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定义：装饰器模式（Decorator Pattern）也叫包装模式（Wrapper Pattern），是指在不改变原有对象的基础之上，将功能附加到对象上，提供了比继承更有弹性的替代方案（扩展原有对象的功能）

属于结构型模式

适用场景

1.用于扩展一个类的功能或给一个类添加附加职责

2.动态的给一个对象添加功能，这些功能可以再动态的撤销

优点

1.装饰器是继承的有力补充，比继承灵活，不改变原有对象的情况下动态地给一个对象扩展功能，即插即用

2.通过使用不同装饰类以及这些装饰类的排列组合，可实现不同效果

3.装饰器完全遵守开闭原则

装饰器模式和代理模式对比

1.装饰器模式就是一种特殊的代理模式

2.装饰器模式强调自身的功能扩展，透明的扩展，可动态定制的扩展

3.代理模式强调代理过程的控制

缺点

1.会出现更多的代码，更多的类，增加程序的复杂性

2.动态装饰时，多层装饰时会更复杂

例子

无装饰器模式

public class BatterCake {
       protected String getMsg(){
   return "煎饼";}    protected int getPrice(){
   return 5;}}

public class BatterCakeWithEgg extends BatterCake{
       protected String getMsg(){
   return super.getMsg() + " + 1 个鸡蛋";};    public int getPrice(){
   return super.getPrice() + 2;}}

public class BatterCakeWithEggAndSauage extends BatterCakeWithEgg {
       protected String getMsg(){
   return super.getMsg() + " + 1 个香肠";};    public int getPrice(){
   return super.getPrice() + 2;}}

public class Test {
       public static void main(String[] args) {
           BatterCake batterCake = new BatterCake();        System.out.println(batterCake.getMsg()+ ",总价：　" + batterCake.getPrice());        BatterCakeWithEgg battercakeWithEgg = new BatterCakeWithEgg();        System.out.println(battercakeWithEgg.getMsg() + ",总价：　" + battercakeWithEgg.getPrice());        BatterCakeWithEggAndSauage battercakeWithEggAndSauage = new BatterCakeWithEggAndSauage();        System.out.println(battercakeWithEggAndSauage.getMsg() + ",总价：　" + battercakeWithEggAndSauage.getPrice());    }}

用装饰器模式之后（装饰器核心思想，继承或实现接口，然后添加接口为属性，并在构造方法中赋值，重写的方法内部是用接口调用相应的方法）

public abstract class BatterCake {
       protected abstract String getMsg();    protected abstract int getPrice();}

public class BatterCakeDecorator extends BatterCake{
       private BatterCake batterCake;    public BatterCakeDecorator(BatterCake batterCake){
           this.batterCake = batterCake;    }    @Override    protected String getMsg() {
           return this.batterCake.getMsg();    }    @Override    protected int getPrice() {
           return this.batterCake.getPrice();    }}

public class BaseBatterCake extends BatterCake{
       @Override    protected String getMsg() {
           return "煎饼";    }    @Override    protected int getPrice() {
           return 5;    }}

public class EggDecorator extends BatterCakeDecorator{
       public EggDecorator(BatterCake batterCake){
           super(batterCake);    }    @Override    protected String getMsg() {
           return super.getMsg() + " + 1 个鸡蛋";    }    @Override    protected int getPrice() {
           return super.getPrice() + 2;    }}

public class SauageDecorator extends BatterCakeDecorator{
       public SauageDecorator(BatterCake batterCake){
           super(batterCake);    }    @Override    protected String getMsg() {
           return super.getMsg() + " + 1 个香肠";    }    @Override    protected int getPrice() {
           return super.getPrice() + 2;    }}

public class PotatoDecorator extends BatterCakeDecorator{
       public PotatoDecorator(BatterCake batterCake) {
           super(batterCake);    }    protected String getMsg(){
   return super.getMsg() + " + 土豆丝";}    protected int getPrice(){
   return super.getPrice() + 1;};}

public class Test {
       public static void main(String[] args) {
           BatterCake batterCake;        batterCake = new BaseBatterCake();        batterCake = new EggDecorator(batterCake);        batterCake = new EggDecorator(batterCake);        batterCake = new SauageDecorator(batterCake);        batterCake = new SauageDecorator(batterCake);        batterCake = new PotatoDecorator(batterCake);        batterCake = new PotatoDecorator(batterCake);        batterCake = new PotatoDecorator(batterCake);        System.out.println(batterCake.getMsg() + ",总价：　" + batterCake.getPrice());    }}

