在构建器模式中将抽象类子类化？

Question

我有两种类型的有效负载来自上游： PayloadA或PayloadB 。 与PayloadB相比， PayloadA具有许多字段，但是PayloadA和PayloadB之间有一些公共字段。 为了简化示例，我仅添加了几个字段。

以下是PayloadA的构建器类：

public final class PayloadA {
  private final String clientId;
  private final String langid;
  private final String deviceId;
  private final Map<String, String> applicationPayload;
  // other fields as well

  private PayloadA(Builder builder) {
    this.clientId = builder.clientId;
    this.langid = builder.langid;
    this.deviceId = builder.deviceId;
    this.applicationPayload = builder.applicationPayload.build();
  }

  public static class Builder {
    protected final String deviceId;
    protected String clientId;
    protected String langid;
    protected ImmutableMap.Builder<String, String> applicationPayload = ImmutableMap.builder();

    public Builder(String deviceId) {
      this.deviceId = deviceId;
    }

    public Builder setClientId(String clientId) {
      this.clientId = clientId;
      return this;
    }

    public Builder setLangid(String langid) {
      this.langid = langid;
      return this;
    }

    public Builder setPayload(Map<String, String> payload) {
      this.applicationPayload.putAll(payload);
      return this;
    }

    public PayloadA build() {
      return new PayloadA(this);
    }
  }

    // getters and to string here
}

现在下面是PayloadB的类：

public final class PayloadB {
  private final String clientid;
  private final String type;
  private final String payId;
  // other fields as well

  private PayloadB(Builder builder) {
    this.clientid = builder.clientid;
    this.type = builder.type;
    this.payId = builder.payId;
  }

  public static class Builder {
    protected final String type;
    protected String payId;
    protected String clientid;

    public Builder(String type) {
      this.type = type;
    }

    public Builder setPayId(String payId) {
      this.payId = payId;
      return this;
    }

    public Builder setClientId(String clientid) {
      this.clientid = clientid;
      return this;
    }

    public PayloadB build() {
      return new PayloadB(this);
    }
  }

    // getters and to string here
}

现在，我创建了另一个类，即Payload类，其中具有PayloadA和PayloadB所有公共字段，因此我也必须以某种方式设置这些字段，而且我不确定如何在下面的类中使用：

public abstract class Payload {
  private long createTimestamp;
  private String key;
  // some other fields are here

  // getters and setters here
}

题：

现在，从下面的代码中，我根据传递的内容来PayloadA或PayloadB 。

  private void run(String name) {
    // .. some code here
    if (name.equalsIgnoreCase("PayloadA")) {
      Payload payload =
          new PayloadA.Builder(getDeviceId()).setClientId("someid").setLangid("anotherid")
              .setPayload("some map").build();
      DataProcessor.getInstance().process(payload);
    } else {
      Payload payload =
          new PayloadB.Builder(getType()).setPayId("someid").setClientId("anotherid").build();
      DataProcessor.getInstance().process(payload);
    }
  }

并在DataProcessor process方法中：

  private void process(Payload payload) {
    // 1) here I need to set createTimestamp and key variables on payload bcoz they are common
    // fields.
    // 2) Also how can I figure out whether payload is PayloadA or PayloadB here?
  }

现在如何在process方法的Payload类中设置createTimestamp和key变量？ 现在，我有一个区分的运行方法，但是通常我将为PayloadA使用不同的上游代码，为PayloadB使用不同的上游代码，因此我们将使用其中一个Payload类。

另外，我应该在这里安排两名不同的建筑商，还是在这里一名大型建筑商？

Answer 1

PayloadA和PayloadB可以如下所示扩展Payload ：

public abstract class Payload {

     private long createTimestamp;
     private String key;
     // some other fields are here
     // getters and setters here
}

public class PayloadA extends Payload  {
    //add existing code
}
public class PayloadB extends Payload {
    //add existing code
}

private void process(Payload payload) {

     //Depending upon the object passed, fields will be set for A or B       

     payload.setCreateTimestamp(ADD_DATA1);
     payload.setKey(ADD_DATA2);
     //set other fields

    //if(payload instanceof PayloadA) {
        //payloadA
    //}
}

如何确定有效载荷是process()内的PayloadA还是PayloadB ？

您可以发现使用instanceof就像上面所示的PayloadA payload instanceof一样。 但是，通常来说，使用instanceof检查进行编码不是一个好主意，因此除非无法避免，否则不要使用它。

我应该在这里安排两名不同的建设者，还是在其中一名大型建设者？

根据上面提供的代码，这些字段的PayloadA和PayloadB不同，因此最好保留单独的bean和相应的构建器。

更新：我需要弄清楚它是什么类型的有效载荷，并基于此我需要为键变量设置值？

里面setKey()将调用传递给对象类型process(Payload payload) （多态性的OOP的基本原则之一），即，如果传递PayloadA从对象run()方法， setKey()上PayloadA对象将叫做。 总而言之，您根本不需要instanceof检查。 由您决定要在哪里设置密钥，可以在process()方法内部（如果您还有其他依赖项来生成key ），也可以按照@Roberto的建议进行操作

Answer 2

abstract public class Payload {
  abstract void setKey();
}

public class PayloadA extends Payload  {
    //add existing code
   void setKey() {
      key = "a";
   }
}
public class PayloadB extends Payload {
    //add existing code
  void setKey() {
    key = "b";
  }
}

private void process(Payload payload) {

     //Depending upon the object passed, fields will be set for A or B       

     payload.setCreateTimestamp(ADD_DATA1);
     payload.setKey();
}

编辑 ：

这里的想法是任何扩展有效载荷的类都必须实现setKey（）方法，或者必须是抽象的。 因此，PayloadA和PayloadB都实现了该方法。 每个类提供不同的实现。

现在假设你做

PayloadA pa = new PayloadA();
pa.setKey()

不出所料，实际执行的实现将是PayloadA中定义的实现。

现在考虑这种情况：

Payload pa = new PayloadA();
pa.setKey()

尽管声明了变量的类型为Payload，但是变量所引用的对象的实际类型为PayloadA，因此setKey（）调用是PayloadA中的对象。 这称为动态调度，因为在运行时（而不是在编译时）知道调用的实现

Answer 3

public class Payload {
 // common fields
 private String clientid;
 private String key;
 private long Timestamp;

 // setter and getters 
}

public class PayloadA extends Payload implements PayloadStrategy {
 // PayloadA specific fields
 private String langid;
 private String deviceId;

 // setters and getters

 public static class Builder {
 // existing code
 } 

 @Override
 public void process() {
    System.out.println("PayloadA specific implementation");
 }

}

public class PayloadB extends Payload implements PayloadStrategy {
 // PayloadA specific fields
 private String type;
 private String payId;

 // setters and getters

 public static class Builder {
 // existing code
 }

 @Override
 public void process() {
    System.out.println("PayloadB specific implementation");
 }
}

}

// define contract
public interface PayloadStrategy {
 public void process();
}

// payload context
public class PayloadContext {

 PayloadStrategy strategy;

 public void setContext(PayloadStrategy payloadStrategy) {
    this.strategy = payloadStrategy;
 }

 public void processPayload() {
    strategy.process();
 }
}

// parameterized (PayloadA or PayloadB) payload run method 

PayloadContext context = new PayloadContext();
context.setContext(new PayloadA());
context.processPayload();