Spring 依赖注入控制反转实现，及编码解析（自制容器）

定义：

在运行期，由外部容器动态的将依赖对象动态地注入到组件中。

两种方式：

手工装配

-set方式

-构造器

-注解方式

自动装配（不推荐）



1利用构造器





2set方法注入

dao：

package dao;

public interface PersonDao {
public void add();
}

daoimpl：

package dao.impl;

import dao.PersonDao;

public class PersonDaoBean implements PersonDao{

@Override
public void add() {
System.out.println("I am person dao");
}

}

service：

package service;

public interface PersonService {

public void save();

}

serviceimpl（set实现依赖注入）：

package service.impl;

import dao.PersonDao;
import service.PersonService;

public class PersonServiceBean implements PersonService {

private PersonDao personDao;

public PersonDao getPersonDao() {
return personDao;
}

public void setPersonDao(PersonDao personDao) {
this.personDao = personDao;
}

public void save(){
personDao.add();
}

}

applicationContext.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-3.1.xsd"> 
<bean id = "personDao" class = "dao.impl.PersonDaoBean"></bean>

<!-- 默认构造方法 -->
<bean id = "personService" class = "service.impl.PersonServiceBean">
<property name = "personDao" ref = "personDao">
</property>
</bean>

</beans>

这样一来，dao方法会直接被spring注入到service里。运行service的save方法可以调用dao的save方法。　


　

　除了注入bean还可以注入基本属性类型，以及各种集合类。

编码剖析：

bean定义类：

package test;

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

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;
}

}

property定义类：

package test;

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;
}

}

自制spring容器

package test;

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;

public class MyClassPathXMLApplicationContext {
private List<BeanDefinition> beanDefines = new ArrayList<BeanDefinition>();
private Map<String, Object> sigletons = new HashMap<String, Object>();

public MyClassPathXMLApplicationContext(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 ,private
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);
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);
}
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);
}
}