IOC浅析
声明：内容并非原创，主要来自《Spring2.0技术手册》一书
IOC: 依赖注入
这里主要通过举简单的例子，来试图解释IOC的复杂原理。
没有IOC的代码：
高层应用调用底层，应用依赖底层模块。
改进1
1> 引入接口
public interface IDeviceWrite {
public void saveToDevice();
}
2>接口实现类
public class FloppyImpl implements IDeviceWrite {
public void saveToDevice() {
// TODO Auto-generated method stub
System.out.println("Save to Floppy...");
}
}
3>上层应用
public class Business {
public void save(IDeviceWrite write){
write.saveToDevice();
}
public static void main(String[] args){
Business business = new Business();
IDeviceWrite floppy = new FloppyImpl();
business.save(floppy);
}
}
可以看到通过引入接口上层与底层的依赖解耦了，不依赖于底层实现，面向接口更灵活了。
改进2：
在改进1的基础上增加了配置文件，通过修改配置文件就可以改变上层应用引用底层的实例，更加灵活。
public class BusinessFactory {
private IDeviceWrite write;
private static BusinessFactory instance = null;
private BusinessFactory(){
this.setWrite();
}
public IDeviceWrite getWrite() {
return write;
}
public void setWrite() {
Properties prop = new Properties();
try{
prop.load(new FileInputStream("./conf.properties"));
String deviceClass = prop.getProperty("writer.class");
write = (IDeviceWrite)Class.forName(deviceClass).newInstance();
}catch (FileNotFoundException e) {
e.printStackTrace();
}catch (IOException e) {
e.printStackTrace();
}catch (IllegalAccessException e) {
e.printStackTrace();
}catch (ClassNotFoundException e) {
e.printStackTrace();
}catch (InstantiationException e) {
e.printStackTrace();
}
}
public static synchronized BusinessFactory getInstance(){
if(null == instance)
return new BusinessFactory();
return instance;
}
public static void main(String[] args){
BusinessFactory business = getInstance();
IDeviceWrite write = business.getWrite();
write.saveToDevice();
}
}
4>几个主要的类
org.springframework.context.ApplicationContext
org.springframework.context.support.ClassPathXmlApplicationContext
org.springframework.context.support.FileSystemXmlApplicationContext
Instantiating a container
// create and configure beans
ApplicationContext context =
new ClassPathXmlApplicationContext(new String[] {"services.xml", "daos.xml"});
// retrieve configured instance
PetStoreServiceImpl service = context.getBean("petStore", PetStoreServiceImpl.class);
// use configured instance
List userList service.getUsernameList();
5> The following example shows the basic structure of XML-based configuration metadata
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> <bean id="..." class="..."> <!-- collaborators and configuration for this bean go here --> </bean> <bean id="..." class="..."> <!-- collaborators and configuration for this bean go here --> </bean> <!-- more bean definitions go here --> </beans>
【编者按】
1 IOC (inversion of Control)
在reference中IOC这部分主要讲的是DI(dependece Inject)
DI 又主要讲的是
构造函数注入 与 Set 注入
推荐Set注入