一、前言

IOC (Inverse of control) - 控制反轉，spring的IOC實現原理為利用Java的反射機制并充當工廠的角色完成對象的裝配和注入。

二、實現細節

附上一張類的結構圖，該例子需要導入jdom.jar和junit.jar

<喎�"http://www.2cto.com/kf/ware/vc/" target="_blank" class="keylink">vcD4KPHA+CqLZINPDu6dCZWFuPC9wPgo8cHJlIGNsYXNzPQ=="brush:java;">package com.zdp.model; // 用戶類 public class User { private String userName; private String password; public String getUserName() { return userName; } public void setUserName(String userName) { this.userName = userName; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } }② UserService

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package com.zdp.service; import com.zdp.dao.UserDao; import com.zdp.model.User; public class UserService { ????private UserDao userDao; ????public void add(User user) { ????????userDao.save(user); ????} ????public UserDao getUserDao() { ????????return userDao; ????} ????public void setUserDao(UserDao userDao) { ????????this.userDao = userDao; ????} }

③ UserDao

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package com.zdp.dao; import com.zdp.model.User; public class UserDao { ????? ????public void save(User user) { ????????System.out.println("user saved!"); ????} ????? }

④ Bean工廠接口

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package com.zdp.spring; // Bean工廠接口 public interface BeanFactory { ????? ????public Object getBean(String id); ????? }

⑤ Bean工廠實現

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package com.zdp.spring; import java.lang.reflect.Method; import java.util.HashMap; import java.util.List; import java.util.Map; import org.jdom.Document; import org.jdom.Element; import org.jdom.input.SAXBuilder; // Bean工廠實現類 public class ClassPathXmlApplicationContext implements BeanFactory { ????private Map<string, object=""> beans = new HashMap<string, object="">(); ????public ClassPathXmlApplicationContext() throws Exception { ????????SAXBuilder sb = new SAXBuilder(); ????????Document doc = sb.build(this.getClass().getClassLoader().getResourceAsStream("beans.xml")); // 構造文檔對象 ????????Element root = doc.getRootElement(); // 獲取根元素HD ????????List list = root.getChildren("bean"); // 取名字為bean的所有元素 ????????for (int i = 0; i < list.size(); i++) { ????????????Element element = (Element) list.get(i); ????????????String id = element.getAttributeValue("id"); ????????????String clazz = element.getAttributeValue("class"); ????????????Object beanObj = Class.forName(clazz).newInstance(); // 反射獲取對象 ????????????beans.put(id, beanObj); // 將對象存入Bean工廠 ????????????for (Element propertyElement : (List<element>) element.getChildren("property")) { ????????????????String name = propertyElement.getAttributeValue("name"); // name="userDao" ????????????????String bean = propertyElement.getAttributeValue("bean"); // bean="userDao" ????????????????Object injectObject = beans.get(bean); // 從Bean工廠中獲取UserDao ????????????????String methodName = "set" + name.substring(0, 1).toUpperCase() + name.substring(1); // setUserDao ????????????????Method method = beanObj.getClass().getMethod(methodName, injectObject.getClass()); ????????????????method.invoke(beanObj, injectObject); // set注入UserDao對象 ????????????} ????????} ????} ????public Object getBean(String id) { ????????return beans.get(id); ????} } </element></string,></string,>

這里為核心代碼，當然在實際情況中，這一塊要復雜的多， 例如：可以一個bean引用另一個bean，還可以有多個配置文件、通過多種方式載入配置文件等等，不過原理還是采用Java的反射機制。

⑥ 配置文件

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<beans> ????<bean id="userDao" class="com.zdp.dao.UserDao"> ????<bean id="userService" class="com.zdp.service.UserService"> ????????<property name="userDao" bean="userDao"> ????</property></bean> </bean></beans>

⑦ 單元測試

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package com.zdp.service; import org.junit.Test; import com.zdp.model.User; import com.zdp.spring.BeanFactory; import com.zdp.spring.ClassPathXmlApplicationContext; // 測試代碼 public class UserServiceTest { ????@Test ????public void testAdd() throws Exception { ????????BeanFactory applicationContext = new ClassPathXmlApplicationContext(); // 獲取上下文 ????????UserService service = (UserService) applicationContext.getBean("userService"); // Spring裝配Bean ????????User user = new User(); ????????user.setUserName("zhangsan"); ????????user.setPassword("123456"); ????????service.add(user); // 將user保存入庫 ????} }

三、小結

上文僅僅是簡單地模擬了spring的IOC的實現，雖然只是完成了spring中依賴注入的一小部分，但還是很好地展現了Java反射機制在spring中的應用，對于初學者理解IOC應該會有一點幫助。

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