Sets the specified attribute on the specified object. - Java Reflection

Java examples for Reflection:Property

Description

Sets the specified attribute on the specified object.

Demo Code

/*// w  ww  . j  av a  2s.  c o  m
 * 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
 *
 * Copyright (C) 2003 Sapient Corporation. All Rights Reserved.
 */
//package com.java2s;
import java.beans.BeanInfo;
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 = "java2s.com";
        String propertyNames = "java2s.com";
        Object value = "java2s.com";
        setObjectAttribute(bean, propertyNames, value);
    }

    /**
     * String used to separate multiple properties inside of embedded
     * beans.
     */
    private static final String PROPERTY_SEPARATOR = ".";
    /**
     * an empty object array used for null parameter method reflection
     */
    private static Object[] NO_ARGUMENTS_ARRAY = new Object[] {};

    /**
     * <p>Sets the specified attribute on the specified object.  For example,
     * <code>getObjectAttribute(o, "address.line1", value)</code> will call
     * <code>o.getAddress().setLine1(value)</code>.<p>
     *
     * <p>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 a <code>NullPointerException</code> is thrown.</p>
     *
     * @param bean the bean to call the getters on
     * @param propertyNames the name of the attribute(s) to set.  If this is
     *        null or the empty string, then an exception is thrown.
     * @param value the value of the object to set on the bean property
     *
     * @throws PropertyNotFoundException indicates the the given property
     *         could not be found on the bean
     * @throws IllegalArgumentException if the supplied parameter is not of
     *   a valid type
     * @throws NoSuchMethodException never
     * @throws IllegalAccessException if a getter or setter method is
     *   not public or property is read-only.
     * @throws InvocationTargetException if a specified getter method throws an
     *   exception.
     */
    public static void setObjectAttribute(Object bean,
            String propertyNames, Object value)
            throws IllegalAccessException, IllegalArgumentException,
            InvocationTargetException, NoSuchMethodException {

        Object result = bean;
        String propertyName = propertyNames;

        // Check if this has some embedded properties.  If it does, use the
        // getObjectAttribute to get the proper object to call this on.
        int indexOfLastPropertySeparator = propertyName
                .lastIndexOf(PROPERTY_SEPARATOR);

        if (indexOfLastPropertySeparator >= 0) {
            String embeddedProperties = propertyName.substring(0,
                    indexOfLastPropertySeparator);

            // Grab the final property name after the last property separator
            propertyName = propertyName
                    .substring(indexOfLastPropertySeparator
                            + PROPERTY_SEPARATOR.length());

            result = getObjectAttribute(result, embeddedProperties);
        }

        Class resultClass = result.getClass();

        PropertyDescriptor propertyDescriptor = getPropertyDescriptor(
                propertyName, resultClass);

        Method writeMethod = propertyDescriptor.getWriteMethod();
        if (writeMethod == null) {
            throw new IllegalAccessException(
                    "User is attempting to write "
                            + "to a property that has no write method.  This is likely "
                            + "a read-only bean property.  Caused by property ["
                            + propertyName + "] on class [" + resultClass
                            + "]");
        }

        writeMethod.invoke(result, new Object[] { value });
    }

    /**
     * <p>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>.<p>
     *
     * <p>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.</p>
     *
     * <p>When reading from a boolean property the underlying bean introspector
     * first looks for an is&lt;Property&gt; read method, not finding one it will
     * still look for a get&lt;Property&gt; read method.  Not finding either, the
     * property is considered write-only.</p>
     *
     * @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.
     * <p>
     * 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.
     * </p>
     *
     * @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 {
                BeanInfo beanInfo = Introspector.getBeanInfo(beanClass);

                PropertyDescriptor[] propertyDescriptors = beanInfo
                        .getPropertyDescriptors();

                for (int i = 0; i < propertyDescriptors.length; i++) {
                    if (propertyDescriptors[i].getName().equals(
                            propertyName)) {

                        // If the names match, this this describes the
                        // property being searched for.  Break out of
                        // the iteration.
                        resultPropertyDescriptor = propertyDescriptors[i];
                        break;
                    }
                }
            } catch (IntrospectionException e2) {
                e2.printStackTrace();
            }
        }

        // If no property descriptor was found, then this bean does not
        // have a property matching the name passed in.
        if (resultPropertyDescriptor == null) {
            System.out.println("resultPropertyDescriptor == null");
        }

        return resultPropertyDescriptor;
    }
}

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