手写spring 框架——第三篇(注解的方式)

﹏ヽ暗。殇╰゛Y 2021-09-21 01:34 331阅读 0赞

(1)注解类

package com.jd.xq.spring.annotation;
    
    /** * @author duanxiaoqiu * @Date 2019-12-27 17:05 **/
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    @Retention(RetentionPolicy.RUNTIME)//注解处理在运行时刻
    @Target({ ElementType.FIELD,ElementType.METHOD})//对字段和方法使用注解
    public @interface YhdResource { 
        String value() default "";//注解里面只能声明属性，不能声明方法，声明属性的方式比较特殊：
    }

(2)使用注解类

package com.jd.xq.spring.bean;
    
    
    import com.jd.xq.spring.annotation.YhdResource;
    
    /** * @author duanxiaoqiu * @Date 2019-12-27 11:54 **/
    public class Person { 
        @YhdResource(value = "xq")
        private String name;
        @YhdResource(value = "12")
        private String age;
    
    
        public String getName() { 
            return name;
        }
    
        public void setName(String name) { 
            this.name = name;
        }
    
        public String getAge() { 
            return age;
        }
    
        public void setAge(String age) { 
            this.age = age;
        }
    }

(3)注解解析

package com.jd.xq.spring.context;
    
    import com.alibaba.fastjson.JSONObject;
    import com.jd.xq.spring.annotation.YhdResource;
    import com.jd.xq.spring.bean.BeanDefinition;
    import com.jd.xq.spring.bean.PropertyDefinition;
    import org.dom4j.Document;
    import org.dom4j.Element;
    import org.dom4j.io.SAXReader;
    
    import java.lang.reflect.Field;
    import java.net.URL;
    import java.util.*;
    
    /** * @author duanxiaoqiu * @Date 2019-12-27 15:06 **/
    public class XqAnnotationClassPathXmlApplicationContext { 
        private List<BeanDefinition> beanDefines = new ArrayList<BeanDefinition>();//用来存储所有的beans
        private Map<String, Object> sigletons = new HashMap<String, Object>();//用来存储实例化后的bean
    
        /** * 构造方法，用来模拟spring的行为 * * @param fileName */
        public XqAnnotationClassPathXmlApplicationContext(String fileName) { 
            try { 
                //1.read xml
                this.readXml(fileName);
                //2.实例化bean
                this.instanceBeans();
                //3.注解方式
                this.annotationInject();
            } catch (Exception e) { 
    
            }
    
        }
    
        /** * 根据文件名读取xml的配置文件 */
        private void readXml(String fileName) { 
            // TODO Auto-generated method stub
            //创建一个读取器
            SAXReader saxReader = new SAXReader();
            Document document = null;
            try { 
                //获取要读取的配置文件的路径
                URL xmlPath = this.getClass().getClassLoader().getResource(fileName);
                //读取文件内容
                document = saxReader.read(xmlPath);
                //获取xml中的根元素
                Element rootElement = document.getRootElement();
                for (Iterator iterator = rootElement.elementIterator(); iterator.hasNext(); ) { 
                    Element element = (Element) iterator.next();
                    String id = element.attributeValue("id");//获取bean的id属性值
                    String clazz = element.attributeValue("class");//获取bean的class属性值
                    BeanDefinition beanDefinition = new BeanDefinition(id, clazz);
                    //获取bean的Property属性
                    for (Iterator subElementIterator = element.elementIterator(); subElementIterator.hasNext(); ) { 
                        Element subElement = (Element) subElementIterator.next();
                        String propertyName = subElement.attributeValue("name");
                        String propertyValue = subElement.attributeValue("value");
                        PropertyDefinition propertyDefinition = new PropertyDefinition(propertyName, propertyValue);
                        beanDefinition.getPropertyDefinitions().add(propertyDefinition);
                    }
                    beanDefines.add(beanDefinition);
                }
            } catch (Exception e) { 
                e.printStackTrace();
            }
        }
    
        /** * 实例化bean */
        private void instanceBeans() { 
            if (beanDefines != null && beanDefines.size() > 0) { 
                //对每个bean进行实例化
                for (BeanDefinition beanDefinition : beanDefines) { 
                    try { 
                        //bean的class属性存在的时候才进行实例化，否则不进行实例化
                        if (beanDefinition.getClassName() != null && !beanDefinition.getClassName().equals("")) { 
                            //实例化的关键操作
                            sigletons.put(beanDefinition.getId(), Class.forName(beanDefinition.getClassName()).newInstance());
                            System.out.println("id为：" + beanDefinition.getId() + "的bean实例化成功");
                        }
                    } catch (Exception e) { 
                        System.out.println("bean实例化失败");
                        e.printStackTrace();
                    }
                }
            }
        }
    
        /** * 注解方式注入 * <p> * Administer * 2013-9-24 下午8:08:29 */
        private void annotationInject() throws IllegalAccessException { 
            //遍历所有的bean
            for (String beanName : sigletons.keySet()) { 
                Object bean = sigletons.get(beanName);//获取需要注入的bean
                if (bean != null) { 
                    //再对字段进行处理，即对字段上标识有注解
                    Field[] fields = bean.getClass().getDeclaredFields();//取得声明的所有字段
                    for (Field field : fields) { 
                        //判断字段上是否存在注解,若存在
                        if (field.isAnnotationPresent(YhdResource.class)) { 
                            YhdResource resource = field.getAnnotation(YhdResource.class);//取得字段上的注解
                            //字段上存在注解，并且字段上注解的name属性不为空
                            System.out.println(JSONObject.toJSONString(field));
                            System.out.println(JSONObject.toJSONString(resource));
                            field.setAccessible(true);
                            field.set(bean, resource.value());
                        }
                    }
    
    
                }
            }
        }
    
    
        public Object getBean(String beanName) { 
            return sigletons.get(beanName);
        }
    }

(4)使用

XqAnnotationClassPathXmlApplicationContext xqAnnotationClassPathXmlApplicationContext = new XqAnnotationClassPathXmlApplicationContext("spring.xml");
            Person person = (Person) xqAnnotationClassPathXmlApplicationContext.getBean("person");
            System.out.println(person.getName());

代码地址：  
https://github.com/zhugezifang/my-spring-framework

2019年最后一篇技术文章，next year ，come on