java/com/google/gerrit/server/config/ConfigUtil.java - gerrit.git - Git at Google

 // Copyright (C) 2009 The Android Open Source Project
 //
 // 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 com.google.gerrit.server.config;

 import static java.util.Objects.requireNonNull;

 import com.google.common.flogger.FluentLogger;
 import java.lang.reflect.Field;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Modifier;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import org.eclipse.jgit.errors.ConfigInvalidException;
 import org.eclipse.jgit.lib.Config;

 public class ConfigUtil {
   private static final FluentLogger logger = FluentLogger.forEnclosingClass();

   @SuppressWarnings("unchecked")
   private static <T> T[] allValuesOf(T defaultValue) {
     try {
       return (T[]) defaultValue.getClass().getMethod("values").invoke(null);
     } catch (IllegalArgumentException
         | NoSuchMethodException
         | InvocationTargetException
         | IllegalAccessException
         | SecurityException e) {
       throw new IllegalArgumentException("Cannot obtain enumeration values", e);
     }
   }

   /**
    * Parse a Java enumeration from the configuration.
    *
    * @param <T> type of the enumeration object.
    * @param section section the key is in.
    * @param subsection subsection the key is in, or null if not in a subsection.
    * @param setting name of the setting to read.
    * @param valueString string value from git Config
    * @param all all possible values in the enumeration which should be recognized. This should be
    *     {@code EnumType.values()}.
    * @return the selected enumeration value, or {@code defaultValue}.
    */
   private static <T extends Enum<?>> T getEnum(
       final String section,
       final String subsection,
       final String setting,
       String valueString,
       final T[] all) {

     String n = valueString.replace(' ', '_').replace('-', '_');
     for (T e : all) {
       if (e.name().equalsIgnoreCase(n)) {
         return e;
       }
     }

     final StringBuilder r = new StringBuilder();
     r.append("Value \"");
     r.append(valueString);
     r.append("\" not recognized in ");
     r.append(section);
     if (subsection != null) {
       r.append(".");
       r.append(subsection);
     }
     r.append(".");
     r.append(setting);
     r.append("; supported values are: ");
     for (T e : all) {
       r.append(e.name());
       r.append(" ");
     }

     throw new IllegalArgumentException(r.toString().trim());
   }

   /**
    * Parse a Java enumeration list from the configuration.
    *
    * @param <T> type of the enumeration object.
    * @param config the configuration file to read.
    * @param section section the key is in.
    * @param subsection subsection the key is in, or null if not in a subsection.
    * @param setting name of the setting to read.
    * @param defaultValue default value to return if the setting was not set. Must not be null as the
    *     enumeration values are derived from this.
    * @return the selected enumeration values list, or {@code defaultValue}.
    */
   public static <T extends Enum<?>> List<T> getEnumList(
       final Config config,
       final String section,
       final String subsection,
       final String setting,
       final T defaultValue) {
     final T[] all = allValuesOf(defaultValue);
     return getEnumList(config, section, subsection, setting, all, defaultValue);
   }

   /**
    * Parse a Java enumeration list from the configuration.
    *
    * @param <T> type of the enumeration object.
    * @param config the configuration file to read.
    * @param section section the key is in.
    * @param subsection subsection the key is in, or null if not in a subsection.
    * @param setting name of the setting to read.
    * @param all all possible values in the enumeration which should be recognized. This should be
    *     {@code EnumType.values()}.
    * @param defaultValue default value to return if the setting was not set. This value may be null.
    * @return the selected enumeration values list, or {@code defaultValue}.
    */
   public static <T extends Enum<?>> List<T> getEnumList(
       final Config config,
       final String section,
       final String subsection,
       final String setting,
       final T[] all,
       final T defaultValue) {
     final List<T> list = new ArrayList<>();
     final String[] values = config.getStringList(section, subsection, setting);
     if (values.length == 0) {
       list.add(defaultValue);
     } else {
       for (String string : values) {
         if (string != null) {
           try {
             list.add(getEnum(section, subsection, setting, string, all));
           } catch (IllegalArgumentException ex) {
             // It's better to ignore a wrongly configured enum, rather than fail to load Gerrit.
             logger.atWarning().log(ex.getMessage());
           }
         }
       }
     }
     return list;
   }

