Get and set properties on a bean : JavaBeans « Development « Java Tutorial

 * 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
 * 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.

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;

 * This class implements the ability to get and set properties on a
 * bean.  This included the concept of embedded properties that may
 * be referenced like <code></code>.
 * Copyright 2002 Sapient
 * @since carbon 1.0
 * @author Greg Hinkle, January 2002
 * @version $Revision: 1.11 $ ($Author: dvoet $)
public final class BeanUtil {
     * String used to separate multiple properties inside of embedded
     * beans.
    private static final String PROPERTY_SEPARATOR = ".";

     * An empty class array used for null parameter method reflection
    private static Class[] NO_PARAMETERS_ARRAY = new Class[] {
     * an empty object array used for null parameter method reflection
    private static Object[] NO_ARGUMENTS_ARRAY = new Object[] {

     * The constructor is private so that <tt>new</tt> cannot be used.
    private BeanUtil() {

     * Retreives 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 {
                BeanInfo beanInfo = Introspector.getBeanInfo(beanClass);

                PropertyDescriptor[] propertyDescriptors =

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

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

        // 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;

     * 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&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.
     * @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)
            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;

     * 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>.
     * 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.
     * @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)
            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 =

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

            // Grab the final property name after the last property separator
            propertyName =
                    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 });

6.56.1.Listening for Changes to the Selected File in a JFileChooser Dialog
6.56.2.Get a list of selected files
6.56.3.Listening for Changes to the Current Directory in a JFileChooser Dialog
6.56.4.Displaying the Current Directory in the Title of a JFileChooser Dialog
6.56.5.Setting an Accessory Component in a JFileChooser Dialog
6.56.6.Convert a bean to XML persistence
6.56.7.Listen for bean's property change event
6.56.8.List property names of a Bean
6.56.9.Prevent bean's property being serialized to XML
6.56.10.Create an instance a Bean
6.56.11.Convert an XML persistence to bean
6.56.12.Determine bean's property type
6.56.13.Listen for a constrained property change
6.56.14.Bean has a single property called property.
6.56.15.Implementing a Bound Property
6.56.16.Implementing a Constrained Property: fires a PropertyChangeEvent whenever its value is about to be changed.
6.56.17.Instantiating a Bean
6.56.18.Listing the Property Names of a Bean
6.56.19.Getting and Setting a Property of a Bean
6.56.20.Get and set the value of a property in a bean using Expression and Statement
6.56.21.Get and set an Object type property
6.56.22.gets and sets a primitive type property
6.56.23.gets and sets an array type property
6.56.24.Serializing a Bean to XML: XMLEncoder only persists the value of public properties.
6.56.25.Deserializing a Bean from XML
6.56.26.Preventing a Bean Property from Being Serialized to XML
6.56.27.Serializing an Immutable Bean Property to XML
6.56.28.Listening for a Property Change Event: A property change event is fired when a bound property is changed.
6.56.29.Listening for a Vetoable Property Change Event
6.56.30.Read bean's property value
6.56.31.extends SimpleBeanInfo
6.56.32.Get and set properties on a bean
6.56.33.Process bean properties getter by applying the JavaBean naming conventions.
6.56.34.Is JavaBean Compliant Setter
6.56.35.Constructs a method name from element's bean name for a given prefix
6.56.36.Returns attribute's setter method. If the method not found then NoSuchMethodException will be thrown.