spring+ibatis实现DB的动态切换2(AbstractRoutingDataSource的原理)

r囧r小猫 2022-08-25 11:58 128阅读 0赞

转：http://www.360doc.com/content/14/0305/16/16118748\_357970326.shtml

最近要为公司多个游戏做类似的统计功能，考虑到模块的复用性，决定做个动态数据源，根据不同的游戏参数切换不同的datasource。

网上查了下，spring2.0以后增加了AbstractRoutingDataSource这个东西。下面是实现方法

首先看下AbstractRoutingDataSource类结构，继承了AbstractDataSource

public abstract class AbstractRoutingDataSource extends AbstractDataSource implements InitializingBean {  
      
    }

既然是AbstractDataSource，当然就是javax.sql.DataSource的子类，于是我们自然地回去看它的getConnection方法：

public Connection getConnection() throws SQLException {  
        return determineTargetDataSource().getConnection();  
    }

原来奥妙就在determineTargetDataSource()里：

/** 
     * 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");  
        Object lookupKey = determineCurrentLookupKey();  
        DataSource dataSource = (DataSource) this.resolvedDataSources.get(lookupKey);  
        if (dataSource == null) {  
            dataSource = this.resolvedDefaultDataSource;  
        }  
        if (dataSource == null) {  
            throw new IllegalStateException("Cannot determine target DataSource for lookup key [" + lookupKey + "]");  
        }  
        return dataSource;  
    }

这里用到了我们需要进行实现的抽象方法determineCurrentLookupKey()，该方法返回需要使用的DataSource的key值，然后根据这个key从resolvedDataSources这个map里取出对应的DataSource，如果找不到，则用默认的resolvedDefaultDataSource

观察上面的配置文件，发现我们配置的是targetDataSources和defaultTargetDataSource

public void afterPropertiesSet() {  
        if (this.targetDataSources == null) {  
            throw new IllegalArgumentException("targetDataSources is required");  
        }  
        this.resolvedDataSources = new HashMap(this.targetDataSources.size());  
        for (Iterator it = this.targetDataSources.entrySet().iterator(); it.hasNext();) {  
            Map.Entry entry = (Map.Entry) it.next();  
            Object lookupKey = resolveSpecifiedLookupKey(entry.getKey());  
            DataSource dataSource = resolveSpecifiedDataSource(entry.getValue());  
            this.resolvedDataSources.put(lookupKey, dataSource);  
        }  
        if (this.defaultTargetDataSource != null) {  
            this.resolvedDefaultDataSource = resolveSpecifiedDataSource(this.defaultTargetDataSource);  
        }  
    }

下面就是我们自己实现的子类DynamicDataSource

public class DynamicDataSource extends AbstractRoutingDataSource{  
          
        @Override  
        public void setTargetDataSources(Map targetDataSources) {  
            super.setTargetDataSources(targetDataSources);  
        }  
          
        @Override  
        public Object unwrap(Class iface) throws SQLException {  
            return null;  
        }  
      
        @Override  
        public boolean isWrapperFor(Class iface) throws SQLException {  
            return false;  
        }  
      
        @Override  
        protected Object determineCurrentLookupKey() {  
            String dataSourceName = DynamicDataSourceHolder.getDataSourceName();  
            return dataSourceName;  
        }

DynamicDataSourceHolder

public class DynamicDataSourceHolder {  
      
        private static final ThreadLocal<String> holder = new ThreadLocal<String>();  
          
        public static void putDataSourceName(String name){  
            holder.set(name);  
        }  
          
        public static String getDataSourceName(){  
            return holder.get();  
        }  
    }