Returns the value of the named attribute from the passed pojo. - Java Reflection

Java examples for Reflection:Property

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Description

Returns the value of the named attribute from the passed pojo.

Demo Code

/**//from  w w  w .j av  a 2 s  .  co m
 * Helios, OpenSource Monitoring
 * Brought to you by the Helios Development Group
 *
 * Copyright 2007, Helios Development Group and individual contributors
 * as indicated by the @author tags. See the copyright.txt file in the
 * distribution for a full listing of individual contributors.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This software is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org. 
 *
 */
//package com.java2s;
import java.beans.*;

import java.util.ArrayList;

import java.util.List;

public class Main {
    public static void main(String[] argv) throws Exception {
        String name = "java2s.com";
        Object target = "java2s.com";
        System.out.println(getAttribute(name, target));
    }

    /**
     * Returns the value of the named attribute from the passed pojo.
     * @param name The name of the attribute.
     * @param target The target pojo to retrieve the value from.
     * @return the value of the named attribute.
     */
    public static Object getAttribute(String name, Object target) {
        try {
            Class<?> targetType = getAttributeType(target.getClass(), name);
            PropertyEditor propertyEditor = PropertyEditorManager
                    .findEditor(targetType);
            if (propertyEditor == null)
                throw new RuntimeException(
                        "No PropertyEditor Found for type ["
                                + targetType.getName()
                                + "] in object of type + ["
                                + target.getClass().getName() + "]");

            Expression expression = new Expression(target,
                    getPropertyDescriptor(target.getClass(), name)
                            .getReadMethod().getName(), new Object[] {});
            expression.execute();
            return expression.getValue();

        } catch (Exception e) {
            throw new RuntimeException("Failed to get attribute [" + name
                    + "] on instance of  [" + target.getClass().getName()
                    + "]");
        }

    }

    /**
     * Determines the type of the named parameter for the passed type.
     * @param targetType The target type to invoke against.
     * @param name The attribute name.
     * @return The class of the parameter type
     */
    public static Class<?> getAttributeType(Class<?> targetType, String name) {
        PropertyDescriptor pd = getPropertyDescriptor(targetType, name);
        return pd.getPropertyType();
    }

    /**
     * Locates the PropertyDescriptor for the passed name in the passed class.
     * @param targetType
     * @param name
     * @return A PropertyDescriptor
     */
    public static PropertyDescriptor getPropertyDescriptor(
            Class<?> targetType, String name) {
        String dName = Introspector.decapitalize(name);
        try {
            BeanInfo bi = Introspector.getBeanInfo(targetType);
            for (PropertyDescriptor pd : bi.getPropertyDescriptors()) {
                if (pd.getName().equals(dName)) {
                    return pd;
                }
            }
            throw new Exception("No PropertyDescriptor found for " + name);
        } catch (Exception e) {
            throw new RuntimeException(
                    "Failed to Acquire PropertyDescriptor for ["
                            + targetType.getName() + "/" + name + "]", e);
        }

    }

    public static BeanInfo getBeanInfo(Object pojo) {
        try {
            return Introspector.getBeanInfo(pojo.getClass());
        } catch (Exception e) {
            throw new RuntimeException("Failed to create bean info", e);
        }
    }

    /**
     * Returns a list of a pojo's <code>PropertyDescriptor</code>s minus the same for <code>java.lang.Object</code>.
     * @param pojo
     * @return A list of <code>PropertyDescriptor</code>s.
     */
    public static List<PropertyDescriptor> getPropertyDescriptors(
            Object pojo) {
        List<PropertyDescriptor> list = getAllPropertyDescriptors(pojo);
        List<PropertyDescriptor> objList = getAllPropertyDescriptors(new Object());
        list.removeAll(objList);
        return list;
    }

    /**
     * Returns a list of all of a pojo's <code>PropertyDescriptor</code>s
     * @param pojo
     * @return A list of <code>PropertyDescriptor</code>s.
     */
    public static List<PropertyDescriptor> getAllPropertyDescriptors(
            Object pojo) {
        List<PropertyDescriptor> list = new ArrayList<PropertyDescriptor>();
        BeanInfo bi = getBeanInfo(pojo);
        for (PropertyDescriptor pd : bi.getPropertyDescriptors()) {
            list.add(pd);
        }
        return list;
    }
}

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