IoC 的底层原理(简易版)

IoC 的底层原理

• 读取配置文件，解析 XML。

• 通过反射机制实例化配置文件中所配置的所有的bean。

  public class MyClassPathXmlApplicationContext implements MyApplicationContext {
         
      private Map<String,Object> ioc = new HashMap<>();
      public MyClassPathXmlApplicationContext(String path){
         
          SAXReader reder = new SAXReader();
          try {
         
              Document document = reder.read("src\\main\\resources\\"+path);
              Element root = document.getRootElement();
              Iterator<Element> iterator = root.elementIterator();
              while(iterator.hasNext()){
         
                  Element bean =  iterator.next();
                  String id = bean.attributeValue("id");
                  String aClass = bean.attributeValue("class");
                  //通过反射机制创建对象
                  Class clazz =  Class.forName(aClass);
                  //获取无参构造,创建目标对象
                  Constructor constructor = clazz.getConstructor();
                  Object object = constructor.newInstance();
                  //给目标对象赋值
                  Iterator<Element> beanIterator = bean.elementIterator();
                  while(beanIterator.hasNext()){
         
                      Element property = beanIterator.next();
                      String name = property.attributeValue("name");
                      String valueStr = property.attributeValue("value");
                      String ref = property.attributeValue("ref");
                      String methodName = "set"+name.substring(0,1).toUpperCase()+name.substring(1);
                      Field field = clazz.getDeclaredField(name);
                      Method method = clazz.getDeclaredMethod(methodName,field.getType());
                      //根据成员变量的数据类型将 value 的类型进行转换
                      Object value = null;
                      if(field.getType().getName() == "int"){
         
                          value = Integer.parseInt(valueStr);
                      }
                      if(field.getType().getName() == "java.lang.String"){
         
                          value = valueStr;
                      }
                      if(field.getType().getName() == "int"){
         
                          value = Integer.parseInt(valueStr);
                      }
                      method.invoke(object,value);
                  }
                  ioc.put(id,object);
              }
          } catch (DocumentException | ClassNotFoundException | NoSuchMethodException e) {
         
              e.printStackTrace();
          } catch (IllegalAccessException e) {
         
              e.printStackTrace();
          } catch (InstantiationException e) {
         
              e.printStackTrace();
          } catch (InvocationTargetException e) {
         
              e.printStackTrace();
          } catch (NoSuchFieldException e) {
         
              e.printStackTrace();
          }
      }
  
      @Override
      public Object getBean(String id) {
         
          return ioc.get(id);
      }
  }