为什么GenericObjectPool.addObject会抛出已检查的异常

Question

有没有任何理由说明Apache（有用）org.apache.commons.pool.impl.commmons.pool.GenericObjectPool.addObject（）被声明为抛出异常？

实际上，org.apache.commons.pool.BaseObjectPool从org.apache.commons.pool接口声明它：

/**
 * Create an object using the {@link PoolableObjectFactory factory} or other
 * implementation dependent mechanism, passivate it, and then place it in the idle object pool.
 * <code>addObject</code> is useful for "pre-loading" a pool with idle objects.
 * (Optional operation).
 *
 * @throws Exception when {@link PoolableObjectFactory#makeObject} fails.
 * @throws IllegalStateException after {@link #close} has been called on this pool.
 * @throws UnsupportedOperationException when this pool cannot add new idle objects.
 */
void addObject() throws Exception, IllegalStateException, UnsupportedOperationException;

为什么不使用RuntimeException的衍生物？

/**
 * Create an object, and place it into the pool.
 * addObject() is useful for "pre-loading" a pool with idle objects.
 */
@Override
public void addObject() throws Exception {
    assertOpen();
    if (_factory == null) {
        throw new IllegalStateException("Cannot add objects without a factory.");
    }
    T obj = _factory.makeObject();
    try {
        assertOpen();
        addObjectToPool(obj, false);
    } catch (IllegalStateException ex) { // Pool closed
        try {
            _factory.destroyObject(obj);
        } catch (Exception ex2) {
            // swallow
        }
        throw ex;
    }
}

Answer 1

嗯，直接答案就在Javadoc中：

@throws Exception when {@link PoolableObjectFactory#makeObject} fails.

（除此之外：工厂界面实际上似乎是PooledObjectFactory，而不是Poolable）

那么，为什么makeObject会抛出异常？对象池的一个常见用例是池化数据库连接，这些连接的创建和销毁成本很高，并且（有时？）有时受到软件许可（N连接许可证）的限制。如果数据库服务器位于远程计算机上，则创建新的数据库连接可能会抛出SQLException，或者可能抛出IOException。 makeObject被声明为抛出Exception，因此当尝试向/从池中放入/重新建立连接时，可以传递和捕获这些已检查的异常。