   /**
    * Parse a numerical time unit, such as "1 minute", from the configuration.
    *
    * @param config the configuration file to read.
    * @param section section the key is in.
    * @param subsection subsection the key is in, or null if not in a subsection.
    * @param setting name of the setting to read.
    * @param defaultValue default value to return if no value was set in the configuration file.
    * @param wantUnit the units of {@code defaultValue} and the return value, as well as the units to
    *     assume if the value does not contain an indication of the units.
    * @return the setting, or {@code defaultValue} if not set, expressed in {@code units}.
    */
   public static long getTimeUnit(
       final Config config,
       final String section,
       final String subsection,
       final String setting,
       final long defaultValue,
       final TimeUnit wantUnit) {
     final String valueString = config.getString(section, subsection, setting);
     if (valueString == null) {
       return defaultValue;
     }

     String s = valueString.trim();
     if (s.length() == 0) {
       return defaultValue;
     }

     if (s.startsWith("-") /* negative */) {
       throw notTimeUnit(section, subsection, setting, valueString);
     }

     try {
       return getTimeUnit(s, defaultValue, wantUnit);
     } catch (IllegalArgumentException notTime) {
       throw notTimeUnit(section, subsection, setting, valueString, notTime);
     }
   }

   /**
    * Parse a numerical time unit, such as "1 minute", from a string.
    *
    * @param valueString the string to parse.
    * @param defaultValue default value to return if no value was set in the configuration file.
    * @param wantUnit the units of {@code defaultValue} and the return value, as well as the units to
    *     assume if the value does not contain an indication of the units.
    * @return the setting, or {@code defaultValue} if not set, expressed in {@code units}.
    */
   public static long getTimeUnit(String valueString, long defaultValue, TimeUnit wantUnit) {
     Matcher m = Pattern.compile("^(0|[1-9][0-9]*)\\s*(.*)$").matcher(valueString);
     if (!m.matches()) {
       return defaultValue;
     }

     String digits = m.group(1);
     String unitName = m.group(2).trim();

     TimeUnit inputUnit;
     int inputMul;

     if ("".equals(unitName)) {
       inputUnit = wantUnit;
       inputMul = 1;

     } else if (match(unitName, "ms", "milliseconds")) {
       inputUnit = TimeUnit.MILLISECONDS;
       inputMul = 1;

     } else if (match(unitName, "s", "sec", "second", "seconds")) {
       inputUnit = TimeUnit.SECONDS;
       inputMul = 1;

     } else if (match(unitName, "m", "min", "minute", "minutes")) {
       inputUnit = TimeUnit.MINUTES;
       inputMul = 1;

     } else if (match(unitName, "h", "hr", "hour", "hours")) {
       inputUnit = TimeUnit.HOURS;
       inputMul = 1;

     } else if (match(unitName, "d", "day", "days")) {
       inputUnit = TimeUnit.DAYS;
       inputMul = 1;

     } else if (match(unitName, "w", "week", "weeks")) {
       inputUnit = TimeUnit.DAYS;
       inputMul = 7;

     } else if (match(unitName, "mon", "month", "months")) {
       inputUnit = TimeUnit.DAYS;
       inputMul = 30;

     } else if (match(unitName, "y", "year", "years")) {
       inputUnit = TimeUnit.DAYS;
       inputMul = 365;

     } else {
       throw notTimeUnit(valueString);
     }

     try {
       return wantUnit.convert(Long.parseLong(digits) * inputMul, inputUnit);
     } catch (NumberFormatException nfe) {
       throw notTimeUnit(valueString, nfe);
     }
   }

   public static String getRequired(Config cfg, String section, String name) {
     final String v = cfg.getString(section, null, name);
     if (v == null || "".equals(v)) {
       throw new IllegalArgumentException("No " + section + "." + name + " configured");
     }
     return v;
   }

