分布式访问框架halo-dal设计思想

/*
 * Copyright 2002-2008 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.jdbc.datasource;

import java.io.PrintWriter;
import java.sql.SQLException;
import javax.sql.DataSource;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.util.Assert;

/**
 * Abstract base class for Spring's {@link javax.sql.DataSource}
 * implementations, taking care of the padding.
 *
 * <p>'Padding' in the context of this class means default implementations
 * for certain methods from the <code>DataSource</code> interface, such as
 * {@link #getLoginTimeout()}, {@link #setLoginTimeout(int)}, and so forth.
 *
 * @author Juergen Hoeller
 * @since 07.05.2003
 * @see DriverManagerDataSource
 */
public abstract class AbstractDataSource implements DataSource {

	/** Logger available to subclasses */
	protected final Log logger = LogFactory.getLog(getClass());


	/**
	 * Returns 0, indicating the default system timeout is to be used.
	 */
	public int getLoginTimeout() throws SQLException {
		return 0;
	}

	/**
	 * Setting a login timeout is not supported.
	 */
	public void setLoginTimeout(int timeout) throws SQLException {
		throw new UnsupportedOperationException("setLoginTimeout");
	}

	/**
	 * LogWriter methods are not supported.
	 */
	public PrintWriter getLogWriter() {
		throw new UnsupportedOperationException("getLogWriter");
	}

	/**
	 * LogWriter methods are not supported.
	 */
	public void setLogWriter(PrintWriter pw) throws SQLException {
		throw new UnsupportedOperationException("setLogWriter");
	}


	//---------------------------------------------------------------------
	// Implementation of JDBC 4.0's Wrapper interface
	//---------------------------------------------------------------------

	@SuppressWarnings("unchecked")
	public <T> T  unwrap(Class<T> iface) throws SQLException {
		Assert.notNull(iface, "Interface argument must not be null");
		if (!DataSource.class.equals(iface)) {
			throw new SQLException("DataSource of type [" + getClass().getName() +
					"] can only be unwrapped as [javax.sql.DataSource], not as [" + iface.getName());
		}
		return (T) this;
	}

	public boolean isWrapperFor(Class<?> iface) throws SQLException {
		return DataSource.class.equals(iface);
	}

}

@SuppressWarnings("unchecked")  
    public <T> T  unwrap(Class<T> iface) throws SQLException {  
        Assert.notNull(iface, "Interface argument must not be null");  
        if (!DataSource.class.equals(iface)) {  
            throw new SQLException("DataSource of type [" + getClass().getName() +  
                    "] can only be unwrapped as [javax.sql.DataSource], not as [" + iface.getName());  
        }  
        return (T) this;  
    }  
  
    public boolean isWrapperFor(Class<?> iface) throws SQLException {  
        return DataSource.class.equals(iface);  
    }