import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;

/**
 * 反射的 Utils 函数集合
 * 提供访问私有变量, 获取泛型类型 Class, 提取集合中元素属性等 Utils 函数
 * @author Administrator
 *
 */
public class ReflectionUtils {

    
    /**
     * 通过反射, 获得定义 Class 时声明的父类的泛型参数的类型
     * 如: public EmployeeDao extends BaseDao<Employee, String>
     * @param clazz
     * @param index
     * @return
     */
    @SuppressWarnings("unchecked")
    public static Class getSuperClassGenricType(Class clazz, int index){
        Type genType = clazz.getGenericSuperclass();
        
        if(!(genType instanceof ParameterizedType)){
            return Object.class;
        }
        
        Type [] params = ((ParameterizedType)genType).getActualTypeArguments();
        
        if(index >= params.length || index < 0){
            return Object.class;
        }
        
        if(!(params[index] instanceof Class)){
            return Object.class;
        }
        
        return (Class) params[index];
    }
    
    /**
     * 通过反射, 获得 Class 定义中声明的父类的泛型参数类型
     * 如: public EmployeeDao extends BaseDao<Employee, String>
     * @param <T>
     * @param clazz
     * @return
     */
    @SuppressWarnings("unchecked")
    public static<T> Class<T> getSuperGenericType(Class clazz){
        return getSuperClassGenricType(clazz, 0);
    }
    
    /**
     * 循环向上转型, 获取对象的 DeclaredMethod
     * @param object
     * @param methodName
     * @param parameterTypes
     * @return
     */
    public static Method getDeclaredMethod(Object object, String methodName, Class<?>[] parameterTypes){
        
        for(Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass.getSuperclass()){
            try {
                //superClass.getMethod(methodName, parameterTypes);
                return superClass.getDeclaredMethod(methodName, parameterTypes);
            } catch (NoSuchMethodException e) {
                //Method 不在当前类定义, 继续向上转型
            }
            //..
        }
        
        return null;
    }
    
    /**
     * 使 filed 变为可访问
     * @param field
     */
    public static void makeAccessible(Field field){
        if(!Modifier.isPublic(field.getModifiers())){
            field.setAccessible(true);
        }
    }
    
    /**
     * 循环向上转型, 获取对象的 DeclaredField
     * @param object
     * @param filedName
     * @return
     */
    public static Field getDeclaredField(Object object, String filedName){
        
        for(Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass.getSuperclass()){
            try {
                return superClass.getDeclaredField(filedName);
            } catch (NoSuchFieldException e) {
                //Field 不在当前类定义, 继续向上转型
            }
        }
        return null;
    }
    
    /**
     * 直接调用对象方法, 而忽略修饰符(private, protected)
     * @param object
     * @param methodName
     * @param parameterTypes
     * @param parameters
     * @return
     * @throws InvocationTargetException 
     * @throws IllegalArgumentException 
     */
    public static Object invokeMethod(Object object, String methodName, Class<?> [] parameterTypes,
            Object [] parameters) throws InvocationTargetException{
        
        Method method = getDeclaredMethod(object, methodName, parameterTypes);
        
        if(method == null){
            throw new IllegalArgumentException("Could not find method [" + methodName + "] on target [" + object + "]");
        }
        
        method.setAccessible(true);
        
        try {
            return method.invoke(object, parameters);
        } catch(IllegalAccessException e) {
            System.out.println("不可能抛出的异常");
        } 
        
        return null;
    }
    
    /**
     * 直接设置对象属性值, 忽略 private/protected 修饰符, 也不经过 setter
     * @param object
     * @param fieldName
     * @param value
     */
    public static void setFieldValue(Object object, String fieldName, Object value){
        Field field = getDeclaredField(object, fieldName);
        
        if (field == null)
            throw new IllegalArgumentException("Could not find field [" + fieldName + "] on target [" + object + "]");
        
        makeAccessible(field);
        
        try {
            field.set(object, value);
        } catch (IllegalAccessException e) {
            System.out.println("不可能抛出的异常");
        }
    }
    
    /**
     * 直接读取对象的属性值, 忽略 private/protected 修饰符, 也不经过 getter
     * @param object
     * @param fieldName
     * @return
     */
    public static Object getFieldValue(Object object, String fieldName){
        Field field = getDeclaredField(object, fieldName);
        
        if (field == null)
            throw new IllegalArgumentException("Could not find field [" + fieldName + "] on target [" + object + "]");
        
        makeAccessible(field);
        
        Object result = null;
        
        try {
            result = field.get(object);
        } catch (IllegalAccessException e) {
            System.out.println("不可能抛出的异常");
        }
        
        return result;
    }
}

/**
     * 通用的查询方法：可以根据传入的 SQL、Class 对象返回 SQL 对应的记录的对象
     * @param clazz: 描述对象的类型
     * @param sql: SQL 语句。可能带占位符
     * @param args: 填充占位符的可变参数。
     * @return
     */
    public <T> T get(Class<T> clazz, String sql, Object... args) {
        T entity = null;

        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;

        try {
            //1. 得到 ResultSet 对象
            connection = JDBCTools.getConnection();
            preparedStatement = connection.prepareStatement(sql);
            for (int i = 0; i < args.length; i++) {
                preparedStatement.setObject(i + 1, args[i]);
            }
            resultSet = preparedStatement.executeQuery();

            //2. 得到 ResultSetMetaData 对象
            ResultSetMetaData rsmd = resultSet.getMetaData();
            
            //3. 创建一个 Map<String, Object> 对象, 键: SQL 查询的列的别名, 
            //值: 列的值
            Map<String, Object> values = new HashMap<>();
            
            //4. 处理结果集. 利用 ResultSetMetaData 填充 3 对应的 Map 对象
            if(resultSet.next()){
                for(int i = 0; i < rsmd.getColumnCount(); i++){
                    String columnLabel = rsmd.getColumnLabel(i + 1);
                    Object columnValue = resultSet.getObject(i + 1);
                    
                    values.put(columnLabel, columnValue);
                }
            }
            
            //5. 若 Map 不为空集, 利用反射创建 clazz 对应的对象
            if(values.size() > 0){
                entity = clazz.newInstance();
                
                //5. 遍历 Map 对象, 利用反射为 Class 对象的对应的属性赋值. 
                for(Map.Entry<String, Object> entry: values.entrySet()){
                    String fieldName = entry.getKey();
                    Object value = entry.getValue();
                    ReflectionUtils.setFieldValue(entity, fieldName, value);
                }
            }
            

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCTools.releaseDB(resultSet, preparedStatement, connection);
        }

        return entity;
    }