   /**
    * Store section by inspecting Java class attributes.
    *
    * <p>Optimize the storage by unsetting a variable if it is being set to default value by the
    * server.
    *
    * <p>Fields marked with final or transient modifiers are skipped.
    *
    * @param cfg config in which the values should be stored
    * @param section section
    * @param sub subsection
    * @param s instance of class with config values
    * @param defaults instance of class with default values
    */
   public static <T> void storeSection(Config cfg, String section, String sub, T s, T defaults)
       throws ConfigInvalidException {
     try {
       for (Field f : s.getClass().getDeclaredFields()) {
         if (skipField(f)) {
           continue;
         }
         Class<?> t = f.getType();
         String n = f.getName();
         f.setAccessible(true);
         Object c = f.get(s);
         Object d = f.get(defaults);
         if (!isString(t) && !isCollectionOrMap(t)) {
           requireNonNull(d, "Default cannot be null for: " + n);
         }
         if (c == null || c.equals(d)) {
           cfg.unset(section, sub, n);
         } else {
           if (isString(t)) {
             cfg.setString(section, sub, n, (String) c);
           } else if (isInteger(t)) {
             cfg.setInt(section, sub, n, (Integer) c);
           } else if (isLong(t)) {
             cfg.setLong(section, sub, n, (Long) c);
           } else if (isBoolean(t)) {
             cfg.setBoolean(section, sub, n, (Boolean) c);
           } else if (t.isEnum()) {
             cfg.setEnum(section, sub, n, (Enum<?>) c);
           } else if (isCollectionOrMap(t)) {
             // TODO(davido): accept closure passed in from caller
             continue;
           } else {
             throw new ConfigInvalidException("type is unknown: " + t.getName());
           }
         }
       }
     } catch (SecurityException | IllegalArgumentException | IllegalAccessException e) {
       throw new ConfigInvalidException("cannot save values", e);
     }
   }

   /**
    * Load section by inspecting Java class attributes.
    *
    * <p>Config values are stored optimized: no default values are stored. The loading is performed
    * eagerly: all values are set.
    *
    * <p>Fields marked with final or transient modifiers are skipped.
    *
    * @param cfg config from which the values are loaded
    * @param section section
    * @param sub subsection
    * @param s instance of class in which the values are set
    * @param defaults instance of class with default values
    * @param i instance to merge during the load. When present, the boolean fields are not nullified
    *     when their values are false
    * @return loaded instance
    */
   public static <T> T loadSection(Config cfg, String section, String sub, T s, T defaults, T i)
       throws ConfigInvalidException {
     try {
       for (Field f : s.getClass().getDeclaredFields()) {
         if (skipField(f)) {
           continue;
         }
         Class<?> t = f.getType();
         String n = f.getName();
         f.setAccessible(true);
         Object d = f.get(defaults);
         if (!isString(t) && !isCollectionOrMap(t)) {
           requireNonNull(d, "Default cannot be null for: " + n);
         }
         if (isString(t)) {
           String v = cfg.getString(section, sub, n);
           if (v == null) {
             v = (String) d;
           }
           f.set(s, v);
         } else if (isInteger(t)) {
           f.set(s, cfg.getInt(section, sub, n, (Integer) d));
         } else if (isLong(t)) {
           f.set(s, cfg.getLong(section, sub, n, (Long) d));
         } else if (isBoolean(t)) {
           boolean b = cfg.getBoolean(section, sub, n, (Boolean) d);
           if (b || i != null) {
             f.set(s, b);
           }
         } else if (t.isEnum()) {
           f.set(s, cfg.getEnum(section, sub, n, (Enum<?>) d));
         } else if (isCollectionOrMap(t)) {
           // TODO(davido): accept closure passed in from caller
           continue;
         } else {
           throw new ConfigInvalidException("type is unknown: " + t.getName());
         }
         if (i != null) {
           Object o = f.get(i);
           if (o != null) {
             f.set(s, o);
           }
         }
       }
     } catch (SecurityException | IllegalArgumentException | IllegalAccessException e) {
       throw new ConfigInvalidException("cannot load values", e);
     }
     return s;
   }

