使用Java反射机制模仿Spring IOC

1. Spring IOC的实现是由工厂模式和Java的反射机制完成的。我们可以自己写一个beanfactory通过反射的方式获取bean。
2. 新建一个bean.xml文件，使用dom4j解析xml文件，并且把bean放到一个map中。

• bean.xml代码为：
  <bean id="helloworld" class="hello.HelloWorld">
  <property name="name" value="yuemingfei"/>
  </bean>

• BeanFactory代码为：
  <pre><code>
  public class BeanFactory {

  private final Map<String, Object> map = new HashMap<String, Object>();
  
  private void parseXml() throws Exception {
      SAXReader reader = new SAXReader();
  InputStream in = ClassLoader.getSystemResourceAsStream("bean.xml");
      Document document = reader.read(in);
  Element root = document.getRootElement();
  String rootName = root.getName();
      // google guava的Preconditions类的静态方法，判断参数是否和期望的一样
  checkArgument("beans".equals(rootName), "获得的根节点不是bean");
  @SuppressWarnings("unchecked")
  List<Element> list = root.elements();
  
  for (Element bean : list) {
      
      if ("bean".equals(bean.getName())) {
          
          String id = bean.attributeValue("id");
          String className = bean.attributeValue("class");
          Object object = null;
          @SuppressWarnings("unchecked")
          Iterator<Element> it = bean.elementIterator();
          Map<String, String> propertyMap = new HashMap<String, String>();
          while(it.hasNext()){
              Element propertyElement = it.next();
              if("property".equals(propertyElement.getName())){
                  String propertyName = propertyElement.attributeValue("name");
                  String propertyValue = propertyElement.attributeValue("value");
                  propertyMap.put(propertyName, propertyValue);
              }
          }
          object = getInstance(className, propertyMap);
          map.put(id, object);
          
      }
      
  }
  

  }

  @SuppressWarnings("unchecked")
      private Object getInstance(String className, Map<String, String> map) throws Exception{
  
  @SuppressWarnings("rawtypes")
      Class instance = Class.forName(className);
  Object obj = instance.newInstance();
      Field[] fields = instance.getDeclaredFields();
  for (Field field : fields) {
          String propertyName = field.getName();
          String propertyValue = map.get(propertyName);
          String methodName = "set" + propertyName.toUpperCase().charAt(0) + propertyName.substring(1);
          Method method = instance.getMethod(methodName, String.class);
          method.invoke(obj, propertyValue);
  }
      return obj;
  

  }

  public Object getBean(String id) throws Exception{
  parseXml();
  return map.get(id);
  }
  }

</code></pre>

• HelloWorld类中只要一个name属性，除了getter，setter方法还有sayHello（）方法。