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.hadoop.gateway.config.impl; import org.apache.commons.beanutils.ConvertUtilsBean2; import org.apache.hadoop.gateway.config.*; import org.apache.hadoop.gateway.config.spi.ConfigurationInjector; import java.lang.annotation.Annotation; import java.lang.reflect.Field; import java.lang.reflect.Method; public class DefaultConfigurationInjector implements ConfigurationInjector { private static ConvertUtilsBean2 DEFAULT_CONVERTER = new ConvertUtilsBean2(); @Override public void configure(Object target, ConfigurationAdapter adapter, ConfigurationBinding binding) throws ConfigurationException { Class type = target.getClass(); while (type != null) { injectClass(type, target, adapter, binding); type = type.getSuperclass(); } } private void injectClass(Class type, Object target, ConfigurationAdapter config, ConfigurationBinding binding) throws ConfigurationException { Field[] fields = type.getDeclaredFields(); for (Field field : fields) { injectFieldValue(field, target, config, binding); } Method[] methods = type.getDeclaredMethods(); for (Method method : methods) { injectMethodValue(method, target, config, binding); } } private void injectFieldValue(Field field, Object target, ConfigurationAdapter adapter, ConfigurationBinding binding) throws ConfigurationException { Configure annotation = field.getAnnotation(Configure.class); if (annotation != null) { Alias alias = field.getAnnotation(Alias.class); String name = getConfigName(field, alias); String bind = getBindName(target, name, binding); Object value = retrieveValue(target, bind, name, field.getType(), adapter, binding); if (value == null) { Optional optional = field.getAnnotation(Optional.class); if (optional == null) { throw new ConfigurationException( String.format("Failed to find configuration for %s bound to %s of %s via %s", bind, name, target.getClass().getName(), adapter.getClass().getName())); } } else { try { if (!field.isAccessible()) { field.setAccessible(true); } field.set(target, value); } catch (Exception e) { throw new ConfigurationException( String.format("Failed to inject field configuration property %s of %s", name, target.getClass().getName()), e); } } } } private void injectMethodValue(Method method, Object target, ConfigurationAdapter adapter, ConfigurationBinding binding) throws ConfigurationException { Configure methodTag = method.getAnnotation(Configure.class); if (methodTag != null) { Alias aliasTag = method.getAnnotation(Alias.class); String methodName = getConfigName(method, aliasTag); Class[] argTypes = method.getParameterTypes(); Object[] args = new Object[argTypes.length]; Annotation[][] argTags = method.getParameterAnnotations(); for (int i = 0; i < argTypes.length; i++) { String argName = getConfigName(methodName, argTags[i]); String bndName = getBindName(target, argName, binding); Object argValue = retrieveValue(target, bndName, argName, argTypes[i], adapter, binding); if (argValue == null) { Default defTag = findAnnotation(argTags[i], Default.class); if (defTag != null) { String strValue = defTag.value(); argValue = convertValue(target, argName, strValue, argTypes[i]); } else { throw new ConfigurationException( String.format("Failed to find configuration for %s as %s of %s via %s", bndName, argName, target.getClass().getName(), adapter.getClass().getName())); } } args[i] = argValue; } if (!method.isAccessible()) { method.setAccessible(true); } try { method.invoke(target, args); } catch (Exception e) { throw new ConfigurationException(String.format("Failed to inject method configuration via %s of %s", methodName, target.getClass().getName()), e); } } } private Object convertValue(Object target, String name, Object strValue, Class<?> type) { Object objValue = null; try { objValue = DEFAULT_CONVERTER.convert(strValue, type); } catch (Exception e) { throw new ConfigurationException(String.format("Failed to convert configuration for %s of %s to %s", name, target.getClass().getName(), type.getName()), e); } return objValue; } private Object retrieveValue(Object target, String bind, String name, Class<?> type, ConfigurationAdapter adapter, ConfigurationBinding binding) { Object value; try { value = adapter.getConfigurationValue(bind); } catch (Exception e) { throw new ConfigurationException( String.format("Failed to retrieve configuration for %s bound to %s of %s via %s", bind, name, target.getClass().getName(), adapter.getClass().getName()), e); } // Otherwise null sometimes ends up being converted to 0. if (value != null) { value = convertValue(target, name, value, type); } return value; } private <T extends Annotation> T findAnnotation(Annotation[] annotations, Class<T> type) { T found = null; for (Annotation current : annotations) { if (type.isAssignableFrom(current.getClass())) { found = (T) current; break; } } return found; } private static String pickName(String implied, Alias explicit) { String name = implied; if (explicit != null) { String tagValue = explicit.value().trim(); if (tagValue.length() > 0) { name = tagValue; } } return name; } private static String getBindName(Object target, String name, ConfigurationBinding binding) { String bind = null; try { bind = binding.getConfigurationName(name); } catch (Exception e) { throw new ConfigurationException(String.format("Failed to bind configuration for %s of %s via %s", name, target.getClass().getName(), binding.getClass().getName()), e); } if (bind == null) { bind = name; } return bind; } private static String getConfigName(Field field, Alias tag) { return pickName(field.getName(), tag); } private static String getConfigName(String name, Annotation[] tags) { if (tags != null) { for (Annotation tag : tags) { if (tag != null && tag instanceof Alias) { Alias aliasTag = Alias.class.cast(tag); String aliasValue = aliasTag.value().trim(); if (aliasValue.length() > 0) { name = aliasValue; break; } } } } return name; } private static String getConfigName(Method method, Alias tag) { return pickName(getConfigName(method), tag); } private static String getConfigName(Method method) { String methodName = method.getName(); if (methodName != null) { StringBuilder name = new StringBuilder(methodName.length()); if (methodName.length() > 3 && methodName.startsWith("set") && Character.isUpperCase(methodName.charAt(3))) { name.append(methodName.substring(3)); name.setCharAt(0, Character.toLowerCase(name.charAt(0))); } else { name.append(name); } return name.toString(); } return null; } }