spring 控制反转与依赖注入原理

转自http://www.iteye.com/topic/1118958

在Spring中有两个非常重要的概念，控制反转和依赖注入；控制反转将依赖对象的创建和管理交由Spring容器，而依赖注入则是在控制反转的基础上将Spring容器管理的依赖对象注入到应用之中；

所谓依赖注入：在运行期，由外部容器动态将依赖对象注入到组件中。

XML文件解析　＋ Java反射技术;

首先是XML文件的解析(dom4j)，Spring框架对于配置文件的选择是XML文件，根据Spring的规范，配置文件的命名是没有特殊要求的，只是在文件的放置位置上有两种选择；类路径下或者操作系统文件目录下（大多数情况是放到类路径下）。

对于Spring的控制反转和依赖注入来说，唯一使用的是配置文件中的<bean>标签，通过这个标签，Spring就完成了对象的创建和依赖对象的注入工作；

1、首先对于配置文件中的<bean>节点，在Spring框架中存在一个对用的定义接口，叫做BeanDefinition；子啊个类定义了获得<bean>节点中出现的所有属性的方法，例如classNam、scope、factory-method、lazy-init 等等属性；

2、对于<bean>节点的子节点property则完成了属性注入的功能；属性注入有三种方式，构造器注入、属性setter方法注入和注解方式注入；

3、如果是setter方法注入，对于类属性XML配置文件中有两种方法，一是使用property节点的ref属性，一是使用property几点的子节点bean进行内部bean配置；如果是对于基本数据类型进行配置，那么要是用property节点的value属性；

定义自己的关于bean节点、property节点的pojo类文件；

使用注入DOM4J等开源包讲配置文件解析读入；

使用Java的反射技术讲配置文件中的信息setter到我们需要的属性中去；common-beanutils.jar

 

<context:component-scan base-package="com.sample"/><bean id="personService" class="com.spring.junit.test.impl.PersonServiceImpl"></bean><bean id="stockService" class="com.spring.junit.test.impl.StockServiceImpl"></bean><bean id="personServiceFactory" class="com.spring.junit.test.impl.PersonServiceBeanFactory" factory-method="createPersonServiceBeanFactory"></bean><bean id="personServiceFactory2" class="com.spring.junit.test.impl.PersonServiceBeanFactory"></bean><bean id="stockServiceFactory" factory-bean="personServiceFactory2" factory-method="createStockServiceBeanFactory"></bean><bean id="randomBean" class="com.spring.junit.bean.StaticFactoryBean" factory-method="createRandom" scope="prototype"></bean><!-- 集合类型的注入 -->通过setter方法注入<bean id="user" class="com.sample.bean.User"></bean><bean id="personDao" class="com.sample.dao.impl.PersonDaoBeanImpl"></bean><bean id="personService" class="com.sample.service.impl.PersonServiceBeanImpl">      <property name="personDao" ref="personDao"></property>   <property name="name" value="jackjson_xu_test"></property>   <property name="id" value="108"></property>   <property name="sets">       <set>           <value>第一个</value>           <value>第二个</value>           <value>第三个</value>       </set>   </property>   <property name="lists">       <list>           <value>第一個list元素</value>           <value>第二個list元素</value>           <value>第三個list元素</value>                  </list>   </property>   <property name="properties">       <props>           <prop key="key1">value1</prop>           <prop key="key2">value2</prop>           <prop key="key3">value3</prop>                  </props>   </property>   <property name="maps">       <map>           <entry key="key-1" value="value-1"></entry>           <entry key="key-2" value="value-2"></entry>           <entry key="key-3" value="value-3"></entry>           <entry key="key-4" value="value-4"></entry>       </map>   </property>   <property name="users">       <map>           <entry key="U_1001">               <ref bean="user"/>           </entry>           <entry key="U_1002">                   <ref bean="user"/>               </entry>       </map>   </property></bean><!-- 采用内部bean的方式注入 --><bean id="personService" class="com.sample.service.impl.PersonServiceBeanImpl">   <property name="personDao">       <bean class="com.sample.dao.impl.PersonDaoBeanImpl"/>   </property>   <property name="name" value="jackjson_xu_test"></property>   <property name="id" value="100"></property></bean><!-- 构造器注入方式 --><bean id="personDao" class="com.sample.dao.impl.PersonDaoBeanImpl"></bean>    <bean id="personService2" class="com.sample.service.impl.PersonServiceBeanImpl2" autowire="byType">        <constructor-arg index="0" type="com.sample.dao.IPersonDao" ref="personDao"></constructor-arg>        <constructor-arg index="1" type="java.lang.String" value="http://www.woyo.com"></constructor-arg>    </bean>  

package com.sample.junit;

import java.util.ArrayList;import java.util.List;/** * Spring xml 属性的方法 * @author DY * */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;}}

package com.sample.junit;

