《Java8实战》

1. 啥是策略模式?

https://www.runoob.com/design-pattern/strategy-pattern.html
程序可以在运行时,动态地决定需要使用哪种策略来处理业务操作.
主要解决：在有多种算法相似的情况下，使用 if...else 所带来的复杂和难以维护,并且难以在运行时动态调整(动态调整：这就需要一些技巧)。

举个栗子 仿照菜鸟教程的栗子 https://www.runoob.com/design-pattern/strategy-pattern.html

1. 定义策略模式的主接口、两个实现类

public interface UploadStrategy {
    void upload();
}
---
public class FtpUploadStrategy implements UploadStrategy {
    @Override
    public void upload() {
        System.out.println("==========ftp文件开始上传……");
    }
}
---
public class OssUploadStrategy implements UploadStrategy {
    @Override
    public void upload() {
        System.out.println("==========oss文件开始上传……");
    }
}

2. 定义动态环境UploadContext类 —— 动态感知环境变化,动态调整需要实现的策略类，这部分可以交给SpringBoot的@PostConstructor来根据xml配置文件来动态初始化选择

public class UploadContext implements UploadStrategy {
    private UploadStrategy uploadStrategy;

    public UploadContext(UploadStrategy uploadStrategy) {
        this.uploadStrategy = uploadStrategy;
    }

    @Override
    public void upload() {
        uploadStrategy.upload();
    }
}

3. 主测试类

public class Main {
    private UploadContext uploadContext;

    @Test
    public void strategyTest() {
        uploadContext = new UploadContext(new OssUploadStrategy());
        uploadContext.upload();

        uploadContext = new UploadContext(new FtpUploadStrategy());
        uploadContext.upload();
    }
}

测试结果

==========oss文件开始上传......
==========ftp文件开始上传......

4.使用 Lambda 重构面向对象

    /**
     * 使用lambda表达式进行简化 不需要新增新的实现类,就可以轻松添加策略,比如下面的第三种策略"hdfs文件开始上传"
     */
    @Test
    public void strategyLambdaTest() {
        uploadContext = new UploadContext(() -> System.out.println("==========oss文件开始上传......"));
        uploadContext.upload();

        uploadContext = new UploadContext(() -> System.out.println("==========ftp文件开始上传......"));
        uploadContext.upload();

        uploadContext = new UploadContext(() -> System.out.println("==========hdfs文件开始上传......"));
        uploadContext.upload();
    }

缺点: lambda表达式可以简化的前提是UploadStrategy 只有一个接口方法，即函数接口，大于一方法lambda表达式会失效；这种简化其实就是把实现方法提前写在了lambda表达式中

其他：实际使用还是需要灵活调整，设计模式是为了重构具体的代码耦合问题，是为了解决问题的！不是纯粹的为了炫技巧，代码安全性和易读性也是需要考虑和权衡的。

还可以融合springboot，发挥一些web的独特特性。