Spring多数据源管理实现原理
[TOC]
应用场景：
大部分单一架构项目连接一台数据库服务器，但随着业务的增加数据库数据量不断飙升，数据库达到性能瓶颈，大部分技术人员都会对数据库主从配置；既然读写分离那就需要连接两个不同的数据库，这时候Spring多数据源管理类AbstractRoutingDataSource就要派上用场了（排除使用数据库集群管理工具统一管理的应用场景）
源码分析：
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;
...
}
通过源码可以看出该类是一个抽象类，定义了6个属性。
targetDataSources：是一个map类型该属性正是用来维护项目中多个数据源
defaultTargetDataSource：通过属性名很直观的可以理解它的作用（默认数据源）
lenientFallback：默认为true，无需改动
dataSourceLookup：查找数据源接口的名称
resolvedDataSources：如果该字段没有赋值，就是targetDataSources
resolvedDefaultDataSource：改变后的数据源
public interface DataSourceLookup {
/**
* Retrieve the DataSource identified by the given name.
* @param dataSourceName the name of the DataSource
* @return the DataSource (never {@code null})
* @throws DataSourceLookupFailureException if the lookup failed
*/
DataSource getDataSource(String dataSourceName) throws DataSourceLookupFailureException;
}
该类是一个interface并且只有一个方法getDataSource，通过方法的参数名称应该清楚传入一个字符类型的数据源名称获取DataSource
深入理解：
使用数据源的目的就是要获取Connection，接下来就从AbstractRoutingDataSource的getConnection方法一探究竟。
@Override
public Connection getConnection() throws SQLException {
return determineTargetDataSource().getConnection();
}
@Override
public Connection getConnection(String username, String password) throws SQLException {
return determineTargetDataSource().getConnection(username, password);
}
直接进入determineTargetDataSource方法
/**
* Retrieve the current target DataSource. Determines the
* {@link #determineCurrentLookupKey() current lookup key}, performs
* a lookup in the {@link #setTargetDataSources targetDataSources} map,
* falls back to the specified
* {@link #setDefaultTargetDataSource default target DataSource} if necessary.
* @see #determineCurrentLookupKey()
*/
protected DataSource determineTargetDataSource() {
Assert.notNull(this.resolvedDataSources, "DataSource router not initialized");
//该方法是一个抽象方法，返回要从resolvedDataSources查找key，该方法还会实现检查线程绑定事务上下文。
Object lookupKey = determineCurrentLookupKey();
//从resolvedDataSources中取出数据源并返回
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 + "]");
}
return dataSource;
}
代码实现
实现AbstractRoutingDataSource重写determineCurrentLookupKey
/**
* @author yangzhao
* Created by 17/2/7.
*/
public class DynamicDataSource extends AbstractRoutingDataSource {
@Override
protected Object determineCurrentLookupKey() {
String dataSourceName = DataSourceContextHolder.getDataSourceName();
return dataSourceName;
}
}
定义DataSourceContextHolder
/**
* 该类内部维护了{@link ThreadLocal}
* @author yangzhao
* Created by 17/2/7.
*/
public class DataSourceContextHolder {
private static final ThreadLocal<String> contextHolder = new ThreadLocal<String>();
/**
* @Description: 设置数据源类型
* @param dataSourceName 数据源名称
* @return void
* @throws
*/
public static void setDataSourceName(String dataSourceName) {contextHolder.set(dataSourceName);}
/**
* @Description: 获取数据源名称
* @param
* @return String
* @throws
*/
public static String getDataSourceName() {
return contextHolder.get();
}
/**
* @Description: 清除数据源名称
* @param
* @return void
* @throws
*/
public static void clearDataSource() {
contextHolder.remove();
}
}
通过ThreadLocal类使每个线程获取独立的数据源，防止并发访问时获取错误的数据源
基于SpringAop实现数据源动态切换
注解类DataSource
/**
* 数据源
* Created by yangzhao on 17/2/7.
