Tomcat中对外观模式的使用

org.apache.catalina.connector.Request

public class Request
implements HttpServletRequest {
    // ...
    protected RequestFacade facade = null;
    // ...
    /**
     * Return the <code>ServletRequest</code> for which this object
     * is the facade.  This method must be implemented by a subclass.
     */
    public HttpServletRequest getRequest() {
        if (facade == null) {
            facade = new RequestFacade(this);
        }
        return facade;
    }
}

org.apache.catalina.connector.RequestFacade

public class RequestFacade implements HttpServletRequest {
    // ...    
}

Spring中对外观模式的使用

org.springframework.jdbc.support.JdbcUtils

• 在 JdbcUtils 封装了对 java.sql.Connection 的使用；
• JdbcUtils 和 java.sql.Connection 都属于抽象层的依赖关系；

public abstract class JdbcUtils {
    // ...
    public static void closeConnection(Connection con) {
        if (con != null) {
            try {
                con.close();
            }
            catch (SQLException ex) {
                logger.debug("Could not close JDBC Connection", ex);
            }
            catch (Throwable ex) {
                // We don't trust the JDBC driver: It might throw RuntimeException or Error.
                logger.debug("Unexpected exception on closing JDBC Connection", ex);
            }
        }
    }
    // ...
}

Mybatis中对外观模式的使用

• Configuration 作为外观类对外提供接口；
• Configuration 中关联了很多其他的类（子系统），Configuration 的接口对这些类的功能进行封装，对外屏蔽对这些成员的组合调用；

public class Configuration {
    // ...
    protected ObjectFactory objectFactory = new DefaultObjectFactory();
    protected ObjectWrapperFactory objectWrapperFactory = new DefaultObjectWrapperFactory();
    protected ReflectorFactory reflectorFactory = new DefaultReflectorFactory();
    // ...
    public MetaObject newMetaObject(Object object) {
        return MetaObject.forObject(object, objectFactory, objectWrapperFactory,  reflectorFactory);
    }
}