Java tutorial
/* * 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.nifi.lookup.configuration2; import java.io.File; import java.lang.reflect.ParameterizedType; import java.util.ArrayList; import java.util.Collections; import java.util.List; import java.util.Map; import java.util.Optional; import java.util.Set; import java.util.stream.Collectors; import java.util.stream.Stream; import org.apache.commons.configuration2.Configuration; import org.apache.commons.configuration2.FileBasedConfiguration; import org.apache.commons.configuration2.builder.ConfigurationBuilderEvent; import org.apache.commons.configuration2.builder.ReloadingFileBasedConfigurationBuilder; import org.apache.commons.configuration2.builder.fluent.FileBasedBuilderParameters; import org.apache.commons.configuration2.builder.fluent.Parameters; import org.apache.commons.configuration2.event.EventListener; import org.apache.commons.configuration2.ex.ConfigurationException; import org.apache.commons.lang3.StringUtils; import org.apache.nifi.annotation.lifecycle.OnEnabled; import org.apache.nifi.components.PropertyDescriptor; import org.apache.nifi.controller.AbstractControllerService; import org.apache.nifi.controller.ControllerServiceInitializationContext; import org.apache.nifi.controller.ConfigurationContext; import org.apache.nifi.lookup.LookupFailureException; import org.apache.nifi.lookup.StringLookupService; import org.apache.nifi.processor.util.StandardValidators; import org.apache.nifi.reporting.InitializationException; /** * This abstract class defines a generic {@link LookupService} backed by an * Apache Commons Configuration {@link FileBasedConfiguration}. * */ public abstract class CommonsConfigurationLookupService<T extends FileBasedConfiguration> extends AbstractControllerService implements StringLookupService { private static final String KEY = "key"; private static final Set<String> REQUIRED_KEYS = Collections .unmodifiableSet(Stream.of(KEY).collect(Collectors.toSet())); public static final PropertyDescriptor CONFIGURATION_FILE = new PropertyDescriptor.Builder() .name("configuration-file").displayName("Configuration File").description("A configuration file") .required(true).addValidator(StandardValidators.FILE_EXISTS_VALIDATOR).expressionLanguageSupported(true) .build(); private final Class<T> resultClass = (Class<T>) ((ParameterizedType) getClass().getGenericSuperclass()) .getActualTypeArguments()[0]; private List<PropertyDescriptor> properties; private volatile ReloadingFileBasedConfigurationBuilder<T> builder; private Configuration getConfiguration() throws LookupFailureException { try { if (builder != null) { return builder.getConfiguration(); } } catch (final ConfigurationException e) { throw new LookupFailureException("Failed to get configuration due to " + e.getMessage(), e); } return null; } @Override protected List<PropertyDescriptor> getSupportedPropertyDescriptors() { return properties; } @Override protected void init(final ControllerServiceInitializationContext context) throws InitializationException { final List<PropertyDescriptor> properties = new ArrayList<>(); properties.add(CONFIGURATION_FILE); this.properties = Collections.unmodifiableList(properties); } @OnEnabled public void onEnabled(final ConfigurationContext context) throws InitializationException { final String config = context.getProperty(CONFIGURATION_FILE).getValue(); final FileBasedBuilderParameters params = new Parameters().fileBased().setFile(new File(config)); this.builder = new ReloadingFileBasedConfigurationBuilder<>(resultClass).configure(params); builder.addEventListener(ConfigurationBuilderEvent.CONFIGURATION_REQUEST, new EventListener<ConfigurationBuilderEvent>() { @Override public void onEvent(ConfigurationBuilderEvent event) { if (builder.getReloadingController().checkForReloading(null)) { getLogger().debug("Reloading " + config); } } }); try { // Try getting configuration to see if there is any issue, for example wrong file format. // Then throw InitializationException to keep this service in 'Enabling' state. builder.getConfiguration(); } catch (ConfigurationException e) { throw new InitializationException(e); } } @Override public Optional<String> lookup(final Map<String, Object> coordinates) throws LookupFailureException { if (coordinates == null) { return Optional.empty(); } final String key = coordinates.get(KEY).toString(); if (StringUtils.isBlank(key)) { return Optional.empty(); } final Configuration config = getConfiguration(); if (config != null) { final Object value = config.getProperty(key); if (value != null) { return Optional.of(String.valueOf(value)); } } return Optional.empty(); } @Override public Set<String> getRequiredKeys() { return REQUIRED_KEYS; } }