手写spring框架——第一篇

男娘i 2021-09-21 01:16 297阅读 0赞

1.xml文件

<?xml version="1.0" encoding="UTF-8"?>
    
    <beans>
        <bean id="person" class="com.jd.xq.spring.bean.Person"/>
    </beans>

2.XqClassPathXmlApplicationContext  
(1)读取xml文件  
(2)实例化bean—用反射的方式

package com.jd.xq.spring.context;
    
    import com.jd.xq.spring.bean.BeanDefinition;
    import org.dom4j.Document;
    import org.dom4j.Element;
    import org.dom4j.io.SAXReader;
    
    import java.net.URL;
    import java.util.Iterator;
    import java.util.*;
    
    /** * @author duanxiaoqiu * @Date 2019-12-27 11:38 **/
    public class XqClassPathXmlApplicationContext { 
    
        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 XqClassPathXmlApplicationContext(String fileName) { 
            //1.read xml
            this.readXml(fileName);
            //2.实例化bean
            this.instanceBeans();
        }
    
        /** * 根据文件名读取xml的配置文件 * * @param fileName * */
        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);
                    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();
                    }
                }
            }
        }
    
        public Object getBean(String beanName) { 
            return sigletons.get(beanName);
        }
    }

3.解析xml工具类

package com.jd.xq.spring.utils;
    
    import java.net.URL;
    import java.util.Iterator;
    
    import org.dom4j.Attribute;
    import org.dom4j.Document;
    import org.dom4j.Element;
    import org.dom4j.io.SAXReader;
    
    /** * @author duanxiaoqiu * @Date 2019-12-27 11:40 **/
    public class XmlParseUtil { 
        @SuppressWarnings("rawtypes")
        public static void parseXml(String xmlPath) { 
            SAXReader saxReader = new SAXReader();
            Document document = null;
            try { 
                document = saxReader.read(xmlPath);
                //获取根节点
                Element elementRoot = document.getRootElement();
                System.out.println("根节点名称：" + elementRoot.getName());
                //遍历根节点下面的节点
                for (Iterator elementIterator = elementRoot.elementIterator(); elementIterator.hasNext(); ) { 
                    Element element = (Element) elementIterator.next();
                    //获取节点的信息，，包括节点的名称以及节点的属性信息
                    System.out.println("节点：" + element.getName());
                    for (Iterator attrIterator = element.attributeIterator(); attrIterator.hasNext(); ) { 
                        Attribute attr = (Attribute) attrIterator.next();
                        //节点的属性信息
                        System.out.println("节点的属性名称为：" + attr.getName() + ",值为：" + attr.getValue());
    
                    }
                    //获取节点下的子节点
                    for (Iterator subElementiterator = element.elementIterator(); subElementiterator.hasNext(); ) { 
                        Element subElement = (Element) subElementiterator.next();
                        //获取子节点的信息，包括子节点的名称以及子节点的属性信息
                        System.out.println("子节点：" + subElement.getName());
                        for (Iterator subElementAttrIterator = subElement.attributeIterator(); subElementAttrIterator.hasNext(); ) { 
                            Attribute subElementAttr = (Attribute) subElementAttrIterator.next();
                            //子节点的属性信息
                            System.out.println("子节点的属性名称为：" + subElementAttr.getName() + ",值为：" + subElementAttr.getValue());
    
                        }
    
                    }
                }
            } catch (Exception e) { 
            }
        }
    }

4.应用

package com.jd.xq.spring;
    
    import com.jd.xq.spring.context.XqClassPathXmlApplicationContext;
    
    /** * @author duanxiaoqiu * @Date 2019-12-27 11:52 **/
    public class SpringMain { 
        public static void main(String[] args) { 
            XqClassPathXmlApplicationContext xqClassPathXmlApplicationContext=new XqClassPathXmlApplicationContext("spring.xml");
            xqClassPathXmlApplicationContext.getBean("person");
        }
    }

思路总结：  
1.读取、解析xml文件  
2.实例化bean(反射)  
3.测试

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