使用装饰器模式将日志打印格式转成json格式

public class LoggerDecorator implements Logger {
       protected Logger logger;    public LoggerDecorator(Logger logger){
           this.logger = logger;    }    @Override    public String getName() {
           return null;    }    @Override    public boolean isTraceEnabled() {
           return false;    }    @Override    public void trace(String s) {
       }    @Override    public void trace(String s, Object o) {
       }    @Override    public void trace(String s, Object o, Object o1) {
       }    @Override    public void trace(String s, Object... objects) {
       }    @Override    public void trace(String s, Throwable throwable) {
       }    @Override    public boolean isTraceEnabled(Marker marker) {
           return false;    }    @Override    public void trace(Marker marker, String s) {
       }    @Override    public void trace(Marker marker, String s, Object o) {
       }    @Override    public void trace(Marker marker, String s, Object o, Object o1) {
       }    @Override    public void trace(Marker marker, String s, Object... objects) {
       }    @Override    public void trace(Marker marker, String s, Throwable throwable) {
       }    @Override    public boolean isDebugEnabled() {
           return false;    }    @Override    public void debug(String s) {
       }    @Override    public void debug(String s, Object o) {
       }    @Override    public void debug(String s, Object o, Object o1) {
       }    @Override    public void debug(String s, Object... objects) {
       }    @Override    public void debug(String s, Throwable throwable) {
       }    @Override    public boolean isDebugEnabled(Marker marker) {
           return false;    }    @Override    public void debug(Marker marker, String s) {
       }    @Override    public void debug(Marker marker, String s, Object o) {
       }    @Override    public void debug(Marker marker, String s, Object o, Object o1) {
       }    @Override    public void debug(Marker marker, String s, Object... objects) {
       }    @Override    public void debug(Marker marker, String s, Throwable throwable) {
       }    @Override    public boolean isInfoEnabled() {
           return false;    }    @Override    public void info(String s) {
       }    @Override    public void info(String s, Object o) {
       }    @Override    public void info(String s, Object o, Object o1) {
       }    @Override    public void info(String s, Object... objects) {
       }    @Override    public void info(String s, Throwable throwable) {
       }    @Override    public boolean isInfoEnabled(Marker marker) {
           return false;    }    @Override    public void info(Marker marker, String s) {
       }    @Override    public void info(Marker marker, String s, Object o) {
       }    @Override    public void info(Marker marker, String s, Object o, Object o1) {
       }    @Override    public void info(Marker marker, String s, Object... objects) {
       }    @Override    public void info(Marker marker, String s, Throwable throwable) {
       }    @Override    public boolean isWarnEnabled() {
           return false;    }    @Override    public void warn(String s) {
       }    @Override    public void warn(String s, Object o) {
       }    @Override    public void warn(String s, Object... objects) {
       }    @Override    public void warn(String s, Object o, Object o1) {
       }    @Override    public void warn(String s, Throwable throwable) {
       }    @Override    public boolean isWarnEnabled(Marker marker) {
           return false;    }    @Override    public void warn(Marker marker, String s) {
       }    @Override    public void warn(Marker marker, String s, Object o) {
       }    @Override    public void warn(Marker marker, String s, Object o, Object o1) {
       }    @Override    public void warn(Marker marker, String s, Object... objects) {
       }    @Override    public void warn(Marker marker, String s, Throwable throwable) {
       }    @Override    public boolean isErrorEnabled() {
           return false;    }    @Override    public void error(String s) {
       }    @Override    public void error(String s, Object o) {
       }    @Override    public void error(String s, Object o, Object o1) {
       }    @Override    public void error(String s, Object... objects) {
       }    @Override    public void error(String s, Throwable throwable) {
       }    @Override    public boolean isErrorEnabled(Marker marker) {
           return false;    }    @Override    public void error(Marker marker, String s) {
       }    @Override    public void error(Marker marker, String s, Object o) {
       }    @Override    public void error(Marker marker, String s, Object o, Object o1) {
       }    @Override    public void error(Marker marker, String s, Object... objects) {
       }    @Override    public void error(Marker marker, String s, Throwable throwable) {
       }}