   public static boolean skipField(Field field) {
     int modifiers = field.getModifiers();
     return Modifier.isFinal(modifiers) || Modifier.isTransient(modifiers);
   }

   private static boolean isCollectionOrMap(Class<?> t) {
     return Collection.class.isAssignableFrom(t) || Map.class.isAssignableFrom(t);
   }

   private static boolean isString(Class<?> t) {
     return String.class == t;
   }

   private static boolean isBoolean(Class<?> t) {
     return Boolean.class == t || boolean.class == t;
   }

   private static boolean isLong(Class<?> t) {
     return Long.class == t || long.class == t;
   }

   private static boolean isInteger(Class<?> t) {
     return Integer.class == t || int.class == t;
   }

   private static boolean match(String a, String... cases) {
     for (String b : cases) {
       if (b != null && b.equalsIgnoreCase(a)) {
         return true;
       }
     }
     return false;
   }

   private static IllegalArgumentException notTimeUnit(
       String section, String subsection, String setting, String valueString, Throwable why) {
     return notTimeUnit(
         section
             + (subsection != null ? "." + subsection : "")
             + "."
             + setting
             + " = "
             + valueString,
         why);
   }

   private static IllegalArgumentException notTimeUnit(
       String section, String subsection, String setting, String valueString) {
     return notTimeUnit(
         section
             + (subsection != null ? "." + subsection : "")
             + "."
             + setting
             + " = "
             + valueString);
   }

   private static IllegalArgumentException notTimeUnit(String val) {
     return new IllegalArgumentException("Invalid time unit value: " + val);
   }

   private static IllegalArgumentException notTimeUnit(String val, Throwable why) {
     return new IllegalArgumentException("Invalid time unit value: " + val, why);
   }

   private ConfigUtil() {}
 }
	// Copyright (C) 2009 The Android Open Source Project
	//
	// 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 com.google.gerrit.server.config;

	import static java.util.Objects.requireNonNull;

	import com.google.common.flogger.FluentLogger;
	import java.lang.reflect.Field;
	import java.lang.reflect.InvocationTargetException;
	import java.lang.reflect.Modifier;
	import java.util.ArrayList;
	import java.util.Collection;
	import java.util.List;
	import java.util.Map;
	import java.util.concurrent.TimeUnit;
	import java.util.regex.Matcher;
	import java.util.regex.Pattern;
	import org.eclipse.jgit.errors.ConfigInvalidException;
	import org.eclipse.jgit.lib.Config;

	public class ConfigUtil {
	private static final FluentLogger logger = FluentLogger.forEnclosingClass();

	@SuppressWarnings("unchecked")
	private static <T> T[] allValuesOf(T defaultValue) {
	try {
	return (T[]) defaultValue.getClass().getMethod("values").invoke(null);
	} catch (IllegalArgumentException
	\| NoSuchMethodException
	\| InvocationTargetException
	\| IllegalAccessException
	\| SecurityException e) {
	throw new IllegalArgumentException("Cannot obtain enumeration values", e);
	}
	}

	/**
	* Parse a Java enumeration from the configuration.
	*
	* @param <T> type of the enumeration object.
	* @param section section the key is in.
	* @param subsection subsection the key is in, or null if not in a subsection.
	* @param setting name of the setting to read.
	* @param valueString string value from git Config
	* @param all all possible values in the enumeration which should be recognized. This should be
	* {@code EnumType.values()}.
	* @return the selected enumeration value, or {@code defaultValue}.
	*/
	private static <T extends Enum<?>> T getEnum(
	final String section,
	final String subsection,
	final String setting,
	String valueString,
	final T[] all) {

