Java tutorial
/* * Copyright (C) 2011 Google Inc. * * 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 bind; import java.io.IOException; import java.io.Reader; import java.util.ArrayList; import java.util.Iterator; import java.util.List; import java.util.Map; import com.google.gson.JsonArray; import com.google.gson.JsonElement; import com.google.gson.JsonObject; import com.google.gson.JsonPrimitive; import com.google.gson.stream.JsonReader; import com.google.gson.stream.JsonToken; /** * This reader walks the elements of a JsonElement as if it was coming from a * character stream. * * @author Jesse Wilson */ public final class JsonTreeReader extends JsonReader { private static final Reader UNREADABLE_READER = new Reader() { @Override public int read(char[] buffer, int offset, int count) throws IOException { throw new AssertionError(); } @Override public void close() throws IOException { throw new AssertionError(); } }; private static final Object SENTINEL_CLOSED = new Object(); private final List<Object> stack = new ArrayList<Object>(); public JsonTreeReader(JsonElement element) { super(UNREADABLE_READER); stack.add(element); } @Override public void beginArray() throws IOException { expect(JsonToken.BEGIN_ARRAY); JsonArray array = ((JsonElement) peekStack()).getAsJsonArray(); stack.add(array.iterator()); } @Override public void endArray() throws IOException { expect(JsonToken.END_ARRAY); popStack(); // empty iterator popStack(); // array } @Override public void beginObject() throws IOException { expect(JsonToken.BEGIN_OBJECT); JsonObject object = ((JsonElement) peekStack()).getAsJsonObject(); stack.add(object.entrySet().iterator()); } @Override public void endObject() throws IOException { expect(JsonToken.END_OBJECT); popStack(); // empty iterator popStack(); // object } @Override public boolean hasNext() throws IOException { JsonToken token = peek(); return token != JsonToken.END_OBJECT && token != JsonToken.END_ARRAY; } @Override public JsonToken peek() throws IOException { if (stack.isEmpty()) { return JsonToken.END_DOCUMENT; } Object o = peekStack(); if (o instanceof Iterator) { Object secondToTop = stack.get(stack.size() - 2); boolean isObject = secondToTop instanceof JsonElement && ((JsonElement) secondToTop).isJsonObject(); Iterator<?> iterator = (Iterator<?>) o; if (iterator.hasNext()) { if (isObject) { return JsonToken.NAME; } else { stack.add(iterator.next()); return peek(); } } else { return isObject ? JsonToken.END_OBJECT : JsonToken.END_ARRAY; } } else if (o instanceof JsonElement) { JsonElement el = (JsonElement) o; if (el.isJsonObject()) { return JsonToken.BEGIN_OBJECT; } else if (el.isJsonArray()) { return JsonToken.BEGIN_ARRAY; } else if (el.isJsonPrimitive()) { JsonPrimitive primitive = (JsonPrimitive) o; if (primitive.isString()) { return JsonToken.STRING; } else if (primitive.isBoolean()) { return JsonToken.BOOLEAN; } else if (primitive.isNumber()) { return JsonToken.NUMBER; } else { throw new AssertionError(); } } else if (el.isJsonNull()) { return JsonToken.NULL; } throw new AssertionError(); } else if (o == SENTINEL_CLOSED) { throw new IllegalStateException("JsonReader is closed"); } else { throw new AssertionError(); } } private Object peekStack() { return stack.get(stack.size() - 1); } private Object popStack() { return stack.remove(stack.size() - 1); } private void expect(JsonToken expected) throws IOException { if (peek() != expected) { throw new IllegalStateException("Expected " + expected + " but was " + peek()); } } @Override public String nextName() throws IOException { expect(JsonToken.NAME); Iterator<?> i = (Iterator<?>) peekStack(); Map.Entry<?, ?> entry = (Map.Entry<?, ?>) i.next(); stack.add(entry.getValue()); return (String) entry.getKey(); } @Override public String nextString() throws IOException { JsonToken token = peek(); if (token != JsonToken.STRING && token != JsonToken.NUMBER) { throw new IllegalStateException("Expected " + JsonToken.STRING + " but was " + token); } return ((JsonPrimitive) popStack()).getAsString(); } @Override public boolean nextBoolean() throws IOException { expect(JsonToken.BOOLEAN); return ((JsonPrimitive) popStack()).getAsBoolean(); } @Override public void nextNull() throws IOException { expect(JsonToken.NULL); popStack(); } @Override public double nextDouble() throws IOException { JsonToken token = peek(); if (token != JsonToken.NUMBER && token != JsonToken.STRING) { throw new IllegalStateException("Expected " + JsonToken.NUMBER + " but was " + token); } double result = ((JsonPrimitive) peekStack()).getAsDouble(); if (!isLenient() && (Double.isNaN(result) || Double.isInfinite(result))) { throw new NumberFormatException("JSON forbids NaN and infinities: " + result); } popStack(); return result; } @Override public long nextLong() throws IOException { JsonToken token = peek(); if (token != JsonToken.NUMBER && token != JsonToken.STRING) { throw new IllegalStateException("Expected " + JsonToken.NUMBER + " but was " + token); } long result = ((JsonPrimitive) peekStack()).getAsLong(); popStack(); return result; } @Override public int nextInt() throws IOException { JsonToken token = peek(); if (token != JsonToken.NUMBER && token != JsonToken.STRING) { throw new IllegalStateException("Expected " + JsonToken.NUMBER + " but was " + token); } int result = ((JsonPrimitive) peekStack()).getAsInt(); popStack(); return result; } @Override public void close() throws IOException { stack.clear(); stack.add(SENTINEL_CLOSED); } @Override public void skipValue() throws IOException { if (peek() == JsonToken.NAME) { nextName(); } else { popStack(); } } @Override public String toString() { return getClass().getSimpleName(); } public void promoteNameToValue() throws IOException { expect(JsonToken.NAME); Iterator<?> i = (Iterator<?>) peekStack(); Map.Entry<?, ?> entry = (Map.Entry<?, ?>) i.next(); stack.add(entry.getValue()); stack.add(new JsonPrimitive((String) entry.getKey())); } }