浅析spring中注解的运行

为了了解注解的运行机制，需要自定义一个注解，如下方式来模拟注解方式实现注入对象：
1.新建一个自定义注解MyResource.java

@Retention(RetentionPolicy.RUNTIME) // 定义注解有效期为运行期@Target({ElementType.FIELD,ElementType.METHOD}) // 定义可以注解的位置public @interface MyResource {    String name() default "";}

2.自定义spring中的注解运行

package com.heying.test;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.dom4j.Document;import org.dom4j.Element;import org.dom4j.XPath;import org.dom4j.io.SAXReader;import com.heying.service.MyResource;import com.heying.service.PropertyDdefinition;import com.heying.service.XmlBeanDefinition;public class MyClassPathXmlApplicationContext {    private List<XmlBeanDefinition> beanDefinitions = new ArrayList<XmlBeanDefinition>();    private Map<Object, Object> sigletons = new HashMap<Object, Object>();    public MyClassPathXmlApplicationContext(String fileName) {        this.readXmlFile(fileName);        this.instanceBeans();        this.annotationInject();        this.injectObject();    }    /**     * 注解     */    private void annotationInject() {        for (Object beanName : sigletons.keySet()) {            Object bean = sigletons.get(beanName);            if(bean != null){                try {                    PropertyDescriptor[] ps = Introspector.getBeanInfo(bean.getClass()).getPropertyDescriptors();                    for (PropertyDescriptor propertyDescriptor : ps) {                        Method setter = propertyDescriptor.getWriteMethod();                            if(setter != null && setter.isAnnotationPresent(MyResource.class)){                            MyResource myTest = setter.getAnnotation(MyResource.class); //获取注解                            if(myTest.name() != null && !"".equals(myTest.name())){                                Object value = sigletons.get(myTest.name());                                setter.setAccessible(true);                                setter.invoke(bean,value); // 引入对象到属性                            }else{                                 Object value = sigletons.get(propertyDescriptor.getName());                                // 没有标注name 或者没有找到的时候就会按照类型去寻找                                if(value == null){                                    for (Object key : sigletons.keySet()) {                                        if(propertyDescriptor.getPropertyType().isAssignableFrom(sigletons.get(key).getClass())){                                            value = sigletons.get(key);                                            setter.setAccessible(true);                                            setter.invoke(bean,value); // 引入对象到属性                                            break;                                        }                                    }                                }                            }                        }                    }                    Field[] fields = bean.getClass().getDeclaredFields();                    for (Field field : fields) {                        if(field.isAnnotationPresent(MyResource.class)){                            MyResource myTest = field.getAnnotation(MyResource.class); //获取注解                            Object value = null;                            if(myTest.name() != null && !"".equals(myTest.name())){                                 value = sigletons.get(myTest.name());                            }else{                                  value = sigletons.get(field.getName());                                // 没有标注name 或者没有找到的时候就会按照类型去寻找                                if(value == null){                                    for (Object key : sigletons.keySet()) {                                        if(field.getType().isAssignableFrom(sigletons.get(key).getClass())){                                            value = sigletons.get(key);                                            break;                                        }                                    }                                }                            }                            field.setAccessible(true);                            field.set(bean, value);                        }                    }                } catch (Exception e) {                    e.printStackTrace();                }            }        }    }    /**     * 依赖注入     */    private void injectObject() {        for ( XmlBeanDefinition beanDefinition : beanDefinitions) {            Object bean = sigletons.get(beanDefinition.getId());            if(bean != null){                try {                    PropertyDescriptor[] propers = Introspector.getBeanInfo(bean.getClass()).getPropertyDescriptors();                    for (PropertyDdefinition propertyDdefinition : beanDefinition.getDdefinitions()) {                        for (PropertyDescriptor propertyDescriptor : propers) {                            if(propertyDdefinition.getName().equals(propertyDescriptor.getName())){  // 判断是否相等                                Method setter = propertyDescriptor.getWriteMethod(); // 获取set方法                                if(setter != null){                                    Object value = sigletons.get(propertyDdefinition.getRef());                                    setter.setAccessible(true);                                    setter.invoke(bean,value); // 引入对象到属性                                }                                break;                            }                        }                    }                } catch (Exception e) {                    e.printStackTrace();                }            }        }    }    /**     * bean 实例化     */    private void instanceBeans(){        for ( XmlBeanDefinition beanDefinition : beanDefinitions) {            try {                if(beanDefinition.getName() != null && !"".equals(beanDefinition.getName())){                    sigletons.put(beanDefinition.getId(), Class.forName(beanDefinition.getName()).newInstance());                }            } catch (Exception e) {                e.printStackTrace();            }        }    }    /**     * 读取XML信息     * @param fileName     */    @SuppressWarnings("unchecked")    private void readXmlFile(String fileName) {        SAXReader saxReader = new SAXReader();        Document document = null;        try {            URL xmlPath = this.getClass().getClassLoader().getResource(fileName); // 获取相对路径            document = saxReader.read(xmlPath); // 读取xml文件            Map<String, String> nsMap = new HashMap<String, String>();            nsMap.put("ns", "http://www.springframework.org/schema/beans"); // 加入命名空间            XPath xPath = document.createXPath("//ns:beans/ns:bean"); // 创建查询路径            xPath.setNamespaceURIs(nsMap); // 设置命名空间            List<Element> beans = xPath.selectNodes(document); // 获取所有节点            for (Element element : beans) {                String id = element.attributeValue("id");                String clazz = element.attributeValue("class");                XmlBeanDefinition xmlBeanDefinition = new XmlBeanDefinition(id, clazz);                XPath propertysub = document.createXPath("ns:property");                propertysub.setNamespaceURIs(nsMap); // 设置空间                List<Element> propertys = propertysub.selectNodes(element);                for (Element property : propertys) {                    String propertyName = property.attributeValue("name");                    String propertyRef = property.attributeValue("ref");                    System.out.println("[propertyName="+propertyName+",propertyRef="+propertyRef+"]");                    PropertyDdefinition ddefinition = new PropertyDdefinition(propertyName, propertyRef);                    xmlBeanDefinition.getDdefinitions().add(ddefinition);                }                beanDefinitions.add(xmlBeanDefinition);            }        } catch (Exception e) {            e.printStackTrace();        }    }    /**     * 获取bean实例     * @param beanName     * @return     */    public Object getBean(String beanName){        return this.sigletons.get(beanName);    }}

输出的结果和使用j2ee的注解有相同的效果