Head First Design Patterns -代理模式

什么是代理模式

代理模式为另一个对象提供替身或者占位符，以便控制客户对对象的访问，管理访问的方式有很多种。例如远程代理、虚拟代理、保护代理等。
远程代理：管理客户和远程对象之间的交互。
虚拟代理：控制访问实例化开销大的对象。
保护代理：基于调用者，控制对对象方法的调用。

类图

代码

案例：防止对person类的访问中，访问了不该访问的方法
以保护代理为例，主要是基于java内置的动态代理，来控制对对象方法的调用，其类图如下：

Person接口

public interface Person {String getName();String getGender();String getInterests();int getGeekRating();void setName(String name);void setGender(String gender);void setInterests(String interests);void setGeekRating(int rating);
}

Person实现类

public class PersonImpl implements Person{String name;String gender;String interests;int rating;int ratingCount = 0;public PersonImpl(String name, String gender, String interests, int rating, int ratingCount) {this.name = name;this.gender = gender;this.interests = interests;this.rating = rating;this.ratingCount = ratingCount;}@Override
public String getName() {return name;
}@Override
public void setName(String name) {this.name = name;
}@Override
public int getGeekRating() {if (ratingCount == 0) {return 0;} else {return rating  / ratingCount;}
}@Override
public void setGeekRating(int rating) {this.rating += rating;ratingCount++;
}@Override
public void setGender(String gender) {this.gender = gender;
}@Override
public String getGender() {return gender;
}@Override
public String getInterests() {return interests;
}@Override
public void setInterests(String interests) {this.interests = interests;
}

NonOwnerInvocationHandler类

//InvocationHandler
public class NonOwnerInvocationHandler implements InvocationHandler {Person person;public NonOwnerInvocationHandler(Person person) {this.person = person;}@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {try {if (method.getName().startsWith("get")) {return method.invoke(person, args);} else if (method.getName().equals("setGeekRating")) {return method.invoke(person, args);} else if (method.getName().startsWith("set")) {throw new Throwable();}} catch (InvocationTargetException e) {e.printStackTrace();}return null;
}
}

OwnerInvocationHandler类

public class OwnerInvocationHandler implements InvocationHandler {Person person;public OwnerInvocationHandler(Person person) {this.person = person;}// 
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {try {if (method.getName().startsWith("get")) {return method.invoke(person, args);} else if (method.getName().equals("setGeekRating")) {throw new Throwable();} else if (method.getName().startsWith("set")) {return method.invoke(person, args);}} catch (InvocationTargetException e) {e.printStackTrace();}return null;
}
}

测试：

public class Test {public static void main(String[] args) {Person kang = new PersonImpl("kwb", "boy", "ball", 1, 3);Person owner = getProxy.getOwnerProxy(kang);System.out.println(owner.getName());}
}

区别

装饰器模式为对象加上行为，而代理则是控制访问。