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Java example source code file (JsonTreeReader.java)

This example Java source code file (JsonTreeReader.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

assertionerror, expected, illegalstateexception, ioexception, iterator, jsonarray, jsonobject, jsonprimitive, jsontoken, jsontreereader, object, override, sentinel_closed, string, util

The JsonTreeReader.java Java example source code

/*
 * 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 com.google.gson.internal.bind;

import com.google.gson.JsonArray;
import com.google.gson.JsonElement;
import com.google.gson.JsonNull;
import com.google.gson.JsonObject;
import com.google.gson.JsonPrimitive;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonToken;
import java.io.IOException;
import java.io.Reader;
import java.util.Iterator;
import java.util.Map;

/**
 * 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();

  /*
   * The nesting stack. Using a manual array rather than an ArrayList saves 20%.
   */
  private Object[] stack = new Object[32];
  private int stackSize = 0;

  /*
   * The path members. It corresponds directly to stack: At indices where the
   * stack contains an object (EMPTY_OBJECT, DANGLING_NAME or NONEMPTY_OBJECT),
   * pathNames contains the name at this scope. Where it contains an array
   * (EMPTY_ARRAY, NONEMPTY_ARRAY) pathIndices contains the current index in
   * that array. Otherwise the value is undefined, and we take advantage of that
   * by incrementing pathIndices when doing so isn't useful.
   */
  private String[] pathNames = new String[32];
  private int[] pathIndices = new int[32];

  public JsonTreeReader(JsonElement element) {
    super(UNREADABLE_READER);
    push(element);
  }

  @Override public void beginArray() throws IOException {
    expect(JsonToken.BEGIN_ARRAY);
    JsonArray array = (JsonArray) peekStack();
    push(array.iterator());
    pathIndices[stackSize - 1] = 0;
  }

  @Override public void endArray() throws IOException {
    expect(JsonToken.END_ARRAY);
    popStack(); // empty iterator
    popStack(); // array
    if (stackSize > 0) {
      pathIndices[stackSize - 1]++;
    }
  }

  @Override public void beginObject() throws IOException {
    expect(JsonToken.BEGIN_OBJECT);
    JsonObject object = (JsonObject) peekStack();
    push(object.entrySet().iterator());
  }

  @Override public void endObject() throws IOException {
    expect(JsonToken.END_OBJECT);
    popStack(); // empty iterator
    popStack(); // object
    if (stackSize > 0) {
      pathIndices[stackSize - 1]++;
    }
  }

  @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 (stackSize == 0) {
      return JsonToken.END_DOCUMENT;
    }

    Object o = peekStack();
    if (o instanceof Iterator) {
      boolean isObject = stack[stackSize - 2] instanceof JsonObject;
      Iterator<?> iterator = (Iterator) o;
      if (iterator.hasNext()) {
        if (isObject) {
          return JsonToken.NAME;
        } else {
          push(iterator.next());
          return peek();
        }
      } else {
        return isObject ? JsonToken.END_OBJECT : JsonToken.END_ARRAY;
      }
    } else if (o instanceof JsonObject) {
      return JsonToken.BEGIN_OBJECT;
    } else if (o instanceof JsonArray) {
      return JsonToken.BEGIN_ARRAY;
    } else if (o instanceof JsonPrimitive) {
      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 (o instanceof JsonNull) {
      return JsonToken.NULL;
    } else if (o == SENTINEL_CLOSED) {
      throw new IllegalStateException("JsonReader is closed");
    } else {
      throw new AssertionError();
    }
  }

  private Object peekStack() {
    return stack[stackSize - 1];
  }

  private Object popStack() {
    Object result = stack[--stackSize];
    stack[stackSize] = null;
    return result;
  }

  private void expect(JsonToken expected) throws IOException {
    if (peek() != expected) {
      throw new IllegalStateException(
          "Expected " + expected + " but was " + peek() + locationString());
    }
  }

  @Override public String nextName() throws IOException {
    expect(JsonToken.NAME);
    Iterator<?> i = (Iterator) peekStack();
    Map.Entry<?, ?> entry = (Map.Entry) i.next();
    String result = (String) entry.getKey();
    pathNames[stackSize - 1] = result;
    push(entry.getValue());
    return result;
  }

  @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 + locationString());
    }
    String result = ((JsonPrimitive) popStack()).getAsString();
    if (stackSize > 0) {
      pathIndices[stackSize - 1]++;
    }
    return result;
  }

  @Override public boolean nextBoolean() throws IOException {
    expect(JsonToken.BOOLEAN);
    boolean result = ((JsonPrimitive) popStack()).getAsBoolean();
    if (stackSize > 0) {
      pathIndices[stackSize - 1]++;
    }
    return result;
  }

  @Override public void nextNull() throws IOException {
    expect(JsonToken.NULL);
    popStack();
    if (stackSize > 0) {
      pathIndices[stackSize - 1]++;
    }
  }

  @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 + locationString());
    }
    double result = ((JsonPrimitive) peekStack()).getAsDouble();
    if (!isLenient() && (Double.isNaN(result) || Double.isInfinite(result))) {
      throw new NumberFormatException("JSON forbids NaN and infinities: " + result);
    }
    popStack();
    if (stackSize > 0) {
      pathIndices[stackSize - 1]++;
    }
    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 + locationString());
    }
    long result = ((JsonPrimitive) peekStack()).getAsLong();
    popStack();
    if (stackSize > 0) {
      pathIndices[stackSize - 1]++;
    }
    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 + locationString());
    }
    int result = ((JsonPrimitive) peekStack()).getAsInt();
    popStack();
    if (stackSize > 0) {
      pathIndices[stackSize - 1]++;
    }
    return result;
  }

  @Override public void close() throws IOException {
    stack = new Object[] { SENTINEL_CLOSED };
    stackSize = 1;
  }

  @Override public void skipValue() throws IOException {
    if (peek() == JsonToken.NAME) {
      nextName();
      pathNames[stackSize - 2] = "null";
    } else {
      popStack();
      pathNames[stackSize - 1] = "null";
    }
    pathIndices[stackSize - 1]++;
  }

  @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();
    push(entry.getValue());
    push(new JsonPrimitive((String) entry.getKey()));
  }

  private void push(Object newTop) {
    if (stackSize == stack.length) {
      Object[] newStack = new Object[stackSize * 2];
      int[] newPathIndices = new int[stackSize * 2];
      String[] newPathNames = new String[stackSize * 2];
      System.arraycopy(stack, 0, newStack, 0, stackSize);
      System.arraycopy(pathIndices, 0, newPathIndices, 0, stackSize);
      System.arraycopy(pathNames, 0, newPathNames, 0, stackSize);
      stack = newStack;
      pathIndices = newPathIndices;
      pathNames = newPathNames;
    }
    stack[stackSize++] = newTop;
  }

  @Override public String getPath() {
    StringBuilder result = new StringBuilder().append('$');
    for (int i = 0; i < stackSize; i++) {
      if (stack[i] instanceof JsonArray) {
        if (stack[++i] instanceof Iterator) {
          result.append('[').append(pathIndices[i]).append(']');
        }
      } else if (stack[i] instanceof JsonObject) {
        if (stack[++i] instanceof Iterator) {
          result.append('.');
          if (pathNames[i] != null) {
            result.append(pathNames[i]);
          }
        }
      }
    }
    return result.toString();
  }

  private String locationString() {
    return " at path " + getPath();
  }
}

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