深入探索spring技术内幕(三): 剖析spring IoC工作原理和配置依赖注入

一、前言

IOC (Inverse of control) - 控制反转，spring的IOC实现原理为利用Java的反射机制并充当工厂的角色完成对象的装配和注入。 

二、实现细节

类结构:

该例子需要导入以下jar包

① Dao接口类: PersonDao

public interface PersonDao {public void save();}

② Dao实现类: PersonDaoImpl

import com.zdp.dao.PersonDao;public class PersonDaoImpl implements PersonDao {public void save(){System.out.println("执行PersonDaoImpl中的save()方法");}}

③ Service接口类: PersonService

public interface PersonService {public void save();}

④ Service实现类: PersonServiceImpl

import com.zdp.dao.PersonDao;import com.zdp.service.PersonService;public class PersonServiceImpl implements PersonService {private PersonDao personDao;private String name;private Integer id;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public PersonDao getPersonDao() {return personDao;}public void setPersonDao(PersonDao personDao) {this.personDao = personDao;}public void save() {System.out.println("id: " + id + ", name: " + name);personDao.save();}}

⑤ Bean定义类: BeanDefinition

import java.util.ArrayList;import java.util.List;/** * 封装Bean * @author zhangjim */public class BeanDefinition {private String id;private String className;private List<PropertyDefinition> propertys = new ArrayList<PropertyDefinition>();public BeanDefinition(String id, String className) {this.id = id;this.className = className;}public String getId() {return id;}public void setId(String id) {this.id = id;}public String getClassName() {return className;}public void setClassName(String className) {this.className = className;}public List<PropertyDefinition> getPropertys() {return propertys;}public void setPropertys(List<PropertyDefinition> propertys) {this.propertys = propertys;}}

⑥ 属性定义类: PropertyDefinition

/** * 封装属性 * @author zhangjim */public class PropertyDefinition {private String name;private String ref;private String value;public String getValue() {return value;}public void setValue(String value) {this.value = value;}public PropertyDefinition(String name, String ref, String value) {this.name = name;this.ref = ref;this.value = value;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getRef() {return ref;}public void setRef(String ref) {this.ref = ref;}}

⑦ Bean工厂类: ClassPathXMLApplicationContext

import java.beans.Introspector;import java.beans.PropertyDescriptor;import java.lang.reflect.Method;import java.net.URL;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import org.apache.commons.beanutils.ConvertUtils;import org.dom4j.Document;import org.dom4j.Element;import org.dom4j.XPath;import org.dom4j.io.SAXReader;/** * Spring Bean Factory */public class ClassPathXMLApplicationContext {private List<BeanDefinition> beanDefines = new ArrayList<BeanDefinition>();private Map<String, Object> sigletons = new HashMap<String, Object>();public ClassPathXMLApplicationContext(String filename) {this.readXML(filename);this.instanceBeans();this.injectObject();}/** * 为bean对象的属性注入值 */private void injectObject() {for (BeanDefinition beanDefinition : beanDefines) {Object bean = sigletons.get(beanDefinition.getId());if (bean != null) {try {PropertyDescriptor[] ps = Introspector.getBeanInfo(bean.getClass()).getPropertyDescriptors();for (PropertyDefinition propertyDefinition : beanDefinition.getPropertys()) {for (PropertyDescriptor properdesc : ps) {if (propertyDefinition.getName().equals(properdesc.getName())) {Method setter = properdesc.getWriteMethod(); // 获取属性的setter方法 if (setter != null) {Object injectBean = null; if (propertyDefinition.getRef() != null && !"".equals(propertyDefinition.getRef().trim())) {injectBean = sigletons.get(propertyDefinition.getRef());} else {injectBean = ConvertUtils.convert(propertyDefinition.getValue(), properdesc.getPropertyType());}setter.setAccessible(true); // private methodsetter.invoke(bean, injectBean); // 把引用对象注入到属性}break;}}}} catch (Exception e) {e.printStackTrace();}}}}/** * 完成bean的实例化 */private void instanceBeans() {for (BeanDefinition beanDefinition : beanDefines) {try {if (beanDefinition.getClassName() != null && !"".equals(beanDefinition.getClassName().trim()))sigletons.put(beanDefinition.getId(), Class.forName(beanDefinition.getClassName()).newInstance());} catch (Exception e) {e.printStackTrace();}}}/** * 读取xml配置文件 *  * @param filename */private void readXML(String filename) {SAXReader saxReader = new SAXReader();Document document = null;try {URL xmlpath = this.getClass().getClassLoader().getResource(filename);document = saxReader.read(xmlpath);Map<String, String> nsMap = new HashMap<String, String>();nsMap.put("ns", "http://www.springframework.org/schema/beans");// 加入命名空间XPath xsub = document.createXPath("//ns:beans/ns:bean");// 创建beans/bean查询路径xsub.setNamespaceURIs(nsMap);// 设置命名空间List<Element> beans = xsub.selectNodes(document);// 获取文档下所有bean节点for (Element element : beans) {String id = element.attributeValue("id");// 获取id属性值String clazz = element.attributeValue("class"); // 获取class属性值BeanDefinition beanDefine = new BeanDefinition(id, clazz);XPath propertysub = element.createXPath("ns:property");propertysub.setNamespaceURIs(nsMap);// 设置命名空间List<Element> propertys = propertysub.selectNodes(element);for (Element property : propertys) {String propertyName = property.attributeValue("name");String propertyRef = property.attributeValue("ref"); String propertyValue = property.attributeValue("value");PropertyDefinition propertyDefinition = new PropertyDefinition(propertyName, propertyRef, propertyValue);beanDefine.getPropertys().add(propertyDefinition);}beanDefines.add(beanDefine);}} catch (Exception e) {e.printStackTrace();}}/** * 获取bean实例 *  * @param beanName * @return */public Object getBean(String beanName) {return this.sigletons.get(beanName);}}