	String n = valueString.replace(' ', '_').replace('-', '_');
	for (T e : all) {
	if (e.name().equalsIgnoreCase(n)) {
	return e;
	}
	}

	final StringBuilder r = new StringBuilder();
	r.append("Value \"");
	r.append(valueString);
	r.append("\" not recognized in ");
	r.append(section);
	if (subsection != null) {
	r.append(".");
	r.append(subsection);
	}
	r.append(".");
	r.append(setting);
	r.append("; supported values are: ");
	for (T e : all) {
	r.append(e.name());
	r.append(" ");
	}

	throw new IllegalArgumentException(r.toString().trim());
	}

	/**
	* Parse a Java enumeration list from the configuration.
	*
	* @param <T> type of the enumeration object.
	* @param config the configuration file to read.
	* @param section section the key is in.
	* @param subsection subsection the key is in, or null if not in a subsection.
	* @param setting name of the setting to read.
	* @param defaultValue default value to return if the setting was not set. Must not be null as the
	* enumeration values are derived from this.
	* @return the selected enumeration values list, or {@code defaultValue}.
	*/
	public static <T extends Enum<?>> List<T> getEnumList(
	final Config config,
	final String section,
	final String subsection,
	final String setting,
	final T defaultValue) {
	final T[] all = allValuesOf(defaultValue);
	return getEnumList(config, section, subsection, setting, all, defaultValue);
	}

	/**
	* Parse a Java enumeration list from the configuration.
	*
	* @param <T> type of the enumeration object.
	* @param config the configuration file to read.
	* @param section section the key is in.
	* @param subsection subsection the key is in, or null if not in a subsection.
	* @param setting name of the setting to read.
	* @param all all possible values in the enumeration which should be recognized. This should be
	* {@code EnumType.values()}.
	* @param defaultValue default value to return if the setting was not set. This value may be null.
	* @return the selected enumeration values list, or {@code defaultValue}.
	*/
	public static <T extends Enum<?>> List<T> getEnumList(
	final Config config,
	final String section,
	final String subsection,
	final String setting,
	final T[] all,
	final T defaultValue) {
	final List<T> list = new ArrayList<>();
	final String[] values = config.getStringList(section, subsection, setting);
	if (values.length == 0) {
	list.add(defaultValue);
	} else {
	for (String string : values) {
	if (string != null) {
	try {
	list.add(getEnum(section, subsection, setting, string, all));
	} catch (IllegalArgumentException ex) {
	// It's better to ignore a wrongly configured enum, rather than fail to load Gerrit.
	logger.atWarning().log(ex.getMessage());
	}
	}
	}
	}
	return list;
	}

	/**
	* Parse a numerical time unit, such as "1 minute", from the configuration.
	*
	* @param config the configuration file to read.
	* @param section section the key is in.
	* @param subsection subsection the key is in, or null if not in a subsection.
	* @param setting name of the setting to read.
	* @param defaultValue default value to return if no value was set in the configuration file.
	* @param wantUnit the units of {@code defaultValue} and the return value, as well as the units to
	* assume if the value does not contain an indication of the units.
	* @return the setting, or {@code defaultValue} if not set, expressed in {@code units}.
	*/
	public static long getTimeUnit(
	final Config config,
	final String section,
	final String subsection,
	final String setting,
	final long defaultValue,
	final TimeUnit wantUnit) {
	final String valueString = config.getString(section, subsection, setting);
	if (valueString == null) {
	return defaultValue;
	}

	String s = valueString.trim();
	if (s.length() == 0) {
	return defaultValue;
	}

	if (s.startsWith("-") /* negative */) {
	throw notTimeUnit(section, subsection, setting, valueString);
	}

	try {
	return getTimeUnit(s, defaultValue, wantUnit);
	} catch (IllegalArgumentException notTime) {
	throw notTimeUnit(section, subsection, setting, valueString, notTime);
	}
	}

	/**
	* Parse a numerical time unit, such as "1 minute", from a string.
	*
	* @param valueString the string to parse.
	* @param defaultValue default value to return if no value was set in the configuration file.
	* @param wantUnit the units of {@code defaultValue} and the return value, as well as the units to
	* assume if the value does not contain an indication of the units.
	* @return the setting, or {@code defaultValue} if not set, expressed in {@code units}.
	*/
	public static long getTimeUnit(String valueString, long defaultValue, TimeUnit wantUnit) {
	Matcher m = Pattern.compile("^(0\|[1-9][0-9])\\s(.*)$").matcher(valueString);
	if (!m.matches()) {
	return defaultValue;
	}

