Java tutorial
/******************************************************************************* * Copyright 2012 Artem Artem'ev * * Licensed 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 net.elsched.utils; import com.google.common.base.Joiner; import com.google.common.collect.ImmutableList; import com.google.common.collect.ImmutableMap; import com.google.inject.AbstractModule; import com.google.inject.Module; import com.google.inject.TypeLiteral; import com.google.inject.name.Names; import org.apache.commons.configuration.CompositeConfiguration; import org.apache.commons.configuration.ConfigurationException; import org.apache.commons.configuration.PropertiesConfiguration; import org.apache.commons.configuration.SystemConfiguration; import java.lang.reflect.Field; import java.lang.reflect.ParameterizedType; import java.lang.reflect.Type; import java.util.*; /** * A property file parsing system that converts a given settings class into a * Guice module with injectable * * @Named parameters. * * Originally based on some CLI work by arb@google.com (Anthony Baxter). * Refactored by tad.glines@gmail.com (Tad Glines) to use Commons * Configuration and add support for List<String>. */ public class SettingsBinder { /** * Used to validate that a type is supported. Some types may have generic * parameters that need to be checked. */ private interface SettingTypeValidator { boolean check(Type type); } /** * This default validator just returns true. */ private static final SettingTypeValidator DEFAULT_TYPE_VALIDATOR = new SettingTypeValidator() { @Override public boolean check(Type type) { return true; } }; /** * This validator checks to make sure the {@link java.util.List}'s generic parameter * is also supported. */ private static final SettingTypeValidator LIST_TYPE_VALIDATOR = new SettingTypeValidator() { @Override public boolean check(Type type) { if (type instanceof ParameterizedType) { Type[] args = ((ParameterizedType) type).getActualTypeArguments(); if (args.length == 1) { // At the moment only List<String> is supported. if (args[0] == String.class) { return true; } } } return false; } }; private static final Map<Type, SettingTypeValidator> supportedSettingTypes; static { ImmutableMap.Builder<Type, SettingTypeValidator> builder = ImmutableMap.builder(); builder.put(int.class, DEFAULT_TYPE_VALIDATOR); builder.put(boolean.class, DEFAULT_TYPE_VALIDATOR); builder.put(String.class, DEFAULT_TYPE_VALIDATOR); builder.put(List.class, LIST_TYPE_VALIDATOR); supportedSettingTypes = builder.build(); } /** * Bind configuration parameters into Guice Module. * * @return a Guice module configured with setting support. * @throws ConfigurationException * on configuration error */ public static Module bindSettings(String propertiesFileKey, Class<?>... settingsArg) throws ConfigurationException { final CompositeConfiguration config = new CompositeConfiguration(); config.addConfiguration(new SystemConfiguration()); String propertyFile = config.getString(propertiesFileKey); if (propertyFile != null) { config.addConfiguration(new PropertiesConfiguration(propertyFile)); } List<Field> fields = new ArrayList<Field>(); for (Class<?> settings : settingsArg) { fields.addAll(Arrays.asList(settings.getDeclaredFields())); } // Reflect on settings class and absorb settings final Map<Setting, Field> settings = new LinkedHashMap<Setting, Field>(); for (Field field : fields) { if (!field.isAnnotationPresent(Setting.class)) { continue; } // Validate target type SettingTypeValidator typeHelper = supportedSettingTypes.get(field.getType()); if (typeHelper == null || !typeHelper.check(field.getGenericType())) { throw new IllegalArgumentException(field.getType() + " is not one of the supported setting types"); } Setting setting = field.getAnnotation(Setting.class); settings.put(setting, field); } // Now validate them List<String> missingProperties = new ArrayList<String>(); for (Setting setting : settings.keySet()) { if (setting.defaultValue().isEmpty()) { if (!config.containsKey(setting.name())) { missingProperties.add(setting.name()); } } } if (missingProperties.size() > 0) { StringBuilder error = new StringBuilder(); error.append("The following required properties are missing from the server configuration: "); error.append(Joiner.on(", ").join(missingProperties)); } // bundle everything up in an injectable guice module return new AbstractModule() { @Override protected void configure() { // We must iterate the settings a third time when binding. // Note: do not collapse these loops as that will damage // early error detection. The runtime is still O(n) in setting // count. for (Map.Entry<Setting, Field> entry : settings.entrySet()) { Class<?> type = entry.getValue().getType(); Setting setting = entry.getKey(); if (int.class.equals(type)) { Integer defaultValue = null; if (!setting.defaultValue().isEmpty()) { defaultValue = Integer.parseInt(setting.defaultValue()); } bindConstant().annotatedWith(Names.named(setting.name())) .to(config.getInteger(setting.name(), defaultValue)); } else if (boolean.class.equals(type)) { Boolean defaultValue = null; if (!setting.defaultValue().isEmpty()) { defaultValue = Boolean.parseBoolean(setting.defaultValue()); } bindConstant().annotatedWith(Names.named(setting.name())) .to(config.getBoolean(setting.name(), defaultValue)); } else if (String.class.equals(type)) { bindConstant().annotatedWith(Names.named(setting.name())) .to(config.getString(setting.name(), setting.defaultValue())); } else { String[] value = config.getStringArray(setting.name()); if (value.length == 0 && !setting.defaultValue().isEmpty()) { value = setting.defaultValue().split(","); } bind(new TypeLiteral<List<String>>() { }).annotatedWith(Names.named(setting.name())).toInstance(ImmutableList.copyOf(value)); } } } }; } }