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Abstract
Factory 是另一種被普遍運用的創建型模式，Abstract Factory 通過專門的 Factory Class
來封裝對象創建的職責，并通過實現 Abstract Factory 來完成不同的創建邏輯。如果被測試單元所使用的外部對象是通過
Abstract Factory 創建的，則實現一個新的 Concrete Factory，并在此 Factory 中創建 Mock
Objects 是一個比較好的解決辦法。對于 Factory 本身，則可以在 setUp 測試的時候指定新的 Concrete Factory
；此外，借助依賴注入框架（如 Spring 的 BeanFactory），通過依賴注入的方式將 Factory
注入也是一種不錯的解決方案。對于簡單的依賴注入需求，可以考慮實現一個應用專有的依賴注入模塊，或者實現一個簡單的實現加載器，即根據配置文件載入相應
的實現，從而無需修改應用代碼，僅通過修改配置文件即可載入不同的實現，進而方便地修改程序的運行路徑，執行單元測試。
下面的代碼實現了一個簡單的 InstanceFactory：
// refer to http://www.opensc-project.org/opensc-java/export/100/trunk/
// pkcs15/src/main/java/org/opensc/pkcs15/asn1/InstanceFactory.java
packagecom.instancefactory.demo;
importjava.lang.reflect.InvocationTargetException;
importjava.lang.reflect.Method;
importjava.lang.reflect.Modifier;
public class InstanceFactory {
private final Method getInstanceMethod;
public InstanceFactory(String type) {
Class clazz =null;
try {
clazz = Class.forName(type);
this.getInstanceMethod = clazz.getMethod("getInstance");
if(!Modifier.isStatic(this.getInstanceMethod.getModifiers())
|| !Modifier.isPublic(this.getInstanceMethod.getModifiers()))
throw new IllegalArgumentException(
"Method [" + clazz.getName()
+ ".getInstance(Object)] is not static public.");
} catch (NoSuchMethodException e) {
throw new IllegalArgumentException(
"Class [" + clazz.getName()
+ "] has no static getInstance(Object) method.", e);
} catch (ClassNotFoundException e) {
throw new IllegalArgumentException("Class [" + type + "] is not found");
}
}
public Object getInstance() {
try{
return this.getInstanceMethod.invoke(null);
} catch (InvocationTargetException e) {
if( e.getCause() instanceof RuntimeException )
throw (RuntimeException)e.getCause();
throw new IllegalArgumentException(
"Method [" +this.getInstanceMethod
+ "] has thrown an checked exception.", e);
} catch( IllegalAccessException e) {
throw new IllegalArgumentException(
"Illegal access to method ["
+this.getInstanceMethod + "].", e);
}
}
public Method getGetInstanceMethod() {
return this.getInstanceMethod;
}
} |
以下代碼演示了 InstanceFactory 的簡單使用：
// BaseObjects.java
package com.instancefactory.demo;
public interface BaseObjects {
voidfunc();
}
// OuterObjects.java
package com.instancefactory.demo;
public class OuterObjects implements BaseObjects {
public static BaseObjects getInstance() {
return new OuterObjects();
}
public void func() {
System.out.println("OuterObjects.func");
}
}
// MockOuterObjects.java
package com.instancefactory.demo;
public class MockOuterObjects implements BaseObjects {
public static BaseObjects getInstance() {
return new MockOuterObjects();
}
public void func() {
System.out.println("MockOuterObjects.func");
}
}
// LogicToBeTested.java
packagecom.instancefactory.demo;
public class LogicToBeTested {
public static final String PROPERTY_KEY= "BaseObjects";
public void doSomething() {
// load configuration file and read the implementation class name of BaseObjects
// read it from properties to simplify the demo
// actually, the property file reader can be implemented by InstanceFactory
String impl = System.getProperty(PROPERTY_KEY);
InstanceFactory factory = new InstanceFactory(impl);
BaseObjects b = (BaseObjects)factory.getInstance();
b.doSomething();
}
}
// LogicTest.java
packagecom.instancefactory.demo;
importjunit.framework.TestCase;
public class LogicTest extends TestCase {
LogicToBeTested c;
protected void setUp() {
// set the property file of class map to a file for MockObjects, omitted
// use System.setProperty to simplify the demo
System.setProperty(LogicToBeTested.PROPERTY_KEY,
"com.instancefactory.demo.MockOuterObjects");
c = new LogicToBeTested();
}
public void testDoSomething() {
c.doSomething();
}
} |
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