	String digits = m.group(1);
	String unitName = m.group(2).trim();

	TimeUnit inputUnit;
	int inputMul;

	if ("".equals(unitName)) {
	inputUnit = wantUnit;
	inputMul = 1;

	} else if (match(unitName, "ms", "milliseconds")) {
	inputUnit = TimeUnit.MILLISECONDS;
	inputMul = 1;

	} else if (match(unitName, "s", "sec", "second", "seconds")) {
	inputUnit = TimeUnit.SECONDS;
	inputMul = 1;

	} else if (match(unitName, "m", "min", "minute", "minutes")) {
	inputUnit = TimeUnit.MINUTES;
	inputMul = 1;

	} else if (match(unitName, "h", "hr", "hour", "hours")) {
	inputUnit = TimeUnit.HOURS;
	inputMul = 1;

	} else if (match(unitName, "d", "day", "days")) {
	inputUnit = TimeUnit.DAYS;
	inputMul = 1;

	} else if (match(unitName, "w", "week", "weeks")) {
	inputUnit = TimeUnit.DAYS;
	inputMul = 7;

	} else if (match(unitName, "mon", "month", "months")) {
	inputUnit = TimeUnit.DAYS;
	inputMul = 30;

	} else if (match(unitName, "y", "year", "years")) {
	inputUnit = TimeUnit.DAYS;
	inputMul = 365;

	} else {
	throw notTimeUnit(valueString);
	}

	try {
	return wantUnit.convert(Long.parseLong(digits) * inputMul, inputUnit);
	} catch (NumberFormatException nfe) {
	throw notTimeUnit(valueString, nfe);
	}
	}

	public static String getRequired(Config cfg, String section, String name) {
	final String v = cfg.getString(section, null, name);
	if (v == null \|\| "".equals(v)) {
	throw new IllegalArgumentException("No " + section + "." + name + " configured");
	}
	return v;
	}

	/**
	* Store section by inspecting Java class attributes.
	*
	* <p>Optimize the storage by unsetting a variable if it is being set to default value by the
	* server.
	*
	* <p>Fields marked with final or transient modifiers are skipped.
	*
	* @param cfg config in which the values should be stored
	* @param section section
	* @param sub subsection
	* @param s instance of class with config values
	* @param defaults instance of class with default values
	*/
	public static <T> void storeSection(Config cfg, String section, String sub, T s, T defaults)
	throws ConfigInvalidException {
	try {
	for (Field f : s.getClass().getDeclaredFields()) {
	if (skipField(f)) {
	continue;
	}
	Class<?> t = f.getType();
	String n = f.getName();
	f.setAccessible(true);
	Object c = f.get(s);
	Object d = f.get(defaults);
	if (!isString(t) && !isCollectionOrMap(t)) {
	requireNonNull(d, "Default cannot be null for: " + n);
	}
	if (c == null \|\| c.equals(d)) {
	cfg.unset(section, sub, n);
	} else {
	if (isString(t)) {
	cfg.setString(section, sub, n, (String) c);
	} else if (isInteger(t)) {
	cfg.setInt(section, sub, n, (Integer) c);
	} else if (isLong(t)) {
	cfg.setLong(section, sub, n, (Long) c);
	} else if (isBoolean(t)) {
	cfg.setBoolean(section, sub, n, (Boolean) c);
	} else if (t.isEnum()) {
	cfg.setEnum(section, sub, n, (Enum<?>) c);
	} else if (isCollectionOrMap(t)) {
	// TODO(davido): accept closure passed in from caller
	continue;
	} else {
	throw new ConfigInvalidException("type is unknown: " + t.getName());
	}
	}
	}
	} catch (SecurityException \| IllegalArgumentException \| IllegalAccessException e) {
	throw new ConfigInvalidException("cannot save values", e);
	}
	}

