java内省

内省(Introspector)是Java 语言对Bean类属性、事件的一种缺省处理方法。例如类 A 中有属性 name, 那我们可以通过 getName,setName 来得到其值或者设置新的值。通过 getName/setName 来访问 name 属性，这就是默认的规则。 

Java 中提供了一套 API 用来访问某个属性的 getter/setter 方法，通过这些 API 可以使你不需要了解这个规则（但你最好还是要搞清楚），这些 API 存放于包 java.beans 中。

测定代码：

package com.beans;

public class User {
	private int age;
	private String name;

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}
	
	public int compute(int n) {
		return 10 * n;
	}

}

package com.beans;

import java.beans.BeanInfo;
import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.beans.MethodDescriptor;
import java.beans.PropertyDescriptor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import junit.framework.TestCase;

import static java.lang.System.out;

public class TestIntrospector extends TestCase {

	public void testIntrospector1() {
		try {
			BeanInfo beanInfo = Introspector.getBeanInfo(User.class);
			PropertyDescriptor[] propertyDescriptors = beanInfo.getPropertyDescriptors();

			User user = new User();
			for (PropertyDescriptor propertyDescriptor : propertyDescriptors) {
				Method writeMethod = propertyDescriptor.getWriteMethod();
				try {
					if ("age".equals(propertyDescriptor.getName())) {
						writeMethod.invoke(user, 18);
					} else if ("name".equals(propertyDescriptor.getName())) {
						writeMethod.invoke(user, "yang");
					}
				} catch (IllegalArgumentException e) {
					e.printStackTrace();
				} catch (IllegalAccessException e) {
					e.printStackTrace();
				} catch (InvocationTargetException e) {
					e.printStackTrace();
				}
			}
			out.println(user.getAge() + ", " + user.getName());
		} catch (IntrospectionException e) {
			e.printStackTrace();
		}
	}

	public void testIntrospector2() {
		try {
			BeanInfo beanInfo = Introspector.getBeanInfo(User.class);
			User user = new User();
			MethodDescriptor[] methodDescriptors = beanInfo.getMethodDescriptors();
			for (MethodDescriptor methodDescriptor : methodDescriptors) {
				Method method = methodDescriptor.getMethod();
				try {
					if ("setAge".equals(methodDescriptor.getName())) {
						method.invoke(user, 28);
					} else if ("setName".equals(methodDescriptor.getName())) {
						method.invoke(user, "yang");
					}
				} catch (IllegalArgumentException e) {
					e.printStackTrace();
				} catch (IllegalAccessException e) {
					e.printStackTrace();
				} catch (InvocationTargetException e) {
					e.printStackTrace();
				}
			}
			out.println(user.getAge() + ", " + user.getName());
		} catch (IntrospectionException e) {
			e.printStackTrace();
		}
	}

	public void testIntrospector3() {
		try {
			User user = new User();
			PropertyDescriptor propertyDescriptor = new PropertyDescriptor("age", User.class);
			Method writeMethod = propertyDescriptor.getWriteMethod();
			writeMethod.invoke(user, 38);
			Method readMethod = propertyDescriptor.getReadMethod();
			Integer age = (Integer) readMethod.invoke(user, (Object[]) null);
			out.println(age);
		} catch (IntrospectionException e) {
			e.printStackTrace();
		} catch (IllegalArgumentException e) {
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			e.printStackTrace();
		} catch (InvocationTargetException e) {
			e.printStackTrace();
		}

	}
}

方法testIntrospector3中的代码，我觉得是最好的。如果要遍历方法或者属性，那么上面两种也很好。