Java泛型实现类型安全的通用类型转换器

public interface Transformer<T, R> {
    R transform(T input);
}

import java.util.Date;

public class LongToDateTransformer implements Transformer<Long, Date> {
    private static final LongToDateTransformer INSTANCE = new LongToDateTransformer();

    private LongToDateTransformer() {}

    public static LongToDateTransformer getInstance() {
        return INSTANCE;
    }

    @Override
    public Date transform(Long input) {
        return new Date(input);
    }
}

import java.util.HashMap;
import java.util.Map;

public class TransformerRegistry {
    private final Map<String, Transformer<?, ?>> registry = new HashMap<>();

    public <T, R> void register(Class<T> sourceType, Class<R> targetType, Transformer<T, R> transformer) {
        String key = sourceType.getName() + "->" + targetType.getName();
        registry.put(key, transformer);
    }

    @SuppressWarnings("unchecked")
    public <T, R> Transformer<T, R> get(Class<T> sourceType, Class<R> targetType) {
        String key = sourceType.getName() + "->" + targetType.getName();
        return (Transformer<T, R>) registry.get(key);
    }
}

TransformerRegistry registry = new TransformerRegistry();
registry.register(Long.class, Date.class, LongToDateTransformer.getInstance());

Transformer<Long, Date> transformer = registry.get(Long.class, Date.class);
Date date = transformer.transform(1698507600000L);
System.out.println(date);