数据源
*/
public DataSource getDataSource(String ds) {
if (StringUtils.isEmpty(ds)) {
return determinePrimaryDataSource();
} else if (!groupDataSources.isEmpty() && groupDataSources.containsKey(ds)) {
log.debug("dynamic-datasource switch to the datasource named [{}]", ds);
return groupDataSources.get(ds).determineDataSource();
} 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();
}
/**
* 添加数据源
*
* @param ds 数据源名称
* @param dataSource 数据源
*/
public synchronized void addDataSource(String ds, DataSource dataSource) {
DataSource oldDataSource = dataSourceMap.put(ds, dataSource);
// 新数据源添加到分组
this.addGroupDataSource(ds, dataSource);
// 关闭老的数据源
if (oldDataSource != null) {
try {
closeDataSource(oldDataSource);
} catch (Exception e) {
log.error("dynamic-datasource - remove the database named [{}] failed", ds, e);
}
}
log.info("dynamic-datasource - load a datasource named [{}] success", ds);
}
/**
* 新数据源添加到分组
*
* @param ds 新数据源的名字
* @param dataSource 新数据源
*/
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 {
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);
}
}
/**
* 删除数据源
*
* @param ds 数据源名称
*/
public synchronized void removeDataSource(String ds) {
if (!StringUtils.hasText(ds)) {
throw new RuntimeException("remove parameter could not be empty");
}
if (primary.equals(ds)) {
throw new RuntimeException("could not remove primary datasource");
}
if (dataSourceMap.containsKey(ds)) {
DataSource dataSource = dataSourceMap.remove(ds);
try {
closeDataSource(dataSource);
} catch (Exception e) {
log.error("dynamic-datasource - remove the database named [{}] failed", ds, e);
}
if (ds.contains(UNDERLINE)) {
String group = ds.split(UNDERLINE)[0];
if (groupDataSources.containsKey(group)) {
DataSource oldDataSource = groupDataSources.get(group).removeDatasource(ds);
if (oldDataSource == null) {
if (log.isWarnEnabled()) {
log.warn("fail for remove datasource from group. dataSource: {} ,group: {}", ds, group);
}
}
}
}
log.info("dynamic-datasource - remove the database named [{}] success", ds);
} else {
log.warn("dynamic-datasource - could not find a database named [{}]", ds);
}
}
/**
* 关闭数据源。
* <pre>
* 从3.2.0开启，如果是原生或使用 DataSourceCreator 创建的数据源会包装成ItemDataSource。
* ItemDataSource保留了最原始的数据源，其可直接关闭。
* 如果不是DataSourceCreator创建的数据源则只有尝试解包装再关闭。
* </pre>
*/
private void closeDataSource(DataSource dataSource) throws Exception {
if (dataSource instanceof ItemDataSource) {
((ItemDataSource) dataSource).close();
} else {
if (seata && dataSource instanceof DataSourceProxy) {
DataSourceProxy dataSourceProxy = (DataSourceProxy) dataSource;
dataSource = dataSourceProxy.getTargetDataSource();
}
if (p6spy && dataSource instanceof P6DataSource) {
Field realDataSourceField = P6DataSource.class.getDeclaredField("realDataSource");
realDataSourceField.setAccessible(true);
dataSource = (DataSource) realDataSourceField.get(dataSource);
}
Class<? extends DataSource> clazz = dataSource.getClass();
Method closeMethod = clazz.getDeclaredMethod("close");
closeMethod.invoke(dataSource);
}
}
@Override
public void destroy() throws Exception {
log.info("dynamic-datasource start closing ....");
for (Map.Entry<String, DataSource> item : dataSourceMap.entrySet()) {
closeDataSource(item.getValue());
}
log.info("dynamic-datasource all closed success,bye");
}
@Override
public void afterPropertiesSet() throws Exception {
// 检查开启了配置但没有相关依赖
checkEnv();
// 添加并分组数据源
Map<String, DataSource> dataSources = provider.loadDataSources();
for (Map.Entry<String, DataSource> dsItem : dataSources.entrySet()) {
addDataSource(dsItem.getKey(), dsItem.getValue());
}
// 检测默认数据源是否设置
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");
}
}
private void checkEnv() {
if (p6spy) {
try {
Class.forName("com.p6spy.engine.spy.P6DataSource");
log.info("dynamic-datasource detect P6SPY plugin and enabled it");