public class JsonLogger extends LoggerDecorator{
       public JsonLogger(Logger logger) {
           super(logger);    }    @Override    public void info(String s) {
           JSONObject result = newJsonObject();        result.put("message: ",s);        logger.info(result.toString());    }    @Override    public void error(String s) {
           JSONObject result = newJsonObject();        result.put("error: ",s);        logger.info(result.toString());    }    public void error(Exception e){
           JSONObject result = newJsonObject();        result.put("exception: ",e);        String trace = Arrays.toString(e.getStackTrace());        result.put("starckTrace: ",trace);        logger.info(result.toString());    }    private JSONObject newJsonObject(){
           return new JSONObject();    }}

public class JsonLoggerFactory {
       public static JsonLogger getLogger(Class clazz){
           Logger logger = LoggerFactory.getLogger(clazz);        return new JsonLogger(logger);    }}

public class Test {
       //private static final Logger logger = LoggerFactory.getLogger(Test.class);    private static final Logger logger = JsonLoggerFactory.getLogger(Test.class);    public static void main(String[] args) {
           logger.error("系统错误");    }}

装饰器模式经典结构

public abstract class Component {
      abstract void operation();}

public abstract class Decorator extends Component {
       //持有组件对象    protected Component component;    /**     * 构造方法，传入组件对象     * @param component     */    public Decorator(Component component){
   this.component = component; };    public void operation(){
           //转发请求给组件对象，可以在转发前后执行一些附加动作        component.operation();    }}

public class ConcreteComponent extends Component{
       @Override    void operation() {
           System.out.println("我是第二级");    }}

public class ConcreteDecoratorA extends Decorator {
       /**     * 构造方法，传入组件对象     *     * @param component     */    public ConcreteDecoratorA(Component component) {
           super(component);    }    private void operationFirst(){
           System.out.println("执行前操作A");    };//在调用父类的operation方法之前需要执行的操作    private void operationLast(){
           System.out.println("执行后操作A");    };//在调用父类的operation方法之后需要执行的操作    public void operation(){
           //调用父类的方法，可以在调用前后执行一些附加动作        operationFirst();//添加的功能        super.operation();//这里可以选择性的调用父类的方法，如果不调用则相当于完全改写了方法，        operationLast();//添加的功能    }}

public class ConcreteDecoratorB extends Decorator{
       /**     * 构造方法，传入组件对象     *     * @param component     */    public ConcreteDecoratorB(Component component) {
           super(component);    }    private void operationFirst(){
           System.out.println("执行前操作B");    };//在调用父类的operation方法之前需要执行的操作    private void operationLast(){
           System.out.println("执行后操作B");    };//在调用父类的operation方法之后需要执行的操作    public void operation(){
           //调用父类的方法，可以在调用前后执行一些附加动作        operationFirst();//添加的功能        super.operation();//这里可以选择性的调用父类的方法，如果不调用则相当于完全改写了方法，        operationLast();//添加的功能    }}

public class Client {
       public static void main(String[] args) {
           Component component = new ConcreteComponent();        Decorator decoratorA = new ConcreteDecoratorA(component);        decoratorA.operation();        Decorator decoratorB = new ConcreteDecoratorB(component);        decoratorB.operation();        Decorator decoratorBandA = new ConcreteDecoratorB(decoratorA);        decoratorBandA.operation();    }}

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