Java tutorial
/* * Copyright (C) 2014 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.initialxy.cordova.themeablebrowser; import org.json.JSONArray; import org.json.JSONException; import org.json.JSONObject; import java.lang.reflect.Array; import java.lang.reflect.Constructor; import java.lang.reflect.Field; import java.lang.reflect.GenericArrayType; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.lang.reflect.ParameterizedType; import java.lang.reflect.Type; import java.util.ArrayList; import java.util.Collection; import java.util.Iterator; import java.util.List; /** * This is a simple and half decent JSON to POJO unmarshaller inspired by * Jackson. It is only a unmarshaller without a marshaller. It is intended to * parse JSON passed to a plugin as options to a POJO. It is nowhere as powerful * as Jackson is, but for most use cases, it will do a pretty decent job since * it is designed to be used for general purpose unmarshalling. This avoid * having to import Jackson or JAXB for merely a Cordova plugin. ~350 lines * isn't too big right? */ public class ThemeableBrowserUnmarshaller { /** * Runtime exception to notify type mismatch between expected class * structure and JSON. */ public static class TypeMismatchException extends RuntimeException { public TypeMismatchException(Type expected, Type got) { super(String.format("Expected %s but got %s.", expected, got)); } public TypeMismatchException(String message) { super(message); } } /** * Runtime exception to notify errors during class initialization. */ public static class ClassInstantiationException extends RuntimeException { public ClassInstantiationException(Class<?> cls) { super(String.format("Failed to instantiate %s", cls)); } public ClassInstantiationException(String message) { super(message); } } /** * Runtime exception to notify parser errors. */ public static class ParserException extends RuntimeException { public ParserException(Exception e) { super(e); } } /** * Given a JSON string, unmarhall it to an instance of the given class. * * @param json JSON string to unmarshall. * @param cls Return an instance of this class. Must be either public class * or private static class. Inner class will not work. * @param <T> Same type as cls. * @return An instance of class given by cls. * @throws com.initialxy.cordova.themeablebrowser.ThemeableBrowserUnmarshaller.TypeMismatchException */ public static <T> T JSONToObj(String json, Class<T> cls) { T result = null; if (json != null && !json.isEmpty()) { try { JSONObject jsonObj = new JSONObject(json); result = JSONToObj(jsonObj, cls); } catch (JSONException e) { throw new ParserException(e); } } return result; } /** * Given a JSONObject, unmarhall it to an instance of the given class. * * @param jsonObj JSON string to unmarshall. * @param cls Return an instance of this class. Must be either public class * or private static class. Inner class will not work. * @param <T> Same type as cls. * @return An instance of class given by cls. * @throws com.initialxy.cordova.themeablebrowser.ThemeableBrowserUnmarshaller.TypeMismatchException */ public static <T> T JSONToObj(JSONObject jsonObj, Class<T> cls) { T result = null; try { Constructor<T> constructor = cls.getDeclaredConstructor(); constructor.setAccessible(true); result = (T) constructor.newInstance(); Iterator<?> i = jsonObj.keys(); while (i.hasNext()) { String k = (String) i.next(); Object val = jsonObj.get(k); try { Field field = cls.getField(k); Object converted = valToType(val, field.getGenericType()); if (converted == null) { if (!field.getType().isPrimitive()) { field.set(result, null); } else { throw new TypeMismatchException( String.format("Type %s cannot be set to null.", field.getType())); } } else { if (converted instanceof List && field.getType().isAssignableFrom(List.class)) { // Class can define their own favorite // implementation of List. In which case the field // still need to be defined as List, but it can be // initialized with a placeholder instance of any of // the List implementations (eg. ArrayList). Object existing = field.get(result); if (existing != null) { ((List<?>) existing).clear(); // Just because I don't want javac to complain // about unsafe operations. So I'm gonna use // more reflection, HA! Method addAll = existing.getClass().getMethod("addAll", Collection.class); addAll.invoke(existing, converted); } else { field.set(result, converted); } } else { field.set(result, converted); } } } catch (NoSuchFieldException e) { // Ignore. } catch (IllegalAccessException e) { // Ignore. } catch (IllegalArgumentException e) { // Ignore. } } } catch (JSONException e) { throw new ParserException(e); } catch (NoSuchMethodException e) { throw new ClassInstantiationException("Failed to retrieve constructor for " + cls.toString() + ", make sure it's not an inner class."); } catch (InstantiationException e) { throw new ClassInstantiationException(cls); } catch (IllegalAccessException e) { throw new ClassInstantiationException(cls); } catch (InvocationTargetException e) { throw new ClassInstantiationException(cls); } return result; } /** * Given an object extracted from JSONObject field, convert it to an * appropriate object with type appropriate for given type so that it can be * assigned to the associated field of the ummarshalled object. eg. * JSONObject value from a JSONObject field probably needs to be * unmarshalled to a class instance. Double from JSONObject may need to be * converted to Float. etc. * * @param val Value extracted from JSONObject field. * @param genericType Type to convert to. Must be generic type. ie. From * field.getGenericType(). * @return Object of the given type so it can be assinged to field with * field.set(). * @throws com.initialxy.cordova.themeablebrowser.ThemeableBrowserUnmarshaller.TypeMismatchException */ private static Object valToType(Object val, Type genericType) { Object result = null; boolean isArray = false; Class<?