Mastering the Strategy Pattern in Java: Real-World Spring Implementation

Concept

The Strategy Pattern, also known as the Policy Pattern, defines a family of algorithms, encapsulates each one, and makes them interchangeable; this allows algorithm changes without affecting the clients that use them.

Practical Application

Business scenario: the system needs to listen to multiple message types, updating a single Elasticsearch index. Different message types use different strategies to supplement data before updating Elasticsearch for merchant search and statistics.

The implementation combines the Spring framework, a simple factory, and the Strategy Pattern.

Service Interface

public interface GatherExecuteService {
    /**
     * Process the message body
     * @param gatherDataVo
     */
    boolean execute(GatherDataVo gatherDataVo);
}

Strategy Implementations

Price strategy

@Service
public class PriceExecuteServiceImpl implements GatherExecuteService {
    @Override
    public boolean execute(GatherDataVo gatherDataVo) {
        // ... implementation omitted
    }
}

Product strategy

@Service
public class ProductExecuteServiceImpl implements GatherExecuteService {
    @Override
    public boolean execute(GatherDataVo gatherDataVo) {
        // ... implementation omitted
    }
}

Stock strategy

@Service
public class StockExecuteServiceImpl implements GatherExecuteService {
    @Override
    public boolean execute(GatherDataVo gatherDataVo) {
        // ... implementation omitted
    }
}

Enum for Strategy Beans

@Getter
@AllArgsConstructor
public enum MessageTypeEnum {
    PRODUCT(0, "productExecuteServiceImpl", "商品基本信息消息"),
    PRICE(1, "priceExecuteServiceImpl", "价格消息"),
    STOCK(2, "stockExecuteServiceImpl", "库存消息");

    private int type;
    private String service;
    private String description;

    public static String getServiceName(int type) {
        for (MessageTypeEnum enumType : MessageTypeEnum.values()) {
            if (enumType.getType() == type) {
                return enumType.getService();
            }
        }
        return null;
    }
}

Using the Strategies

// Retrieve the appropriate strategy bean based on message type
String serviceName = MessageTypeEnum.getServiceName(gatherDataVo.getMessageType());
if (StringUtils.isNotBlank(serviceName)) {
    GatherExecuteService gatherExecuteService = (GatherExecuteService) SpringContextUtil.getBean(
        serviceName, GatherExecuteService.class);
    // execute the strategy
}

The Strategy Pattern is a simple design pattern often combined with other patterns in real projects; this example shares a practical usage.