Java 从指定的对象获取指定的属性。

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/*

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

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

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

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

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 *

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

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

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

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 *

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 * The Original Code is The Carbon Component Framework.

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 *

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 * The Initial Developer of the Original Code is Sapient Corporation

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 *

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 * Copyright (C) 2003 Sapient Corporation. All Rights Reserved.

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 */

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//package com.nowjava;

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

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import java.beans.IntrospectionException;

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import java.beans.Introspector;

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import java.beans.PropertyDescriptor;

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import java.lang.reflect.InvocationTargetException;

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import java.lang.reflect.Method;

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import java.util.StringTokenizer;

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public class Main {

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

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        Object bean = "nowjava.com";

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        String propertyNames = "nowjava.com";

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

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    }

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    /**

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     * String used to separate multiple properties inside of embedded

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     * beans.

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     */

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    private static final String PROPERTY_SEPARATOR = ".";

    /**

     from

    * n o w  j a v a  . c o m 

    **/

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    /**

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     * an empty object array used for null parameter method reflection

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     */

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

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    /**

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     * <p>Gets the specified attribute from the specified object.  For example,

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

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

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     *

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

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

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     * getter methods, then the return value from this method is also null.</p>

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     *

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     * <p>When reading from a boolean property the underlying bean introspector

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

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

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     * property is considered write-only.</p>

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     *

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     * @param bean the bean to set the property on

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

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

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     * @return the object value of the bean attribute

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     *

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     * @throws PropertyNotFoundException indicates the the given property

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     *         could not be found on the bean

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     * @throws NoSuchMethodException Not thrown

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     * @throws InvocationTargetException if a specified getter method throws an

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     *   exception.

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     * @throws IllegalAccessException if a getter method is

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     *   not public or property is write-only.

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     */

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    public static Object getObjectAttribute(Object bean,

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            String propertyNames) throws NoSuchMethodException,

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            InvocationTargetException, IllegalAccessException {

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        Object result = bean;

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        StringTokenizer propertyTokenizer = new StringTokenizer(

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                propertyNames, PROPERTY_SEPARATOR);

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        // Run through the tokens, calling get methods and

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        // replacing result with the new object each time.

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

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

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            Class resultClass = result.getClass();

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            String currentPropertyName = propertyTokenizer.nextToken();

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            PropertyDescriptor propertyDescriptor = getPropertyDescriptor(

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                    currentPropertyName, resultClass);

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            Method readMethod = propertyDescriptor.getReadMethod();

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            if (readMethod == null) {

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                throw new IllegalAccessException(

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                        "User is attempting to "

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

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

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                                + "by property [" + currentPropertyName

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

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            }

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            result = readMethod.invoke(result, NO_ARGUMENTS_ARRAY);

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        }

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        return result;

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    }

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    /**

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     * Retrieves a property descriptor object for a given property.

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     * <p>

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

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

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     * properties will have a slower return time.

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     * </p>

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     *

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     * @param propertyName The programmatic name of the property

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

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     *                  For example sun.beans.OurButton.class.

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     * @return a PropertyDescriptor for a property that follows the

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     *         standard Java naming conventions.

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     * @throws PropertyNotFoundException indicates that the property

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     *         could not be found on the bean class.

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     */

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    private static final PropertyDescriptor getPropertyDescriptor(

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            String propertyName, Class beanClass) {

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        PropertyDescriptor resultPropertyDescriptor = null;

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        char[] pNameArray = propertyName.toCharArray();

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

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        propertyName = new String(pNameArray);

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        try {

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            resultPropertyDescriptor = new PropertyDescriptor(propertyName,

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                    beanClass);

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        } catch (IntrospectionException e1) {

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

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            // exception.  The properties must be looked up using

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            // brute force.

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

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            // through looking for one that matches the property

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            // name passed into the method.

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            try {

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