理解Spring依赖注入（模拟Spring容器）
仿spring容器 ,也就是传智播客容器 ItcastClassPathXMLApplicationContext
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.dom4j.Document; import org.dom4j.Element; import org.dom4j.XPath; import org.dom4j.io.SAXReader; /** * 传智传客版容器 * */ public class ItcastClassPathXMLApplicationContext { private List<BeanDefinition> beanDefines = new ArrayList<BeanDefinition>(); private Map<String, Object> sigletons = new HashMap<String, Object>(); public ItcastClassPathXMLApplicationContext(String filename){ this.readXML(filename); this.instanceBeans(); this.annotationInject(); this.injectObject(); } /** * 通过注解实现注入依赖对象 */ private void annotationInject() { for(String beanName : sigletons.keySet()){ Object bean = sigletons.get(beanName); if(bean!=null){ try { PropertyDescriptor[] ps = Introspector.getBeanInfo(bean.getClass()).getPropertyDescriptors(); for(PropertyDescriptor properdesc : ps){ Method setter = properdesc.getWriteMethod();//获取属性的setter方法 /*如果setter方法不为空,并且上面有注解*/ if(setter!=null && setter.isAnnotationPresent(ItcastResource.class)){ /*得到注解*/ ItcastResource resource = setter.getAnnotation(ItcastResource.class); Object value = null; //如果注解的name属性不为空,也就是这种情况 @ItcastResource(name="persionDao") if(resource.name()!=null && !"".equals(resource.name())){ value = sigletons.get(resource.name()); }else{ /*如果注解的name为空,则根据属性的名字来得到bean*/ value = sigletons.get(properdesc.getName()); if(value==null) { /*如果的得到的bean为空,则根据key遍历容器中所有的bean,如果发现和属性类型相同的bean,就开始注入*/ for(String key : sigletons.keySet()){ if(properdesc.getPropertyType().isAssignableFrom(sigletons.get(key).getClass())){ value = sigletons.get(key); break; } } } } setter.setAccessible(true); setter.invoke(bean, value);//把引用对象注入到属性 } } /*对字段处理,也就是字段上有注解的情况*/ Field[] fields = bean.getClass().getDeclaredFields(); for(Field field : fields){ if(field.isAnnotationPresent(ItcastResource.class)){ ItcastResource resource = field.getAnnotation(ItcastResource.class); Object value = null; if(resource.name()!=null && !"".equals(resource.name())){ value = sigletons.get(resource.name()); }else{ value = sigletons.get(field.getName()); if(value==null){ for(String key : sigletons.keySet()){ if(field.getType().isAssignableFrom(sigletons.get(key).getClass())){ value = sigletons.get(key); break; } } } } field.setAccessible(true);//允许访问private字段 field.set(bean, value); } } } catch (Exception e) { e.printStackTrace(); } } } } /** * 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); } } ?
? 测试：
ItcastClassPathXMLApplicationContext ctx = new ItcastClassPathXMLApplicationContext("beans.xml");
PersionSevice ps=(PersionSevice)ctx.getBean("persionServiceBean");
ps.save();