/** * Spring xml bean 子节点property属性方法 *  * @author DY *  */public class PropertyDefinition {private String name;private String ref;private String 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;}public String getValue() {return value;}public void setValue(String value) {this.value = value;}}

package com.sample.junit;

import java.beans.Introspector;import java.beans.PropertyDescriptor;import java.lang.reflect.Field;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.apache.log4j.Logger;import org.dom4j.Document;import org.dom4j.Element;import org.dom4j.XPath;import org.dom4j.io.SAXReader;/** * spring装配applicationContext.xml文件 * @author DY * */public class SampleClassPathXMLApplicationContext {private Logger logger = Logger.getLogger(SampleClassPathXMLApplicationContext.class);private List<BeanDefinition> beanDefines = new ArrayList<BeanDefinition>();private Map<String, Object> sigletons = new HashMap<String, Object>();public SampleClassPathXMLApplicationContext(String filename) {this.readXML(filename);this.instanceBeans();//bean的实例化 Class.forName().newInstance()this.annotationInject();//注解this.injectObject();//bean对象的属性注入值}/** * 注解处理器 * 如果注解SampleResouce配置了name属性，则根据name所指定的名称获取要注入的实例引用 * 如果注解SampleResouce没有配置name属性，则根据属性所属类型来扫描配置文件获取要注入的实例引用 */private void annotationInject() {for (String beanName : sigletons.keySet()) {Object bean = sigletons.get(beanName);if (bean != null) {this.propertyAnnotation(bean);this.fieldAnnotation(bean);}}}/** * 处理在所有set方法加入的注解 * @param bean 处理的bean对象 */private void propertyAnnotation(Object bean) {try {//获取其属性的描述PropertyDescriptor[] ps = Introspector.getBeanInfo(bean.getClass()).getPropertyDescriptors();for (PropertyDescriptor properdesc : ps) {//获取属性的setter方法Method setter = properdesc.getWriteMethod();//setter方法上是否存在注解if (setter != null && setter.isAnnotationPresent(SampleResource.class)) {//获取当前注解，判断name属性是否为空SampleResource resouce = setter.getAnnotation(SampleResource.class);Object value = null;if (resouce.name() != null && !"".equals(resouce.name())) {value = sigletons.get(resouce.name());setter.setAccessible(true);setter.invoke(bean, value);//把引用对象注入到属性} else {//如果当前属性没有指定name，则根据类型匹配value = sigletons.get(resouce.name());if (value == null) {for (String key : sigletons.keySet()) {//判断当前属性所属类型是否在配置文件中存在if (properdesc.getPropertyType().isAssignableFrom(sigletons.get(key).getClass())) {value = sigletons.get(key);//获取类型匹配的实例对象}}}//允许访问private方法setter.setAccessible(true);//把引用对象注入属性setter.invoke(bean, value);}}}} catch (Exception e) {logger.error(e.getLocalizedMessage());}}/** * 处理在字段上的注解 * @param bean */private void fieldAnnotation (Object bean) {try {//获取全部属性对象数组Field[] fields = bean.getClass().getFields();for (Field field : fields) {if (field.isAnnotationPresent(SampleResource.class)) {SampleResource resouce = field.getAnnotation(SampleResource.class);Object value = null;if (resouce.name() != null && !"".equals(resouce.name())) {value = sigletons.get(resouce.name());} else {value = sigletons.get(field.getName());if (value == null) {for (String key : sigletons.keySet()) {//根据字段类型匹配if (field.getType().isAssignableFrom(sigletons.get(key).getClass())) {value = sigletons.get(key);break;}}}}field.setAccessible(true);field.set(bean, value);}}} catch (Exception e) {e.getLocalizedMessage();logger.error("字段注解解析异常:" + e.getLocalizedMessage());}}/** * 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 value = null;if (propertyDefinition.getRef() != null && !"".equals(propertyDefinition.getRef().trim())) {value = sigletons.get(propertyDefinition.getRef());} else {value = ConvertUtils.convert(propertyDefinition.getValue(), properdesc.getPropertyType());}setter.setAccessible(true);//私有方法给与访问权限setter.invoke(bean, value);// 把引用对象注入到属性}break;}}}} catch (Exception e) {}}}}/** * 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);System.out.println("propertyName:" + propertyName + "|propertyref:" + propertyref + "|propertyValue:" + propertyValue);}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);}}

package com.sample.junit;

import org.junit.BeforeClass;import org.junit.Test;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;import com.sample.service.IPersonService;public class SpringTest {static ApplicationContext ctx = null;@BeforeClasspublic static void setUpBeforeClass() throws Exception {ctx = new ClassPathXmlApplicationContext(new String[]{"applicationContext.xml"});}@Test public void instanceSpring(){IPersonService personService = (IPersonService)ctx.getBean("personService");System.out.println(personService);personService.save();}}