设计模式之代理模式

最新推荐文章于 2025-07-30 20:14:45 发布

Mr.Future771

最新推荐文章于 2025-07-30 20:14:45 发布

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文章标签：设计模式代理模式 java

本文链接：https://blog.youkuaiyun.com/qq_64312423/article/details/146218382

代理模式 是一种结构型设计模式，它为其他对象提供一个代理或占位符，以控制对这个对象的访问。代理模式的核心思想是通过一个代理对象间接访问目标对象，从而在不改变目标对象的情况下增强其功能。

代理模式的核心角色包括：

抽象主题（Subject）：定义目标对象和代理对象的共同接口，客户端通过该接口与目标对象交互。
真实主题（Real Subject）：实际的目标对象，代理对象最终会调用它的方法。

代理（Proxy）：实现与目标对象相同的接口，并持有对目标对象的引用。以下是我写的一个简单的代理模式例子，用于控制对论坛用户（ForumUser）的访问。通过 ForumProxy 类，游客（Guest）和已注册用户（RegisteredUser）可以以不同的方式访问论坛功能。

public class ForumDemo {
    public static void main(String[] args) {
        // 游客只能通过代理访问
        ForumUser guestUser = new ForumProxy("Guest");
        guestUser.postMessage("This should not work for a guest");

        // 已注册用户可以直接访问
        RegisteredUser registeredUser = new RegisteredUser("Alice");
        registeredUser.postMessage("Hello, everyone!");
    }
}

class ForumProxy implements ForumUser {
    private String username;
    private RegisteredUser user;

    public ForumProxy(String username) {
        this.username = username;
    }

    @Override
    public void postMessage(String message) {
        if (user == null) {
            user = new RegisteredUser(username);
        }
        user.postMessage(message);
    }

    @Override
    public void editProfile(String profile) {
        if (user == null) {
            user = new RegisteredUser(username);
        }
        user.editProfile(profile);
    }

    @Override
    public void editPost(String postId, String newContent) {
        if (user == null) {
            user = new RegisteredUser(username);
        }
        user.editPost(postId, newContent);
    }
}

interface ForumUser {
    void postMessage(String message);
    void editProfile(String profile);
    void editPost(String postId, String newContent);
}

class RegisteredUser implements ForumUser {
    private String username;

    public RegisteredUser(String username) {
        this.username = username;
    }

    @Override
    public void postMessage(String message) {
        System.out.println(username + " posted a message: " + message);
    }

    @Override
    public void editProfile(String profile) {
        System.out.println(username + " updated profile: " + profile);
    }

    @Override
    public void editPost(String postId, String newContent) {
        System.out.println(username + " edited post " + postId + ": " + newContent);
    }
}

这个例子有个不合理的地方，当游客（Guest）通过代理访问时，会自动创建一个 RegisteredUser 对象，让游客也可以发帖。应该限制游客的权限，禁止其发帖或编辑内容。还可以对代码进行优化，再加入一些新的功能比如删帖和查看帖子。优化后的代码如下：

public class ForumDemo {
    public static void main(String[] args) {
        // 游客只能通过代理访问
        ForumUser guestUser = new ForumProxy("Guest");
        guestUser.postMessage("This should not work for a guest");
        guestUser.editProfile("New profile");
        guestUser.editPost("123", "New content");
        guestUser.deletePost("123");
        guestUser.viewPost("123");

        System.out.println("-----------------------------");

        // 已注册用户可以直接访问
        ForumUser registeredUser = new ForumProxy("Alice");
        registeredUser.postMessage("Hello, everyone!");
        registeredUser.editProfile("Updated profile");
        registeredUser.editPost("456", "Updated content");
        registeredUser.deletePost("456");
        registeredUser.viewPost("456");
    }
}


public class ForumProxy implements ForumUser {
    private String username;
    private RegisteredUser user;

    public ForumProxy(String username) {
        this.username = username;
        if (!username.equals("Guest")) {
            user = new RegisteredUser(username);
        }
    }

    @Override
    public void postMessage(String message) {
        System.out.println("Log: Attempt to post message by " + username);
        if (username.equals("Guest")) {
            System.out.println("Guests are not allowed to post messages.");
        } else {
            user.postMessage(message);
        }
    }

    @Override
    public void editProfile(String profile) {
        System.out.println("Log: Attempt to edit profile by " + username);
        if (username.equals("Guest")) {
            System.out.println("Guests are not allowed to edit profiles.");
        } else {
            user.editProfile(profile);
        }
    }

    @Override
    public void editPost(String postId, String newContent) {
        System.out.println("Log: Attempt to edit post by " + username);
        if (username.equals("Guest")) {
            System.out.println("Guests are not allowed to edit posts.");
        } else {
            user.editPost(postId, newContent);
        }
    }

    @Override
    public void deletePost(String postId) {
        System.out.println("Log: Attempt to delete post by " + username);
        if (username.equals("Guest")) {
            System.out.println("Guests are not allowed to delete posts.");
        } else {
            user.deletePost(postId);
        }
    }

    @Override
    public void viewPost(String postId) {
        System.out.println("Log: Attempt to view post by " + username);
        if (username.equals("Guest")) {
            System.out.println("Guest is viewing post " + postId);
        } else {
            user.viewPost(postId);
        }
    }
}

public interface ForumUser {
    void postMessage(String message); // 发帖
    void editProfile(String profile); // 编辑个人资料
    void editPost(String postId, String newContent); // 编辑帖子
    void deletePost(String postId); // 删除帖子
    void viewPost(String postId); // 查看帖子
}

public class RegisteredUser implements ForumUser {
    private String username;

    public RegisteredUser(String username) {
        this.username = username;
    }

    @Override
    public void postMessage(String message) {
        System.out.println(username + " posted a message: " + message);
    }

    @Override
    public void editProfile(String profile) {
        System.out.println(username + " updated profile: " + profile);
    }

    @Override
    public void editPost(String postId, String newContent) {
        System.out.println(username + " edited post " + postId + ": " + newContent);
    }

    @Override
    public void deletePost(String postId) {
        System.out.println(username + " deleted post " + postId);
    }

    @Override
    public void viewPost(String postId) {
        System.out.println(username + " is viewing post " + postId);
    }
}

运行结果：新增方法deletePost(String postId)：删除指定帖子和viewPost(String postId)：查看指定帖子。游客（Guest）只能查看帖子，不能发帖、编辑帖子、删除帖子或编辑个人资料；已注册用户可以执行所有操作。每次操作都会记录日志，便于跟踪用户行为。