Java tutorial
/* * RHQ Management Platform * Copyright (C) 2005-2008 Red Hat, Inc. * All rights reserved. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License, version 2, as * published by the Free Software Foundation, and/or the GNU Lesser * General Public License, version 2.1, also as published by the Free * Software Foundation. * * This program 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 General Public License and the GNU Lesser General Public License * for more details. * * You should have received a copy of the GNU General Public License * and the GNU Lesser General Public License along with this program; * if not, write to the Free Software Foundation, Inc., * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ package org.rhq.core.pluginapi.util; import java.beans.Introspector; import java.beans.PropertyDescriptor; import java.util.HashSet; import java.util.Set; import java.lang.reflect.Method; import javax.management.openmbean.CompositeData; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.jetbrains.annotations.Nullable; import org.rhq.core.domain.measurement.MeasurementScheduleRequest; import org.rhq.core.util.exception.ThrowableUtil; /** * @author Greg Hinkle */ public class ObjectUtil { private static final Log LOG = LogFactory.getLog(ObjectUtil.class); /** * Returns the value of the property with the specified name for the given Object, or null if the Object has no such * property. * * @param obj an Object * @param propertyName the name of the property whose value should be returned * * @return the value of the property with the specified name for the given Object, or null if the Object has no such * property */ @Nullable public static Object lookupAttributeProperty(Object obj, String propertyName) { Object value = null; if (obj instanceof CompositeData) { CompositeData compositeData = ((CompositeData) obj); if (compositeData.containsKey(propertyName)) { value = compositeData.get(propertyName); } else { LOG.debug("Unable to read attribute/property [" + propertyName + "] from object [" + obj + "] using OpenMBean API - no such property."); } } else { // Try to use reflection. try { PropertyDescriptor[] pds = Introspector.getBeanInfo(obj.getClass()).getPropertyDescriptors(); boolean propertyFound = false; for (PropertyDescriptor pd : pds) { if (pd.getName().equals(propertyName)) { propertyFound = true; Method readMethod = pd.getReadMethod(); if (readMethod == null) { LOG.debug("Unable to read attribute/property [" + propertyName + "] from object [" + obj + "] using Reflection - property is not readable (i.e. it has no getter)."); } else { value = readMethod.invoke(obj); } } } if (!propertyFound) { LOG.debug("Unable to read attribute/property [" + propertyName + "] from object [" + obj + "] using Reflection - no such property."); } } catch (Exception e) { LOG.debug("Unable to read attribute/property [" + propertyName + "] from object [" + obj + "] using Reflection - cause: " + ThrowableUtil.getAllMessages(e)); } } return value; } private static Set<String> getAttributeNames(Set<MeasurementScheduleRequest> requests) { Set<String> names = new HashSet<String>(); for (MeasurementScheduleRequest request : requests) { names.add(getAttributeName(request.getName())); } return names; } private static String getAttributeName(String property) { if (property.startsWith("{")) { return property.substring(1, property.indexOf('.')); } else { return property; } } private static String getAttributeProperty(String property) { if (property.startsWith("{")) { return property.substring(property.indexOf('.') + 1, property.length() - 1); } else { return null; } } /** * Reads a numeric value from a deep object graph as per {@see ObjectUtil.lookupDeepAttributeProperty()} * * @param value The object to look into * @param propertyPath the property path to search * * @return the double value read from the object's property path or Double.NaN if it can't be read */ public static Double lookupDeepNumericAttributeProperty(Object value, String propertyPath) { Object val = lookupDeepAttributeProperty(value, propertyPath); if (val instanceof Number) { return ((Number) val).doubleValue(); } else { return Double.NaN; } } /** * Looks up deep object graph attributes using a dot delimited java bean spec style path. So if I have an object A * with a Member object B with a String value C I can refer to it as "b.c" and pass in the object A and I'll get * back the value of a.getB().getC() * * @param value The object to look into * @param propertyPath the property path to search * * @return the value read from the object's property path */ public static Object lookupDeepAttributeProperty(Object value, String propertyPath) { if (value == null) return null; String[] ps = propertyPath.split("\\.", 2); String searchProperty = ps[0]; if (value instanceof CompositeData) { CompositeData compositeData = ((CompositeData) value); if (compositeData.containsKey(searchProperty)) { value = compositeData.get(searchProperty); } else { LOG.debug("Unable to read attribute property [" + propertyPath + "] from composite data value"); } } else { // Try to use reflection try { PropertyDescriptor[] pds = Introspector.getBeanInfo(value.getClass()).getPropertyDescriptors(); for (PropertyDescriptor pd : pds) { if (pd.getName().equals(searchProperty)) { value = pd.getReadMethod().invoke(value); } } } catch (Exception e) { LOG.debug("Unable to read property from measurement attribute [" + searchProperty + "] not found on [" + ((value != null) ? value.getClass().getSimpleName() : "null") + "]"); } } if (ps.length > 1) { value = lookupDeepAttributeProperty(value, ps[1]); } return value; } // Prevent instantiation of this class. private ObjectUtil() { } }