2023.4.6周四每日博客

为了实现多表间相互的查询，今天学习的多表连接，

我们都知道，在SSM框架中，我们在applicationContext.xml

配置文件中添加数据源就可以实现数据库增删改查

但是只能连接一个数据库，这个时候我们就要从spring提供的源码下手看看有没有有关数据源切换的方法

，找到关键源码（AbstractRoutingDataSource类，

该类就相当于一个dataSource的调度者，用于根据key值来进行切换对应的dataSource。）：

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

@Override
public Connection getConnection(String username, String password) throws SQLException {
return determineTargetDataSource().getConnection(username, password);
}

/**
* 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 = 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;
}

/**
* Determine the current lookup key. This will typically be
* implemented to check a thread-bound transaction context.
* <p>Allows for arbitrary keys. The returned key needs
* to match the stored lookup key type, as resolved by the
* {@link #resolveSpecifiedLookupKey} method.
*/
protected abstract Object determineCurrentLookupKey();
可以看出方法getConnection()调用的determineTargetDataSource则是关键方法，这个方法返回了具体使用的是哪个数据库；而

determineCurrentLookupKey()方法来返回当前数据源的key值。

通过对这个方法的调用·可初步实现不同表单间的连接