1.什么是模板设计模式
定义：有一个抽象父类定义了模板方法，子类继承父类的方法，按照各自的需求来实现父类的方法。
2.类图如下：
image
3.代码示例：
package com.buka.designer.template;
/** 编程是门艺术，设计源于生活！
*/
public abstract class Ticket {
//模板方法
public void buyTicket() {
login();
selectTicket();
pay();
}
public final void login() {
System.out.println("登录。。。");
}
//子类必须实现
public abstract void selectTicket();
//子类可以不实现
public void pay() {
System.out.println("支付宝。。。");
}
}
package com.buka.designer.template;
/**
* 火车票
*/
public class TrainTicket extends Ticket{
@Override
public void selectTicket() {
System.out.println("选择火车票。。。");
}
@Override
public void pay() {
System.out.println("使用微信支付。。。");
}
}
package com.buka.designer.template;
/**
* 船票
*/
public class ShipTicket extends Ticket{
@Override
public void selectTicket() {
System.out.println("选择船票。。。");
}
}
package com.buka.designer.template;
/**
* 测试
*/
public class TemplateTest {
public static void main(String[] args) {
Ticket trainTicket = new TrainTicket();
trainTicket.buyTicket();
Ticket shipTicket = new ShipTicket();
shipTicket.buyTicket();
}
}
4.使用场景：
spring源码中使用模板方法设计模式，例如：AbstractXmlApplicationContext作为父类，其子类有ClassPathXmlApplicationContext，FileSystemXmlApplicationContext等等。
FileSystemXmlApplicationContext集成getResourceByPath方法：
/* Resolve resource paths as file system paths.
* <p>Note: Even if a given path starts with a slash, it will get
* interpreted as relative to the current VM working directory.
* This is consistent with the semantics in a Servlet container.
* @param path path to the resource
* @return the Resource handle
* @see org.springframework.web.context.support.XmlWebApplicationContext#getResourceByPath
*/
@Override
protected Resource getResourceByPath(String path) {
if (path.startsWith("/")) {
path = path.substring(1);
}
return new FileSystemResource(path);
}
}
ClassPathXmlApplicationContext类继承了AbstractXmlApplicationContext的getConfigResources方法
@Override
@Nullable
protected Resource[] getConfigResources() {
return this.configResources;
}
XmlWebApplicationContext类继承了父类的loadBeanDefinitions，getDefaultConfigLocation两个方法。
/**
* Loads the bean definitions via an XmlBeanDefinitionReader.
* @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
* @see #initBeanDefinitionReader
* @see #loadBeanDefinitions
*/
@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
// Configure the bean definition reader with this context's
// resource loading environment.
beanDefinitionReader.setEnvironment(getEnvironment());
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
// Allow a subclass to provide custom initialization of the reader,
// then proceed with actually loading the bean definitions.
initBeanDefinitionReader(beanDefinitionReader);
loadBeanDefinitions(beanDefinitionReader);
}
/**
* The default location for the root context is "/WEB-INF/applicationContext.xml",
* and "/WEB-INF/test-servlet.xml" for a context with the namespace "test-servlet"
* (like for a DispatcherServlet instance with the servlet-name "test").
*/
@Override
protected String[] getDefaultConfigLocations() {
if (getNamespace() != null) {
return new String[] {DEFAULT_CONFIG_LOCATION_PREFIX + getNamespace() + DEFAULT_CONFIG_LOCATION_SUFFIX};
}
else {
return new String[] {DEFAULT_CONFIG_LOCATION};
}
}