} catch (Exception e) {
throw new RuntimeException("dynamic-datasource enabled P6SPY ,however without p6spy dependency", e);
}
}
if (seata) {
try {
Class.forName("io.seata.rm.datasource.DataSourceProxy");
log.info("dynamic-datasource detect ALIBABA SEATA and enabled it");
} catch (Exception e) {
throw new RuntimeException("dynamic-datasource enabled ALIBABA SEATA,however without seata dependency", e);
}
}
}
}
这个类就是核心动态数据源组件。它将DataSource维护在map里，这里重点看如何创建数据源连接池。它所做的操作就是：afterPropertiesSet这个方法在当前Bean对象所有属性设置之后执行的，从provider获取创建好的数据源map，然后解析这个map对其分组。下面来看看这个provider里面是如何创建这个数据源map的 还是返回最开始的自动配置类，看下provider对象创建:
@Bean
@ConditionalOnMissingBean
public DynamicDataSourceProvider dynamicDataSourceProvider() {
Map<String, DataSourceProperty> datasourceMap = properties.getDatasource();
return new YmlDynamicDataSourceProvider(datasourceMap);
}
在自动装配中注入的这个YmlDynamicDataSourceProvider，是通过yml读取配置文件生成的，调用构造方法时传递进去DynamicDataSourceProperties中的 数据源名称和数据源下面配置(url,username,password等等)的map映射集合 继续跟进，看下YmlDynamicDataSourceProvider中的内容，除了传递进来的**Map<String, DataSourceProperty>**外，有且只有一个方法：
@Override
public Map<String, DataSource> loadDataSources() {
return createDataSourceMap(dataSourcePropertiesMap);
}
我们继续跟进，一直到DefaultDataSourceCreator这个类的createDataSource方法为止，上问提到过creator就是用来根据properties配置创建数据池对象的，下面看下这个类的代码，重点是createDataSource方法：
@Slf4j
@Setter
public class DefaultDataSourceCreator implements DataSourceCreator {
private DynamicDataSourceProperties properties;
private List<DataSourceCreator> creators;
@Override
public DataSource createDataSource(DataSourceProperty dataSourceProperty) {
return createDataSource(dataSourceProperty, properties.getPublicKey());
}
@Override
public DataSource createDataSource(DataSourceProperty dataSourceProperty, String publicKey) {
DataSourceCreator dataSourceCreator = null;
for (DataSourceCreator creator : this.creators) {
if (creator.support(dataSourceProperty)) {
dataSourceCreator = creator;
break;
}
}
if (dataSourceCreator == null) {
throw new IllegalStateException("creator must not be null,please check the DataSourceCreator");
}
DataSource dataSource = dataSourceCreator.createDataSource(dataSourceProperty, publicKey);
this.runScrip(dataSource, dataSourceProperty);
return wrapDataSource(dataSource, dataSourceProperty);
}
private void runScrip(DataSource dataSource, DataSourceProperty dataSourceProperty) {
String schema = dataSourceProperty.getSchema();
String data = dataSourceProperty.getData();
if (StringUtils.hasText(schema) || StringUtils.hasText(data)) {
ScriptRunner scriptRunner = new ScriptRunner(dataSourceProperty.isContinueOnError(), dataSourceProperty.getSeparator());
if (StringUtils.hasText(schema)) {
scriptRunner.runScript(dataSource, schema);
}
if (StringUtils.hasText(data)) {
scriptRunner.runScript(dataSource, data);
}
}
}
private DataSource wrapDataSource(DataSource dataSource, DataSourceProperty dataSourceProperty) {
String name = dataSourceProperty.getPoolName();
DataSource targetDataSource = dataSource;
Boolean enabledP6spy = properties.getP6spy() && dataSourceProperty.getP6spy();
if (enabledP6spy) {
targetDataSource = new P6DataSource(dataSource);
log.debug("dynamic-datasource [{}] wrap p6spy plugin", name);
}
Boolean enabledSeata = properties.getSeata() && dataSourceProperty.getSeata();
SeataMode seataMode = properties.getSeataMode();
if (enabledSeata) {
if (SeataMode.XA == seataMode) {
targetDataSource = new DataSourceProxyXA(dataSource);
} else {
targetDataSource = new DataSourceProxy(dataSource);
}
log.debug("dynamic-datasource [{}] wrap seata plugin transaction mode [{}]", name, seataMode);
}
return new ItemDataSource(name, dataSource, targetDataSource, enabledP6spy, enabledSeata, seataMode);
}
public void setDataSourceCreators(List<DataSourceCreator> dataSourceCreator) {
