深刻探索spring技術內幕(三): 剖析spring IoC工做原理和配置依賴注入

1、前言

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

 

2、實現細節

類結構:

該例子須要導入如下jar包

① Dao接口類: PersonDao

public interface PersonDao {
	public void save();
}

② Dao實現類: PersonDaoImpl

import com.zdp.dao.PersonDao;

public class PersonDaoImpl implements PersonDao {
	public void save(){
		System.out.println("執行PersonDaoImpl中的save()方法");
	}
}

③ Service接口類: PersonService

public interface PersonService {  
    public void save();  
}

④ Service實現類: 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定義類: BeanDefinition

import java.util.ArrayList;
import java.util.List;

/**
 * 封裝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 屬性定義類: PropertyDefinition

/**
 * 封裝屬性
 * @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工廠類: 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();
	}

	/**
	 * 爲bean對象的屬性注入值
	 */
	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(); // 獲取屬性的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 method
									setter.invoke(bean, injectBean); // 把引用對象注入到屬性
								}
								break;
							}
						}
					}
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		}
	}

	/**
	 * 完成bean的實例化
	 */
	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();
			}
		}

	}

	/**
	 * 讀取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");// 加入命名空間
			XPath xsub = document.createXPath("//ns:beans/ns:bean");// 建立beans/bean查詢路徑
			xsub.setNamespaceURIs(nsMap);// 設置命名空間
			List<Element> beans = xsub.selectNodes(document);// 獲取文檔下全部bean節點
			for (Element element : beans) {
				String id = element.attributeValue("id");// 獲取id屬性值
				String clazz = element.attributeValue("class"); // 獲取class屬性值
				BeanDefinition beanDefine = new BeanDefinition(id, clazz);
				XPath propertysub = element.createXPath("ns:property");
				propertysub.setNamespaceURIs(nsMap);// 設置命名空間
				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();
		}
	}

	/**
	 * 獲取bean實例
	 * 
	 * @param beanName
	 * @return
	 */
	public Object getBean(String beanName) {
		return this.sigletons.get(beanName);
	}
}

這裏爲核心代碼，固然在實際狀況中，這一塊要複雜的多， 例如：能夠一個bean引用另外一個bean，還能夠有多個配置文件、經過多種方式載入配置文件等等，

不過原理仍是採用Java的反射機制。

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 單元測試

import org.junit.Test;
import com.zdp.myspring.ClassPathXMLApplicationContext;
import com.zdp.service.PersonService;

public class PersonServiceImplTest {
	@Test
	public void testSave() {
		ClassPathXMLApplicationContext ctx = new ClassPathXMLApplicationContext("beans.xml");
		PersonService personService = (PersonService)ctx.getBean("personService");
		personService.save();
	}
}

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，但仍是很好地展示了Java反射機制在spring中的應用，對於初學者理解IOC應該會有一點幫助。 

源碼下載地址: http://download.csdn.net/detail/zdp072/7330769

 

 

3、spring的依賴注入

1. 使用構造函數注入:

<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:

注入對象, 基本屬性, 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>

對應Java類:

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. 使用註解注入:

具體內容見第四章: http://blog.csdn.net/zdp072/article/details/25558563