> rawType = null; if (genericType instanceof ParameterizedType) { rawType = (Class<?>) ((ParameterizedType) genericType).getRawType(); } else if (genericType instanceof GenericArrayType) { rawType = List.class; isArray = true; } else { rawType = (Class<?>) genericType; } isArray = isArray || rawType.isArray(); if (val != null && val != JSONObject.NULL) { if (rawType.isAssignableFrom(String.class)) { if (val instanceof String) { result = val; } else { throw new TypeMismatchException(rawType, val.getClass()); } } else if (isPrimitive(rawType)) { result = convertToPrimitiveFieldObj(val, rawType); } else if (isArray || rawType.isAssignableFrom(List.class)) { if (val instanceof JSONArray) { Type itemType = getListItemType(genericType); result = JSONToList((JSONArray) val, itemType); if (isArray) { List<?> list = (List<?>) result; Class<?> itemClass = null; if (itemType instanceof ParameterizedType) { itemClass = (Class<?>) ((ParameterizedType) itemType).getRawType(); } else { itemClass = (Class<?>) itemType; } result = Array.newInstance(itemClass, list.size()); int cnt = 0; for (Object i : list) { Array.set(result, cnt, i); cnt += 1; } } } else { throw new TypeMismatchException(JSONArray.class, val.getClass()); } } else if (val instanceof JSONObject) { result = JSONToObj((JSONObject) val, rawType); } } return result; } /** * Given a generic type representing a List or array, retrieve list or array * item type. * * @param type * @return */ private static Type getListItemType(Type type) { Type result = null; if (type instanceof GenericArrayType) { result = ((GenericArrayType) type).getGenericComponentType(); } else if (type instanceof ParameterizedType) { result = ((ParameterizedType) type).getActualTypeArguments()[0]; } else { result = ((Class<?>) type).getComponentType(); } return result; } /** * Given an JSONArray retrieved from JSONObject, and the destination item * type, unmarshall this list to a List of given item type. * * @param jsonArr * @param itemType * @return */ private static List<?> JSONToList(JSONArray jsonArr, Type itemType) { List<Object> result = new ArrayList<Object>(); Class<?> rawType = null; ParameterizedType pType = null; if (itemType instanceof ParameterizedType) { pType = (ParameterizedType) itemType; rawType = (Class<?>) pType.getRawType(); } else { rawType = (Class<?>) itemType; } int len = jsonArr.length(); for (int i = 0; i < len; i++) { try { Object item = jsonArr.get(i); Object converted = valToType(item, itemType); if (converted != null) { result.add(converted); } } catch (JSONException e) { throw new ParserException(e); } } return result; } /** * Checks if given class is one of the primitive types or more importantly, * one of the classes associated with a primitive type. eg. Integer, Double * etc. * * @param cls * @return */ private static boolean isPrimitive(Class<?> cls) { return cls.isPrimitive() || cls.isAssignableFrom(Byte.class) || cls.isAssignableFrom(Short.class) || cls.isAssignableFrom(Integer.class) || cls.isAssignableFrom(Long.class) || cls.isAssignableFrom(Float.class) || cls.isAssignableFrom(Double.class) || cls.isAssignableFrom(Boolean.class) || cls.isAssignableFrom(Character.class); } /** * Gracefully convert given Object to given class given the precondition * that both are primitives or one of the classes associated with * primitives. eg. If val is of type Double and cls is of type int, return * Integer type with appropriate value truncation so that it can be assigned * to field with field.set(). * * @param cls * @param val * @return * @throws com.initialxy.cordova.themeablebrowser.ThemeableBrowserUnmarshaller.TypeMismatchException */ private static Object convertToPrimitiveFieldObj(Object val, Class<?> cls) { Class<?> valClass = val.getClass(); Object result = null; try { Method getter = null; if (cls.isAssignableFrom(Byte.class) || cls.isAssignableFrom(Byte.TYPE)) { getter = valClass.getMethod("byteValue"); } else if (cls.isAssignableFrom(Short.class) || cls.isAssignableFrom(Short.TYPE)) { getter = valClass.getMethod("shortValue"); } else if (cls.isAssignableFrom(Integer.class) || cls.isAssignableFrom(Integer.TYPE)) { getter = valClass.getMethod("intValue"); } else if (cls.isAssignableFrom(Long.class) || cls.isAssignableFrom(Long.TYPE)) { getter = valClass.getMethod("longValue"); } else if (cls.isAssignableFrom(Float.class) || cls.isAssignableFrom(Float.TYPE)) { getter = valClass.getMethod("floatValue"); } else if (cls.isAssignableFrom(Double.class) || cls.isAssignableFrom(Double.TYPE)) { getter = valClass.getMethod("doubleValue"); } else if (cls.isAssignableFrom(Boolean.class) || cls.isAssignableFrom(Boolean.TYPE)) { if (val instanceof Boolean) { result = val; } else { throw new TypeMismatchException(cls, val.getClass()); } } else if (cls.isAssignableFrom(Character.class) || cls.isAssignableFrom(Character.TYPE)) { if (val instanceof String && ((String) val).length() == 1) { char c = ((String) val).charAt(0); result = Character.valueOf(c); } else if (val instanceof String) { throw new TypeMismatchException( "Expected Character, " + "but received String with length other than 1."); } else { throw new TypeMismatchException( String.format("Expected Character, accept String, but got %s.", val.getClass())); } } if (getter != null) { result = getter.invoke(val); } } catch (NoSuchMethodException e) { throw new TypeMismatchException(String.format("Cannot convert %s to %s.", val.getClass(), cls)); } catch (SecurityException e) { throw new TypeMismatchException(String.format("Cannot convert %s to %s.", val.getClass(), cls)); } catch (IllegalAccessException e) { throw new TypeMismatchException(String.format("Cannot convert %s to %s.", val.getClass(), cls)); } catch (InvocationTargetException e) { throw new TypeMismatchException(String.format("Cannot convert %s to %s.", val.getClass(), cls)); } return result; } }