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Java 从指定的对象获取指定的属性。

欢马劈雪

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从指定的对象获取指定的属性。

实例源码：

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* The contents of this file are subject to the Sapient Public License

* Version 1.0 (the "License"); you may not use this file except in compliance

* with the License. You may obtain a copy of the License at

* http://carbon.sf.net/License.html.

* Software distributed under the License is distributed on an "AS IS" basis,

* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for

* the specific language governing rights and limitations under the License.

* The Original Code is The Carbon Component Framework.

* The Initial Developer of the Original Code is Sapient Corporation

//package com.nowjava;

import java.beans.BeanInfo;// 来 自 时 代 J a v a - nowjava.com

import java.beans.IntrospectionException;

import java.beans.Introspector;

import java.beans.PropertyDescriptor;

import java.lang.reflect.InvocationTargetException;

import java.lang.reflect.Method;

import java.util.StringTokenizer;

public class Main {

public static void main(String[] argv) throws Exception {

Object bean = "nowjava.com";

String propertyNames = "nowjava.com";

System.out.println(getObjectAttribute(bean, propertyNames));

}

/**

* String used to separate multiple properties inside of embedded

* beans.

private static final String PROPERTY_SEPARATOR = ".";
    /**
     from
    * n o w  j a v a  . c o m 
    **/

/**

* an empty object array used for null parameter method reflection

private static Object[] NO_ARGUMENTS_ARRAY = new Object[] {};

/**

* Gets the specified attribute from the specified object. For example,

* <code>getObjectAttribute(o, "address.line1")</code> will return

* the result of calling <code>o.getAddress().getLine1()</code>.

* The attribute specified may contain as many levels as you like. If at

* any time a null reference is acquired by calling one of the successive

* getter methods, then the return value from this method is also null.

* When reading from a boolean property the underlying bean introspector

* first looks for an is<Property> read method, not finding one it will

* still look for a get<Property> read method. Not finding either, the

* property is considered write-only.

* @param bean the bean to set the property on

* @param propertyNames the name of the propertie(s) to retrieve.  If this is

* null or the empty string, then <code>bean</code> will be returned.

* @return the object value of the bean attribute

* @throws PropertyNotFoundException indicates the the given property

*         could not be found on the bean

* @throws NoSuchMethodException Not thrown

* @throws InvocationTargetException if a specified getter method throws an

*   exception.

* @throws IllegalAccessException if a getter method is

*   not public or property is write-only.

public static Object getObjectAttribute(Object bean,

String propertyNames) throws NoSuchMethodException,

InvocationTargetException, IllegalAccessException {

Object result = bean;

StringTokenizer propertyTokenizer = new StringTokenizer(

propertyNames, PROPERTY_SEPARATOR);

// Run through the tokens, calling get methods and

// replacing result with the new object each time.

// If the result equals null, then simply return null.

while (propertyTokenizer.hasMoreElements() && result != null) {

Class resultClass = result.getClass();

String currentPropertyName = propertyTokenizer.nextToken();

PropertyDescriptor propertyDescriptor = getPropertyDescriptor(

currentPropertyName, resultClass);

Method readMethod = propertyDescriptor.getReadMethod();

if (readMethod == null) {

throw new IllegalAccessException(

"User is attempting to "

+ "read from a property that has no read method.  "

+ " This is likely a write-only bean property.  Caused "

+ "by property [" + currentPropertyName

+ "] on class [" + resultClass + "]");

}

result = readMethod.invoke(result, NO_ARGUMENTS_ARRAY);

}

return result;

}

/**

* Retrieves a property descriptor object for a given property.

*

* Uses the classes in <code>java.beans</code> to get back

* a descriptor for a property.  Read-only and write-only

* properties will have a slower return time.

*

* @param propertyName The programmatic name of the property

* @param beanClass The Class object for the target bean.

*                  For example sun.beans.OurButton.class.

* @return a PropertyDescriptor for a property that follows the

*         standard Java naming conventions.

* @throws PropertyNotFoundException indicates that the property

*         could not be found on the bean class.

private static final PropertyDescriptor getPropertyDescriptor(

String propertyName, Class beanClass) {

PropertyDescriptor resultPropertyDescriptor = null;

char[] pNameArray = propertyName.toCharArray();

pNameArray[0] = Character.toLowerCase(pNameArray[0]);

propertyName = new String(pNameArray);

try {

resultPropertyDescriptor = new PropertyDescriptor(propertyName,

beanClass);

} catch (IntrospectionException e1) {

// Read-only and write-only properties will throw this

// exception.  The properties must be looked up using

// brute force.

// This will get the list of all properties and iterate

// through looking for one that matches the property

// name passed into the method.

try {
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编辑于 2020-03-26 09:23:272020-03-26 09:23:27

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