this.creators = dataSourceCreator;
}
@Override
public boolean support(DataSourceProperty dataSourceProperty) {
return true;
}
}
上文提到过creator见名知意，这里的createDataSource方法，就是根据对应的properties对象中的属性来判断使用哪个creator去创建datasource对象，拿到这里所有的过程都明朗了，这也就是dynamic集成多种数据池创建数据源的关键
4 @DS注解是如何被拦截增强的
先总结下，上面聊了，DynamicRoutingDataSource内部维持了一个map集合存储数据源名称和数据源对象的映射，而这个map映射是provider对象进行的，然后具体的类型的datasource又是由creator进行的 那么具体是如何通过注解实现的切换数据源的，众所周知，spring中注解拦截处理离不开AOP，这里介绍代码中如何使用AOP
再次返回最开始的自动配置类，从DynamicDataSourceAutoConfiguration入口配置类中dynamicDatasourceAnnotationAdvisor(DsProcessor dsProcessor)方法入手，该方法注入了一个DynamicDataSourceAnnotationAdvisor类型的bean对象 讲解之前，先简单介绍下spring中的advisor，几个概念：
- advice: 具体进行的增强
- pointcut：配置需要增强的规则，可以是切点表达式等
- advisor: Advice 和 Pointcut 组成的独立的单元，并且能够传给 proxy factory 对象
我们看下DynamicDataSourceAnnotationAdvisor这个切面的代码：
public class DynamicDataSourceAnnotationAdvisor extends AbstractPointcutAdvisor implements BeanFactoryAware {
// 通知
private final Advice advice;
// 切入点
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() {
// 类级别
Pointcut cpc = new AnnotationMatchingPointcut(DS.class, true);
// 方法级别
Pointcut mpc = new AnnotationMethodPoint(DS.class);
// 合并类和方法上添加的注解，类上的注解会绑定到每个方法上。
return new ComposablePointcut(cpc).union(mpc);
}
/**
* In order to be compatible with the spring lower than 5.0
*/
private static class AnnotationMethodPoint implements Pointcut {
private final Class<? extends Annotation> annotationType;
public AnnotationMethodPoint(Class<? extends Annotation> annotationType) {
Assert.notNull(annotationType, "Annotation type must not be null");
this.annotationType = annotationType;
}
@Override
public ClassFilter getClassFilter() {
return ClassFilter.TRUE;
}
@Override
public MethodMatcher getMethodMatcher() {
return new AnnotationMethodMatcher(annotationType);
}
private static class AnnotationMethodMatcher extends StaticMethodMatcher {
private final Class<? extends Annotation> annotationType;
public AnnotationMethodMatcher(Class<? extends Annotation> annotationType) {
this.annotationType = annotationType;
}
@Override
public boolean matches(Method method, Class<?> targetClass) {
if (matchesMethod(method)) {
return true;
}
// Proxy classes never have annotations on their redeclared methods.
if (Proxy.isProxyClass(targetClass)) {
return false;
}
// The method may be on an interface, so let's check on the target class as well.
Method specificMethod = AopUtils.getMostSpecificMethod(method, targetClass);
return (specificMethod != method && matchesMethod(specificMethod));
}
private boolean matchesMethod(Method method) {
return AnnotatedElementUtils.hasAnnotation(method, this.annotationType);
}
}
}
}
先现在看下@DS注解的advisor实现，在buildPointcut方法里拦截了被@DS注解的方法或类，并且使用ComposablePointcut组合切入点，可以实现方法优先级大于类优先级的特性。DynamicDataSourceAnnotationAdvisor通过构造方法传过来的参数类型是DynamicDataSourceAnnotationInterceptor类，跟进观察该类
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 {
String dsKey = determineDatasourceKey(invocation);
// 把获取到的数据源标识(如master)存入本地线程
DynamicDataSourceContextHolder.push(dsKey);
try {
return invocation.proceed();
} finally {
DynamicDataSourceContextHolder.poll();
}
}
private String determineDatasourceKey(MethodInvocation invocation) {
String key = dataSourceClassResolver.findDSKey(invocation.getMethod(), invocation.getThis());
// 如果DS注解内容是以#开头，则解析动态最终值；否则，直接返回。
return (!key.isEmpty() && key.startsWith(DYNAMIC_PREFIX)) ? dsProcessor.determineDatasource(invocation, key) : key;
}
}
这是它的advice通知（也可以说是方法拦截器）执行的动作：在要切换数据源的方法执行前，将“切换的数据源”放入了holder里，等方法执行完后在finally中释放掉，完成当前数据源的切换。该类的determineDatasource()方法决定具体使用哪个数据源
5 总结
通过阅读dynamic源码，熟悉了spring aop、spring事务管理、spring boot自动配置等spring知识点，本质上dynamic的源码并不难，主要是去理解其对spring的一些机制的使用，还有其中涉及到的设计模式和编码方式
转载自:https://juejin.cn/post/7347165355586502693