Java design pattern template method example analysis

Concept

The template method pattern is one of the most common patterns among all patterns. It is a basic technology of code reuse based on inheritance and has no correlation. Therefore, in the class structure diagram of the template method pattern, there is only inheritance relationship.

Core design points

AbstractClass: abstract class, defines and implements a template method. This template method defines the skeleton of the algorithm, and the logical composition steps are postponed to subclasses in the corresponding abstract operations.

ConcreteClass: Implement one or more abstract methods defined by the parent class.

Advantages and Disadvantages

Advantages

• Using the template method to put the code with the same processing logic into the abstract parent class can improve the reusability of the code .

• Put different codes into different subclasses and add new behaviors through the extension of subclasses to improve the scalability of the code.

• Write the unchanged behavior in the parent class, remove the duplicate code of the subclass, and provide a good code reuse platform that complies with the opening and closing principle.

Disadvantages

As the number of classes increases, each abstract class requires a subclass to implement, which results in an increase in the number of classes and an increase in complexity. The increase in the number of classes indirectly increases the complexity of system implementation. The inheritance relationship has its own shortcomings. If the parent class adds a new abstract method, all subclasses will have to change it.

Application scenario

• Parent class perspective: implement the unchanged part of an algorithm at one time, and leave the variable part to the subclass for implementation;

• Subclass perspective: In each subclass, the common parts are extracted and concentrated into a common parent class to avoid code duplication;

Template method pattern The purpose is to allow subclasses to extend or specifically implement a specific step of a fixed method; for a template, it is a set of fixed algorithms, and certain algorithm steps in the fixed algorithm can be extended through subclasses.

The difference between template method and strategy pattern

The strategy pattern is an encapsulation of algorithms. It encapsulates a series of algorithms into corresponding classes, and these classes implement the same interface and interact with each other. can be replaced. There is another pattern

that also focuses on the encapsulation of algorithms - the template method pattern. By comparing the class diagram, you can see that the difference between the strategy pattern and the template method pattern is only the addition of a separate encapsulation class

Context, the difference between it and the template method pattern is that in the template method pattern, the main body of the calling algorithm is in the abstract parent class, while in the strategy pattern, the main body of the calling algorithm is encapsulated When it comes to the encapsulated class Context, the abstract strategy Strategy is generally an interface. Its purpose is only to define specifications and generally does not contain logic. In fact, this is just a general implementation, but in actual programming, because there is inevitably some same logic between specific strategy implementation classes, in order to avoid duplication of code, we often use abstract classes to play the role of Strategy and encapsulate them inside Public code, therefore, in many application scenarios, you will generally see the shadow of the template method pattern in the strategy pattern.

Code case

Template method abstract class

@Slf4j
public abstract class AbstractPayCallbackTemplate {
    /**
     * 异步回调业务
     *
     * @return
     */
    public String asyncCallBack() {
        // 1. 支付回调验证参数
        Map<String, String> verifySignatureMap = verifySignature();
        // 2. 参数验证成功，写入日志中..
        payLog(verifySignatureMap);
        String analysisCode = verifySignatureMap.get("analysisCode");
        if (!analysisCode.equals("200")) {
            return resultFail();
        }
        // 3. 执行回调异步相关逻辑
        return asyncService(verifySignatureMap);
    }
    /**
     * 支付回调验证参数
     *
     * @return
     */
    protected abstract Map<String, String> verifySignature();
    /**
     * 使用多线程异步写入日志
     *
     * @param verifySignatureMap
     */
    @Async
    void payLog(Map<String, String> verifySignatureMap) {
        log.info(">>>>>>>>>>第二步 写入payLog........");
    }
    /**
     * 每个子类需要实现 实现业务解析操作
     *
     * @return
     */
    protected abstract String asyncService(Map<String, String> verifySignatureMap);
    /**
     * 异步返回结果..
     *
     * @return
     */
    protected abstract String resultSuccess();
    /**
     * 异步返回失败
     *
     * @return
     */
    protected abstract String resultFail();
}