	/**
	* Load section by inspecting Java class attributes.
	*
	* <p>Config values are stored optimized: no default values are stored. The loading is performed
	* eagerly: all values are set.
	*
	* <p>Fields marked with final or transient modifiers are skipped.
	*
	* @param cfg config from which the values are loaded
	* @param section section
	* @param sub subsection
	* @param s instance of class in which the values are set
	* @param defaults instance of class with default values
	* @param i instance to merge during the load. When present, the boolean fields are not nullified
	* when their values are false
	* @return loaded instance
	*/
	public static <T> T loadSection(Config cfg, String section, String sub, T s, T defaults, T i)
	throws ConfigInvalidException {
	try {
	for (Field f : s.getClass().getDeclaredFields()) {
	if (skipField(f)) {
	continue;
	}
	Class<?> t = f.getType();
	String n = f.getName();
	f.setAccessible(true);
	Object d = f.get(defaults);
	if (!isString(t) && !isCollectionOrMap(t)) {
	requireNonNull(d, "Default cannot be null for: " + n);
	}
	if (isString(t)) {
	String v = cfg.getString(section, sub, n);
	if (v == null) {
	v = (String) d;
	}
	f.set(s, v);
	} else if (isInteger(t)) {
	f.set(s, cfg.getInt(section, sub, n, (Integer) d));
	} else if (isLong(t)) {
	f.set(s, cfg.getLong(section, sub, n, (Long) d));
	} else if (isBoolean(t)) {
	boolean b = cfg.getBoolean(section, sub, n, (Boolean) d);
	if (b \|\| i != null) {
	f.set(s, b);
	}
	} else if (t.isEnum()) {
	f.set(s, cfg.getEnum(section, sub, n, (Enum<?>) d));
	} else if (isCollectionOrMap(t)) {
	// TODO(davido): accept closure passed in from caller
	continue;
	} else {
	throw new ConfigInvalidException("type is unknown: " + t.getName());
	}
	if (i != null) {
	Object o = f.get(i);
	if (o != null) {
	f.set(s, o);
	}
	}
	}
	} catch (SecurityException \| IllegalArgumentException \| IllegalAccessException e) {
	throw new ConfigInvalidException("cannot load values", e);
	}
	return s;
	}

	public static boolean skipField(Field field) {
	int modifiers = field.getModifiers();
	return Modifier.isFinal(modifiers) \|\| Modifier.isTransient(modifiers);
	}

	private static boolean isCollectionOrMap(Class<?> t) {
	return Collection.class.isAssignableFrom(t) \|\| Map.class.isAssignableFrom(t);
	}

	private static boolean isString(Class<?> t) {
	return String.class == t;
	}

	private static boolean isBoolean(Class<?> t) {
	return Boolean.class == t \|\| boolean.class == t;
	}

	private static boolean isLong(Class<?> t) {
	return Long.class == t \|\| long.class == t;
	}

	private static boolean isInteger(Class<?> t) {
	return Integer.class == t \|\| int.class == t;
	}

	private static boolean match(String a, String... cases) {
	for (String b : cases) {
	if (b != null && b.equalsIgnoreCase(a)) {
	return true;
	}
	}
	return false;
	}

	private static IllegalArgumentException notTimeUnit(
	String section, String subsection, String setting, String valueString, Throwable why) {
	return notTimeUnit(
	section
	+ (subsection != null ? "." + subsection : "")
	+ "."
	+ setting
	+ " = "
	+ valueString,
	why);
	}

	private static IllegalArgumentException notTimeUnit(
	String section, String subsection, String setting, String valueString) {
	return notTimeUnit(
	section
	+ (subsection != null ? "." + subsection : "")
	+ "."
	+ setting
	+ " = "
	+ valueString);
	}

	private static IllegalArgumentException notTimeUnit(String val) {
	return new IllegalArgumentException("Invalid time unit value: " + val);
	}

	private static IllegalArgumentException notTimeUnit(String val, Throwable why) {
	return new IllegalArgumentException("Invalid time unit value: " + val, why);
	}

	private ConfigUtil() {}
	}