手写SpringIOC 实现原理

什么是SpringIOC

spring ioc指的是控制反转，IOC容器负责实例化、定位、配置应用程序中的对象及建立这些对象间的依赖。交由Spring来管理这些，实现解耦

SpringIOC原理

使用反射机制+XML技术

手写Spring专题 XML方式注入bean

/**  * 手写Spring专题 XML方式注入bean  *  *  */ public class ClassPathXmlApplicationContext {       // xml路径地址       private String xmlPath;         public ClassPathXmlApplicationContext(String xmlPath) {             this.xmlPath = xmlPath;       }         public Object getBean(String beanId) throws Exception {             // 1. 读取配置文件             List elements = readerXml();             if (elements == null) {                   throw new Exception("该配置文件没有子元素");             }             // 2. 使用beanId查找对应的class地址             String beanClass = findXmlByIDClass(elements, beanId);             if (StringUtils.isEmpty(beanClass)) {                   throw new Exception("未找到对应的class地址");             }             // 3. 使用反射机制初始化，对象             Class forName = Class.forName(beanClass);             return forName.newInstance();       }         // 读取配置文件信息       public List readerXml() throws DocumentException {             SAXReader saxReader = new SAXReader();             if (StringUtils.isEmpty(xmlPath)) {                   new Exception("xml路径为空...");             }             Document read = saxReader.read(getClassXmlInputStream(xmlPath));             // 获取根节点信息             Element rootElement = read.getRootElement();             // 获取子节点             List elements = rootElement.elements();             if (elements == null || elements.isEmpty()) {                   return null;             }             return elements;       }         // 使用beanid查找该Class地址       public String findXmlByIDClass(List elements, String beanId) throws Exception {             for (Element element : elements) {                   // 读取节点上是否有value                   String beanIdValue = element.attributeValue("id");                   if (beanIdValue == null) {                        throw new Exception("使用该beanId为查找到元素");                   }                   if (!beanIdValue.equals(beanId)) {                        continue;                   }                   // 获取Class地址属性                   String classPath = element.attributeValue("class");                   if (!StringUtils.isEmpty(classPath)) {                        return classPath;                   }             }             return null;       }         // 读取xml配置文件       public InputStream getClassXmlInputStream(String xmlPath) {             InputStream resourceAsStream = getClass().getClassLoader().getResourceAsStream(xmlPath);             return resourceAsStream;       }   }

 

测试：

public class Test002 {             public static void main(String[] args) throws Exception {                        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring.xml");                        User user = (User) applicationContext.getBean("user");                        System.out.println(user);             }   }