SpringIOC容器手写(二)--基于XML的容器

1. 解析XML文件拿到rootElement

    public List<Element> readXML() throws DocumentException {
        SAXReader reader = new SAXReader();
        Document document = reader.read(getResourceAsStream(xmlPath));
        Element rootElement = document.getRootElement();
        List<Element> elements = rootElement.elements();
        return elements;
    }

2. 根据传入的beanId，在xml中找到相应的class name和属性名称和它的值

• 找到beanId的Element

 private Element findElement(List<Element> elements, String beanId) {
        for (Element element : elements) {
            String xmlBeanId = element.attributeValue("id");
            if (StringUtils.isEmpty(xmlBeanId)) {
                continue;
            }
            if (xmlBeanId.equals(beanId)) {
                return element;
            }
        }
        return null;
    }

• 找到beanId对应的className

    public String findClassPath(List<Element> elements, String beanId) throws Exception {
        Element element = findElement(elements, beanId);
        if (element == null) {
            throw new Exception("配置文件中没有该bean: " + beanId);
        } else return element.attributeValue("class");
    }

• 找到beanId对应的属性值

 public Map<String, String> findProperties(List<Element> elements, String beanId) throws Exception {
        Map propertyMap = new HashMap();

        Element element = findElement(elements, beanId);
        if (element == null) {
            throw new Exception("配置文件中没有该bean: " + beanId);
        } else {
            List<Element> properties = element.elements("property");
            if (properties.isEmpty()) {
            } else {
                properties.stream().forEach(property -> {
                    propertyMap.put(property.attributeValue("name"), property.attributeValue("value"));
                });
            }
        }
        return propertyMap;
    }

3. 利用反射，创建对象

public Object newInstance(String className, Map<String, String> properties) throws ClassNotFoundException, IllegalAccessException, InstantiationException {
        Class<?> classInfo = Class.forName(className);
        Object obj = classInfo.newInstance();
        if (properties.isEmpty()) {
        } else {
            properties.entrySet().stream().forEach(entry -> {
                String key = entry.getKey();
                String value = entry.getValue();
                String setKey = "set" + key.toUpperCase().charAt(0) + key.substring(1);
                try {
                    Method f = obj.getClass().getMethod(setKey, String.class);
                    f.setAccessible(true);
                    f.invoke(obj, value);
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                } catch (NoSuchMethodException e) {
                    e.printStackTrace();
                } catch (InvocationTargetException e) {
                    e.printStackTrace();
                }
            });
        }

4. 定义getBean方法

 public Object getBean(String beanId) throws Exception {
        if (StringUtils.isEmpty(beanId)) {
            throw new Exception("beanId 不能为空");
        }

        List<Element> elements = readXML();
        if (elements == null || elements.isEmpty()) {
            throw new Exception("配置文件中没有配置bean信息");
        }

        String className = findClassPath(elements, beanId);
        Map propeties = findProperties(elements, beanId);

        return newInstance(className, propeties);

    }