| /** |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache 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.apache.org/licenses/LICENSE-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.apache.s4.base; |
| |
| import java.lang.reflect.Field; |
| import java.util.List; |
| |
| import org.slf4j.Logger; |
| import org.slf4j.LoggerFactory; |
| |
| import com.google.common.collect.Lists; |
| |
| /** |
| * |
| * Implementation of {@link KeyFinder} that uses introspection on the target Event to create the key finder. |
| * <p> |
| * The search for the key is as follows: |
| * <p> |
| * <ul> |
| * <li>If the event object class extends {@link Event}, find a field that matches the key name. |
| * <li>If there is no match and the {@link Event} class has arbitrary attributes, search for the key. |
| * <li>Otherwise, fail. |
| * </ul> |
| * |
| * |
| * @param <T> |
| */ |
| public class GenericKeyFinder<T extends Event> implements KeyFinder<T> { |
| |
| private static final Logger logger = LoggerFactory.getLogger(GenericKeyFinder.class); |
| |
| final private String keyName; |
| private final Class<T> eventType; |
| private final Field field; |
| |
| public GenericKeyFinder(String keyName, Class<T> eventType) throws SecurityException { |
| this.keyName = keyName; |
| this.eventType = eventType; |
| |
| logger.debug("Creating a generic key finder for key [{}] with event type [{}].", keyName, eventType.getName()); |
| field = getField(); |
| } |
| |
| @Override |
| public List<String> get(T event) { |
| |
| List<String> list = Lists.newArrayList(); |
| |
| if (field != null) { |
| |
| try { |
| list.add(String.valueOf(field.get(event))); |
| } catch (IllegalArgumentException e) { |
| logger.error("Unable to access field [{}] in event of type [{}].", field.getName(), eventType.getName()); |
| throw e; |
| } catch (IllegalAccessException e) { |
| logger.error("Could not access field.", e); |
| return null; |
| } |
| |
| } else { |
| list.add(event.get(keyName)); |
| } |
| return list; |
| } |
| |
| private Field getField() throws SecurityException { |
| |
| Field f; |
| |
| /* Find a field with name keyName. */ |
| try { |
| f = eventType.getDeclaredField(keyName); |
| logger.debug("Found field [{}] of type [{}].", f.getName(), f.getType()); |
| |
| f.setAccessible(true); |
| return f; |
| } catch (NoSuchFieldException e) { |
| |
| logger.debug( |
| "Field [{}] could not be found in class [{}]. I will check if this is an Event attribute at run-time.", |
| keyName, eventType.getName()); |
| } |
| return null; |
| } |
| } |