*/
@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface DataSource {
String value() default "defaultSource";
}
增强类（DataSouceAdvisor）
/**
* 增强类
* 实现MethodInterceptor接口，通过反射动态解析方法是否标注@DataSource {@link DataSource}注解。
* 如果已标注@DataSource注解取值，set到{@link DataSourceContextHolder}
* @author yangzhao
* create by 17/10/20
*/
@Component("dataSourceAdvisor")
public class DataSouceAdvisor implements MethodInterceptor {
@Override
public Object invoke(MethodInvocation methodInvocation) throws Throwable {
Method method = methodInvocation.getMethod();
Object aThis = methodInvocation.getThis();
//设置默认数据库
DataSourceContextHolder.setDataSourceName("defaultSource");
DataSource dataSource = aThis.getClass().getAnnotation(DataSource.class);
if (dataSource!=null){
DataSourceContextHolder.setDataSourceName(dataSource.value());
}
dataSource = method.getAnnotation(DataSource.class);
if (dataSource!=null){
DataSourceContextHolder.setDataSourceName(dataSource.value());
}
Object proceed = null;
try {
proceed = methodInvocation.proceed();
}catch (Exception e){
throw e;
}finally {
DataSourceContextHolder.clearDataSource();
}
return proceed;
}
}
核心管理类（DataSourceManager真正实现切换）
/**
* 数据源切换管理类
*
* @author yangzhao
* Created by 17/2/7.
*/
@Component
public class DataSourceManager implements BeanFactoryPostProcessor {
private final Logger logger = LogManager.getLogger(DataSourceManager.class);
/**
* 扫描包
* 一般项目都是以com开头所以这里默认为com
*/
private String pacakgePath = "com";
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
//getconfigs
List<String> configs = getconfigs().stream().collect(Collectors.toList());
//打印所有生成的expression配置信息
configs.forEach(s -> logger.info(s));
//设置aop信息
setAopInfo(configs,beanFactory);
}
/**
* 设置注册bean动态AOP信息
* @param configs
* @param beanFactory
*/
private void setAopInfo(List<String> configs, ConfigurableListableBeanFactory beanFactory) {
if (beanFactory instanceof BeanDefinitionRegistry){
BeanDefinitionRegistry beanDefinitionRegistry = (BeanDefinitionRegistry) beanFactory;
for (String config :configs) {
//增强器
RootBeanDefinition advisor = new RootBeanDefinition(DefaultBeanFactoryPointcutAdvisor.class);
advisor.getPropertyValues().addPropertyValue("adviceBeanName",new RuntimeBeanReference("dataSourceAdvisor").getBeanName());
//切点类
RootBeanDefinition pointCut = new RootBeanDefinition(AspectJExpressionPointcut.class);
pointCut.setScope(BeanDefinition.SCOPE_PROTOTYPE);
pointCut.setSynthetic(true);
pointCut.getPropertyValues().addPropertyValue("expression",config);
advisor.getPropertyValues().addPropertyValue("pointcut",pointCut);
//注册到spring容器
String beanName = BeanDefinitionReaderUtils.generateBeanName(advisor, beanDefinitionRegistry,false);
beanDefinitionRegistry.registerBeanDefinition(beanName,advisor);
}
}
}
public Set<String> getconfigs() {
Set<String> configs = new HashSet<>();
Reflections reflections = new Reflections(new ConfigurationBuilder().addUrls(ClasspathHelper.forPackage(pacakgePath)));
//获取所有标记@DataSource的类
Set<Class<?>> typesAnnotatedWith = reflections.getTypesAnnotatedWith(DataSource.class);
Iterator<Class<?>> iterator = typesAnnotatedWith.iterator();
while (iterator.hasNext()){
Class<?> next = iterator.next();
//获取该类所有方法
Method[] declaredMethods = next.getDeclaredMethods();
for (Method method:declaredMethods){
String classAndMethod = method.getDeclaringClass().getCanonicalName()+"."+method.getName();
//生成expression配置
String expression = "execution (* "+classAndMethod+"(..))";
configs.add(expression);
}
}
reflections = new Reflections(new ConfigurationBuilder().setUrls(ClasspathHelper.forPackage(pacakgePath)).setScanners(new MethodAnnotationsScanner()));
//获取所有类中标记@DataSource的方法
Set<Method> methodsAnnotatedWith = reflections.getMethodsAnnotatedWith(DataSource.class);
Iterator<Method> it = methodsAnnotatedWith.iterator();
while (it.hasNext()){
Method method = it.next();
String classAndMethod = method.getDeclaringClass().getCanonicalName()+"."+method.getName();
//生成expression配置
String expression = "execution (* "+classAndMethod+"(..))";
configs.add(expression);
}
return configs;
}
}
项目地址：https://github.com/yz-java/multiple-data-sources
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