How to choose a class based on strategy using Java SPI?

In Java SPI, you can choose a class based on a strategy by following these steps:

1. Create an interface that defines the methods of the strategy.
2. Create different implementation classes, each of which implements the strategy interface and provides different implementation logic.
3. Create a META-INF/services folder in the project’s classpath.
4. Create a file in the META-INF/services directory with the fully qualified name of the strategy interface as the file name, for example com.example.Strategy.
5. Write the fully qualified class name of the implementation needed in this file.
6. Load the implementation class of the strategy interface using ServiceLoader.
7. Iterate through the implementations obtained from ServiceLoader, and select the appropriate one based on the required strategy.

Here is an example code:

// 定义策略接口
public interface Strategy {
    void execute();
}

// 实现策略接口的实现类
public class StrategyImpl1 implements Strategy {
    @Override
    public void execute() {
        System.out.println("Strategy 1 executed.");
    }
}

public class StrategyImpl2 implements Strategy {
    @Override
    public void execute() {
        System.out.println("Strategy 2 executed.");
    }
}

// 在META-INF/services文件夹下创建一个以策略接口全限定名为名称的文件，例如com.example.Strategy
// 在文件中写入需要使用的实现类的全限定名，一行一个实现类
// com.example.StrategyImpl1
// com.example.StrategyImpl2

// 使用ServiceLoader加载策略接口的实现类
ServiceLoader<Strategy> strategies = ServiceLoader.load(Strategy.class);

// 遍历ServiceLoader获取到的实现类，根据需要的策略选择相应的实现类
for (Strategy strategy : strategies) {
    // 根据需要的策略选择相应的实现类
    if (需要选择的策略条件) {
        strategy.execute();
    }
}

Through this method, it is possible to choose the appropriate implementation class based on the needed strategy, enabling the functionality of dynamically loading and switching strategies.