英文:
Template method pattern with arbitrary exception throwing
问题
假设我有一个抽象类 Base，其中有一个具体方法 execute 和三个抽象方法 stepOne、stepTwo 和 stepThree...
public abstract class Base {protected abstract void stepOne();protected abstract void stepTwo();protected abstract void stepThree();public final void execute() {// 做一些事情stepOne();// 做一些事情stepTwo();// 做一些事情stepThree();// 做一些事情}}
...并且有一个具体类 Sub1 继承自该抽象类：
public class Sub1 extends Base {protected void stepOne() {//...}protected void stepTwo() {//...}protected void stepThree() {//...}}
现在假设我有一个第二个子类 Sub2，在 stepOne 和 stepTwo 方法中可能会抛出已检查异常：
public class Sub2 extends Base {protected void stepOne() throws Exception1 {//...}protected void stepTwo() throws Exception2 {//...}protected void stepThree() {//...}}
我希望按以下方式使用这些类：
Sub1 s1 = new Sub1();try {s1.execute();} catch (Exception1 e1) {// 处理 e1} catch (Exception2 e2) {// 处理 e2}Sub2 s2 = new Sub2();s2.execute();
显然，这并不起作用，因为 Base 类中的方法没有声明任何异常。
如何在实现类中任意地抛出异常呢？
有没有一种方法，不必在 execute 方法中声明 throws Exception，也不必始终使用 try-catch 块？
我还想避免将 execute 中的公共逻辑重复放入其子类中。
在这种情况下，有什么最佳解决方案？是否有更好的设计模式？
英文:
Let's say I have an abstract class Base that has a concrete method execute and three abstract methods stepOne, stepTwo and stepThree...
public abstract class Base {protected abstract void stepOne();protected abstract void stepTwo();protected abstract void stepThree();public final void execute() {//do stuffstepOne();//do stuffstepTwo();//do stuffstepThree();//do stuff}}
...and is subclassed by a concrete class Sub1
public class Sub1 extends Base {protected void stepOne() {//...}protected void stepTwo() {//...}protected void stepThree() {//...}}
Now let's suppose I have a second subclass Sub2 that can throw a checked exception in stepOne and stepTwo
public class Sub2 extends Base {protected void stepOne() throws Exception1 {//...}protected void stepTwo() throws Exception2 {//...}protected void stepThree() {//...}}
I would like to use these classes as follows:
Sub1 s1 = new Sub1();try {s1.execute();} catch (Exception1 e1) {//handle e1} catch (Exception2 e2) {//handle e2}Sub2 s2 = new Sub2();s2.execute();
Clearly this doesn't work since the methods in Base aren't declared with any exceptions.
How can I have arbitrary exception throwing in the implementing classes?
Is there a way without having to declare execute with throws Exception and always having to use a try-catch for it?
I'd also like to avoid duplicating the common logic in execute into its subclasses.
What's the best solution here? Is there a better design pattern for this?
答案1
得分: 0
这是如何通过使Base类方法抛出通用异常来解决这个问题的方法：
public abstract class Base<E1 extends Exception, E2 extends Exception, E3 extends Exception> {protected abstract void stepOne() throws E1;protected abstract void stepTwo() throws E2;protected abstract void stepThree() throws E3;public final void execute() throws E1, E2, E3 {// 执行一些操作stepOne();// 执行一些操作stepTwo();// 执行一些操作stepThree();// 执行一些操作}}
您可以通过扩展Base<RuntimeException, RuntimeException, RuntimeException>创建一个不抛出任何受检异常的子类，如下所示：
public class Sub1 extends Base<RuntimeException, RuntimeException, RuntimeException> {protected void stepOne() {//...}protected void stepTwo() {//...}protected void stepThree() {//...}}
以下是如何创建一个在某些步骤中可以抛出受检异常的子类：
public class Sub2 extends Base<Exception1, Exception2, RuntimeException> {protected void stepOne() throws Exception1 {//...}protected void stepTwo() throws Exception2 {//...}protected void stepThree() {//...}}
您可以像这样使用这些类：
Sub2 s2 = new Sub2();try {s2.execute();} catch (Exception1 e1) {// 处理 e1} catch (Exception2 e2) {// 处理 e2}Sub1 s1 = new Sub1();s1.execute();
注意：代码部分不需要翻译，已经包含在您提供的原始文本中。
英文:
Here is how you can solve this problem by making Base class methods throw generic exceptions:
public abstract class Base<E1 extends Exception, E2 extends Exception, E3 extends Exception> {protected abstract void stepOne() throws E1;protected abstract void stepTwo() throws E2;protected abstract void stepThree() throws E3;public final void execute() throws E1, E2, E3 {//do stuffstepOne();//do stuffstepTwo();//do stuffstepThree();//do stuff}}
You can create a subclass that doesn't throw any checked exceptions by extending Base<RuntimeException, RuntimeException, RuntimeException> as follows:
public class Sub1 extends Base<RuntimeException, RuntimeException, RuntimeException> {protected void stepOne() {//...}protected void stepTwo() {//...}protected void stepThree() {//...}}
And here is how you can create a subclass that can throw a checked exception in some steps:
public class Sub2 extends Base<Exception1, Exception2, RuntimeException> {protected void stepOne() throws Exception1 {//...}protected void stepTwo() throws Exception2 {//...}protected void stepThree() {//...}}
You can use these classes as follows:
Sub2 s2 = new Sub2();try {s2.execute();} catch (Exception1 e1) {//handle e1} catch (Exception2 e2) {//handle e2}Sub1 s1 = new Sub1();s1.execute();
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