java设计模式之------装饰者模式

java设计模式之------装饰者模式

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装饰模式(Decorator),动态的给一个对象添加一些额外的职责，就增加功能来说，装饰模式比生成子类更为灵活。

可以有效的把类的核心职责和装饰功能区分开。



举例:

Cooking炒菜

CookingEgg炒鸡蛋

Condimen调料基类(只是抽象了一层行为,跟装饰者模式没关系)

Oil油

Salt盐

abstract class Cooking {
public abstract void doCooking();
}

public class CookingEgg extends Cooking {

public void doCooking(){
System.out.println("do Egg Cooking");
}

}

public abstract class Condimen extends Cooking {

public abstract void doCooking();

}

public class Oil extends Condimen {

Cooking cooking;

public Oil(Cooking cooking){
this.cooking = cooking;
}

public void doCooking(){
cooking.doCooking();
//一些功能扩展
System.out.println("add Oil");
}

}

public class Salt extends Condimen {

Cooking cooking;

public Salt(Cooking cooking){
this.cooking = cooking;
}

public void doCooking(){
cooking.doCooking();
//一些功能扩展
System.out.println("add Salt");
}

}

public abstract class Test {

public static void main(String[] args) {
Cooking cooking = new CookingEgg();
Oil oil = new Oil(cooking);
Salt salt = new Salt(oil);
salt.doCooking();

//addCondimen("Oil");
//addCondimen("Salt");
addCondimen("OilSalt");
}

public static void addCondimen(String condimen) {
Cooking cooking = new CookingEgg();
if(condimen.contains("Oil")){
cooking = new Oil(cooking);
}
if(condimen.contains("Salt")){
cooking = new Salt(cooking);
}
cooking.doCooking();
}

}

Mybatis缓存设计和I/O流的设计，就是应用装饰者模式思想设计的


1.Mybatis缓存设计

Executor执行类

public Executor newExecutor(Transaction transaction, ExecutorType executorType, boolean autoCommit) {  

    Executor executor;

    if (ExecutorType.BATCH == executorType) {

      executor = new BatchExecutor(this, transaction);

    } else if (ExecutorType.REUSE == executorType) {

      executor = new ReuseExecutor(this, transaction);

    } else {

      executor = new SimpleExecutor(this, transaction);

    }

    if (cacheEnabled) {

      executor = new CachingExecutor(executor, autoCommit);//装饰

    }    

    return executor;

}

结构类图：



executor.query()[BaseExecutor.query()-->SimpleExecutor.doQuery()]

executor.query()[CachingExecutor.query()-->BaseExecutor.query()-->SimpleExecutor.doQuery()]

CachingExecutor包装BaseExecutor

2.I/O流