这里为核心代码，当然在实际情况中，这一块要复杂的多， 例如：可以一个bean引用另一个bean，还可以有多个配置文件、通过多种方式载入配置文件等等，

不过原理还是采用Java的反射机制。

⑧ beans.xml

<?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-2.5.xsd">               <bean id="personDao" class="com.zdp.dao.impl.PersonDaoImpl"></bean>    <bean id="personService" class="com.zdp.service.impl.PersonServiceImpl">    <property name="personDao" ref="personDao"/>    <property name="name" value="zhangsan"/>    <property name="id" value="123"/>    </bean></beans>

⑨ 单元测试

import org.junit.Test;import com.zdp.myspring.ClassPathXMLApplicationContext;import com.zdp.service.PersonService;public class PersonServiceImplTest {@Testpublic void testSave() {ClassPathXMLApplicationContext ctx = new ClassPathXMLApplicationContext("beans.xml");PersonService personService = (PersonService)ctx.getBean("personService");personService.save();}}

上文仅仅是简单地模拟了spring的IOC的实现，虽然只是完成了spring中依赖注入的一小部分，但还是很好地展现了Java反射机制在spring中的应用，对于初学者理解IOC应该会有一点帮助。 

源码下载地址: http://download.csdn.net/detail/zdp072/7330769

三、spring的依赖注入

1. 使用构造函数注入:

<bean id="personDao" class="com.zdp.dao.impl.PersonDaoImpl" /> 
<bean id="personService" class="com.zdp.service.impl.PersonServiceImpl">
       <constructor-arg index="0" ref="personDao" />
</bean>

public class PersonServiceImpl implements PersonService {private PersonDao personDao;public PersonServiceImpl(PersonDao personDao) {this.personDao = personDao;}public void save() {personDao.save();}}

2. setter方法注入:

注入对象, 基本属性, 集合

<bean id="personDao" class="com.zdp.dao.impl.PersonDaoImpl" /><bean id="personService" class="com.zdp.service.impl.PersonServiceImpl"><!-- <property name="personDao"> <ref bean="personDao"/> </property> --><property name="personDao" ref="personDao" /><property name="name" value="zhangsan" /><property name="id" value="123" /><property name="sets"><set><value>1</value><value>2</value></set></property><property name="lists"><list><value>1</value><value>2</value><value>3</value></list></property><property name="maps"><map><entry key="1" value="1"></entry><entry key="2" value="2"></entry><entry key="3" value="3"></entry><entry key="4" value="4"></entry></map></property></bean>

对应Java类:

import java.util.List;import java.util.Map;import java.util.Set;import com.zdp.dao.PersonDao;import com.zdp.service.PersonService;public class PersonServiceImpl implements PersonService {private PersonDao personDao;private String name;private Integer id;private Set<String> sets;private List<String> lists;private Map<String, String> maps;// 省略get set方法public void save() {System.out.println("id: " + id + ", name: " + name);System.out.println("sets: " + sets.size() + ", lists: " + lists.size() + ", maps: " + maps.size());personDao.save();}}

3. 使用注解注入:

具体内容见第四章: http://blog.csdn.net/zdp072/article/details/25558563