Concrete implementation template class

@Log4j2
public class AliPayCallbackTemplate extends AbstractPayCallbackTemplate {
    @Override
    protected Map<String, String> verifySignature() {
        //>>>>假设一下为银联回调报文>>>>>>>>>>>>>>>>
        log.info(">>>>>第一步 解析支付宝据报文.....verifySignature()");
        Map<String, String> verifySignature = new HashMap<>();
        verifySignature.put("price", "1399");
        verifySignature.put("orderDes", "充值永久会员");
        // 支付状态为1表示为成功....
        verifySignature.put("aliPayMentStatus", "1");
        verifySignature.put("aliPayOrderNumber", "201910101011");
        // 解析报文是否成功 200 为成功..
        verifySignature.put("analysisCode", "200");
        return verifySignature;
    }
    @Override
    protected String asyncService(Map<String, String> verifySignatureMap) {
        log.info(">>>>>第三步asyncService()verifySignatureMap:{}", verifySignatureMap);
        String paymentStatus = verifySignatureMap.get("aliPayMentStatus");
        if (paymentStatus.equals("1")) {
            String aliPayOrderNumber = verifySignatureMap.get("aliPayOrderNumber");
            log.info(">>>>orderNumber:{aliPayOrderNumber},已经支付成功 修改订单状态为已经支付...");
        }
        return resultSuccess();
    }
    @Override
    protected String resultSuccess() {
        return "ok";
    }
    @Override
    protected String resultFail() {
        return "fail";
    }
}
@Slf4j
public class UnionPayCallbackTemplate extends AbstractPayCallbackTemplate {
    @Override
    protected Map<String, String> verifySignature() {
        //>>>>假设一下为银联回调报文>>>>>>>>>>>>>>>>
        log.info(">>>>>第一步 解析银联数据报文.....verifySignature()");
        Map<String, String> verifySignature = new HashMap<>();
        verifySignature.put("price", "1399");
        verifySignature.put("orderDes", "充值永久会员");
        // 支付状态为1表示为成功....
        verifySignature.put("paymentStatus", "1");
        verifySignature.put("orderNumber", "201910101011");
        // 解析报文是否成功 200 为成功..
        verifySignature.put("analysisCode", "200");
        return verifySignature;
    }
    @Override
    protected String asyncService(Map<String, String> verifySignatureMap) {
        log.info(">>>>>第三步asyncService()verifySignatureMap:{}", verifySignatureMap);
        String paymentStatus = verifySignatureMap.get("paymentStatus");
        if (paymentStatus.equals("1")) {
            String orderNumber = verifySignatureMap.get("orderNumber");
            log.info(">>>>orderNumber:{orderNumber},已经支付成功 修改订单状态为已经支付...");
        }
        return resultSuccess();
    }
    @Override
    protected String resultSuccess() {
        return "success";
    }
    @Override
    protected String resultFail() {
        return "fail";
    }
}

Factory mode acquisition template

public class TemplateFactory {
    private final static Map<String, AbstractPayCallbackTemplate> templateMap = new ConcurrentHashMap<>();
    static {
        templateMap.put("aliPay", new AliPayCallbackTemplate());
        templateMap.put("unionPay", new UnionPayCallbackTemplate());
    }
    public static AbstractPayCallbackTemplate getPayCallbackTemplate(String templateId) {
        AbstractPayCallbackTemplate payCallbackTemplate = (AbstractPayCallbackTemplate) templateMap.get(templateId);
        return payCallbackTemplate;
    }
}

Test class

public class Test {
    public static void main(String[] args) {
        AbstractPayCallbackTemplate aliPay = TemplateFactory.getPayCallbackTemplate("aliPay");
        String s = aliPay.asyncCallBack();
        System.out.println(s);
    }
}

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