Java tutorial
/********************************************************************************** * $URL$ * $Id$ *********************************************************************************** * * Copyright (c) 2004, 2005, 2006, 2008 The Sakai Foundation * * Licensed under the Educational Community License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.opensource.org/licenses/ECL-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. * **********************************************************************************/ package org.sakaiproject.metaobj.utils.ioc; import java.lang.reflect.Field; import org.springframework.beans.factory.BeanNameAware; import org.springframework.beans.factory.FactoryBean; import org.springframework.beans.factory.InitializingBean; import org.springframework.util.ClassUtils; /** * FactoryBean which retrieves a static or non-static field value. * Typically used for retrieving public static final constants. * <p/> * <p>Usage example: * <p/> * <pre> * // standard definition for exposing a static field, specifying the "staticField" property * <bean id="myField" class="org.springframework.beans.factory.config.FieldRetrievingFactoryBean"> * <property name="staticField"><value>java.sql.Connection.TRANSACTION_SERIALIZABLE</value></property> * </bean> * <p/> * // convenience version that specifies a static field pattern as bean name * <bean id="java.sql.Connection.TRANSACTION_SERIALIZABLE" class="org.springframework.beans.factory.config.FieldRetrievingFactoryBean"/></pre> * </pre> * * @author Juergen Hoeller * @see #setStaticField * @since 1.1 */ public class FieldRetrievingFactoryBean implements FactoryBean, BeanNameAware, InitializingBean { private Class targetClass; private Object targetObject; private String targetField; private String staticField; private String beanName; // the field we will retrieve private Field fieldObject; /** * Set the target class on which the field is defined. * Only necessary when the target field is static; else, * a target object needs to be specified anyway. * * @see #setTargetObject * @see #setTargetField */ public void setTargetClass(Class targetClass) { this.targetClass = targetClass; } /** * Return the target class on which the field is defined. */ public Class getTargetClass() { return targetClass; } /** * Set the target object on which the field is defined. * Only necessary when the target field is not static; * else, a target class is sufficient. * * @see #setTargetClass * @see #setTargetField */ public void setTargetObject(Object targetObject) { this.targetObject = targetObject; } /** * Return the target object on which the field is defined. */ public Object getTargetObject() { return targetObject; } /** * Set the name of the field to be retrieved. * Refers to either a static field or a non-static field, * depending on a target object being set. * * @see #setTargetClass * @see #setTargetObject */ public void setTargetField(String targetField) { this.targetField = targetField; } /** * Return the name of the field to be retrieved. */ public String getTargetField() { return targetField; } /** * Set a fully qualified static field name to retrieve, * e.g. "example.MyExampleClass.MY_EXAMPLE_FIELD". * Convenient alternative to specifying targetClass and targetField. * * @see #setTargetClass * @see #setTargetField */ public void setStaticField(String staticField) { this.staticField = staticField; } /** * The bean name of this FieldRetrievingFactoryBean will be interpreted * as "staticField" pattern, if neither "targetClass" nor "targetObject" * nor "targetField" have been specified. * This allows for concise bean definitions with just an id/name. */ public void setBeanName(String beanName) { this.beanName = beanName; } public void afterPropertiesSet() throws ClassNotFoundException, NoSuchFieldException { if (this.targetClass != null && this.targetObject != null) { throw new IllegalArgumentException("Specify either targetClass or targetObject, not both"); } if (this.targetClass == null && this.targetObject == null) { if (this.targetField != null) { throw new IllegalArgumentException( "Specify targetClass or targetObject in combination with targetField"); } // If no other property specified, consider bean name as static field expression. if (this.staticField == null) { this.staticField = this.beanName; } // try to parse static field into class and field int lastDotIndex = this.staticField.lastIndexOf('.'); if (lastDotIndex == -1 || lastDotIndex == this.staticField.length()) { throw new IllegalArgumentException("staticField must be a fully qualified class plus method name: " + "e.g. 'example.MyExampleClass.MY_EXAMPLE_FIELD'"); } String className = this.staticField.substring(0, lastDotIndex); String fieldName = this.staticField.substring(lastDotIndex + 1); this.targetClass = ClassUtils.forName(className); this.targetField = fieldName; } else if (this.targetField == null) { // either targetClass or targetObject specified throw new IllegalArgumentException("targetField is required"); } // try to get the exact method first Class targetClass = (this.targetObject != null) ? this.targetObject.getClass() : this.targetClass; this.fieldObject = targetClass.getField(this.targetField); } public Object getObject() throws IllegalAccessException { if (this.targetObject != null) { // instance field return this.fieldObject.get(this.targetObject); } else { // class field return this.fieldObject.get(null); } } public Class getObjectType() { return this.fieldObject.getType(); } public boolean isSingleton() { return true; } }