Java 接口 - 防止代码重复

Question

我正在尝试为一组类创建一个接口， 但我未能找到解决方案，这 防止为中的每个新方法复制几乎相似的代码 接口。

界面

public interface P6BO<T extends BusinessObject> {
String[] getFields();
void create(T businessObject) throws P6BOException;
void delete(T businessObject) throws P6BOException;
}

接口的 30+ 实现。

public class ActivityBO implements P6BO<Activity> {
...
@Override
public void create(Activity activity) throws P6BOException {
...
}
@Override
public void delete(Activity activity) throws P6BOException {
...
}
}

用于初始化所有实现的容器类和 提供对每个站点的单一访问点。

public class P6Bom {
public final ActivityBO activity = new ActivityBO();
public final EpsBO eps = new EpsBO();
public final ResourceBO resource = new ResourceBO();
public P6Bom(P6Info p6Info) throws P6BOException {
activity.activate(p6Info, p6Cache, p6Buffer);
eps.activate(p6Info, p6Cache, p6Buffer);
resource.activate(p6Info, p6Cache, p6Buffer);
}
...
public void create(BusinessObject businessObject) throws P6BOException {
if (businessObject instanceof Activity) {
activity.create((Activity) businessObject);
} else if (businessObject instanceof EPS) {
eps.create((EPS) businessObject);
} else if (businessObject instanceof Resource) {
resource.create((Resource) businessObject);
}
}
public void delete(BusinessObject businessObject) throws P6BOException {
if (businessObject instanceof Activity) {
activity.delete((Activity) businessObject);
} else if (businessObject instanceof EPS) {
eps.delete((EPS) businessObject);
} else if (businessObject instanceof Resource) {
resource.delete((Resource) businessObject);
}
}
public P6BO<? extends BusinessObject> getBO(BusinessObject businessObject) throws P6BOException {
if (businessObject instanceof Activity) {
return activity;
} else if (businessObject instanceof EPS) {
return eps;
} else if (businessObject instanceof Resource) {
return resource;
} else {
throw new P6BOException("not implemented.");
}
}
}

测试类

public class Test() {
/* Works: but is not generic (I cannot call the delete method for any BusinessObject). */
Activity activity = new Activity("MyNewActivity");
P6Bom.activity.create(activity);
P6Bom.activity.delete(activity);
/* Works: but results in a double administration in the P6Bom */
Activity activity = new Activity("MyNewActivity");
P6Bom.create(activity);
P6Bom.delete(activity);
/* Compiler error
The method delete(capture#1-of ? extends BusinessObject)
in the type P6BO<capture#1-of ? extends BusinessObject>
is not applicable for the arguments (Activity)
*/
p6Bom.getBO(activity).delete(activity);
}

防止在P6Bom接口中重复管理每种方法的优雅解决方案是什么？

Answer 1

您可以使用地图：

public class P6Bom {
public final Map<Class<? extends P6BO<? extends BusinessObject>>, P6BO<? extends BusinessObject>>> classMap;
public P6Bom(P6Info p6Info) throws P6BOException {
classMap = new HashMap<>();
classMap.put(ActivityBo.class, new ActivityBO());
...
for(var bo: classMap.values()) {
bo.activate(p6Info, p6Cache, p6Buffer);
}
}
...
public void create(BusinessObject businessObject) throws P6BOException {
getBO(businessObject).create(businessObject);
}
public P6BO<? extends BusinessObject> getBO(BusinessObject businessObject) throws P6BOException {
if (classMap.containsKey(businessObject.getClass())) {
return classMap.get(businessObject.getClass());
} else {
throw new P6BOException("not implemented.");
}
}
}

我忘记了<? extends BusinessObject>是否允许你这样做。如果编译器抱怨，请在类映射声明和 getBO 签名中省略该部分并忽略警告 ;-(

这里要记住的是，在字节码中，泛型被删除，因此实际的方法签名允许您始终传入业务对象。一旦进入方法，如果类不匹配，它将被强制转换并抛出 RuntimeException，但从编译器/接口端，完全可以编写这样的代码。

Answer 2

这似乎是一个经典的factory和strategy模式问题，违反了Open/Closed原则。您希望扩展应用程序，但不对其进行修改。

@kutschkem的解决方案是迄今为止最优雅的方式。此外，我建议在创建第一个业务对象时实例化策略/业务对象管理器。

这将使您的双手免于枚举BOM，因为建议的方式，仍然违反了Open/Closed原则。引入新的业务对象后，需要在类中添加其各自的管理器。

解决方案可能如下：

public class P6Bom {
private final Map<String, P6BO<? extends BusinessObject>> classMap;
private final P6Info info;
private final P6Cache cache;
private final P6Buffer buffer;
public P6Bom(P6Info info, P6Cache cache, P6Buffer buffer) {
this.classMap = new HashMap<>();
this.info = info;
this.cache = cache;
this.buffer = buffer;
}
public <T extends BusinessObject> void create(T businessObject) throws P6BOException {
this.getBO(businessObject).create(businessObject);
}
public <T extends BusinessObject> P6BO<T> getBO(T businessObject) throws P6BOException {
if (!this.classMap.containsKey(businessObject.getClass().getName())) {
try {
var bo = (P6BO<T>)Class.forName(businessObject.getClass().getPackageName() + ".bo." + businessObject.getClass().getSimpleName() + "BO").getConstructors()[0].newInstance();
bo.activate(this.info, this.cache, this.buffer)
this.classMap.put(
businessObject.getClass().getName(),
bo
);
} catch (Exception e) {
throw new P6BOException("not implemented.");
}
}
return (P6BO<T>)this.classMap.get(businessObject.getClass().getName());
}
}

当然，对于该解决方案，需要有一个约定(或配置(如何为BusinessObjects找到策略(例如 ActivityBO(。在示例中，它们位于名为bo的子包中。