【java_基礎深入】使用內省技術模仿實現BeanUtils

原BeanUtils出處

import org.apache.commons.beanutils.BeanUtils;

原BeanUtils常用法

populate(Object bean, Map<String, ? extends Object> properties); // 傳入Map參數注入bean

    public void getBean() {
        HashMap<String, String> map = new HashMap<>();
        map.put("age", "19");
        map.put("name", "kkk");
        map.put("address","shenzhen");
        Student student = new Student();
        try {
            BeanUtils.populate(student, map);
        } catch (Exception e) {
            e.printStackTrace();
        }

        System.out.println(student);

    }

原BeanUtils應用場景

servlet中獲取請求參數，封裝成JavaBean

        Map<String, String[]> parameterMap = request.getParameterMap();
        Contact contact = new Contact();
        try {
            BeanUtils.populate(contact, parameterMap);
        } catch (Exception e) {
            e.printStackTrace();
        }

使用內省技術模仿實現BeanUtils

    public static <T> T populate(T t, HashMap<String, String> map) {
        Set<String> keys = map.keySet();
        Class clazz = t.getClass();
        for (String key : keys) {
            //目標:根據字段名獲取對應的set方法,這是另外一種技術叫做 todo 內省, 通過Class對象解析set方法
            PropertyDescriptor descriptor = null;
            try {
                descriptor = new PropertyDescriptor(key, clazz);
            } catch (IntrospectionException e) {
                e.printStackTrace();
            }
            assert descriptor != null;
            Method writeMethod = descriptor.getWriteMethod();//獲取set方法
            try {
                writeMethod.invoke(t, map.get(key));
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return t;
    }

關鍵API

public static <T> T populate(T t, HashMap<String, String> map) {
	// 獲取類的描述器，key傳setXXX/getXXX 的XXX
	PropertyDescriptor descriptor = new PropertyDescriptor(key, clazz); 
	// 獲取set方法
	Method writeMethod = descriptor.getWriteMethod();
	// 反射調用Bean對象的set方法, 從map獲取方法參數
	 writeMethod.invoke(t, map.get(key));
}