Java反射 Introspector

Posted 2020-09-06 CodingBoy

一、解释

Introspector  内省，自我检查。

位于java中的java.beans包中，其原文说明文为：

The Introspector class provides a standard way for tools to learn about the properties, events, and methods supported by a target Java Bean.

中文大意为

Introspector提供了一种标准的方式作为工具来获取类的属性，时间，方法。

通常用在反射中，查看类的内部信息。

以下为收集到的一个，空间换时间的反射类。

// 类属性缓存，空间换时间
private static final ConcurrentMap, PropertyDescriptor[]> classPropCache =
        new ConcurrentHashMap, PropertyDescriptor[]>(64);
 
/**
 * 获取Bean的属性
 * @param bean
 * @return
 */
private static PropertyDescriptor[] getPropertyDescriptors(Object bean) {
    Class beanClass = bean.getClass();
    PropertyDescriptor[] cachePds = classPropCache.get(beanClass);
    if (null != cachePds) {
        return cachePds;
    }
    try {
        BeanInfo beanInfo = Introspector.getBeanInfo(beanClass);
        cachePds = beanInfo.getPropertyDescriptors();
        classPropCache.put(beanClass, cachePds);
        return cachePds;
    } catch (IntrospectionException e) {
        throw new RuntimeException(e);
    }
}
 
/**
 * 获取Bean的属性
 * @param bean bean
 * @param propertyName 属性名
 * @return 属性值
 */
public static Object getProperty(Object bean, String propertyName) {
    PropertyDescriptor[] beanPds = getPropertyDescriptors(bean);
    for (PropertyDescriptor propertyDescriptor : beanPds) {
        if (propertyDescriptor.getName().equals(propertyName)){
            Method readMethod = propertyDescriptor.getReadMethod();
            if (null == readMethod) {
                continue;
            }
            if (!readMethod.isAccessible()) {
                readMethod.setAccessible(true);
            }
            try {
                return readMethod.invoke(bean);
            } catch (Throwable ex) {
                throw new RuntimeException("Could not read property ‘" + propertyName + "‘ from bean", ex);
            }
        }
    }
    return null;
}
 
/**
 * 设置Bean属性
 * @param bean bean
 * @param propertyName 属性名
 * @param value 属性值
 */
public static void setProperty(Object bean, String propertyName, Object value) {
    PropertyDescriptor[] beanPds = getPropertyDescriptors(bean);
    for (PropertyDescriptor propertyDescriptor : beanPds) {
        if (propertyDescriptor.getName().equals(propertyName)){
            Method writeMethod = propertyDescriptor.getWriteMethod();
            if (null == writeMethod) {
                continue;
            }
            if (!writeMethod.isAccessible()) {
                writeMethod.setAccessible(true);
            }
            try {
                writeMethod.invoke(bean, value);
            } catch (Throwable ex) {
                throw new RuntimeException("Could not set property ‘" + propertyName + "‘ to bean", ex);
            }
        }
    }
}