bridge模式-优快云博客

本文链接：https://blog.youkuaiyun.com/iteye_8208/article/details/82649817

本文深入探讨了Java JDBC API中桥接模式的应用，并通过实例展示了如何通过对象组合的方式，使抽象与其实现分离，实现不同数据库驱动的灵活切换。同时，文章还介绍了桥接模式与其他设计模式的区别，如适配器模式和装饰器模式，旨在帮助开发者更好地理解和运用设计模式解决实际问题。

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import java.io.Serializable;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
interface IConnection {
	public void query(String sql);
}
interface IDriver {
	public DIALECT getDialect();
 	public IConnection getConnection();
}
public class Bridge {

	public static void main(String[] args) {
	
		DriverManager.registerDriver(new MySqlDriver());
		IConnection mysql = DriverManager.getConnection();
		mysql.query("select * from table");
		
		DriverManager.registerDriver(new OracleDriver());
		IConnection oracle = DriverManager.getConnection(DIALECT.ORACLE);
		oracle.query("insert into table");
		
		IConnection db2 = DriverManager.getConnection(DIALECT.DB2);
		db2.query("update table");
	}
}

enum DIALECT implements Serializable {
	MYSQL,ORACLE,DB2;
}

class DriverManager {
	
	private static Map<DIALECT, IDriver> drivers = 
			new ConcurrentHashMap<DIALECT, IDriver>();
	private static final DIALECT DEFAULT_DIALECT = DIALECT.MYSQL;

	private DriverManager() { }
	
	public static void registerDriver(IDriver driver) {
		drivers.put(driver.getDialect(), driver);
	}
	
	public static IConnection getConnection() {
		return getConnection(DEFAULT_DIALECT); 
	}
	public static IConnection getConnection(DIALECT dialect) {
		IDriver driver = drivers.get(dialect);
		if (driver == null)
			throw new IllegalArgumentException("no driver register with " + dialect);
		
		return driver.getConnection();
	}
}

class MySqlDriver implements IDriver {
	@Override public IConnection getConnection() {
		return new IConnection() {
			@Override public void query(String sql) {
				System.out.println("MySql query ('" + sql + "') is executing......");
			}
		};
	}
	@Override public DIALECT getDialect() {
		return DIALECT.MYSQL;
	}
}

class OracleDriver implements IDriver {
	@Override public IConnection getConnection() {
		return new IConnection() {
			@Override public void query(String sql) {
				System.out.println("Oracle query ('" + sql + "') is executing......");
			}
		};
	}
	@Override public DIALECT getDialect() {
		return DIALECT.ORACLE;
	}
}

class DB2Driver implements IDriver {
	@Override public IConnection getConnection() {
		return new IConnection() {
			@Override public void query(String sql) {
				System.out.println("DB2 query ('" + sql + "') is executing......");
			}
		};
	}
	@Override public DIALECT getDialect() {
		return DIALECT.DB2;
	}
}

输出为：

MySql query ('select * from table') is executing......
Oracle query ('insert into table') is executing......
Exception in thread "main" java.lang.IllegalArgumentException: no driver register with DB2

* jdbc api使用bridge模式 Service / DAO

* bridge是在设计之初的模式，adapter是针对已有系统的代码。

* 通过对象组合的方式，Bridge模式把两个角色之间的继承关系改为了耦合的关系，从而使这两者可以

   从容自若的各自独立的变化，这也是Bridge模式的本意。
public abstract class Abstraction {
        protected Implementor implementor;
        public Abstraction(Implementor implementor) {
                this.implementor = implementor;
        }
        public void operation() {
                implementor.operationImpl();
        }
}
public interface Implementor {
        public void operationImpl();
}
class ConcreteImplementorA implements Implementor {
        @Override public void operationImpl() {
                // 真正的实现
                System.out.println("具体实现A");
        }
}
class ConcreteImplementorB implements Implementor {
        @Override public void operationImpl() {
                // 真正的实现
                System.out.println("具体实现B");
        }
}
class RefinedAbstraction extends Abstraction {
        public RefinedAbstraction(Implementor implementor) {
                super(implementor);
        }
        @Override public void operation() {
                //do someting
                super.operation();
                //do other thing
        }
}